Open AccessArticle

Subsidence and Uplift in Active and Closed Lignite Mines: Impacts of Energy Transition and Climate Change

Artur Guzy

Faculty of Geo-Data Science, Geodesy and Environmental Engineering, AGH University of Krakow, 30-059 Kraków, Poland

Energies 2024, 17(22), 5540; https://doi.org/10.3390/en17225540

Submission received: 16 October 2024 / Revised: 1 November 2024 / Accepted: 4 November 2024 / Published: 6 November 2024

(This article belongs to the Section B: Energy and Environment)

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Abstract

This study examines the combined effects of decommissioning lignite mining operations and long-term climate trends on groundwater systems and land surface movements in the Konin region of Poland, which is characterised by extensive open-pit lignite extraction. The findings reveal subsidence rates ranging from −26 to 14 mm per year within mining zones, while land uplift of a few millimetres per year occurred in closed mining areas between 2015 and 2022. Groundwater levels in shallow Quaternary and deeper Paleogene–Neogene aquifers have declined significantly, with drops of up to 26 m observed near active mining, particularly between 2009 and 2019. A smaller groundwater decline of around a few metres was observed outside areas influenced by mining. Meteorological data show an average annual temperature of 8.9 °C from 1991 to 2023, with a clear warming trend of 0.0050 °C per year since 2009. Although precipitation patterns show a slight increase from 512 mm to 520 mm, a shift towards drier conditions has emerged since 2009, characterised by more frequent dry spells. These climatic trends, combined with mining activities, highlight the need for adaptive groundwater management strategies. Future research should focus on enhanced monitoring of groundwater recovery and sustainable practices in post-mining landscapes.

Keywords:

land subsidence; land uplift; lignite mining; aquifer system depletion; aquifer system recovery; InSAR; energy transition; climate change

1. Introduction

The ongoing energy transition and climate change remain critical scientific, economic, and social issues [1,2,3]. These phenomena are interconnected, necessitating integrated analyses for a comprehensive understanding. A central part of the energy transition is the shift from fossil fuels to more sustainable energy sources. In the European Union (EU), lignite continues to be a widely used fossil fuel, accounting for around four times the production of hard coal [4,5]. In 2022, the EU produced 145.5 megatons of lignite, with Germany (44%), Poland (19%), Bulgaria (12%), Czechia (11%), Romania (6%), and Greece (5%) collectively making up 97% of the total production. Lignite plays a significant role in electricity generation, with 92% of the extracted lignite used for electricity and heat in 2021 [6].

Despite its significance, lignite is less energy-dense and more carbon-intensive compared to other coals, substantially contributing to greenhouse gas emissions [7]. The reliance on lignite, particularly in open-pit mining, poses environmental risks and challenges linked to climate change and the transition to cleaner energy [8]. While numerous EU countries intend to phase out lignite by the 2030s, Poland, which generates around 70% of its power from coal, has yet to set an end date for coal-fuelled power, despite increasing wind and solar generation in recent years [9,10]. The energy transition in Poland requires implementing new technologies, policies, and social approaches to address the miscellaneous challenges of moving away from the dominance of coal [11,12,13]. However, the country is committed to a target for the EU to cut emissions by 90% by 2040 [14]. The gradual closure of lignite mines across Europe is anticipated to bring about significant environmental changes, including impacts on groundwater and land surface stability [9].

Mining activities, particularly open-pit lignite extraction, disrupt hydrogeological systems, leading to land subsidence due to groundwater depletion [15]. This process can reduce aquifer storage, cause structural damage to the rock mass and land surface, and pose other hazards [16]. Typically, mining drainage-induced subsidence is modest but widespread, ranging from a few millimetres to several centimetres [17,18]. Conversely, mine closures often involve flooding of decommissioned pits, resulting in groundwater rebound that can induce land uplift [19]. However, uplift rates are usually lower than subsidence rates [20]. Nevertheless, risks such as sinkholes may emerge, especially in regions with a history of shallow mining [21].

To monitor these land surface movements, remote sensing technologies, particularly Satellite Radar Interferometry (InSAR), have been used since the 1990s [22,23]. While InSAR has been extensively applied to study mining-induced subsidence [24,25,26,27,28], significantly less research has focused on land uplift following mine closures [19,29,30,31,32]. This gap in understanding is critical to address, as the formal framework for the phase-out of lignite regions in the EU has been outlined in European strategic documents [12,33]. The energy transition poses geotechnical challenges that must be carefully considered to ensure the safety and cost-effectiveness of proposed solutions, such as the reclamation of coal areas by renewable energy systems and the development of recreational areas with open-pit lakes and green zones [34].

In contrast to the localised impacts of mining, broader environmental changes related to climate trends further influence hydrogeological systems [35,36,37]. Climate change significantly affects temperature and precipitation patterns. Since the 1970s, global temperatures have risen at approximately 0.2 °C per decade, with Europe experiencing an even higher rate of +0.5 °C per decade over the past 30 years [38]. These shifts have resulted in extreme weather events, such as heatwaves [39], wildfires [40], floods [41,42], and droughts [43,44]. Of particular interest, the changes in temperature and precipitation patterns, combined with increased water demands, can further deplete groundwater resources, compounding subsidence due to regional aquifer system compaction. This process further reduces groundwater storage and increases subsidence risk, potentially leading to adverse consequences for water security and land stability [45,46,47,48].

To combat this, the EU has made significant progress in reducing greenhouse gas emissions, achieving a 31% reduction from 1990 to 2020, with a target of 55% by 2030. However, further efforts are required to prevent accelerated warming [48]. The transition from lignite to cleaner energy sources, driven by economic policies such as the EU Emissions Trading System, will necessitate extensive mine closures [33]. This shift presents a critical need to understand the interplay between past mining activities, mining closures, and ongoing climate change, and their combined effects on the environment. Comprehending this relationship is crucial for mitigating potential risks and informing sustainable land management strategies for post-mining landscapes [48].

This study focuses on the “Konin” Lignite Mine area in Poland, a region affected by nearly 80 years of lignite mining and facing the impacts of climate change. The primary objective of the study is to disentangle the intertwined effects of these two forces on land surface dynamics and groundwater resources. Specifically, this research addresses the following objectives:

Quantify and differentiate land surface movements in both mining-affected and unaffected areas using InSAR data to distinguish between subsidence caused by lignite extraction and broader regional impacts related to climate factors.
Evaluate the impacts of lignite extraction and climate change on aquifer systems by assessing changes in groundwater levels and aquifer storage capacity retrieved from extensive networks of piezometers, under both anthropogenic influences and natural climatic conditions.
Investigate long-term climate trends and their environmental impacts on groundwater level changes and land surface dynamics to provide insights into the complex relationship between climate change, groundwater resources, and land stability in a region transitioning away from lignite mining.

This study will provide an assessment of the coupled effects of lignite mining and climate change on the environment. The findings will be crucial for informing sustainable land management strategies, mitigating risks associated with mining legacies and climate change, and supporting the transition towards a more sustainable and resilient post-mining future.

2. Study Area

The area of interest (AOI) is located in the central region of Poland, encompassing historical and ongoing open-pit lignite mining sites around the city of Konin (Figure 1). This AOI covers a rectangular region of approximately 53 by 68 km, totalling around 3646 km². The AOI is predominantly an agricultural landscape with fertile soils, limited forest cover, and a moderately urbanized character. The urban centres within the AOI are numerous but generally small, with the largest cities being Konin, Koło, and Radziejów. The geographic positioning of the AOI in central Poland means it is traversed by several national roads, including No. 15, 25, 62, and 92, as well as a small segment of the A2 motorway. This motorway runs latitudinally through Poland, connecting Germany to Belarus and constituting a portion of the international E30 route. Additionally, the AOI is crossed by national railway lines No. 3 and 131 (Figure 1A) [49,50].

2.1. Morphology and Hydrology

The AOI is situated within the Kuyavian Lakeland, a region part of the broader South Baltic Lakeland and Central European Lowland. The terrain exhibits a distinct morphology comprising moraine uplands and valleys with the characteristics of tunnel valleys or glacial lakes. The moraine hills, remnants of the Baltic glaciation, reach maximum elevations of approximately 140 m above sea level (masl). Numerous river tunnels and glacial lakes intersect these hills, while the intervening areas consist of clayey ground moraine plains, sandy outwash plains, and accumulation terraces (Figure 1B) [51].

The southern portion of the AOI is drained by the Warta River valley, which is part of the larger Warsaw–Berlin proglacial valley. On the other hand, the northern part of the Kuyavian Lakeland is drained by the Noteć River, which flows through a narrow and poorly defined valley (Figure 1B) [49,50].

The AOI is further characterised by a dense network of glacial lakes, predominantly of the tunnel valley type. The largest of these include Lake Gopło, Lake Powidzkie, and Lake Głuszyńskie, as well as a chain of interconnected lakes located north of Konin, such as Lake Gosławskie, Lake Pątnowskie, and Lake Mikorzyńskie (Figure 1B) [49,50].

2.2. Geology

The Konin lignite deposit area is situated in a sedimentary basin, where geological formations from the Palaeozoic, Mesozoic, and Cenozoic eras are present (Figure 2). Beneath the lignite seams, at depths of 50–200 m, there are Cretaceous carbonate rocks, predominantly marls and calcareous sandstones, with a thickness of approximately 3000 m near Konin. Several-metre-thick marls and limestones represent the Upper Cretaceous. The top surface of the Cretaceous is highly variable in elevation, generally dipping northward and reaching up to +80 masl in the Konin region, with local depressions reaching −70 masl [52,53,54,55].

Overlying the Cretaceous deposits are Tertiary sediments, ranging from several to 100 m thick, comprising Oligocene, Lower Miocene, Upper Miocene, and Pliocene formations. The Oligocene and Lower Miocene sediments are sands and gravels, while the Upper Miocene and Pliocene deposits are clays, silts, and interbedded sands. The lignite deposit occurs in the Upper Miocene as a single main seam, with a thickness ranging from 0.1 m to 15 m, occasionally interspersed with sand lenses.

Figure 1. AOI overview. (A) Location of the AOI within Poland. (B) Detailed map of the AOI, indicating current mining operations, major lakes and rivers, roads, railways, urban areas, the meteorological station, landscape features, and the locations of boreholes and hydrogeological cross-sections. Data sources: National Geoportal of Poland [49], Polish Geological Institute–National Research Institute [52]. Basemap: OpenStreetMap contributors [50].

The Quaternary sediments in the area include fluvial and glacial deposits, such as clays, silts, and sands, with thicknesses ranging from 0 to 30 m. The lignite deposits formed during the Tertiary period in river valleys, originating from extensive lowland peatlands. Sedimentation across the region occurred under similar conditions of shallow lakes and marshes, resulting in lignite layers typically measuring a few to 10 m in thickness with a deposition depth of around 45–50 m.

Overlying the clays are Quaternary Pleistocene deposits, including a primary layer of glacial tills interspersed with lenses of sands and gravels, measuring 20 to 40 m; a layer of interglacial deposits comprising sands, gravels, and silts, with a thickness of 2 to 20 m; and a secondary layer of glacial tills, occasionally including interbedded sands or gravels, not exceeding 5 m.

Locally, Holocene deposits, such as peat, gyttja, silt, and thin sand layers, have accumulated on the Pleistocene formations, limited to closed depressions, marshes, old lakes, and river valleys.

The described geological structure applies to the upland areas. However, in the river valleys and lake sequences, deep erosive washouts occurred during the Eemian Interglacial and the Middle Polish Glaciation, cutting through the glacial till layers and sometimes the Pliocene and Miocene formations. These valleys were later refilled in the Pleistocene with sandy material, silts, clays, and occasionally gravels.

Figure 2. Schematic hydrogeological cross-sections through the AOI. See Figure 1 for the locations of the cross-sections. Geological formations are interpolated using kriging with semi-variogram analysis of data from 30 boreholes retrieved from the Polish Geological Institute–National Research Institute [52]. The approximate positions of Quaternary, Paleogene–Neogene, and Cretaceous aquifer systems are based on data from the Polish Geological Institute–National Research Institute [52] and from Wilk et al. [54].

2.3. Hydrogeology

The aquifer system in the AOI can be divided into three main levels: Quaternary, Tertiary, and Cretaceous (Figure 2) [52,54,56].

The Quaternary aquifer consists of three layers: groundwater, upper intergranular, and lower intergranular. The groundwater level exhibits high variability due to recharge, drainage, and seasonal precipitation differences.

The upper intergranular aquifer comprises sands and gravels separating glacial tills, with a few up to around 20 m thick and a variable filtration coefficient of up to about 5.8 × 10⁻⁴ m/s. The lower intergranular aquifer consists of sand beneath the lower glacial tills. In the excavation valleys, the aquifer sediments range from 5 to 60 m thick, and within fluvioglacial sediments, they are up to 20 m thick. The water table has a confined character, and the filtration coefficient is similar to the upper intergranular level.

In erosional troughs, there is a single aquifer complex with high filtration coefficients and a local thickness of up to 80 m. The water table is very close to the terrain surface and associated with surface watercourses and lakes.

The annual amplitude of groundwater level fluctuations under natural drainage can reach 1–2 m for free-flowing waters and up to 6 m for the lower aquifer on the uplands. Following the terrain, the free water table stabilises at 0.5 to 10–13 m. The Quaternary aquifer within the lignite mine depression cone is typically completely drained.

The Tertiary aquifer system is associated with Lower Miocene sands, which are present throughout the AOI, except in deep lake troughs that have been partially or completely eroded. Depending on the underlying Cretaceous basement configuration, this aquifer system has a variable thickness ranging from 40 to 70 m. The aquifer’s filtration coefficient is approximately 0.4 × 10⁻⁴ m/s. Originally, the water table in this aquifer was several to about a dozen metres below the surface, and it was artesian in some areas. However, this aquifer system has been extensively drained by mining activities. In the vicinity of erosional troughs, the Tertiary aquifer is recharged by surface waters through hydraulic contacts with the overlying Quaternary formations. Nevertheless, the waters of this aquifer are primarily fed by the underlying Cretaceous aquifer, with which the Tertiary sub-coal aquifer maintains a strong hydraulic relationship.

The Cretaceous aquifer comprises permeable Upper Cretaceous formations, which are fractured and consist of sandy marls, with sandstones in the northern part of the AOI. The main water-bearing features are numerous cracks and fissures, whose frequency decreases with depth. This aquifer has an average filtration coefficient of approximately 0.3–0.5 × 10⁻⁴ m/s. The Cretaceous aquifer is hydraulically connected to the Tertiary aquifer, forming a Tertiary–Cretaceous aquifer complex. The waters of this aquifer system have been subject to mining drainage, resulting in lowered levels. Recharge of the Cretaceous aquifer occurs in areas of hydraulic connectivity with the overlying Quaternary formations, such as the Warta River valley and lake troughs outside the deposit area, as well as through filtration from the upper aquifer layers.

2.4. Mining Exploitation in the “Konin” Lignite Basin

The “Konin” Lignite Basin is one of the four active lignite mining regions currently operating in Poland, alongside the “Bełchatów”, “Turów”, and “Sieniawa” Lignite Basins [57]. The “Konin” Lignite Basin hosts the active “Konin” Lignite Mine and the “Pątnów-Adamów-Konin” Thermal Power Plant Complex, which utilizes lignite and biomass to generate over 1100 MW of electricity, accounting for 4% of Poland’s total power production. Lignite mining was also previously carried out in the “Konin” Lignite Basin at the “Adamów” Lignite Mine from the 1960s to 2021 (Figure 3) [58].

2.4.1. Past and Current Open-Pit Mines

The research was conducted within the “Konin” Lignite Mine area. The use of lignite for heating purposes in this region dates back to the 19th century when residents initially extracted it from outcrops. An experimental open-pit mine was operational in the area north of Koło Town between 1922 and 1930, during which time the Polish Geological Institute’s exploratory drilling activities led to a more comprehensive understanding of the lignite deposits in this region [54,58].

The “Konin” Lignite Mine was established during World War II in connection with the “Morzysław” mine. Since then, 10 open-pit mines have been developed, with only the “Tomisławice” mine operating in 2024 (Figure 3, Table 1) [58].

The “Morzysław” mine began large-scale industrial coal exploitation in 1945 for electricity generation. It operated until 1953, extracting 1 million tons of coal. The former excavation site is now a park with recreational and sports facilities.

The “Niesłusz” mine operated from 1953 to 1961, extracting 4 million tons of coal. After exploitation ceased, an 18.5-hectare lake formed in the post-mining basin, and the area was reclaimed for recreation.

The “Gosławice” mine operated from 1957 to 1974, extracting almost 39 million tons of coal. It was the first in the Konin region to use large-capacity, high-performance machinery, modernizing the exploitation. A 32.5-hectare lake formed in the former excavation and the area was reclaimed for recreation.

The “Pątnów” mine operated from 1962 to 2001, extracting almost 130 million tons of coal. It was created due to increasing demand for lignite after constructing the “Konin” and “Pątnów” power plants. The area was reclaimed for forestry and agriculture, and a 360-hectare water reservoir was created in the final excavation.

From 1965 to 2011, the “Kazimierz” mine extracted 131 million tons of lignite from the “Pątnów III” deposit. The mining area was divided into two fields: “Kazimierz South”, where extraction ended in 1997, and “Kazimierz North”, which operated until 2011. The reclaimed “Kazimierz South” area covers 110 hectares, including a 65-hectare water reservoir. A sports airfield is located on the reclaimed internal dump. In the “Kazimierz North” area west of Kleczew, a 52-hectare water body is being formed.

Mining at the “Jóźwin” mine was carried out from 1971 to 2023. Lignite was initially extracted from the “Jóźwin I” field in the “Pątnów II” deposit, followed by the “Jóźwin IIA” field in the “Pątnów III” deposit. Exploitation of the “Pątnów IV” deposit at the “Jóźwin IIB” mine began in 1999 and ended in late 2023. The “Jóźwin IIA” area has been reclaimed for recreational and sports use. The largest post-mining water reservoir covering 763 hectares is being flooded in the final “Jóźwin IIB” excavation.

The “Lubstów” mine was exploited from 1982 to 2009, producing 107 million tons of lignite. The deposit had unique characteristics, with a seam thickness reaching up to 90 m, making it the thickest in the region. It was also Poland’s deepest lignite open-pit mine, reaching a depth of −55 masl with a surface elevation of +103 masl. The mine pit was flooded upon completion, forming a 480-hectare water reservoir.

The “Drzewce” mine operated from 2005, with industrial reserves of 35 million tons. Mining was conducted in the “Bilczew” and “Drzewce A” fields, as well as the “Drzewce B” field, and was ultimately completed in August 2022. A 33-hectare water reservoir has formed in the former “Bilczew” field, and the flooding of the “Drzewce B” field began in May 2023, creating a final reservoir of 125 hectares by 2031.

The only currently active lignite mine in the “Konin” Lignite Basin is the “Tomisławice” mine. Overburden removal began in May 2010, with industrial reserves estimated at 41 million tons. Mining operations commenced in September 2011 and were planned to continue until 2031. However, the mine owner has indicated the possibility of an earlier closure. Upon mining, the site will be transformed into a sports and recreational complex, with a water reservoir covering an area of over 200 hectares.

2.4.2. From Mining Impacts to Energy Transition and Mine Closure

Lignite mining and waste piles have significantly altered the landscape in the AOI, resulting in artificial landforms with substantial elevation changes (Figure 3). The external waste heap at the “Pątnów” mine reaches an elevation of 160 masl, while the bottom of the “Lubstów” mine extends down to −50 masl.

Mining activities necessitated the extraction of large volumes of groundwater, leading to extensive modification of the natural drainage system (Table 1). Several canals were constructed to manage the discharge of drainage water from the lignite open pits. Each open-pit mine developed a depression cone, with the drainage level determined by the depth of the installed water discharge systems. The proximity of the “Pątnów”, “Jóźwin”, “Kazimierz Południe”, and “Kazimierz Północ” pits resulted in the formation of a common depression cone, while smaller cones formed around the “Lubstów”, “Drzewce”, and “Tomisławice” pits (Figure 3) [54,60].

The primary drainage centre, located in the “Pątnów” deposit within the Tertiary–Cretaceous aquifer, spanned approximately 350 km². Mining operations and associated drainage of the aquifer system significantly increased the infiltration rate, namely by roughly 2.5 times compared to the natural drainage regime through rivers and lakes. This heightened infiltration resulted in reduced groundwater discharge to rivers, the disappearance of groundwater evapotranspiration, and decreased surface water evaporation. In the Quaternary aquifer, the extent of the depression cone is largely determined by the layer’s permeability and typically extends only a few hundred metres from the pit edges, often forming an irregular shape (Figure 3) [61].

With lignite resources dwindling, mining efficiency declining, and electricity production from lignite becoming increasingly costly, a complete cessation of mining activities is planned for the AOI in the coming years [62]. The AOI is characterised by intense anthropogenic pressure, including a highly developed drainage network, regulated river channels, and mining dewatering activities. Climatic factors, particularly low precipitation levels, can further exacerbate these challenges. In central-western Poland, water levels in most bodies have decreased by an average of 0.2 to 0.5 m over the past 60 years. However, in areas subject to significant anthropogenic pressure, the declines have been more pronounced, ranging from 1 to 6 m [60].

The planned cessation of lignite mining aims to restore and reclaim the degraded areas. This effort involves replenishing water resources in rivers and lake districts and creating new water bodies in the abandoned mine pits. Additionally, the program seeks to enhance water retention in agricultural catchments, develop retention strategies to mitigate water shortages, and construct retention reservoirs [61].

3. Materials and Methods

The methodology of this study comprised three main components.

InSAR-Based Spatial and Temporal Land Surface Movement

The first phase involved the use of InSAR data to identify and analyse vertical land surface movements within the AOI, focusing on both subsidence and uplift. The analysis included regions affected by historical and ongoing mining activities, as well as areas located outside the mining influence zones. This approach allowed for the assessment of land surface movements directly associated with lignite mining and those attributable to broader regional impacts, such as climate change. Spatial analysis techniques were used to distinguish between these overlapping patterns, enabling the identification of mining-related and climate-related influences on observed land surface movements in the AOI.

Aquifer System Depletion Analysis

The second phase consisted of an analysis of groundwater level time series data from two observation networks. The first network monitored the impacts of mining activities, while the second was part of the Polish national observational research network, which covered areas outside the mining influence zones. This dual approach facilitated the evaluation of aquifer system changes under both anthropogenic influences and natural conditions driven by climate change in non-mining regions. The groundwater level time series were then correlated with the land surface movement data to characterise the groundwater storage capacity of the aquifer system within the AOI.

Meteorological Data, Groundwater Level, and Land Surface Movement Correlation

The final phase focused on analysing meteorological time series data to identify long-term climate trends within the AOI. Additionally, the meteorological data were cross-correlated with the findings from the first two phases, namely land surface movement and groundwater levels, to explore the interrelationships between these variables. This analysis facilitated the evaluation of the impact of climatic changes on the observed fluctuations in land surface movements and groundwater levels.

The study utilized InSAR data from the periods 2015–2021 and 2018–2022. These time frames partially overlapped with the available groundwater level data, which spanned 2009–2019 for the mine piezometer network and 2009–2023 for the Polish national observational research network. To ensure consistency, meteorological data from 2009 to 2023 were also employed. Given the availability of InSAR data, groundwater level, and meteorological data, the analysis of land surface movement in mining areas was conducted specifically for four mining regions where exploitation has been carried out since 2009. These include the mines “Jóźwin”, “Lubstów”, “Drzewce”, and “Tomisławice”.

3.1. InSAR-Based Spatial and Temporal Land Surface Movement

The study utilized data from the European Ground Motion Service (EGMS) to identify and analyse land surface movement within the AOI [63]. The EGMS provides consistent, regular, and reliable information on land surface movements across Europe with millimetre-level accuracy. This dataset, derived from interferometric analysis of Sentinel-1 radar imagery acquired every six days, offers comprehensive spatial and temporal resolution. The land surface movement products are updated annually and generated using persistent and distributed scatterer radar interferometry techniques. As the first publicly available dataset for continental-scale land movement, the EGMS supports a wide range of applications and research endeavours.

The EGMS data have been validated through various investigations across European regions, demonstrating robustness and reliability [63,64,65]. The data, available for download in CSV format, include time series of land surface motion with information on mean velocity, standard deviation, Root Mean Square Error, and spatial coordinates for observation points over the study period.

For this analysis, ortho-level data from the initial and secondary EGMS releases, covering the periods 2015–2021 and 2018–2022, were used. Given the limited range of land movement within the AOI, the analysis focused on the vertical component of land surface motion, as vertical displacements tend to be more significant than horizontal ones. Spatial and temporal patterns of vertical land surface movement were examined within both mining-affected and non-mining areas, using spatial analysis in a Geographic Information System (GIS).

3.2. Aquifer System Depletion Analysis

To investigate the spatial and temporal characteristics of the aquifer system within the AOI, time series data from two groundwater monitoring networks were analysed (Figure 3).

The first network was established to monitor the impacts of mining at the “Tomisławice” open-pit mine [59]. Piezometer clusters recorded groundwater levels in the Quaternary, Paleogene, Neogene, and Cretaceous formations. These piezometers were divided into two groups based on spatial positioning: external and internal. The external network, comprising 40 piezometers numbered PI, PII, and PIII, assessed the effects of mine dewatering on the area between the lignite deposit and nearby lakes. The internal network included 63 piezometers, labelled PT, situated within the mining terrain, dewatering well barriers, and a depression cone. Groundwater levels were measured quarterly since June 2009, with data from 8 piezometers (4 from each network) used in this study to monitor the deeper aquifers. These piezometers have hydraulic connections and are subject to strong anthropogenic pressures, indicating a semiconfined aquifer system (Figure 3, Table 2).

The second network is part of the national observational research network operated by the Polish Geological Institute–National Research Institute, active since 1974 [52]. This network monitors groundwater levels, spring discharges, and chemical composition at numerous points, some with automated daily measurements. It distinguishes between first-order stations (multiple piezometers monitoring aquifer horizons) and second-order stations (single piezometers or cased springs). Data from 12 piezometers, including 11 s-order stations and 1 first-order station, located outside mining areas, were used to identify groundwater level changes due to non-mining factors (Figure 3, Table 3). Among these, 4 piezometers monitor unconfined groundwater, while the others focus on confined aquifers (Table 3).

The analysis involved examining spatial distributions and linear trends in groundwater levels from both networks. The 2016–2021 joint observation period, when both groundwater level and land surface movement data overlapped, was used to assess the spatial and temporal behaviour of these phenomena. This approach enabled the evaluation of the impact of mining-induced drainage on aquifer depletion and the separation of changes attributable to non-mining factors.

Additionally, the joint observation period was used to characterise the aquifer’s storage properties by determining storativity (S), a parameter indicating the volume of groundwater released or stored per unit area per unit change in hydraulic head [66]. In confined aquifers, reduced hydraulic head increases effective stress, causing aquifer compaction. The storage coefficient was estimated based on the relationship between aquifer compaction and hydraulic head decline [67,68,69]:

S \approx S_{k} = S_{s k} \cdot b_{0} = \frac{Δ b}{Δ h},

(1)

where

S_{s k}

is the skeletal-specific storage,

b_{0}

is the original thickness of the confined aquifer,

Δ b

is the vertical component of the land surface motion, and

Δ h

is the groundwater level change.

It was assumed that skeletal compressibility far exceeds that of water, rendering water storativity negligible. Consequently, the storage coefficient was approximated as skeletal storativity. As skeletal storativity can vary with effective stress, two forms were distinguished: elastic skeletal storativity and inelastic skeletal storativity [66]. Inelastic skeletal storativity, which is typically one to two orders of magnitude greater, represents long-term, irreversible deformation. Given the observed long-term declining trends in both groundwater levels and land surface movements within the AOI, in this study, inelastic skeletal storativity was calculated, providing a more accurate representation of aquifer behaviour over extended periods [68].

3.3. Meteorological Data, Groundwater Level, and Land Surface Movement Correlation

To evaluate the impact of long-term climate trends on the environment, time series data from the Kołuda Wielka meteorological station were analysed (Figure 1B). This station is representative of the lignite mining areas within the AOI and is managed by the Polish Institute of Meteorology and Water Management–National Research Institute [70], which has been in operation since 1919. It is part of a network that includes 63 synoptic stations, over 900 climatic and precipitation stations, and more than 900 hydrological stations across Poland.

Continuous climate change necessitates ongoing updates to the understanding of climatic variability, which includes extending historical data records. This allows for the analysis of climatic trends over extended periods, often exceeding 100 years. However, using historical data introduces challenges, particularly in ensuring the homogeneity of data series. Homogeneity is crucial to ensure that variability in the data reflects actual climatic conditions, free from external influences such as changes in station location, equipment modifications, or alterations to the surrounding environment. The data from the Polish Institute of Meteorology and Water Management–National Research Institute meet these criteria, ensuring reliable and consistent analysis [70].

Observations at the meteorological stations were conducted hourly, with data collected at eight specific times: 00, 03, 06, 09, 12, 15, 18, and 21 UTC. Parameters measured included atmospheric pressure, air temperature, relative humidity, wind direction and speed, cloud cover, precipitation, sunshine duration, and snow cover depth. For this study, the analysis was focused on air temperature and precipitation data, as these variables directly affect groundwater level fluctuations and land surface movement [70].

Air temperature was recorded in degrees Celsius [°C] using automated equipment placed in a meteorological enclosure at a height of 2 m above ground level. Daily maximum and minimum temperatures were reported for a standard period from 18.01 UTC on the previous day to 18.00 UTC on the current day. Precipitation data were collected at 00, 06, 12, and 18 UTC using rain gauges with a reception area of 200 cm², positioned 1 m above the ground. Daily totals for precipitation were calculated for the period from 06.01 UTC of the current day to 06.00 UTC the following day [70].

Time series analysis was conducted over two distinct periods: a long-term period from 1991 to 2023, which enabled the identification of long-term meteorological trends in the AOI, and a more recent period from 2009 to 2023, corresponding to the availability of groundwater level data from piezometers in the Polish national hydrogeological network. The analysis of the latter period aimed to provide insights into climate variability and its effects on groundwater levels in recent years.

To investigate the relationship between climate variables and groundwater levels, cross-correlation analysis was employed using the cross-correlation function (CCF). This statistical method identifies potential time lags, where past values of one time series (e.g., meteorological data) may influence current values of another time series (e.g., groundwater levels). In this study, each time lag represents one month, with the CCF calculating correlations at different monthly intervals. Identifying significant time lags allows for an understanding of how changes in climate variables, such as temperature and precipitation, may precede variations in groundwater levels over monthly timescales. The cross-correlation analysis was undertaken solely for piezometers located outside of zones impacted by mining, within the national observational research network. The trend component pertaining exclusively to climate changes is distinctly evident in these piezometers. Conversely, the time series of groundwater levels recorded at piezometers situated within the mining network are considerably dominated by a long-term declining trend attributable to mining operations. Consequently, such cross-correlation analysis would not produce reliable findings.

4. Results and Discussion

4.1. Land Surface Movement in Mining and Non-Mining Areas

The land surface movement in the AOI, as determined by the EGMS, is relatively minor, ranging from −23 to 14 mm/year for the period 2015–2021 (Figure 4A, Table 4) and −26 to 8 mm/year for the period 2018–2022 (Figure 4B, Table 5). The average value of land surface movement across the entire AOI is 1.11 mm/year for the period 2015–2021 and −1.18 mm/year for the period 2018–2022. For both measurement periods, the land surface movements exhibit a similar range of values, indicating that, on average, the land surface in the AOI has experienced slight but continuous subsidence during the analysed periods, with slightly higher subsidence rates in recent years compared to the previous measurement period.

The spatial and temporal distribution of land surface movement in the AOI is highly irregular (Figure 4). Generally, the average value of land surface movement determined exclusively within mining areas, mining terrains, and depression cones is −1.08 mm in 2015–2021 (Table 4) and −1.35 mm in 2018–2021 (Table 5), suggesting smaller subsidence in these areas compared to the regions outside the mining and depression zones, where subsidence amounts to −1.11 mm and −1.13 mm in 2015–2021 (Table 4) and 2018–2022 (Table 5), respectively. Notably, the standard deviations of these values are ±0.765 mm and ±0.862 mm for the periods 2015–2021 and 2018–2022, respectively, which are the lowest among all the regions analysed in this study. This suggests a strong spatial and temporal correlation of the InSAR signal outside mining-influenced zones, indicating a high reliability of determining land surface movement in these regions.

In the case of mining areas and terrains, three zones of subsidence and three zones of uplifts can be distinguished (Figure 4).

The first and largest subsidence zone is located in the vicinity of the “Tomisławice” mine, covering an area similar to the mining terrain boundaries (Figure A1, Table 4 and Table 5). However, subsidence also occurs north of this area, within the depression cone associated with the mine’s operation. Between 2015 and 2021, subsidence within the mining area averaged −5.17 mm/year, while in the surrounding mining terrain, it was −2.26 mm/year, amounting to a total of around −35 mm. In the later period of 2018–2022, subsidence in the mining area was −4.92 mm/year, and in the surrounding mining terrain −1.67 mm/year, reaching a total of around −40 mm. Both the values and the extent of subsidence in the “Tomisławice” mine were smaller in the second analysis period compared to the earlier years, indicating a greater intensity of subsidence in the initial stage of the mine’s operation, which commenced in 2011. During 2015–2021, the subsidence centre covered practically the entire “Tomisławice” open pit, while in 2018–2022, the largest subsidence occurred in a smaller central and eastern part of the mining area.

The second subsidence zone can be distinguished in the eastern part of the “Drzewce” mine, specifically the “Drzewce A” and “Drzewce B” open pits (Figure A2, Table 4 and Table 5). This subsidence is evident in both analysis periods, reaching total values of up to 20 mm. In 2015–2021, the subsidence zone was centred east of the “Drzewce B” open pit, covering a large area in the eastern part of the “Drzewce” mine. However, in 2018–2022, the highest subsidence was concentrated mainly in the central part of the “Drzewce A” open pit. The reduced intensity of subsidence over time is most likely related to the cessation of lignite mining, which occurred in 2022, and the subsequent preparation of the area for reclamation, including water reclamation.

The third subsidence zone was observed within the “Jóźwin” mine, exclusively during the 2018–2022 period (Figure A3, Table 4 and Table 5). This zone is centred around the “Jóźwin” open pit and extends south-eastward, between the “Kazimierz Północ” and “Pątnów” open pits. The subsidence rates in this period averaged −2.49 mm/year, culminating in up to 60 mm of total subsidence. However, this subsidence zone occupies only a small portion of the “Jóźwin” mine’s operational area and is most likely linked to the lignite mining activities conducted there, which ultimately ceased in 2023. Additionally, the high standard deviation of land surface movement in the “Jóźwin” mining area, reaching ±6.94 mm, namely the highest among all analysed regions across the two measurement periods, may also indicate the changing terrain model associated with mining operations in this area.

The largest zone of surface uplift is situated in the “Jóźwin” mine (Figure A3, Table 4 and Table 5). This uplift predominantly covers the central and western parts of the mining region, occurring in a broad buffer surrounding the “Kazimierz Południe” and “Kazimierz Północ” open-pit mines, where operations concluded in 1997 and 2011, respectively. Over the past decade, water reservoirs have formed in the mining excavations, which are still undergoing impoundment. The highest uplift values are observed east of the “Kazimierz Północ” open pit, in the Kleczew Town area and adjacent to the newly created water reservoir. Uplift rates were higher from 2015 to 2021, reaching approximately 20 mm total, compared to around 5 mm from 2018 to 2022, indicating a decrease in uplift intensity as the degree and duration of reservoir flooding increased. Conversely, in the “Pątnów” open pit, where mining ceased in 2001 and a water reservoir was formed, the observed land surface movements do not indicate ongoing uplift. This suggests the area has reached a new hydrodynamic equilibrium due to the rising groundwater table and is no longer experiencing uplift.

The second zone of uplifts, observed across the two analysed measurement periods, occurs north of the former open pit of the decommissioned “Lubstów” mine, which ceased operations in 2009 (Figure A2, Table 4 and Table 5). In this location, a water reservoir approximately 140 m deep is forming. The uplifts exhibit a trough-like shape stretching northward, which infiltrates the subsidence trough caused by the activity of the “Tomisławice” mine and partially overlaps with the depression cone of the former “Lubstów” mine. The total uplift values in this area reached up to around 10 mm between 2015 and 2021 and decreased to approximately 0 mm between 2018 and 2022, indicating a reduction in the intensity of uplifts over time as the water reservoir continued to fill.

Finally, a third, smaller zone of uplifts was detected in the “Drzewce” mine, specifically in its central and western parts around the “Bilczew” open pit, where a water reservoir covering an area of over 30 hectares is being created (Figure A2, Table 4 and Table 5). The uplift values in this zone reached approximately 2–3 mm/year and were lower during the second measurement period from 2018–2022. This uplift zone connects with the uplift zone around the former “Lubstów” open pit, forming a continuous belt of land surface movement reaching the “Tomisławice” mine area.

In general, subsidence and uplifts occur in close proximity and are linked to local hydrogeological conditions. These conditions are driven primarily by mining exploitation and ongoing reclamation of post-mining areas, and are specifically linked to the construction of reservoirs in former open-pit mines. However, subsidence in mining and post-mining areas is the result of human activity on a micro-scale and should be considered within the broader, macro-scale context. These macro-scale land surface movements are not directly related to mining activities but stem from broader climatic conditions. Therefore, understanding the interplay of these two phenomena is essential for reliable assessment of land surface movement in mining and post-mining areas.

Furthermore, considering the average value of subsidence outside mining influence zones, the observed land surface movement in mining areas directly related to human activity must be adjusted for these background trends (Figure 4, Table 4 and Table 5). This indicates that subsidence in mining areas is smaller, and the uplifts are larger than the raw observations would suggest.

Land subsidence was recorded across the entire AOI, including regions outside the influence of mining. On a regional scale, given the modest subsidence values, they are unlikely to pose a direct threat to the infrastructure or inhabitants of the affected areas. They will also not impact the topography, nor alter the hydrographic network. Nevertheless, these subsidence rates indicate a gradual loss of land surface elevation due to the progressive deficit of groundwater in the near-surface aquifers, as described in more detail in Section 4.2.

4.2. Spatial and Temporal Characteristics of the Aquifer System

The majority of piezometers monitoring in the AOI suggest a decline in the groundwater level in recent years (Figure 5, Figure 6, Figure 7 and Figure 8, Table A1 and Table A2). In general, two aquifer systems have been depleted, with the deeper-lying Paleogene–Neogene system experiencing greater depletion than the near-surface Quaternary aquifer. However, the groundwater levels exhibit a high degree of variability both temporally and spatially, showing large differences depending on the type of monitoring network. This is most likely due to the combined impact of anthropogenically driven groundwater level decline and the corresponding aquifer system compaction caused by the climate posing stress on groundwater resources.

The groundwater level monitoring data from the “Tomisławice” mine network indicate that the most substantial declines during the analysis period from December 2009 to December 2019 occurred in piezometers situated closest to the centre of the mine’s drainage area, namely PT20, PI-1, and PT3 (Figure 5, Table A1). In the Paleogene + Neogene aquifer system, these piezometers recorded decreases of approximately 26 m, 18 m, and 12 m, respectively. Similarly, the Quaternary aquifer system exhibited declines of around 8 m, 11 m, and 12 m in these piezometers. In contrast, the smallest groundwater level decreases of around 1 m for both the Quaternary and Paleogene + Neogene aquifers were observed in piezometer PIII-3, located farthest from the centre of the mine’s drainage area. Overall, these groundwater level declines coincide with previous studies on the impacts of mining activities on the regional hydrogeological system.

The spatial distribution of groundwater level changes observed in the piezometers of the “Tomisławice” mine monitoring network exhibits a non-uniform pattern, correlating with the distance from the centre of the drainage area (Figure 3 and Figure 5, Table A1). Generally, groundwater level declines tend to be smaller at greater distances from the drainage centre. However, this relationship is not linear, confirming the asymmetric nature of the depression cone, as depicted in Figure 3. The cone of depression appears to be constrained by the presence of lakes located northwest of the mine and is elongated towards the north. The variability in groundwater level changes across the monitoring network can be attributed to the heterogeneity of the aquifer and the complex hydrogeological characteristics of the aquifer system, which were not the focus of this study.

The most significant declines in groundwater levels were observed during the initial period of the monitoring, i.e., 2011–2013 (Figure 5). This was evident in the piezometers situated closest to the centre of the drainage area, namely PT3, PT20, and PI-1, and was observed in both the Quaternary and Paleogene + Neogene aquifer systems. This dynamic may suggest a correlation between the commencement of lignite extraction in 2011 and the decline in groundwater levels. Interestingly, in the subsequent monitoring period from 2013 onwards, as well as in the case of other piezometers in the “Tomisławice” mine monitoring network located further from the drainage centre, the rate of groundwater level decline was lower. Notably, during the latter years of the analysed period, between 2016 and 2019, a strong stabilisation of groundwater levels is observed in most of the piezometers in this monitoring network. In some piezometers located closer to the drainage centre, particularly in the Quaternary aquifer, a slight groundwater rebound is even visible. This may indicate the stabilisation of groundwater levels at a new hydrostatic level in the near-surface aquifer layers. However, this trend is less pronounced for the deeper Paleogene + Neogene aquifer, suggesting greater depletion of the deeper aquifer system.

The observed declines in groundwater levels have been accompanied by subsidence, which has been observed around all piezometers in the “Tomisławice” mine monitoring network (Figure 5, Table A1). Although the time series of land surface movement only partially overlapped with the groundwater level time series, covering the period from December 2015 to December 2021, a relationship between the magnitude of groundwater level declines and subsidence is evident. The largest subsidence during this period was observed for the piezometers PT20, PT3, and PI-1, with values of approximately −38 mm, −34 mm, and −18 mm, respectively. In contrast, the subsidence was significantly smaller, ranging from around −12 mm to −3 mm, for the remaining piezometers. This difference is reflected in the high determination coefficients, R², and correlation coefficients, R, of the linear trends fitted to the land surface movement observation time series for the three piezometers with the largest subsidence values. This is likely due to the dominance of the subsidence trend over seasonality, which is at least an order of magnitude smaller in value than the trend. For piezometers PIII-1, PT34, PIII-2, and PIII-3, the R² and R coefficients are much lower, which is likely due to a smaller decreasing trend and more pronounced seasonality in the land surface movement time series around these piezometers. The observed subsidence has likely resulted from compaction of the aquifer materials and other geomechanical effects induced by the mining-related groundwater drawdown.

The groundwater storage coefficients determined from the joint observations of groundwater levels and land surface movement across all piezometers are very similar, averaging 1.83 × 10⁻² ± 1.60 × 10⁻² for the Quaternary aquifer and 7.23 × 10⁻³ ± 7.91 × 10⁻³ for the Paleogene + Neogene aquifer (Table A1). These values align with literature data for Quaternary and Paleogene + Neogene formations [71]. Generally, the groundwater storage coefficients are smaller for the deeper layers and larger for the shallower layers, consistent with the principle that storage capacity decreases with increasing depth [72].

In contrast, a different hydrogeological situation is observed for piezometers belonging to the Polish national hydrogeological monitoring network, located outside the mining influence zone of all mines in the AOI (Figure 6, Figure 7 and Figure 8, Table A2). Here, groundwater level declines are much smaller compared to the piezometers belonging to the “Tomisławice” mine monitoring network. Additionally, a strong seasonality is evident in the time series, particularly in piezometers monitoring unconfined aquifers, and to a lesser extent in piezometers monitoring confined aquifers. This suggests the existence of hydraulic connections between these two aquifer layers and the land surface.

The long-term time series between December 2009 and December 2023 for all piezometers in the national network have observed groundwater level declines ranging from approximately −0.3 m for piezometers II/27/3 and I/999/1 to around −3.8 m for piezometer II/72/1. Notably, the groundwater level decline during this period exceeded 1 m in only 3 out of the 12 piezometers in the national hydrogeological network: II/72/1, II/197/1, and II/902/1. Of these three, two—II/72/1 and II/902/1—are located at a significant distance, around 6.9 km and 18.3 km, respectively, from the mining areas, terrains, and the depression cones caused by mining activities in the AOI (Figure 3). The relatively large groundwater level declines observed in these piezometers compared to the remaining ones may be attributed, in the case of piezometer II/902/1, to its upland location, where the Quaternary aquifer layers are generally thinner than in river and lake valley areas (Figure 3). The significant decline in groundwater levels for piezometer II/72/1 may also be associated with a potential measurement error, evident as a substantial drop over a relatively short period between January 2015 and January 2016 (Figure 8). For piezometer II/197/1, which is near the depression cone of the “Tomisławice” mine, the groundwater level declines may be influenced by the dewatering of rock layers due to mining activities (Figure 3). However, an analysis of the groundwater level declines observed in all piezometers of the national observation network does not indicate a statistically significant relationship between the magnitude of the declines and the distance from the nearest mining-influenced zone, suggesting that other factors, most likely climatic changes (see Section 4.3), rather than mining-related causes, may be responsible for the groundwater level declines in these piezometers.

The land surface movement dynamics at piezometers in the national hydrogeological observation network demonstrate a relatively uniform pattern for the majority of piezometers, characterised by a dominant, steady trend in land surface movements (Figure 6, Figure 7 and Figure 8, Table A2). This temporal trend is similar to the observed declines in groundwater levels across selected piezometers. Furthermore, the groundwater storage coefficient values calculated based on the joint observations of groundwater levels and land surface movements across all piezometers are relatively consistent, with an average of 5.54 × 10⁻² ± 8.93 × 10⁻² (Table A2). This value is slightly higher than the groundwater storage coefficient determined for the piezometers in the “Tomisławice” mine monitoring network for the Quaternary aquifer layers but remains within the same order of magnitude (Table A1 and Table A2). The calculated groundwater storage coefficient values, coupled with the distinct seasonal fluctuations observed in groundwater levels and land surface movements, further indicate the existence of hydraulic connections between the land surface and the aquifer layers analysed in this study. This suggests that factors other than mining-related causes may have a significant influence on the water balance changes in the area of interest (see Section 4.3).

In general, the results indicate widespread declines in groundwater levels across the monitored piezometers, both within and outside the mining influence zones. These declines are most pronounced in areas affected by active mining drainage, particularly within the “Tomisławice” mine. Here, groundwater levels have dropped significantly, impacting the region’s water retention capacity and potentially leading to the drying of shallow wells and reduced water availability. However, a precise assessment of these effects requires localised evaluations using detailed numerical models.

Beyond the actively mined areas, gradual groundwater level declines are also visible across the entire AOI, albeit at a smaller magnitude. Despite their lower scale, these ongoing reductions over several years could contribute to intensified hydrogeological drought conditions and a worsening of water resources in the region. This process may be mitigated by the closure of open-pit mines and the development of retention reservoirs, projects currently underway and scheduled to continue in the coming years (see Section 2.4.2). Although this study could not directly assess groundwater level rebound near the newly constructed reservoirs due to limited data, post-mining excavation reservoirs appear to aid in raising groundwater levels. This is indirectly observed through localised land surface uplift zones, as described in Section 4.1. On one hand, groundwater level recovery should help re-establish the region’s hydrogeological balance to pre-mining conditions. Furthermore, it may also counteract the regional effects of climate change, manifested as hydrogeological drought. However, achieving these benefits will require further detailed studies to fully understand the impact.

4.3. Long-Term Climate Trends and Their Environmental Impact

The AOI is situated in a transitional climate zone. Long-term climate data from 1991–2023 indicate that the average annual air temperature recorded at the Kołuda Wielka meteorological station is +8.9 °C (Figure 9A). Seasonal variations are evident, with periodic peaks corresponding to summer and winter months. The linear trend line suggests a gradual warming trend over the 32 years, with an increase of about 0.0017 °C per year. In the more recent 13-year period, from 2009 to 2023, the mean monthly temperature was slightly higher at 9.2 °C, suggesting warmer conditions during this more recent period (Figure 9B). The rate of increase is higher compared to the longer time frame, at 0.0050 °C per year, indicating an accelerated warming trend since 2009. While seasonal cycles remain consistent, the increase in the temperature trend may be linked to recent climatic changes or increased anthropogenic influences.

The rate of air temperature increase may seem relatively small, but it represents a consistent and gradual warming trend over both the long and short term. Such small incremental changes, when compounded over several decades, can have significant impacts on the local climate and ecosystem. While the rate of change may appear modest, it is crucial to monitor these trends closely, as they could further accelerate in the future.

Furthermore, examining extreme temperature indices reveals that the frequency of warm months has increased over the last 13 years (Figure 9). This suggests a decline in the number of days with snow cover in the AOI in recent years. The lack of snow cover and increasingly warmer winter months, in turn, result in reduced groundwater recharge during winter, with potential further negative consequences for local ecosystems.

The AOI is characterised by low precipitation, leading to water deficits. The mean monthly precipitation values between 1991 and 2023 are around 42.7 mm, equating to a mean annual precipitation of 512.4 mm, with a slight upward trend of approximately 0.0044 mm per year (Figure 9A). This positive trend suggests a small increase in overall precipitation, although there are alternating periods of higher and lower rainfall.

More recently, between 2009 and 2023, the mean monthly precipitation was higher, at 43.5 mm (522 mm per year), but there was a downward trend of about 0.0053 mm per year, indicating a shift towards drier conditions despite the overall higher mean (Figure 9B). This may reflect changes in precipitation patterns, such as increased frequency of dry spells or fewer intense rainfall events, which could be characteristic of the transitional climate changes observed in Europe in recent decades.

The observed increase in temperature and alterations in precipitation patterns could have significant implications for groundwater recharge, surface water availability, and the overall regional water balance. However, while the trends observed in the AOI align with regional climate change projections, the high variability and complex interactions between temperature and precipitation since 2009 may be linked to increased anthropogenic activities, such as urbanization or land use changes, which could also influence local climatic conditions. The divergence in precipitation trends suggests that despite a long-term increase, recent years have been marked by drier conditions, potentially stressing water resources, particularly in confined aquifers reliant on consistent recharge rates.

This correlation between climatic conditions and groundwater level is evident from the analysis of groundwater levels in the AOI, encompassing both unconfined, shallow aquifer systems (Figure 10) and confined, deeper-lying layers (Figure 11).

Generally, for unconfined aquifer systems, the cross-correlation results exhibit periodic fluctuations, suggesting a seasonal relationship between temperature and groundwater levels (Figure 10). This pattern is observed across the four piezometers analysed, indicating a widespread seasonal effect. However, differences in the correlation values are noted over the years, particularly for precipitation and groundwater levels, most notably in the case of piezometer II/1270/1. This is likely attributed to the variability of precipitation and the local hydrogeological conditions at the individual piezometer locations.

Notably, the negative cross-correlation peaks between temperature and groundwater levels are larger than the positive peaks. The negative peaks may indicate an inverse relationship, where groundwater levels decrease due to higher temperatures causing increased evaporation. Conversely, positive peaks at certain lags suggest that temperature changes could lead to changes in groundwater levels several months later, potentially due to delayed effects such as changes in evapotranspiration.

The cross-correlation for precipitation shows significant peaks at shorter lags, indicating a more immediate response to precipitation events. This is typical for unconfined aquifers, as they are more directly influenced by rainfall. The patterns suggest that groundwater levels rise shortly after precipitation events, reflecting the rapid recharge of the aquifer, which is consistent with the high permeability of the Quaternary sediments.

Unconfined aquifers, especially those of Quaternary origin, are typically characterised by high permeability and are closely connected to surface water. They also exhibit higher water storage capacity than the deeper aquifer layers, as evident from the specific yield coefficient (see Section 4.2, Table A1 and Table A2). This means that groundwater levels in these aquifers are expected to respond more quickly to changes in climatic conditions, such as temperature and precipitation variations.

In contrast, groundwater in confined aquifers is trapped between layers of low-permeability material, which restricts the direct recharge from surface water. This typically results in a delayed response to climatic conditions compared to unconfined aquifers.

Therefore, the cross-correlation patterns show weaker and less distinct peaks for temperature compared to unconfined aquifers (Figure 11). This aligns with the nature of confined aquifers, which are insulated from direct temperature changes due to the presence of impermeable layers. Specifically, there is a sinusoidal pattern in all analysed piezometers, indicating periodic influences, but the peaks are generally lower, suggesting a less direct relationship between temperature and groundwater levels in confined aquifers. However, as in the case of unconfined aquifers, there is a predominant negative correlation over a positive correlation. The negative correlation with a delay of about 1–3 months indicates a relationship between high temperatures and increased evaporation leading to low groundwater levels. Conversely, the positive correlation with a time lag of about 2–4 months suggests decreased evaporation during winter periods leading to an increase in groundwater level. The delay in these correlations at various lags suggests delayed responses, possibly due to slower temperature propagation through deeper geological formations.

The cross-correlation values between precipitation and groundwater levels are generally stronger compared to temperature correlations but still weaker than those observed in unconfined aquifers. The peaks range up to about ±0.25–0.30. In most of the analysed piezometers, the pattern is rather regularly sigmoidal, reflecting a similar response to precipitation events despite the confinement. There is a greater positive correlation over negative correlation, of about 4–5 months over 2–3 months. This indicates an inverse relationship between precipitation and groundwater levels. These seasonal influences suggest that precipitation effects become more noticeable over time due to delayed recharge in confined aquifers.

5. Conclusions

This investigation examines the combined impacts of decommissioning lignite mines and long-term climate patterns on groundwater systems and land surface movement within the Konin region of Poland, an area of extensive open-pit lignite extraction and associated groundwater dewatering. Given the low annual precipitation in the AOI, it is crucial to explore the overlapping climate-related drivers of hydrogeological changes.

The research objectives include assessing spatial and temporal variations in land surface movements, evaluating groundwater level alterations due to mining activities and climate change, and analysing long-term meteorological trends. The study spans from 1991 to 2023, with a particular focus on 2009–2023 to utilize groundwater level monitoring data, as well as 2015–2022 for land surface movement data. Both mining and non-mining areas were considered to differentiate between land surface movement caused by mining and broader regional impacts potentially linked to climate change.

The findings indicate relatively modest land surface movements, with subsidence rates ranging from −26 to 14 mm/year within the “Tomisławice” mining area and approximately −1 mm/year in zones unaffected by mining. In contrast, land uplift of only a few millimetres per year is observed in the “Jóźwin” mining terrain, specifically in the area of the closed mine, suggesting that the uplift values are lower than the subsidence observed due to mining activities. After accounting for background subsidence in non-mining zones, the actual subsidence in mining areas attributable to aquifer system dewatering is less pronounced, while the uplift appears more significant than the raw data implies.

Groundwater monitoring revealed significant declines in both the shallow Quaternary and deeper Paleogene–Neogene aquifers, particularly near mining areas. The most marked groundwater level drops occurred between 2009 and 2019, with declines of up to 26 m in the deeper aquifers near the “Tomisławice” mine. The sharpest declines were observed from 2011 to 2013, followed by a stabilisation in later years. In the case of piezometers located outside zones influenced by mining, groundwater level changes were significantly smaller, but still indicated a steady drawdown of a maximum of a few metres. A correlation was observed between groundwater level drops and land surface subsidence.

Analysis of cross-correlations reveals that unconfined aquifer systems respond rapidly to precipitation fluctuations but more gradually to temperature variations, while confined aquifers exhibit muted responses due to the insulating effect of overlying layers. Mining-driven dewatering represents a primary driver of hydrogeological changes. However, climatic factors, including rising temperatures and shifting precipitation patterns, also significantly contribute.

Meteorological data spanning 1991 to 2023 indicate an average annual temperature of +8.9 °C (9.2 °C for 2009–2023), with an accelerated warming trend of about +0.0050 °C per year observed from 2009 onwards. Precipitation patterns exhibited a slight long-term increase, from mean yearly precipitation of approximately 512 mm between 1991 and 2023 to 520 mm between 2009 and 2023. However, a shift towards drier conditions occurred from 2009 to 2023, characterised by more frequent dry spells and fewer intense rainfall events. These climatic trends are likely to intensify groundwater stress and impact recharge.

This study highlights the intricate relationship between mining and climate change, complicating the attribution of hydrogeological changes to a single driver. As lignite mining operations cease, groundwater recovery and altered subsidence patterns may emerge; however, ongoing climate change will continue to challenge sustainable groundwater management. The findings underscore the necessity for adaptive strategies that integrate both climate and mining considerations into groundwater policies in regions experiencing significant energy transitions.

There are certain limitations of the study. Firstly, the assessment of land surface movement relied on EGMS data, which approaches the detection threshold for such fine-scale changes. Future research incorporating higher-resolution data could enhance result accuracy. Secondly, the groundwater analysis was constrained to eight piezometers near the “Tomisławice” mine due to data availability. Given the variability in groundwater declines caused by mining, more extensive monitoring would improve assessment reliability. Furthermore, data from piezometers tracking groundwater rebound in decommissioned mining sites would facilitate a better understanding of land uplift linked to groundwater recovery and support predictions of future uplift trends. Finally, developing hydrogeological models and undertaking environmental assessments of mine flooding are crucial for comprehending the long-term impacts of increased groundwater retention and climate change. This approach would support the development of sustainable groundwater management practices in post-mining areas in light of ongoing climate change.

Funding

This research was funded by the Excellence Initiative Research University Program of AGH University of Krakow, Poland. Additional support was provided by the National Science Centre of Poland, grant no. 2023/49/B/ST10/01803, grant title “3MAP: Monitoring, Modelling and Mitigation of land subsidence in delta areas”.

Data Availability Statement

The morphological and hydrological data employed in this investigation are publicly available from the National Geoportal of Poland, https://www.geoportal.gov.pl/en/ (accessed on 3 November 2024). The land cover data required for the preparation of Figure 1, Figure 2, Figure 3, Figure A1, Figure A2 and Figure A3 were retrieved from OpenStreetMap, https://www.openstreetmap.org/ (accessed on 3 November 2024). Geological data can be accessed through the Polish Geological Institute–National Research Institute, https://www.pgi.gov.pl/en/ (accessed on 3 November 2024). Land surface movement data were obtained from the publicly accessible European Ground Motion Service, which is part of the Copernicus Programme of the European Space Agency, https://egms.land.copernicus.eu/ (accessed on 3 November 2024). Hydrogeological data for the Polish national network are publicly available from the Polish Geological Institute–National Research Institute, https://www.pgi.gov.pl/en/ (accessed on 3 November 2024). Hydrogeological data specific to the “Tomisławice” mine were retrieved from the publication “Analysis of the development of the depression cone of the Tomisławice lignite open pit mine in 2009–2019 and its impact on the soil and water relations of the Kujawy Lakeland” by Przybyłek J. [59]. Meteorological data can be accessed through the Polish Institute of Meteorology and Water Management–National Research Institute, https://www.imgw.pl/ (accessed on 3 November 2024). All data employed in this study are available and have been utilized solely for research purposes.

Acknowledgments

The author acknowledges the valuable contributions of the anonymous reviewers, whose comments and suggestions have substantially improved the quality of this article. This work contributes to the UNESCO International Initiative on Land Subsidence, https://www.landsubsidence-unesco.org/ (accessed on 3 November 2024).

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Appendix A. Land Surface Movement in the AOI from EGMS Data

Figure A1. Land surface movement in the vicinity of the “Tomisławice” mine from EGMS data for periods (A) 2015–2021 and (B) 2018–2022. Points indicate measurement locations and annual displacement rate (mm/year), while contour lines represent interpolated total displacement (mm) for the respective periods.

Figure A2. Land surface movement in the vicinity of “Drzewce” and “Lubstów” mines from EGMS data for periods (A) 2015–2021 and (B) 2018–2022. Points indicate measurement locations and annual displacement rate (mm/year), while contour lines represent interpolated total displacement (mm) for the respective periods.

Figure A3. Land surface movement in the vicinity of the “Jóźwin” mine from EGMS data for periods (A) 2015–2021 and (B) 2018–2022. Points indicate measurement locations and annual displacement rate (mm/year), while contour lines represent interpolated total displacement (mm) for the respective periods.

Appendix B. Observation Data for Groundwater Levels and Land Surface Movements

Table A1. Observation data for groundwater levels and land surface movements in the “Tomisławice” mine network. Results are provided for the full observation periods of each parameter and for the overlapping period where both were measured. Refer to Figure 3 for the spatial distribution of piezometers.

No.	Number	Change in Groundwater Level [m]				Change in Land Surface Movement [m]				Ratio of the Change in Land Surface Movement to Groundwater Level
		December 2009–December 2019 *		December 2015–December 2019		December 2015–December 2021		December 2015–December 2019
		[m]	[m/year]	[m]	[m/year]	[mm]	[mm/ year]	[mm]	[mm/ year]
1	PT3 (Q)	−12.33	−1.23	+3.57	+0.89	−34.2	−5.7	−35.9	−8.8	9.89 × 10⁻³
1	PT3 (P + N)	−16.09	−1.61	+1.32	+0.33	−34.2	−5.7	−35.9	−8.8	2.67 × 10⁻²
2	PT20 (Q)	−7.92	−0.79	−2.10	−0.52	−38.4	−6.4	−36.2	−9.1	1.75 × 10⁻²
2	PT20 (P + N)	−25.97	−2.60	−14.94	−3.74	−38.4	−6.4	−36.2	−9.1	2.43 × 10⁻³
3	PI-1 (Q)	−11.10	−1.11	−3.32	−0.83	−18.0	−3.0	−19.7	−4.9	5.90 × 10⁻³
3	PI-1 (P + N)	−18.30	−1.83	−5.76	−1.44	−18.0	−3.0	−19.7	−4.9	3.40 × 10⁻³
4.	PT15 (Q)	−5.29	−0.53	+0.85	+0.21	−3.0	−0.5	−4.5	−1.1	5.24 × 10⁻³
4.	PT15 (P + N)	−5.75	−0.58	+0.50	+0.12	−3.0	−0.5	−4.5	−1.1	9.17 × 10⁻³
5.	PIII-1 (Q)	−1.26	−0.13	+0.27	+0.07	−8.4	−1.4	−11.0	−2.8	4.00 × 10⁻²
5.	PIII-1 (P + N)	−12.84	−1.28	−5.22	−1.30	−8.4	−1.4	−11.0	−2.8	2.15 × 10⁻³
6.	PT34 (Q)	−2.95	−0.42	−1.31	−0.33	−12.0	−2.0	−12.6	−3.1	9.39 × 10⁻³
6.	PT34 (P + N)	−8.14	−1.16	−7.21	−1.80	−12.0	−2.0	−12.6	−3.1	1.72 × 10⁻³
7.	PIII-2 (Q)	−1.11	−0.11	+0.51	+0.17	−6.0	−1.0	−5.4	−1.4	8.24 × 10⁻³
7.	PIII-2 (P + N)	−6.96	−0.70	−1.46	−0.49	−6.0	−1.0	−5.4	−1.4	2.86 × 10⁻³
8.	PIII-3 (Q)	−0.99	−0.10	−0.08	−0.03	−4.8	−0.8	−6.0	−1.5	5.00 × 10⁻²
8.	PIII-3 (P + N)	−0.95	−0.09	−0.49	−0.16	−4.8	−0.8	−6.0	−1.5	9.38 × 10⁻³

* Observation periods for groundwater levels vary slightly in length between individual piezometers. To minimize the influence of seasonal variations on the analysis, specific observation periods were selected for certain piezometers. Namely, for PT34, data from December 2012–December 2019 were used instead of the full December 2009–December 2019 period. Similarly, for PIII-2 and PIII-3, periods of September 2009–September 2019 and June 2016–June 2019 were utilized, respectively, instead of the full December 2009–December 2019 and December 2015–December 2019 periods. Refer to Table 3 for detailed observation periods for each piezometer.

Table A2. Observation data for groundwater levels and land surface movements in the Polish national hydrogeological network in the AOI. Results are provided for the full observation periods of each parameter and for the overlapping period where both were measured. Refer to Figure 3 for the spatial distribution of piezometers.

No.	Number	Change in Groundwater Level [m] *				Change in Land Surface Movement [m]		Ratio of the Change in Land Surface Movement to Groundwater Level (December 2015–December 2019)
		December 2009–December 2023 **		December 2015/–December 2021		December 2015/–December 2021
		[m]	[m/year]	[m]	[m/year]	[mm]	[mm/year]
1.	II/1270/1	−0.98	−0.07	−0.26	−0.04	−4.8	−0.8	1.85 × 10⁻²
2.	II/1273/1	−0.56	−0.04	−0.23	−0.04	−7.2	−1.2	3.13 × 10⁻²
3.	II/1271/1	−0.85	−0.06	−0.03	0.00	+0.6	+0.1	2.08 × 10⁻²
4.	II/27/3	−0.28	−0.02	+0.04	+0.01	−6.6	−1.1	1.83 × 10⁻¹
5.	II/197/1	−2.48	−0.18	No data	No data	−7.2	−1.2	-
6.	II/1270/2	−0.28	−0.02	0.78	0.13	−4.8	−0.8	1.85 × 10⁻²
7.	II/909/1	−0.26	−0.02	−0.01	0.00	−4.2	−0.7	2.92 × 10⁻¹
8.	II/902/1	−2.24	−0.16	−0.80	−0.13	−4.2	−0.7	5.26 × 10⁻³
9.	II/1277/1	−0.39	−0.03	+0.35	+0.06	−6.0	−1.0	1.70 × 10⁻²
10.	II/72/1	−3.78	−0.27	−0.25	−0.04	−4.8	−0.8	1.90 × 10⁻²
11.	II/536/1	−0.59	−0.04	+0.47	0.08	0.0	0.0	1.28 × 10⁻³
12.	I/999/1	−0.28	−0.02	+0.21	0.03	+0.6	+0.1	2.87 × 10⁻³

* Changes in groundwater levels were calculated based on the mean groundwater level values for each respective observation period. ** Observation periods for groundwater levels vary slightly in length between individual piezometers. To minimize the influence of seasonal variations on the analysis, specific observation periods were selected for certain piezometers. Namely, for PT34, data from December 2012–December 2019 were used instead of the full December 2009–December 2019 period. Similarly, for PIII-2 and PIII-3, the periods of September 2009–September 2019 and June 2016–June 2019 were utilized, respectively, instead of the full December 2009–December 2019 and December 2015–December 2019 periods. Refer to Table 3 for detailed observation periods for each piezometer. Due to a lack of observations, the ratio of the change in groundwater level to land surface for the period December 2015–December 2019 was not calculated.

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Figure 3. Lignite mining history, current operations, and water recultivation areas in the AOI, including prospective lignite deposits. The extent of current lignite mines is based on data from the Polish Geological Institute–National Research Institute [52]. Although active lignite mining in September 2024 was limited to the “Tomisławice” mine, the delineated areas of the “Jóźwin” and “Drzewce” mines, where operations ceased in 2023 and 2022, respectively, are still designated as mining areas undergoing water recultivation [52]. The approximate extent of depression cones primarily affecting the Quaternary aquifer system is also shown, based on Wilk et al. [54]. Additionally, the map displays piezometers monitoring groundwater levels in the “Tomisławice” mine [59], as well as the national monitoring network of the Polish Geological Institute–National Research Institute [52].

Figure 4. Land surface movement in the AOI from EGMS data for periods (A) 2015–2021 and (B) 2018–2022. Points indicate measurement locations and annual displacement rate (mm/year), while contour lines represent interpolated total displacement (mm) for the respective periods.

Figure 5. Groundwater level and land surface movement time series from piezometers at the “Tomisławice” mine. Raw data, LOESS trend lines, and linear regression fits. Coefficients of determination (R²) and Pearson correlation coefficients (R) are provided for each linear regression. The joint observation period is highlighted in red.

Figure 6. Groundwater level and land surface movement time series from piezometers monitoring the unconfined Quaternary aquifer system, located outside the mining influence zone. Raw data, LOESS trend lines, and linear regression fits. Coefficients of determination (R²) and Pearson correlation coefficients (R) are provided for each linear regression. The joint observation period is highlighted in red.

Figure 7. Groundwater level and land surface movement time series from piezometers monitoring the confined aquifer system, located outside, but proximal to, the mining influence zone. Raw data, LOESS trend lines, and linear regression fits. Coefficients of determination (R²) and Pearson correlation coefficients (R) are provided for each linear regression. The joint observation period is highlighted in red.

Figure 8. Groundwater level and land surface movement time series from piezometers monitoring the confined aquifer system, located outside and farther from the mining influence zone. Raw data, LOESS trend lines, and linear regression fits. Coefficients of determination (R²) and Pearson correlation coefficients (R) are provided for each linear regression. The joint observation period is highlighted in red.

Figure 9. Time series of mean monthly temperature and precipitation with linear trends and confidence intervals as well as means recorded at Kołuda Wielka meteorological station over periods (A) 1991–2023 and (B) 2009–2023.

Figure 10. Cross-correlation between groundwater level and meteorological data: (A) mean monthly temperature and (B) monthly precipitation data for the period 2009–2023, for piezometers of the Polish national hydrogeological network monitoring the unconfined aquifer.

Figure 11. Cross-correlation between groundwater level and meteorological data: (A) mean monthly temperature and (B) monthly precipitation data for the period 2009–2023, for piezometers of the Polish national hydrogeological network monitoring the confined aquifer system.

Table 1. Mining characteristics of lignite open-pit mines in the “Konin” Lignite Basin. Source of data: PAK Kopalnia Węgla Brunatnego Konin S.A. [58], Polish Geological Institute–National Research Institute [52], and Wilk et al. [54].

No.	Mine	Start Year of Construction	Start Year of Exploitation	End Year of Exploitation	Average Overburden Thickness [m]	Average Lignite Seam Thickness [m]	Lignite Production		Volume of Water Pumped
No.	Mine	Start Year of Construction	Start Year of Exploitation	End Year of Exploitation	Average Overburden Thickness [m]	Average Lignite Seam Thickness [m]	Average [Mg/year]	Total [Mg]	Average [×10⁶ m³/ year]	Total [×10⁶ m³]
1.	Morzysław	1945	1945	1955	9.5	5.5	0.06	1.04	No data	No data
2.	Niesłusz	1946	1953	1961	14.5	9.5	0.45	4.08	2.00	18.00
3.	Gosławice	1953	1958	1974	18.7	8.3	2.70	38.85	9.06	181.26
4.	Pątnów	1957	1962	2001	50.5	8.8	3.05	129.78	33.53	1173.63
5.	Kazimierz Południe	1962	1965	1997	47.5	6.6	2.46	76.11	23.42	726.12
6.	Kazimierz Północ	1992	1995	2011	48.0	6.5	3.43	54.89	No data	No data
7.	Jóźwin	1965	1971	2023	46.9	7.0	2.81	159.27	19.88	556.52
8.	Lubstów	1979	1982	2009	46.1	28.8	4.26	107.33	13.93	195.00
9.	Drzewce	2003	2005	2022	51.6	5.8	2.40	40.81	No data	No data
10.	Tomisławice	2010	2011	2031	42.5	6.2	2.50	27.80	16.59	215.65

Table 2. Details of piezometers monitoring groundwater levels in the “Tomisławice” mine network. Refer to Figure 3 for the spatial distribution of piezometers.

No.	Number	Stratigraphy	Aquifer Type	Observation Period [mm/yyyy]	Observation Frequency [months]	Elevation [masl]	Piezometer Depth [m]
1.	PT3	Quaternary/ Paleogene+ Neogene	Unconfined /Confined	March 2009–December 2019	3	96.0	50
2.	PT20	Quaternary/ Paleogene+ Neogene	Unconfined /Confined	March 2009–December 2019	3	105.2	79
3.	PI-1	Quaternary/ Cretaceous	Unconfined /Confined	March 2009–December 2019	3	102.2	69
4.	PT15	Quaternary/ Paleogene+ Neogene	Unconfined /Confined	March 2009–December 2019	3	93.8	41
5.	PIII-1	Quaternary/ Cretaceous	Unconfined /Confined	March 2009–December 2019	3	102.9	79
6.	PT34	Quaternary/ Paleogene+ Neogene	Unconfined /Confined	March 2012–December 2019	3	105.8	72
7.	PIII-2	Quaternary/ Cretaceous	Unconfined /Confined	March 2009–September 2019	3	92.9	74
8.	PIII-3	Quaternary/ Paleogene+ Neogene	Unconfined /Confined	March 2009–September 2019	3	89.5	94

Table 3. Details of piezometers of the Polish national hydrogeological network monitoring groundwater levels in the AOI. Refer to Figure 3 for the spatial distribution of piezometers.

No.	Number	Stratigraphy	Aquifer Type	Observation Period [mm/yyyy]	Observation Frequency [months]	Elevation [masl]	Piezometer Depth [m]
1.	II/1270/1	Quaternary	Unconfined	January 2009–December 2023	1	107.9	23
2.	II/1273/1	Quaternary	Unconfined	January 2009–December 2023	1	79.8	19
3.	II/1271/1	Quaternary	Unconfined	January 2009–December 2023	1	101.3	28
4.	II/27/3	Quaternary/ Cretaceous	Unconfined	January 2009–December 2023	1	100.0	80
5.	II/197/1	Quaternary/ Paleogene+ Neogene	Confined	January 2009–October 2015	1	106.2	98
6.	II/1270/2	Quaternary	Confined	November 2020–December 2023	1	107.9	23
7.	II/909/1	Quaternary	Confined	November 2009–December 2023	1	88.2	9
8.	II/902/1	Quaternary/ Cretaceous	Confined	January 2009–December 2023	1	114.8	56
9.	II/1277/1	Quaternary	Confined	January 2009–December 2023	1	107.8	22
10.	II/72/1	Quaternary/ Paleogene+ Neogene	Confined	April 2010–December 2023	1	100.0	60
11.	II/536/1	Quaternary	Confined	January 2009–December 2023	1	100.0	50
12.	I/999/1	Quaternary/ Jurassic	Confined	January 2011–December 2023	1	118.5	181.3

Table 4. Statistics on land surface movement in the AOI as detected by EGMS for the period 2015–2021, including mining areas, terrains, and depression cones.

No.	Region	Area [km²]	Number of EGMS-Retrieved Points	Land Surface Movement [mm/year]
No.	Region	Area [km²]	Number of EGMS-Retrieved Points	Minimum	Maximum	Mean	Standard Deviation
1.	AOI	3646.3	52,115	−23.3	13.7	−1.11	±1.027
2.	Mining areas, terrains, and depression cones	915.9	12,855	−17.6	7.2	−1.08	±1.578
3.	AOI excluding mining areas, terrains, and depression cones	2730.4	39,260	−23.3	13.7	−1.11	±0.765
4.	“Tomisławice” mining area	17.4	143	−10.5	3.2	−5.17	±2.109
5.	“Tomisławice” mining terrain	135.6	1637	−14.2	2.6	−2.26	±1.736
6.	“Jóźwin” mining area	47.2	404	−7.4	3.4	−0.65	±1.572
7.	“Jóźwin” mining terrain	372.3	5557	−17.6	6.7	−0.56	±1.390
8.	“Drzewce” mining area	17.1	117	−9.2	2.2	−1.36	±1.720
9.	“Drzewce” mining terrain	124.8	2048	−8.6	1.9	−1.39	±1.329
10.	“Tomisławice” depression cone area	269.8	3297	−14.2	7.2	−1.72	±1.574
11.	“Jóźwin” depression cone area	360.7	5068	−17.6	6.7	−0.46	±1.459
12.	“Lubstów” depression cone area	96.7	1546	−9.2	4.4	−0.90	±1.152

Table 5. Statistics on land surface movement in the AOI as detected by EGMS for the period 2018–2022, including mining areas, terrains, and depression cones.

No.	Region	Area [km²]	Number of EGMS-Retrieved Points	Land Surface Movement [mm/year]
No.	Region	Area [km²]	Number of EGMS-Retrieved Points	Minimum	Maximum	Mean	Standard Deviation
1.	AOI	3646.3	57,440	−73.2	11.2	−1.18	±1.356
2.	Mining areas, terrains, and depression cones	915.9	14,938	−73.2	11.2	−1.35	±2.217
3.	AOI excluding mining areas, terrains, and depression cones	2730.4	42,502	−22.5	7.5	−1.13	±0.862
4.	“Tomisławice” mining area	17.4	320	−25.7	6.7	−4.92	±4.621
5.	“Tomisławice” mining terrain	135.6	1888	−20.8	4.1	−1.67	±1.185
6.	“Jóźwin” mining area	47.2	595	−73.2	11.2	−2.49	±6.935
7.	“Jóźwin” mining terrain	372.3	6412	−28.5	8.1	−0.74	±1.660
8.	“Drzewce” mining area	17.1	304	−15.2	2.5	−3.53	±3.381
9.	“Drzewce” mining terrain	124.8	2207	−12.0	2.4	−1.66	±1.027
10.	“Tomisławice” depression cone area	269.8	3703	−20.8	4.5	−1.54	±1.078
11.	“Jóźwin” depression cone area	360.7	6040	−73.2	11.2	−0.87	±2.780
12.	“Lubstów” depression cone area	96.7	1669	−9.3	1.8	−1.40	±0.888

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Guzy, A. Subsidence and Uplift in Active and Closed Lignite Mines: Impacts of Energy Transition and Climate Change. Energies 2024, 17, 5540. https://doi.org/10.3390/en17225540

AMA Style

Guzy A. Subsidence and Uplift in Active and Closed Lignite Mines: Impacts of Energy Transition and Climate Change. Energies. 2024; 17(22):5540. https://doi.org/10.3390/en17225540

Chicago/Turabian Style

Guzy, Artur. 2024. "Subsidence and Uplift in Active and Closed Lignite Mines: Impacts of Energy Transition and Climate Change" Energies 17, no. 22: 5540. https://doi.org/10.3390/en17225540

APA Style

Guzy, A. (2024). Subsidence and Uplift in Active and Closed Lignite Mines: Impacts of Energy Transition and Climate Change. Energies, 17(22), 5540. https://doi.org/10.3390/en17225540

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