DROUGHT ASSESSMENT IN DATA SCARCE REGIONS OF AFGHANISTAN USING STATISTICAL APPROACHES

Abstract

Drought in Afghanistan significantly impacts both the environment and socioeconomic factors within the agriculture and water supply sectors. This is mainly due to arid and semiarid climate of the region coupled with its complex topography, leading to high spatial and temporal variations in precipitation patterns, further exacerbated by climate change impacts. Managing water resources in such a context presents numerous challenges. This study aimed to evaluate drought in regions of Afghanistan with limited data by employing statistical methods to analyze the spatiotemporal variations of drought characteristics and indices. It utilized observed monthly precipitation data collected from 23 stations situated across five river basins spanning the entire country from 1970 to 2016. The statistical approaches involved in the analysis include: 1) determining the spatial-temporal variations of water resource sustainability concerning drought risk assessment through reliability-resiliency-vulnerability (RRV) indicators by utilizing long-term historical precipitation data and the change point method, 2) identifying homogeneous regions to assess regional drought risk and develop regional drought intensity-duration-frequency (IDF) curves using regional frequency analysis (RFA) with L-moment statistics, 3) quantifying and mapping the spatial variations of regional drought severity and return periods throughout Afghanistan. Spatial-Temporal Variations of Water Resource Sustainability in Response to Drought Risk The study focuses on assessing the sustainability of water resources amidst drought progression and illustrating the potential impacts of drought on water resource sustainability. Based on the severe drought estimation, 2000 and 2001 were identified as change points. Accordingly, the dataset pertaining to before and after the change point was partitioned to analyze the long-term temporal shift of the drought. The spatiotemporal variability of sustainability indicators was estimated using the Reliability Resiliency and Vulnerability (RRV) concept. The results indicated a positive trend of precipitation (increase in precipitation in the recent past) in most of the river basins after the change point leading to an increase in sustainability. However, the major portion in the upstream of the Kabul River basin showed a decrease in the sustainability of around 15% due to a reduction in precipitation. Regional Drought Risk and Drought IDF Relationships Examining drought frequency alone is not adequate without considering duration, severity, and intensity, which are encapsulated in drought intensity-duration-frequency (IDF) relationships. These relationships explore the interconnections among various drought characteristics. Consequently, the study investigated regional drought analysis (RDA) using regional drought intensity-duration-frequency (RD-IDF) curves and regional drought risk assessment (RDRA) based on the drought hazard indicator (DHI) and drought vulnerability indicator (DVI) for scarce data regions in Afghanistan. The drought characteristics were analyzed using the regional standardized-precipitation-index (SPI), and standardized precipitation-deficit distribution (SPDD). Further, L-moment statistics were used to classify different homogenous regions based on regional frequency analysis (RFA). Based on the analysis performed, the area was classified into six homogeneous regions R-1, R-2, R-3, R-4, R-5, and R-6. The drought was very consistent almost 50% of the years irrespective of the homogeneous region classified. The higher drought risk indicators, 0.21 and 0.22 were exposed to very high risk in the southwest and southeast of Afghanistan respectable indicating the occurrence of a long and severe drought. The central part of the country which has a semi-arid climate and highland area that feeds all river and water resources in Afghanistan is also in high drought risk regions, that could impact on 80% of the population in the country whose lives are related to agriculture. Furthermore, the drought IDF curves showed high drought intensity with increasing drought return periods. In contrast, the intensity significantly decreased when the time scale increased, and fewer were enhanced within the increasing drought return period. Spatial-Temporal Variations of Regional Drought Frequency Subsequently, this study prepared spatial maps of regional drought severity and return period in Afghanistan. The arithmetic mean precipitation data of the homogeneous sites were used to calculate SPI for determining the drought characteristics. The plotting position method was used to prepare a regional SPI duration curve to estimate mild, moderate, and severe drought percentages and their return periods. Furthermore, the longest regional drought durations and return periods were determined through the dry and wet episodes in the SPI series. In addition, spatial maps of the drought severity, duration, and return periods were plotted using kriging method. Consequently, six homogeneous regions were categorized from the analysis. The percentage of dry years overall ranged between 44% and 54%, from which the mild, moderate, and severe droughts ranged between 29% - 37%, 5% - 17%, and 4% - 10%, respectively. The extreme drought, with a return period of 48 years, occurred in the northeast of the country. Also, the most severe droughts were found in the central and south of the study area. Moreover, the west, central and south areas of the country had long-duration droughts with high frequency. It was found that the long duration of drought with a short return period in the central region of the country affects all river basins. Overall, the comprehensive analyses reported in this study discuss the possible implications of drought risk assessment and its impact on largely varying sustainability both spatially and temporally in Afghanistan. The central and southeast areas of the country have high population density, and the area is upstream to north, south and west zones. According to the higher frequency of severe droughts and the long period of droughts, majority of the regions were more vulnerable to drought. Therefore, it needs immediate attention in wisely managing the surface and groundwater resources, and effectively planning and managing available water resources. Also, the study recommends that the country needs to implement various regional planning for short and long-duration droughts having a high frequency of occurring. The regional drought IDF curves that provide necessary information for droughts-related hydro-climatic and agro-climatic planning in a different region of Afghanistan could be the tools to plan the water resources and agriculture effectively.