Characterizing Drought in India Using GRACE Observations of Terrestrial Water Storage Deficit

Frequent recurrences of drought in India have had major societal, economical, and environmental impacts. While region-specific assessments are abundant, exhaustive appraisal over large spatial scales has been insubstantial. Here a new drought index called Water Storage Deficit Index (WSDI) is devised and analyzed for holistic representation of drought. The crux of the method is the employment of terrestrial water storage (TWS) variations from Gravity Recovery and Climate Experiment (GRACE) for quantification of drought intensity and severity. Drought events in recent times are well identified and quantified using the approach over four homogenous rainfall regions of India over the period from April 2002 to April 2015. Among the four regions, the highest peak deficit of -158.00 mm is observed in January 2015 over central India. While the drought of 2002-04 is prominent in peninsular and west-central India, the drought of 2009-10 and 2012-13 is conspicuous in almost all four regions of India. The longest deficit period of 23 months (from February 2009 to December 2010) and the highest severity value of -26.31 are observed in central and northwestern India, respectively. WSDI values show an increasing trend in west-central India (0.07 yr(-1)), indicating recovery from previously existing drought conditions. On the contrary, a decreasing trend in WSDI is observed in north-western (-0.07 yr(-1)) and central (-0.18 yr(-1)) India. Results demonstrate considerable confidence in the potential of WSDI for robust characterization of drought over large spatial scales.