An integrated water deficit index to evaluate multifaceted impacts of drought in a semi-arid river basin

The multifaceted nature and widespread impacts have resulted in numerous definitions and indices for drought characterization. However, the existing indices cannot capture the overall water availability by considering all storage fluxes, particularly for large river basins. Being the key contributors to water balance, climatic water (precipitation minus potential evapotranspiration) and catchment storage (terrestrial water storage) are essential in quantifying the basin resources. This study is aimed at developing an integrated water deficit index (IWDI) by combining standardized precipitation evapotranspiration index (SPEI) (proxy for climatic water deficit) and terrestrial water storage index (TWSI) (proxy for storage deficit) using Clayton copula function. The robustness of IWDI to represent basin-scale water availability is tested over a large, semi-arid river basin of India. Run theory was employed to identify and characterize drought events, with variable motion studies used to track the internal propagation of drought. Structural equation modeling (SEM) was considered to ascertain the role of controlling variables on SPEI and TWSI, whereas correlation studies were employed to quantify the role of external factors on IWDI. Our results highlighted a clear spatiotemporal variation in drought characteristics across the basin. Upper sub-basins had a prolonged duration (> 22 months) and severity (15 months, < -10) due to limited water availability. This resulted in a longer development period (12 \ (\) 6 months) with an extended recovery period (13 \ (\) 8 months) for the upper sub-basins, particularly for the devastating droughts. Lower sub-basins experienced frequent, short-term droughts with low severity (< -1) due to low precipitation in spite of adequate resources. Role of external factors confirmed that reduction in storage and incoming fluxes or increase in outgoing fluxes can intensify the drought. Correlation studies conclude that droughts have reduced the water bodies by 15% and crop production by 25% during 2002–17. Study findings can help to understand the drought-induced tolerance mechanism in large-scale, semi-arid river basins and to adopt mitigation strategies for optimum utilization of resources.