Utilizing combined deviations of precipitation and GRACE-based terrestrial water storage as a metric for drought characterization: A case study over major Indian river basins

Drought is a recurring natural hazard that significantly affects the economy and environment of large areas worldwide. It is therefore imperative to develop techniques that enable comprehensive monitoring and assessment of drought. Here we propose a novel drought index (Combined Climatologic Deviation Index (CCDI)) that encompasses all the aspects of meteorologic, agricultural, hydrologic and human-induced drought occurrences. Critical to the proposed framework is the concept of combining deviations in precipitation and terrestrial water storage, observed by Gravity Recovery and Climate Experiment (GRACE) satellites, from climatologic (normal) conditions as a measure of drought. In order to evaluate the applicability of this new index, it is analyzed over four major river basins in India (i.e. Ganga, Krishna, Godavari and Mahanadi). The propounded drought index (CCDI) has demonstrated its ability to identify drought events and render rational quantification of its severity. Results also depict an improved understanding of holistic drought conditions compared to other available drought indices. Comparison of CCDI with commonly used drought indices highlighted some of the fundamental differences while demonstrating good correspondence with PDSI (r = 0.79) and GRACE DSI (r = 0.94). Further, it is evident that in almost all the river basins there have been at least two drought periods with intensities ranging from D1 (moderate drought) to D4 (exceptional drought). The longest drought period, extending for 36 months, from July 2002 to June 2005, is observed in the Krishna Basin. Results from this study show appreciable reliance on the potential for quantifying droughts using CCDI, which will only improve with better quantification and extended availability of terrestrial water storage observations from the recently launched GRACE-Follow On mission.