Flash drought intensification due to enhanced land-atmospheric coupling in India

Abstract

Land-atmospheric feedback influences the occurrence and severity of flash droughts. However, the observed and projected changes in flash droughts and associated land-atmospheric coupling have not been examined over India. Moreover, the causes of the rapid depletion of soil moisture during flash droughts are not well known. We identify major flash droughts and associated soil moisture-vapor pressure deficit (SM-VPD) coupling in India using ERA5 reanalysis and simulations from global climate models (CMIP6-GCMs). The summer monsoon season (June-September) witnesses more than 60% of flash drought events and a relatively higher rate of flash drought development. The flash drought frequency has mainly decreased during India's observed climate (1980-2019), which is projected to decline further in the future warming climate. On the other hand, the flash drought development rate has significantly increased during the observed (1980-2019) period, which is projected to enhance further under the warming climate. The SM-VPD coupling during the flash drought onset-development phase is considerably higher (three to five-fold) than during the normal condition (in the absence of flash drought). The high (low) SM-VPD coupling explains the faster (slower) flash drought development rate in the observed and future warming climate. The strength of the SM-VPD coupling has increased in the recent period and is projected to increase further in the future warming climate. The increased SM-VPD coupling can intensify future flash droughts in India, especially during the summer monsoon season, with considerable implications for agriculture, water resources, and ecosystems.