Integrated Drought Index (IDI) for drought monitoring and assessment in India

Abstract

Drought monitoring and declaration in India is challenging due to the requirement of multiple drought indicesrepresenting meteorological, hydrological, and agricultural droughts that are often not available in near real-time. To overcome this, we develop an Integrated Drought Index (IDI) that combines the response of meteorological, hydrological, and agricultural droughts. We use Gaussian copula to integrate the 12-month Standardized Precipitation Index (SPI), 4-month Standardized Runoff Index (SRI), 1-month Standardized Soil moisture Index (SSI),and 1-month Standardized Groundwater Index (SGI) to develop IDI. Hydrologic variables (total runoff, soil moisture, and groundwater) required in IDI were simulated using the VIC with SIMple Groundwater Model (VIC-SIMGM). We evaluated IDI against the Drought Severity Index (DSI), terrestrial and groundwater storage anomalies from the Gravity Recovery and Climate Experiment (GRACE) satellites, groundwater well, and streamflow anomalies. Moreover, we identify the three major droughts with the highest severity(based on IDI) that occurred in 1965, 1987, and 2002 in the Sabarmati River Basin. The three most severe droughts occurred in 1966, 1979, and 2010 in the Brahmani River Basin. The projections based on IDI and bias-corrected data suggest drier conditions in the near (2011-2040) and mid (2041-2070) periods in both the basins under Representative Concentration Pathways (RCP) 2.6 and 4.5. However, the drought frequency based on IDI is projected to increase in the late 21stcentury in both the basins under the high-emission scenario of RCP 8.5. Our results show that IDI can be effectively used for drought monitoring and assessment under retrospective and future climate in India.