Characterization of Indian Summer Monsoon Drought and its Elevation Dependance over Indus River Basin, India

Drought, a natural disaster, possess a great threat to a nation as well as to human society by stressing the water availability, agricultural production and economy of the country. As per the studies, India is highly vulnerable to droughts, occurring once in every three years from the past three decades. India receives 70-80% of its annual mean precipitation brought by south-west summer monsoon. Monsoon failure leads to the acute deficiency of available water that ultimately causes droughts and water scarce conditions. This study is an attempt to analyse the spatio-temporal variations of meteorological drought and to investigate the effect of topographical variable (elevation) on Indian summer monsoon drought characteristics over Indus River Basin. Indian extent of Indus River basin has been considered as a case. Heterogeneity of the elevation spread over the basin makes it suitable for the study. Therefore, to serve the purpose, daily gridded precipitation and temperature data at a spatial resolution of 0.12⁰ x 0.12⁰ for a time period of 42 years (1979-2020) is utilized to analyse the drought characterization. Modified Mann-Kendall method and Sen’s slope estimator have been used to detect significant trends in the study region. Standardized Precipitation Evapotranspiration Index (SPEI) has been employed to identify the dry events on the basis of climatic water-balance. Indian summer monsoon lasts for four months (June-September), thus SPEI-4 has been computed to characterize the summer monsoon droughts. Results revealed that around 18% (5%) of the stations shows wetting (drying) trends for the monsoon time series analysis. Additionally, in relation to SPEI trends, larger area (25%) of the basin depicts increasing precipitation and decreasing Potential Evapotranspiration (PET) trends. Moreover, the study region experiences 1-10% and 1-5% severe and extreme drought frequency (percentage) respectively over the time period 1979-2020. Further, the relationship of SPEI trend with respect to elevation is explored because highlands are more vulnerable to climate change as compared to low altitude regions. In case of altitude up-to 2000 m, Sen’s slope exhibits positive magnitude thus, wetting trend is observed. A very minimalistic drying trend is seen between 2000-3000 m elevation and beyond that almost no trend pattern is followed. The possible causes of this certain behaviour of SPEI trend with elevation is determined by further analysis of trend of meteorological parameters (precipitation and PET) that were used to calculate SPEI. Both precipitation and PET trends are found to be responsible for the SPEI trends.