From the peaks to the plains: Investigating the role of elevation in governing drought dynamics over the Indus river basin

Abstract

Drought is referred as a natural calamity which negatively affects various sectors especially water resources, food security and the economy of the country. High altitude regions as compared to low-lying areas, are more vulnerable and sensitive to changing climate. In order to comprehend the entire drought phenomena, analyzing drought trends with respect to elevation for different time scales is of great significance. Therefore, the present study is an attempt to investigate the spatiotemporal variation of meteorological droughts and to explore the relationship between elevation and drought dynamics over the Indian extent of Indus river basin, which is an important drainage system of the Indian sub-continent as far as agricultural productivity and water supply is concerned. Heterogeneity of the elevation spread over the basin ranging from 93 to 8489 m, makes it suitable for exploring the elevation relationship with drought characteristics. For this purpose, gridded monthly precipitation, maximum and minimum temperature data of 0.120 × 0.120 spatial resolution (1956 grids) for a time period of 42 years (1979–2020) is utilized to study the drought characteristics. Drought events are identified based on Standardized Precipitation Evapotranspiration Index (SPEI). Computation of SPEI-annual and SPEI-seasonal (pre-monsoon, monsoon, post-monsoon and winter) is done on the basis of climatic water balance, connecting to the droughts. Modified Mann-Kendall test and Sen's slope method have been used to detect significant trends in the region. Results show that the trends in the drought indices have very high heterogeneity across different seasons. Overall, 13% (14%) grids show drying (wetting) trends for annual SPEI time series analysis. However, seasonally, it is found that monsoon and post- monsoon seasons have larger areas in the basin with wetting trends. Moreover, the pre-monsoon season has a larger area with drying trends. The study region has experienced 0%–10% and 0%–5% severe and extreme drought frequency respectively, over the time period 1979–2020. A relationship between drought and elevation is observed, depicting wetting trend is associated with elevations up-to around 2000 m with decreasing rate of wetting whereas, for the altitudes from 2000 to 6000 m drying trends prevails. However, a lesser rate of drying is observed for the higher elevations above around 4000 m as compared to altitudes between 2000 and 4000 m. The plausible causes of this certain behavior of SPEI trend with elevation is determined by further analysis of the trend of meteorological parameters (precipitation and PET) which were utilized for the computation of SPEI. Both precipitation and PET trends are found to be responsible for the SPEI trends along the elevation gradient. © 2023