Modelling for drought evolution and some hydrological implications over a semi-arid terrain using earth observation techniques

Abstract

Droughts are climate change phenomena that affect watersheds, causing reduced stream flows and poor groundwater recharge. Their evolution seeks a greater understanding of meteorological conditions that perpetually propagate into the hydrological system and gradually results into reduced stream flows. The present study investigated the Shetrunji river basin in Saurashtra region of western India and detected 14 hydrological droughts between 1984 and 2021. The Soil and Water Assessment Tool (SWAT)-based simulations helped to construct past drought cycles using Standardized Runoff Index (SRI) and Standardized Precipitation Index (SPI). Multi-site calibration and validation processes resulted in a higher accuracy of ranking among influential factors with baseflow and curve number as the top two sensitive parameters. Evaluation metrics for acceptable scores were set for R2 (>0.50), NSE (≥0.60) and PBIAS (±25 %) for streamflow. The mean drought intensity ranged from 1.31 to 0.92, with peak severity values of −3.03 for meteorological and −4.14 for hydrological droughts respectively. June and July are the most common months for long-term droughts of hydro-met origin. Hydrological droughts followed meteorological droughts, had slower progression, longer duration, and more severity. The region has experienced distributive phases of change over 38 years, highlighting the region's deviated hydro-meteorological patterns. Evaluation and understanding of the nature of historic droughts of this region shall benefit the policy-makers at an upscaled level to provide thus, adaptive solutions at the local level.