Feasibility of Multi-decadal Satellite Soil Moisture for Drought Monitoring over India

Drought is an insidious scourge faced by many regions of the world and thus, demands the involvement of scientific community. Lack of any proper monitoring or index measure and the spatio-temporal extent of drought further worsens the issue. The present study explores the feasibility of using multi-decadal Satellite Soil Moisture (SSM) products for drought monitoring and analysis as satellites can monitor the spatio-temporal extent of soil wetness, which, can then be used to investigate its short-term and long-term trends. Three multi-decadal SSM products, obtained by merging two active and six passive products, all-active (CCI-Act), all-passive (CCI-Pas) and all-active-passive (CCI-Combined), from European Space Agency's Climate Change Initiative (ESA-CCI) program are used in this study to estimate soil moisture based drought indices (CCI-Idx: CCI-Act-Idx, CCI-Pas-Idx and CCI-Combined-Idx) over India. The drought index is estimated based on the relative position of SSM within its probability distribution. A preliminary rank correlation analysis of the original and anomaly timeseries of SSM and rainfall revealed that CCI-Act and CCI-Combined are more consistent with the rainfall timeseries than CCI-Pas. To better evaluate the signature of meteorological drought signal in ESA-CCI products, CCI-Idx is compared against Palmer Drought Severity Index (PDSI). The three soil moisture drought indices are also explored in terms of their magnitude, duration and severity as the impact of a drought in a region is decided by these three characteristics. The CCI-Idx are also checked against well-known drought events (2002, 2004, 2009 and 2014) over India. Finally the spatial distribution of soil moisture based drought indices are classified, in terms of severity, for different homogeneous climatic zones over India to analyse the effect regional climate has on drought.