Extreme Rainfall

Along with other causes, such as rapid urbanization, the high intensity rainfall has significant contribution in urban area flooding. Understanding this high intensity rainfall over urban area may help us to reduce the damage caused by urban floods. Recent studies reported the relationship between El Niño-Southern Oscillation (ENSO) and Indian extreme rainfall characteristics. In this paper, the extreme precipitation events of the Hyderabad are studied using the Indian Meteorological Department (IMD) hourly rainfall records to understand the effect of ENSO cycle on extreme rainfall events. The forty-three years (1-1-1971 to 31-12-2013) hourly rainfall data is used to construct the intensity-probability distribution curve. The five percent probability extreme rainfall event's frequency is studied for the period of same 43 years. The study results show that the ENSO cycle is inversely proportional to the Hyderabad city extreme rainfall frequency. The results also show that the ext...

Many people live in rural areas in tropical regions. Rural development is not merely a contribution to the growth of individual countries. It can be a way to reduce poverty and to increase access to water, health care, and ducation. Sustainable rural development can also help stop deforestation and reduce live-stock, which generate most of the greenhouse gas emissions. However, efforts to achieve a sustainable rural development are often thwarted by oods, drought, heat waves, and hurricanes, which local communities are not very prepared to tackle. Agricultural practices and local planning are still not very risk-informed. These deficiencies are particularly acute in tropical regions, where many Least Developed Countries are located and where there is, however, great potential for rural development. This Special Issue contains 22 studies on best practices for risk awareness; on local risk reduction; on several cases of soil depletion, water pollution, and sustainable access to safe water; and on agronomy, earth sciences,
ecology, economy, environmental engineering, geomatics, materials science, and spatial and regional planning in 12 tropical countries.

Twelve commonly used probability distributions are evaluated to identify the most suitable model that could provide accurate extreme rainfall estimates in Egypt. Three popular parameter estimation methods are applied: the method of moments, L-moments and maximum likelihood. The performance of the models is evaluated based on several numerical and graphical goodness-of-fit criteria. The proposed procedure is applied to annual maximum daily rainfall data from a network of 31 stations located in Egypt. The results indicate that no single distribution performed the best at all stations. Log-Normal, Log-Pearson Type III and Exponential are the top three distributions for the frequency analysis of daily annual extreme rainfalls in Egypt, i.e. they are selected as the “optimum” models for 23%, 19% and 19% of the total stations, respectively. In contrast, the distributions: Normal, Gumbel, Logistic and Generalized Logistic are not suitable for describing the extreme rainfalls in the country...

Climate change is a reality which affects many climatic variables, including precipitation. The objective of this article is to study the extreme rain variability from a historical database (1941-2000). For this purpose, eleven (11) rainfall indices were calculated at the Adiaké, Bianouan, Ayamé, and Agnibilekro rainfall stations in Côte d'Ivoire. Due to lack of data on daily rainfall on the Ghanaian section of watershed, nine (9) monthly precipitations indices were estimated from monthly rainfall at the Enshi and Buakuc stations.

Graphical abstract Abstract In December 2014, Kelantan was hit by the worst flood ever recorded. Did the rainfall exceed historical records, how rare are they and what causes them? This paper answers these questions. Estimation of the return periods uses the GEV distribution model and stations with more than 25 years records. Spatial distribution plots of the cumulated rainfall depths were constructed using IDW interpolation method. Four major outcomes are: 1) Spatial rainfall patterns show high amounts of rainfall accumulated by phases (Phase 1-daily rainfall up to 300 mm; Phase 2-daily rainfall up to 500 mm); 2) record breaking rainfall events occurred at 9 stations significantly at Gunung Gagau (1598.9 mm compared to 976.5 mm 7-day cumulated rainfall). Many stations upstream of the river basin experienced ARIs near and over 100 years and several experienced more than 200 years; and 4) Enhanced rainfall were experienced due to the combined effect of the monsoon season, Madden Julian Oscillation and temperature below anomalies at the Siberian High.

Three pairs of small, fourth-to sixth-order catchments (approximately 5-80 km 2), draining the margin of the Darjeeling Himalayas into the piedmont, were selected for a comparison of the land-use impact on the morphology and sedimentology of their stream channels. Each pair experienced similar annual rainfall and comprised similar metamorphic bedrock, steep topography, and brown soils; the members of each pair contrast with respect to their land-use structure as they comprise large forest cover (forest > 90%) and a significant contribution of agricultural land with tea plantations (forest < 63%), respectively. A set of rainfall, cross-sectional, and sediment data were collected for the characterization of the stream channels. The obtained results revealed that, under extreme rainfall and high denudation rates as well as frequent flash floods, the geomorphic response to land-use changes involving agricultural expansion at the expense of forest cover was less pronounced in the mountain channels than in the piedmont. Significant differences between the studied pairs of mountain streams draining forested and agricultural catchments were observed only at bankfull width and baseflow depth in fourth-order streams and baseflow depth in fifth-order streams. Local environmental factors such as bedrock channel boundaries, steep topography, high material supply to river networks, and selective sediment mobilization during extreme rainfall and floods override the effects of land use and exert dominant control over stream channels in mountain catchments. However, the effects of agricultural activity in mountains are propagated downstream. In the agricultural catchment in the piedmont, a local rapid decrease in river slope and an increase in water infiltration into alluvia facilitates the deposition of eroded material. In addition, the stream in the agricultural catchment exhibited a rise in the riverbed with the expansion of a braided channel over a dozen kilometers below the Himalayan front in the piedmont, while the streams in the forested catchment revealed a distinct tendency towards incision. The present-day channel morphologies and sediment patterns observed in forested catchments are most likely similar to those that existed in the studied rivers prior to the development of tea plantations and settlements in the mid-19th century.

– Le bassin versant de Sebou est soumis à des pluies diluviennes d'une fréquence rare. L'étude propose une estimation des intensités et des périodes de retour des pluies journalières extrêmes dans 8 stations pluviométriques. La mise en oeuvre d'une application informatique sous MatLab, (Cheng et al. 2014) a été utilisée. La méthode déployée est basée sur une approche bayésienne pour estimer les paramètres du modèle des valeurs extrêmes (GEV : Generalized Extreme Value) sous l'hypothèse de stationnarité et de non-stationnarité des événements climatiques exceptionnelles. Les résultats obtenus montrent une hétérogénéité spatiale dans les tendances des pluies extrêmes, avec une dominance de stationnarité des séries temporelles. Tenant compte de cette évolution tendancielle, l'étude présente aussi les intensités et les périodes de retour des pluies exceptionnelles pour chaque station. Mots-clés : Pluies exceptionnelles, modèle GEV, stationnarité et non stationnarité, intensité et période de retour, bassin versant de Sebou, Maroc. Abstract – Outstanding rainfall variability in the catchment area of Sebou (Morocco) : Intensity and return period according the assumption of no time stationarity. The catchment area of Sebou is subject to torrential rains of a rare frequency. The study provides an estimate of intensities and return periods of extreme daily rainfall in 8 pluviometric stations. The implementation of a computer application MatLab, (Cheng et al. 2014) was used. The method uses a Bayesian approach for estimating model parameters extreme value (GEV: Generalized Extreme Value) under the assumption of stationary and non-stationary exceptional climatic events.. The results show spatial heterogeneity in patterns of extreme rainfall, with a dominance of stationary time series. Taking into account such a trend, the study also shows the intensities and return periods of extreme rainfall for each station.

The estimation of rainfall intensity is commonly required for the design of hydraulic and water resources engineering control structures. The intensity-duration-frequency (IDF) relationship is a mathematical relationship between the rainfall intensity, the duration and the return period. The present study aimed the derivation of IDF curves of Manvi Taluk of Raichur District using four Rain gauge Station with rain gauge stations with 19 years of rainfall data (1998 to 2016). The Normal Distribution, Log Normal Distribution, Gumbel distribution techniques are used to derived the rainfall intensity values of 2,5,10,15,30,60,120,720,1440 minutes of rainfall duration with different return period. The short duration IDF using daily rainfall data are presented, which is input for water resources projects.

Los eventos extremos, meteorológicos y climáticos, han recibido una atención especial durante los últimos años debido a la pérdida de vidas humanas que provocan y al aumento exponencial de las pérdidas económicas asociadas. Además, la sociedad es más sensible a estos eventos, ya que ha habido un aumento de la vulnerabilidad de bienes y personas. El riesgo natural más importante tanto en España como en Europa son las inundaciones, producidas por fenómenos meteorológicos ocasionales o estacionales, en que la magnitud de la inundación dependerá de las caracterísitcas geomorfológicas del territorio y de las actividades humanas desarrolladas en él.

Una de las amenazas naturales más relevantes que impactan sobre el margen costero carabobeño, lo constituyen las inundaciones, procesos naturales cuyos episodios importantes son activados por lluvias extraordinarias. Por ello, el presente trabajo tiene como propósito, caracterizar y analizar la distribución espacio-temporal y los eventos extremos de las precipitaciones en la franja costera-montañosa Morón – Puerto Cabello – Patanemo del estado Carabobo, con la finalidad de establecer su vinculación con escenarios de inundaciones. La metodología se basó en el tratamiento de datos de precipitación de las estaciones Puerto Cabello-Base Naval, Morón-Dique, Hacienda El Manglar, Santa Rita, Borburata y El Cambur (período 1973-1990), para los cuales se realizaron cálculos de parámetros estadísticos y de anomalías pluviométricas, y análisis de tendencia. Se estudiaron datos de láminas máximas anuales de precipitación para distintas duraciones de la lluvia, correspondientes a las estaciones Borburata (período 1962-1995) y Santa Rita (período 1974-1995), a los cuales se les realizó análisis de intensidad-duración-frecuencia (IDF) para distintos períodos de retorno. Los resultados muestran promedios anuales que oscilan entre 478,4 mm y 1649,6 mm, cuya distribución espacial está determinada por la orientación de la línea de costa, el relieve montañoso (altitud), y la orientación de los valles fluvio-marinos y de las laderas de los estribos montañosos. La distribución temporal de las lluvias exhibe regímenes unimodales y bimodales. A excepción de la estación Borburata, se observa una ligera tendencia a la disminución de los montos totales anuales en las otras estaciones. Las anomalías por exceso de lluvia alcanzan valores de hasta 1366,63 mm, y por déficit de 710,20 mm. El análisis de IDF indica valores críticos para 1 hora de duración de 91,63 mm/h y 102,94 mm/h en un período de retorno de 50 años, y valores de 102,55 mm/h y 115,11 mm/h para un período de retorno de 100 años.

Los eventos de lluvias extraordinarias son objeto de investigación en distintas regiones del mundo, donde su ocurrencia ha provocado impactos socio-ambientales negativos, expresados en cuantiosas pérdidas humanas y materiales. El objetivo de este trabajo es analizar las causas y consecuencias de las lluvias extraordinarias registradas en Manabí en febrero y marzo de 2017, haciendo énfasis en las afectaciones de orden social, económico y ambiental. Se asume como supuesto, que estos eventos guardan estrecha relación con las anomalías de la temperatura superficial del mar en el océano Pacífico ecuatorial. Se realizó una investigación de campo mediante el análisis de datos de temperatura superficial del mar (TSM) en imágenes de satélite, empleando el algoritmo matemático Split Night Multi Channel Sea Surface Temperature, el cual permite identificar anomalías térmicas. Con los registros de precipitación de estaciones meteorológicas de la región costera ecuatoriana, se realizó un análisis estadístico descriptivo, para conocer el comportamiento anual (régimen) e histórico de las lluvias. Las afectaciones socio-económicas se estudiaron a partir de entrevistas no estructuradas a informantes clave, a través de un muestreo no probabilístico, así como información primaria de organismos gubernamentales. Los resultados indican que las lluvias extraordinarias observadas durante el período febrero-marzo de 2017 fueron consecuencia de la conjugación de factores como anomalías térmicas positivas en el Pacífico ecuatorial, convergencia intertropical e inestabilidad atmosférica en la Amazonía. Esto generó impactos negativos en localidades urbanas y rurales como Manta, Portoviejo, Lodana, Calceta y Chone.

The present study aims with the analysis of rainfall and rainstorms over the Gujarat State during 2010-2017. The spatial and temporal distribution of rainfall and its variability in different monsoon seasons revealed that heavy rainfall over the state occurs in small spells and in short duration and more over south Gujarat. Two meteorological subdivisions , Gujarat and Saurashtra-Kachchh showed increase in rainfall during were found to be the most severe rainstorms which caused serious floods in different rivers of the state. Comparison of these rainstorms with the past most severe rainstorms revealed that 1-3 Jul.,1941 rainstorm is the most severe rainstorm till date. The analysis also shows effect of climate changes over smaller spatial scales. The study will be useful to agriculturists, fishing industry, and for better water management practices of the state.

Along the Mediterranean coastlines, intense and localized rainfall events are responsible for numerous casualties and several million euros of damage every year. Numerical forecasts of such events are rarely skillful, because they lack information in their initial and boundary conditions at the relevant spatio-temporal scales, namely O(km) and O(h). In this context, the tropospheric delay observations (strongly related to the vertically integrated water vapor content) of the future geosynchronous Hydroterra satellite could provide valuable information at a high spatio-temporal resolution. In this work, Observing System Simulation Experiments (OSSEs) are performed to assess the impact of assimilating this new observation in a cloud-resolving meteorological model, at different grid spacing and temporal frequencies, and with respect to other existent observations. It is found that assimilating the Hydroterra observations at 2.5 km spacing every 3 or 6 h has the largest positive impact ...

Rainfall is considered a highly valuable climatological resources and is a fundamental component of any water resource assessment strategy. Rainfall characterization has important repercussions, among others, on climate change scenarios,
flood risk mitigation, water resources availability and drought assessment. We use a hierarchical modeling approach to investigate a collection of spatially referenced time series of extreme values. We implement a geoadditive mixed model for
extremes with a temporal random effect, where we assume that the observations follow generalized extreme value (GEV) distributions whose locations are spatially dependent where the dependence is captured using the geoadditive model. The analyzed territory is the catchment area of Arno River in Tuscany in Central Italy. The dataset is composed by the time series of annual maxima of daily rainfall recorded in about 400 rain gauges, spatially distributed over an area of about 8.830 km2. The record period covers mainly the second half of 20th century.

Why did some African smallholders adopt cash crops on a considerable scale, while most others were hesitant to do so? This study sets out to explore the importance of factor endowments in shaping the degrees to which cash crops were adopted in colonial tropical Africa. We conduct an in-depth case study of the ‘cotton revolution’ in colonial Uganda to put the factor endowments perspective to the test. Our empirical findings, based on an annual panel data analysis at the district-level from 1925 till 1960, underscore the importance of Uganda’s equatorial bimodal rainfall distribution as an enabling factor for Uganda’s ‘cotton revolution’. We also provide evidence at a unique spatial micro-level, by capitalizing on detailed household surveys from the same period. We demonstrate that previous explanations associating variegated responses of African farmers to cash crops either to the role of colonial coercion, or to a distinction between ‘forest/banana’ and ‘savannah/grain’ zones cannot...

Una de las amenazas naturales más relevantes que impactan sobre el margen costero carabobeño, lo constituyen las inundaciones, procesos naturales cuyos episodios importantes son activados por lluvias extraordinarias. Por ello, el presente trabajo tiene como propósito, caracterizar y analizar la distribución espacio-temporal y los eventos extremos de las precipitaciones en la franja costera-montañosa Morón – Puerto Cabello – Patanemo del estado Carabobo, con la finalidad de establecer su vinculación con escenarios de inundaciones. La metodología se basó en el tratamiento de datos de precipitación de las estaciones Puerto Cabello-Base Naval, Morón-Dique, Hacienda El Manglar, Santa Rita, Borburata y El Cambur (período 1973-1990), para los cuales se realizaron cálculos de parámetros estadísticos y de anomalías pluviométricas, y análisis de tendencia. Se estudiaron datos de láminas máximas anuales de precipitación para distintas duraciones de la lluvia, correspondientes a las estaciones Borburata (período 1962-1995) y Santa Rita (período 1974-1995), a los cuales se les realizó análisis de intensidad-duración-frecuencia (IDF) para distintos períodos de retorno. Los resultados muestran promedios anuales de precipitación que oscilan entre 478,4 mm y 1649,6 mm, cuya distribución espacial está determinada por la orientación de la línea de costa, el relieve montañoso (altitud), y la orientación de los valles fluvio-marinos y de las laderas de los estribos montañosos. La distribución temporal de las lluvias exhibe regímenes unimodales y bimodales. A excepción de la estación Borburata, se observa una ligera tendencia a la disminución de los montos totales anuales en las otras estaciones. Las anomalías por exceso de lluvia alcanzan valores de hasta 1366,63 mm, y por déficit de 710,20 mm. El análisis de IDF indica valores críticos para 1 hora de duración de 91,63 mm/h y 102,94 mm/h en un período de retorno de 50 años, y valores de 102,55 mm/h y 115,11 mm/h para un período de retorno de 100 años.

The susceptibility of physical environment to the occurrence of mass movements in a mountainous catchment is mainly linked to the impact of rainfall on the soil as a trigger element. The aim of this research is to analyze the erosive potential of rainfalls on the Chichiriviche River catchment, in order to check if their characteristics are related with the activation of erosive processes. The methodology considered the processing of monthly and annual total and mean rainfall data, and rainfall annual maximum sheeting, with which the following analyzes were conducted: spatio-temporal distribution of rainfall; frequency analysis of extreme events; and estimate of the Annual Fournier Index (AFI), Modified Fournier Index (MFI), Rainfall Concentration Index (RCI), Total Erosivity Index (TEI), and the Rain Erosive Potential Index (R). The spatial distribution of rainfall in the area is controlled mainly by the altitude (relief), and its annual regime is characterized by a greater proportion of pluviometric amounts at year end. The rainfall maximum intensities ranging between 56.43 mm/h and 81.95 mm/h for events of 1 hour and 100-year return period. In general terms the AFI, MFI, RCI, TEI and R indicate a low to moderate rainfall erosive potential, so it is concluded that the occurrence of mass removal processes is more related to extraordinary rainfall as isolated punctual events.

Intensity-duration-frequency (IDF) curves are among the most demandable information in meteorology, hydrology and engineering water resources design, planning, operation, and management works. The IDF Curves accessible are for the most part done by fitting arrangement of yearly greatest precipitation force to parametric dispersions. Intensity-duration-frequency (IDF) curves represent the relationship between storm intensity, storm duration and return period. Environmental change is relied upon to intensify the boundaries in the atmosphere factors. Being prone to harsh climate impacts, it is very crucial to study extreme rainfall-induced flooding for short durations over regions that are rapidly growing. One way to approach the extremes is by the application of the Intensity-Duration-Frequency (IDF) curves. The annual maximum rainfall intensity (AMRI) characteristics are often used to construct these IDF curves that are being used in several infrastructure designs for urban areas. Thus, there is a necessity to obtain high temporal and spatial resolution rainfall information. Many urban areas of developing countries lack long records of short-duration rainfall. The shortest duration obtained is normally at a daily scale/24 h. This paper suggests their generation based on annual daily maximum rainfall (ADMR) records. Rainfall data of 23 (Twenty three) hydrological years of all stations were used. Maximum rainfall frequency analysis was made by Log-Normal Distribution method.

In this article an analysis of urban rainfall from hourly to seasonal scales is conducted for the Netherlands, with a focus on its capital, Amsterdam. In addition, the potential of synoptic weather types and local wind directions to categorize extreme rainfall in Amsterdam is assessed. An analysis of gauge-adjusted daily radar rainfall retrievals with 1 km spatial resolution for 10 years shows that rainfall is enhanced over Dutch cities compared to their rural surroundings, with a maximum of a 14.2% increase over the largest cities in winter. The annual cumulative rainfall in Amsterdam appears to be significantly higher compared to its surroundings. This is due both to the higher frequency of occurrence of urban rainfall and to the higher hourly mean intensities. Extreme hourly rainfall rates appear to be affected by urban areas only in summer. Diurnal and weekly rainfall cycles do not reveal any significant urban influence. A wind direction analysis reveals that extreme rainfall events can primarily be attributed to westerly and next to southerly air masses. An analysis of the Jenkinson and Collinson (JC) and the German Weather Service (Deutscher Wetterdienst, DWD) weather types with rainfall and extreme rainfall events reveals that the JC weather types are more indicative of situations associated with rainfall extremes, whereas the DWD weather types are more indicative of situations resulting in higher accumulated rainfall amounts.

Using Generalized Extreme Value analysis, this study details the independent seasonal impacts of the El Niño–Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) on rainfall extremes that cause many hydro-meteorological hazards and affect vulnerable populations in Indonesia, based on indices defined by the Expert Team on Climate Change Detection and Indices (ETCCDI), for the period 1981–2019. Gridded Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS) is used to calculate maximum consecutive 5-day precipitation (Rx5d), total precipitation from days above 95 percentile (R95p), and maximum number of consecutive dry days (CDD). Consistent with previous studies, the ENSO and IOD impacts on rainfall extremes are shown to be strongest during the dry seasons (JJA-SON) and weaker in the wet seasons (DJF-MAM). Rainfall extremes appear to be widely influenced throughout Indonesia by ENSO, whereby extremes become drier (wetter) during El Niño (La Niña). Similarly, positive (negative) phases of the IOD lead to more extreme dry (wet) conditions. However, distinct from previous studies, as ENSO and IOD often co-occur, we also provide independent influences of the two climate modes. Low-level circulation northeast and southwest of Indonesia, both previously suggested as main drivers of impacts on Maritime Continent rainfall, are more closely associated with independent ENSO and IOD, respectively. For example, ENSO, independent of IOD, impacts rainfall extremes more in the northern and eastern regions of Indonesia, and the IOD, independent of ENSO, modulates rainfall extremes more over southern and western regions. Despite independent ENSO and IOD impacts understandably being found more eastward and westward of the country, respectively, details provided here help explain regional differences between rainfall extremes and ENSO and IOD, such as Jakarta in west Java, which is predominantly influenced by local forcing associated with the IOD.

The dependence of rainfall on elevation has frequently been documented in the scientific literature and may be relevant in Italy, due to the high degree of geographical and morphological heterogeneity of the country. However, a detailed analysis of the spatial variability of short-duration annual maximum rainfall depths and their connection to the landforms does not exist. Using a new, comprehensive and position-corrected rainfall extreme dataset (I2-RED, the Improved Italian-Rainfall Extreme Dataset), we present a systematic study of the relationship between geomorphological forms and the average annual maxima (index rainfall) across the whole of Italy. We first investigated the dependence of sub-daily rainfall depths on elevation and other landscape indices through univariate and multivariate linear regressions. The results of the national-scale regression analysis did not confirm the assumption of elevation being the sole driver of the variability of the index rainfall. The inclusion of longitude, latitude, distance from the coastline, morphological obstructions and mean annual rainfall contributes to the explanation of a larger percentage of the variance, even though this was in different ways for different durations (1 to 24 h). After analyzing the spatial variability of the regression residuals, we repeated the analysis on geomorphological subdivisions of Italy. Comparing the results of the best multivariate regression models with univariate regressions applied to small areas, deriving from morphological subdivisions, we found that “local” rainfall–topography relationships outperformed the country-wide multiple regressions, offered a uniform error spatial distribution and allowed the effect of morphology on rainfall extremes to be better reproduced.

Background and Objectives: Occurrence of extreme rainfalls specifically in short-time scales causes heavy damages to human communities, municipal crowd regions and natural ecosystems. Studying and precise identifying of extreme rainfalls is essential and crucial in different agriculture and natural resources, meteorology and hydrology, engineering and natural environment aspects. The damage intensity of extreme rainfalls does not equally act in different regions and it is essential to assess the risk extent of such hazardeous rainfalls in regions with different climatic conditions. Therefore, the aim of this study is to identify and zoning of extreme rainfall occurrence risk in different 6, 12 and 24-hour time scales for West parts of Iran, which has a noticeable diversity in terms of the climatic and topographic conditions.
Materials and Methods: to perform this research, a number of 27 synoptic stations located in five provinces including Kurdistan, Kermanshah, Hamedan, Ilam and Lorestan were selected and the maximum annual values of extreme rainfalls in three time scales of 6, 12 and 24-hours in a 25 year time period (1992-2016) were extracted and by fitting different statistically distributions to each of these time series and by adopting the Chi-square test, the statistical distributions with best fit were regoized and were used to performing propabilitistic analyses. The 30, 40 and 50 mm thresholds were used to defining the torrential extreme rainfalls in 6, 12 and 24-hours time scales, respectively and after calculating the risk extents of the mentioned torrential extreme rainfalls for all of the studied stations, the risk zoning of torrential extreme rainfalls occurrence was performed by applying the multiple linear regression models between the risk extents and geographical properties (longitude, latitude and elevation) for all of the studied region. To enhancing the models accuracy, the long-term average of the number of days per year with precipitation greater than 1 mm was employed in the structure of the regression models as auxiliary variable in some cases and to achieve higher accuracy of regression models, the studied region was divided into three distinct regions.

Results: The results showed that among different fitted statistical distributions to the time series of extreme rainfalls of 6, 12 and 24-hours in the studied region, three distributions including Log-Logistic, Pearson and Gama were recognized as the best fit distributions. In terms of the accuracy of the multiple linear regression models, the results showed the high accuracy of these models for all of the three distinct regions and whole of three time scales of 6, 12 and 24-hours. The overall results of this research showed that the risk occurrence of the torrential extreme rainfalls in West of Iran has a notable diversity so that this risk is very low in some centarl parts and very high in some west and south parts of the studied region.
Conclusion: The overall results of this research revealed that the general applied algorithm of this research to estimating spatial distribution of torrential extreme rainfalls ocuurence risk was led to obtaining the appropriate and acceptable accuracy in regional estimating and generalizing the stational point results to the regional scale. Therefore, it is essential to adopt appropriate tasks and more attention in contrast to the negative consequences of the extreme rainfalls in the parts with higher degree of risk occurence.