Mechanism and Characteristics of Flash Droughts in India and their Evaluation Using Evaporative Soil Moisture Index (ESMI)

Flash droughts can cause a short-term but severe devastating impacts to agriculture and the ecosystem. However, the mechanism and characteristics of flash droughts remain unexplored in the monsoon dominating climate over India. Here, we use the hydro-meteorological variables from ERA-5 reanalysis to derive surface vapour pressure deficit (VPD), and soil moisture (SM) from GLEAM to construct a copula based SM-VPD index [named as Evaporative Soil Moisture Index (ESMI)], which is used to identify flash droughts in India. First, we evaluate the land-atmospheric coupling, which suggests that SM-VPD has a strong negative correlation in both monsoon and non-monsoon seasons. Soil Moisture and evapotranspiration (ET) show a strong negative and positive relationship in the monsoon and non-monsoon season, respectively. Our results show that unlike ET based indices (e.g. evaporative stress index), ESMI captures flash droughts in both monsoon and non-monsoon seasons over India. We identified and evaluated six major flash drought that occurred during the 1980-2018 period using ESMI along with their driving mechanism.