Characteristics Of Dry Spells Research Articles

Dry and Wet Spells in Poland in the Period 1966–2023

The aim of this study is to present the spatial and temporal variability of the frequency of dry and wet days and dry and wet spells against the background of changes in precipitation and atmospheric circulation. The study is based on daily precipitation totals from 46 meteorological stations in Poland from 1966 to 2023. Additionally, seven circulation indices were used, namely GBI, NAO, AO, EA, EA/WR, SCAND, and AMO. Dry days are defined as days without precipitation. Wet days are days with at least 1 mm of precipitation. It was shown that dry spells are much more common than wet spells, are longer, and cover larger areas. Long-term changes in the annual characteristics of dry and wet days and spells are not statistically significant. Only the length of the most extended dry spell in the year increases. However, there are significant changes in their annual cycles. Spring is drier; in summer, precipitation decreases in the south and increases in the north; November and December, symbols of gloomy rainy weather, are increasingly drier; and rainy weather has shifted to January and February. The impact of circulation varies according to the season, with the NAO, AO, SCAND, and GBI indices having the greatest influence.

Characterisation of dry spells for agricultural applications in Malawi

Dry spells are one of the climate change hazards that continue to exert pressure on the agriculture sector, hence affecting food security. Understanding dry spell characteristics of an area helps in coming up with interventions and adaptive measures among other advantages. This study aimed at understanding characteristics of dry spells for Malawi by using climate hazards group infrared precipitation with stations precipitation data from 1981 to 2019. The study focused on the spatial distribution, maximum number of dry days, trend of maximum dry days and time of occurrence of dry spells. Data was analysed using Mann–Kendal trend analysis in R software. The results indicate a high number of occurrences of dry spells in the southern region than the other two regions of Malawi. In addition, the southern region experienced the highest maximum number of dry days. However, there is an upward trend for maximum days of dry spells in central region than all other regions. Local scale topographic influences on dry spell occurrence were also apparent. The study further established that the number of dry spell occurrence in the rainfall season starts to increase towards end of March. In this regard, although rainfall season in the study area is considered to be from November to April, the study recommends that growing season should be considered to be November to March so that crops are not affected by end of season dry spells which are common. Farmers should ensure that they plant crops that will mature with this growing period.

Seasonal and regional variability of wet and dry spell characteristics over Turkey

Understanding the variations and leading atmospheric mechanisms causing wet and dry episodes are very important for the water management strategies. For this purpose, this study investigates the spatiotemporal variation and background environmental conditions for wet and dry spell lengths in Turkey. With this aim, Mann-Kendall rank statistic test and fitted ordinary least squares regression method are implemented to the 92 meteorology stations, which are homogenously distributed over Turkey, for the period 1966–2018. In terms of atmospheric circulation mechanisms, synoptic composites of NCEP/NCAR Reanalysis data (sea level pressure, air temperature at 850-hPa level, geopotential height at 500-hPa level) and sea surface temperature from NOAA High Resolution data are applied to the five years of highest frequency long dry/wet spells. According to the results, both the increasing frequencies of wet spells and their highest contribution to the precipitation are mainly found in the eastern Black Sea Region (BSR) of Turkey during all seasons, especially in spring. In this sub-region, statistically significant increasing (decreasing) springtime wet (dry) spell lengths in the neighboring five stations (i.e. Ardahan, Artvin, Bayburt, Hopa, Rize) indicated that the majority of wet spells (almost 30%) appear to occur between 3 and 5 days and the maximum number of the wet spell days are shown in the last two decades of the eastern BSR. Local quasi-stationary surface high located over eastern Black Sea (1016-hPa core) and associated weak northerly winds transfer relatively warm moist air from the sea surface (11.8 °C in average). This air mass meets with cold- land and low level (6 °C at 850 hPa) air masses, developing instability conditions and resulting in low precipitation rates in wet spells for the eastern BSR. On the other hand, by the extension of the south-west Asian Monsoon to the inner parts of Turkey, relatively hot dry air is transferred to the eastern BSR via southerly winds. As a result of this long-staying Asiatic monsoon characteristics, more dry days are shown in the region due to insufficient moisture and associated lack of precipitation.

Regional patterns of dry spell durations in Croatia

AbstractThe spatiotemporal characteristics of mean and maximum dry spells (DSs) in Croatia were analysed through general climatology and the return values associated with different return periods. An analysis was performed across seven regions with different precipitation regimes comprising data from 131 meteorological stations for 1961–2015. Daily precipitation limits of 1, 5, and 10 mm were used to define dry days, and DSs were defined as consecutive series of dry days. Generalized extreme value (GEV) and generalized Pareto (GP) distributions were applied to the DS annual maxima (AM) and the peak over threshold (POT) series, respectively. The respective distribution parameter methodology and interpretation combined both frequentist and Bayesian approaches. The regional mean DS lengths clearly indicated a dominance of DS durations in easternmost Croatia during the cold season (mainly winter) and in the southern Adriatic during the warm season (mainly summer). Elsewhere, combined climatic influences were reflected, with the shortest DSs found in the highlands. This spatial pattern was more pronounced for DS5 and DS10, whereas differences in DS1 durations were not evident. Spatial DS distribution return values associated with various return periods obtained by the GEV and GP distributions followed the general DS climatology. The visual inspection of an appropriate threshold for GP‐POT modelling, using the GP parameter stability graphs and L‐moment ratio diagrams, indicated that the 75th percentile value was best for all three DS categories. Although the estimates obtained by the two methods could not be directly compared, the GP model generally found longer DS return values than those obtained by the GEV, particularly in the regions with long DS. This study provides a climatological basis for drought parameters and drought risk assessment in Croatia. Moreover, the results are relevant for adjacent regions, complementing and enriching the current DS characteristics knowledge in southeastern Europe.

Probabilistic Evaluation of Drought in CMIP6 Simulations.

As droughts have widespread social and ecological impacts, it is critical to develop long‐term adaptation and mitigation strategies to reduce drought vulnerability. Climate models are important in quantifying drought changes. Here, we assess the ability of 285 CMIP6 historical simulations, from 17 models, to reproduce drought duration and severity in three observational data sets using the Standardized Precipitation Index (SPI). We used summary statistics beyond the mean and standard deviation, and devised a novel probabilistic framework, based on the Hellinger distance, to quantify the difference between observed and simulated drought characteristics. Results show that many simulations have less than ±10% error in reproducing the observed drought summary statistics. The hypothesis that simulations and observations are described by the same distribution cannot be rejected for more than 80% of the grids based on our H distance framework. No single model stood out as demonstrating consistently better performance over large regions of the globe. The variance in drought statistics among the simulations is higher in the tropics compared to other latitudinal zones. Though the models capture the characteristics of dry spells well, there is considerable bias in low precipitation values. Good model performance in terms of SPI does not imply good performance in simulating low precipitation. Our study emphasizes the need to probabilistically evaluate climate model simulations in order to both pinpoint model weaknesses and identify a subset of best‐performing models that are useful for impact assessments.

Future Changes in Wet and Dry Season Characteristics in CMIP5 and CMIP6 simulations

AbstractClimate change will result in more dry days and longer dry spells, however, the resulting impacts on crop growth depend on the timing of these longer dry spells in the annual cycle. Using an ensemble of Coupled Model Intercomparison Project Phase 5 and Phase 6 (CMIP5 and CMIP6) simulations, and a range of emission scenarios, here we examine changes in wet and dry spell characteristics under future climate change across the extended tropics in wet and dry seasons separately. Delays in the wet seasons by up to two weeks are projected by 2070-2099 across South America, Southern Africa, West Africa and the Sahel. An increase in both mean and maximum dry spell length during the dry season is found across Central and South America, Southern Africa and Australia, with a reduction in dry season rainfall also found in these regions. Mean dry season dry spell lengths increase by 5-10 days over north-east South America and south-west Africa. However, changes in dry spell length during the wet season are much smaller across the tropics with limited model consensus. Mean dry season maximum temperature increases are found to be up to 3°C higher than mean wet season maximum temperature increases over South America, Southern Africa and parts of Asia. Longer dry spells, fewer wet days, and higher temperatures during the dry season may lead to increasing dry season aridity, and have detrimental consequences for perennial crops.

Spatial and Temporal Analysis of Dry and Wet Spells in the Wadi Cheliff Basin, Algeria

The Mediterranean Basin, located in a transition zone between the temperate and rainy climate of central Europe and the arid climate of North Africa, is considered a major hotspot of climate change, subject to water scarcity and drought. In this work, dry and wet spells have been analyzed in the Wadi Cheliff basin (Algeria) by means of annual precipitation observed at 150 rain gauges in the period 1970–2018. In particular, the characteristics of dry and wet spells (frequency, duration, severity, and intensity) have been evaluated by means of the run theory applied to the 12-month standardized precipitation index (SPI) values. Moreover, in order to detect possible tendencies in the SPI values, a trend analysis has been performed by means of two non-parametric tests, the Theil–Sen and Mann–Kendall test. The results indicated similar values of frequency, severity, duration, and intensity between the dry and the wet spells, although wet events showed higher values in the extreme. Moreover, the results of the trend analysis evidenced a different behavior between the northern side of the basin, characterized by a negative trend in the 12-month SPI values, and the southern side, in which positive trends were detected.

Recent changing characteristics of dry and wet spells in Canada

Under the possible impact of climate warming, recent changes in dry and wet spells have contributed significantly to climate-related hazards around the world. In this work, spatial and temporal variations in dry and wet spells over Canada are investigated using daily precipitation data from 1979 to 2018. The time-varying relationships between precipitation spells and large-scale climate anomalies are modeled using a nonstationary generalized extreme value (GEV) distribution and Bayesian quantile regression. Over the period 1979–2018, significant changes in dry and wet spells have been observed across Canada, particularly in the southern Canadian Prairies (CP), where both the number and duration of dry spells show positive trends. Dry and wet spells over many parts of Canada are nonstationary under the effects of the El Nino–Southern Oscillation (ENSO) and the Pacific–North American pattern (PNA), with PNA having stronger effects on annual maximum dry spells than ENSO, especially in the central CP and eastern Ontario. For western Canada, the influence of ENSO on dry spells tends to be relatively strong, especially for dry spells of high quantiles, as El Nino generally induces atmospheric moisture deficit. For central Canada, ENSO and PNA have a negative (positive) impact on the wet spell duration of low (high) quantiles. For eastern Canada, PNA is negatively correlated with the duration of wet spells, especially for wet spells of high quantiles. Therefore, a better understanding of the spatial and temporal variability in dry and wet spell return periods will be useful for the effective management of water resources, and for developing effective disaster mitigation measures against the possible social and economic impacts of climate-related hazards.

Actual Precipitation Index (API) for Drought Classification

The Standard Precipitation Index (SPI) is a widely used statistical technique for the characterization of droughts. It is based on a probabilistic standardization procedure, which converts a Gamma-type probability distribution function (PDF) into a normal (Gaussian) standard series with zero mean and unit standard deviation. Drought classification based on SPI indicates dry and wet spell characteristics, provided that the hydro-meteorological records abide by normal (Gaussian) PDF only, otherwise the results will be biased. Therefore, in this paper, the actual precipitation index (API) method is presented, which provides drought classification and information regardless of the underlying PDFs. The main purpose of this paper is to explain the main differences between SPI and API and to prove that the use of API is the more reliable solution for classification of droughts into five categories described as “Normal dry”, “Slightly dry”, “Medium dry”, “Very dry” and “Extremely dry”. The application of the methodology is presented for two sets of precipitation data; one with exponential PDF monthly precipitation records from Istanbul City, Turkey and one for New Jersey, USA with almost normal (Gaussian) PDF based on annual precipitation records. The comparisons indicate that API is applicable regardless of the underlying PDF of the hydro-meteorology data. It produces real drought classification from the original data without recourse to standard normal PDF conversion.

Analysis of the Characteristics of Dry and Wet Spells in a Mediterranean Region

Climate change could increase the risk of future hydrological extremes over large regional areas and trigger further pressure on water resource availability. In this study, the overall characteristics of dry and wet spells during a 56-year period (1951–2006) were analysed in the Calabria region (southern Italy), considering both yearly and seasonal scales. In particular, the mean and maximum lengths of dry/wet spells, the number of dry and wet spells with different lengths, and the contribution of dry/wet spells with different lengths to the total number of dry/wet days have been investigated. The results showed similar behaviour of both dry and wet spells in the spatial distribution of the mean lengths, with a difference between the two opposite sides (Ionian and Tyrrhenian) of the region. In fact, mean values ranging between 6 and 8 days, and higher than 8 days have been detected on the Tyrrhenian and on the Ionian side, respectively. The results regarding the maximum values of the lengths show much higher values of dry spells than the wet ones, and different temporal distributions throughout the year. In particular, with respect to dry spells, in autumn the maximum lengths reached values higher than 200 days, while the longest wet spells have been identified in winter, with a maximum value of 44 consecutive days with rain. The outcomes of this study can be useful for both water resources (with respect to the dry sequences) and risk reduction (regarding the wet spells) management.

Evaluation of CORDEX Regional Climate Models in Simulating Extreme Dry Spells in Southwest China

In recent decades, Southwest China (SWC) has experienced a series of severe and extensive droughts resulting in tremendous socioeconomic losses. The annual maximum dry spell length (AMDSL), which refers to the number of consecutive days without rainfall, or days with rainfall below a threshold, plays an important role in triggering drought. The main objective of this study is to provide a comparison of the capabilities of current regional climate models (RCMs) in simulating extreme dry spell characteristics in mountainous SWC. Five available RCM simulations utilized in the Coordinated Regional Climate Downscaling Experiment (CORDEX)-East Asia project over 1981 to 2005 were employed in this study; the RCMs being NIMR-HadGEM3, SNU-MM5, SNU-WRF, KNU-RegCM4 and YSU-RSM. Firstly, it was found that all RCMs reasonably simulate the main seasonality features of rainfall and dry days in SWC. Furthermore, besides YSU-RSM, the other four RCMs can accurately capture the spatial pattern of dry-day occurrence based on Taylor diagram diagnosis. Secondly, we assessed the performance of five RCMs to detect and reproduce the climatology and variability of the AMDSL. In general, RCMs simulate the spatial pattern of long-term mean and interannual variability of the AMDSL in SWC well. Based on Taylor diagram evaluation, NIMR-HadGEM3 was the best among 5 RCMs in simulating the AMDSL characteristics. Thirdly, the generalized extreme value (GEV) distribution is considered the most suitable model fitting the AMDSL in both observation and RCM experimental data in comparison to other three-parameter probabilistic models. Higher value centers of the scale parameter and the location parameter indicate a wider and amplified distribution of the AMDSL over the low-latitude highlands (LLH) region against other areas in Southwest China, which is consistent with spatial patterns of climatological AMDSL. In addition, sensitivity analysis of different thresholds for dry days show that the 1 mm threshold is suitable for this study and different threshold choices have little effect on simulation ability.

Three resampling approaches based on method of fragments for daily‐to‐subdaily precipitation disaggregation

ABSTRACTPrecipitation data of finer timescale and higher spatial density are crucial for continuous hydrological modelling and flood risk assessment. Disaggregation methods are often used to transform the coarser‐timescale precipitation data into finer resolutions. The nonparametric approach based on method of fragments (MOF) has received broad attention in precipitation disaggregation literature, given its superiority in reproducing the at‐site statistical attributes. However, a detailed literature review has shown that the MOF‐based resampling approaches are mainly focused in the single‐site precipitation disaggregation context, which may subject to limitations such as the unavailability of at‐site precipitation records and the incapability to preserve the inter‐site correlation structure. To address these issues, we propose three resampling approaches based on MOF. The first approach is a single‐site interval‐based resampling approach which only draws subdaily fragment vectors from at‐site record. The second one extends the first one to a regionalized version where subdaily fragment vectors are drawn from both the at‐site and neighbouring stations. The third one is a multi‐site approach developed to preserve the observed inter‐site correlation. The performances of the three methods are evaluated with applications to daily‐to‐hourly precipitation disaggregation at six rain gauges in Singapore and eight precipitation stations in Wangkuai reservoir catchment in northern China. An elaborate list of performance measures, including standard validation statistics, spatial correlation, inter‐day connectivity, annual extreme analysis, and intra‐day dry and wet spell characteristics are used to assess the performance. The proposed three methods are shown to be effective in reproducing the at‐site attributes, and no significant deterioration of performance is observed when moving from the single‐site method to the regionalized and multi‐site versions. As expected, the multi‐site approach is the only one method that is able to reconstruct the spatial correlation in the disaggregated precipitation field. The approaches can be applied for daily‐to‐subdaily precipitation disaggregation in different regions.

Using long-term daily satellite based rainfall data (1983–2015) to analyze spatio-temporal changes in the sahelian rainfall regime

The sahelian rainfall regime is characterized by a strong spatial as well as intra- and inter-annual variability. The satellite based African Rainfall Climatology Version 2 (ARC2) daily gridded rainfall estimates with a 0.1°×0.1° spatial resolution provides the possibility for in-depth studies of seasonal changes over a 33-year period (1983–2015). Here we analyze rainfall regime variables that require daily observations: onset, cessation, and length of the wet season; seasonal rainfall amount; number of rainy days; intensity and frequency of rainfall events; number, length, and cumulative duration of dry spells. Rain gauge stations and MSWEP (Multi-Source Weighted-Ensemble Precipitation) data were used to evaluate the agreement of rainfall variables in both space and time, and trends were analyzed. Overall, ARC2 rainfall variables reliably show the spatio-temporal dynamics of seasonal rainfall over 33years when compared to gauge and MSWEP data. However, a higher frequency of low rainfall events (<10mmday−1) is found for satellite estimates as compared to gauge data, which also causes disagreements between satellite and gauge based variables due to sensitivity to the number of days with observations (frequency, intensity, and dry spell characteristics). Most rainfall variables (both ARC2 and gauge data) show negative anomalies (except for onset of rainy season) from 1983 until the end of the 1990s, from which anomalies become mostly positive and inter-annual variability is higher. ARC2 data show a strong increase in seasonal rainfall, wet season length (caused by both earlier onset and a late end), number of rainy days, and high rainfall events (>20mmday−1) for the western/central Sahel over the period of analysis, whereas the opposite trend characterizes the eastern part of the Sahel.

Dry spell frequency in West Java, Indonesia

The climatology and variability of dry spells are valuable information for scientists, engineers, planners, and managers working in water-related sectors such as agriculture, ecology, hydrology, and water resources. The dry spell concerns consecutive dry days which are the largest number of consecutive days with less than 1 mm of daily precipitation within a year. The objective of this study is to analyse the spatial and temporal characteristics of dry spells and also specifically investigate the frequency patterns of the dry spell distribution based on historical observed daily precipitation from 1981 to 2010. The longest dry spell occured at Pasirukem with the length of 252 days. The northern coast of West Java have higher probabilities of dry spells more than 5, 10, 15, and 20 days.

Characteristics of wet and dry spells in the West African monsoon system

AbstractUsing 17 years (1998–2014) of daily TRMM 3B42 rainfall data, we provide a climatological characterization of wet and dry spells in West Africa, which should serve to assess the ability of climate model to simulate these high impact events. The study focuses on four subregions (Western and Central Sahel, Sudanian zone and Guinea Coast). Defining wet (dry) spells as sequences of consecutive days with precipitation higher (lower) than 1 mm, we describe the space‐time variability of wet and dry spell occurrence. This climatology stresses the influence of the relief on the number and duration of these spells. The spatio‐temporal variability of the wet and dry spells also appears to be closely related to the spatio‐temporal variability of the West African monsoon. The number of wet spells of all durations and of 2–3 day dry spells have similar features with a maximum occurrence during the local rainy seasons and a spatial pattern similar to the mean annual rainfall with a north–south gradient. In contrast, dry spells lasting more than four days show some singularities such as a low occurrence over the Sahelian band or high occurrence along the Guinea Coast mainly from Ivory Coast to Benin. Moreover, the seasonal cycle of these longer dry spells presents higher occurrences at the beginning and the end of the rainy seasons.

Dry and wet spell variability during monsoon in gauge-based gridded daily precipitation datasets over India

Accurate estimates of monsoonal rainfall at daily time scales are essential inputs for various water-related sectors such as drought and flood forecasting, crop and water management for agriculture. To serve this purpose, a variety of rainfall products, especially the gauge based products which serve as the ground-truth for other derived rainfall products, are available over India. In this study, three different daily gauge based gridded rainfall datasets, namely Indian Meteorological Department (IMD), Asian Precipitation Highly Resolved Observational Data Integration Towards Evaluation of water resources (APHRODITE) and Climate Prediction Center (CPC) unified rain gauge data are compared over India for the monsoon season of 1979–2007. The comparison among the datasets is based on the duration, frequency and intensity of three different spell characteristics, namely dry, wet and extreme wet spells, and their associated trends. Wet (dry) spells are defined as the consecutive period of wet (dry) days, where a wet (dry) day is defined using rainfall threshold of 1mm. Extreme wet spells are defined using the 90th percentile of rainfall above the depth of wet day. All datasets capture the spatial distribution of precipitation characteristics, albeit with pronounced differences at heavy rainfall regions. CPC and IMD show a close match in spell characteristics while APHRODITE significantly deviates. APHRODITE shows increased intensity of rainfall during dry periods, leading to over-estimation of wet days and under-estimation of dry days. Northern extreme of India (Jammu and Kashmir) show major differences in replicating the spell characteristics. Trend patterns are also not consistent between the three datasets. The present study will provide information on the spatio-temporal pattern of dry, wet and extreme wet spell characteristics over India and aid in selecting appropriate datasets for studying the Indian monsoon rainfall depending on their scope and application of research.

Evaluation of ERA-Interim, MERRA, NCEP-DOE R2 and CFSR Reanalysis precipitation Data using Gauge Observation over Ethiopia for a period of 33 years

The vital demand of reliable climatic and hydrologic data of fine spatial and temporal resolution triggered the employment of reanalysis datasets as a surrogate in most of the hydrological modelling exercises. This study examines the performance of four widely used reanalysis datasets: ERA-Interim, NCEP-DOE R2, MERRA and CFSR, in reproducing the spatio-temporal characteristics of observed daily precipitation of different stations spread across Ethiopia, East Africa. The appropriateness of relying on reanalysis datasets for hydrologic modelling, climate change impact assessment and regional modelling studies is assessed using various statistical and non-parametric techniques. ERA-Interim is found to exhibit higher correlation and least root mean square error values with observed daily rainfall, which is followed by CFSR and MERRA in most of the stations. The variability of daily precipitation is better captured by ERA, CFSR and MERRA, while NCEP-DOE R2 overestimated the spread of the precipitation data. While ERA overestimates the probability of moderate rainfall, it is seemingly better in capturing the probability of low rainfall. CFSR captures the overall distribution reasonable well. NCEP-DOE R2 appears to be outperforming others in capturing the probabilities of higher magnitude rainfall. Climatological seasonal cycle and the characteristics of wet and dry spells are compared further, where ERA seemingly replicates the pattern more effectively. However, observed rainfall exhibits higher frequency of short wet spells when compared to that of any reanalysis datasets. MERRA relatively underperforms in simulating the wet spell characteristics of observed daily rainfall. CFSR overestimates the mean wet spell length and mean dry spell length. Spatial trend analysis indicates that the northern and central western Ethiopia show increasing trends, whereas the Central and Eastern Ethiopia as well as the Southern Ethiopia stations show either no trend or decreasing trend. Overall, ERA-Interim and CFSR are better in depicting various characteristics of daily rainfall in Ethiopian region.

The characteristics of wet and dry spells for the diverse climate in China

Using a large precipitation dataset from 692 gauge stations across China for the period of 1960–2013, this study analyzed the characteristics of wet/dry spells related to four types of climate including arid, semiarid, semiarid to subhumid, and humid climate. A wet/dry spell is defined as the consecutive days with precipitation amount greater/less than a threshold. The frequency of wet/dry spells, the contributions of wet/dry spells with different lengths to the total number of wet/dry days and total precipitation amount were analyzed for different climate types. The wet/dry spells with the greatest contributions to the total wet/dry days or total precipitation amount vary with climate. For drier climate, long-duration dry spells contribute more to the total number of dry days, while short-duration wet spells contribute more to the total number of wet days and the total precipitation amount. The characteristics of wet/dry spells are closely related to local climate. Good regression relationships were obtained for the number of dry/wet spell versus spell length, and precipitation amount versus wet spell length. Although the correlation between precipitation amount and wet spell length has rarely been considered in stochastic precipitation generation, the relationships identified in this study justify the necessity of taking it into account.

Contributions of soil moisture interactions to future precipitation changes in the GLACE-CMIP5 experiment

Changes in soil moisture are likely to contribute to future changes in latent heat flux and various characteristics of daily precipitation. Such contributions during the second half of the twenty-first century are assessed using the simulations from the GLACE-CMIP5 experiment, applying a linear regression analysis to determine the magnitude of these contributions. As characteristics of daily precipitation, mean daily precipitation, the frequency of wet days and the intensity of precipitation on wet days are considered. Also, the frequency and length of extended wet and dry spells are studied. Particular focus is on the regional (for nine selected regions) as well as seasonal variations in the magnitude of the contributions of the projected differences in soil moisture to the future changes in latent heat flux and in the characteristics of daily precipitation. The results reveal the overall tendency that the projected differences in soil moisture contribute to the future changes in response to the anthropogenic climate forcing for all the meteorological variables considered here. These contributions are stronger and more robust (i.e., there are smaller deviations between individual climate models) for the latent heat flux than for the characteristics of daily precipitation. It is also found that the contributions of the differences in soil moisture to the future changes are generally stronger and more robust for the frequency of wet days than for the intensity of daily precipitation. Consistent with the contributions of the projected differences in soil moisture to the future changes in the frequency of wet days, soil moisture generally contributes to the future changes in the characteristics of wet and dry spells. The magnitude of these contributions does not differ systematically between the frequency and the length of such extended spells, but the contributions are generally slightly stronger for dry spells than for wet spells. Distinguishing between the nine selected regions and between the different seasons, it is found that the strength of the contributions of the differences in soil moisture to the future changes in the various meteorological variables varies by region and, in particular, by season. Similarly, the robustness of these contributions varies between the regions and in the course of the year. The importance of soil moisture changes for the future changes in various aspects of daily precipitation and other aspects of the hydrological cycle illustrates the need for a comprehensive and realistic representation of land surface processes and of land surface conditions in climate models.

Changing characteristics of extreme wet and dry spells of Indian monsoon rainfall

AbstractModeling of extreme events and its dynamic behavior have always been an intriguing topic. Increase in the magnitude and frequency of extreme events has widely been reported in recent decades, which is attributed to abrupt changes in climate. Numerous studies on extreme Indian monsoon characteristics, using a coarse‐resolution data set, have pointed out significant changes in heavy precipitation pattern over India. However, these studies differ in their conclusions, emphasizing the need for a fine‐resolution analysis. The present study aims to analyze the spatiotemporal variations and trends in the extreme (wet and dry) Indian monsoon precipitation, using 0.25° × 0.25° high‐resolution gridded data for a period of 113 years (1901–2013). Significant increase in the maximum intensity of rainfall and spatial heterogeneity is observed over the past half century. In addition, significant negative trends in wet spell durations and positive trends in dry spell durations are observed over wet regions; whereas contrasting trends are observed over dry regions. A shift in the frequency distribution of extreme events during the monsoon period is also noticed. The 50 year return level of maximum intensity clearly shows positive trends over the past century. Though characteristics of extremes are observed to be highly localized, apparent signs of wet regions turning drier and dry regions turning wetter are obtained. A comprehensive insight into different characteristics (intensity, spell, onset, and frequency) of Indian monsoon extremes is provided, which will help in effective water resources management and flood/drought hazard preparedness.