Flash drought as a new climate threat: drought indices, insights from a study in India and implications for future research

A flash drought (FD) event is a relatively new form of severe occurrence, described by the quick onset and intensification of drought situations with serious consequences. This paper aims to understand the wide variety of studies and serve as a basis for future research potentials of FDs. An effort has been made to understand the advantages and limitations of the existing indices used for FD identification. A study in India was carried out for the identification of FDs using daily gridded data of soil moisture for eight days (octad). The results reveal that the Indus basin faced around 82% and the Cauvery basin faced about 88% of severe FDs during the monsoon and non-monsoon seasons, respectively. Additionally, the results show that the Indus basin faces FD in the monsoon season since the basin has mostly barren areas and wasteland. This review also highlights the role of humidity, wind and radiation, soil characteristics, climate oscillations, and the relation between FDs and heavy-rainfall-induced flash floods. Furthermore, the paper has depicted some specific research-needs to monitor, forecast, plan, and respond with crucial points. HIGHLIGHTS This study discusses the most extensive indices used to identify FDs.; A study is carried out in India to identify FDs using daily gridded soil moisture data for eight days (octad).; The study briefly explains the factors that need to be included in identifying and monitoring FDs.; The study also depicts the crucial points for future research-needs to monitor, forecast, plan, and respond to FDs.;