Hydroclimatic Stress in India: Methodological Innovation and Agricultural Relevance of Stand-Alone Flash Droughts

Rapid onset, swift intensification, and pronounced hydroclimatic stress define flash drought, which emerges from an initial precipitation shortfall combined with persistently elevated air and land surface temperatures. These conditions substantially increase evaporative demand, driving a sharp decline in soil moisture. In contrast to conventional seasonal droughts that develop gradually, flash droughts escalate to peak intensity within two to three weeks and may continue for several weeks (up to 18 pentads). Their abrupt nature poses a serious threat to agricultural productivity, with cascading effects on food security and the national economy, especially under a warm climate. This nature of flash drought imposes significant hydroclimatic stress, and numerous recent studies highlight the urgent need for a deeper understanding of these rapidly developing drought conditions. However, the absence of a consistent and universally accepted definition has hindered efforts to assess and monitor flash droughts effectively. While multiple climatic drivers, including abrupt transitions in monsoon, elevated temperatures, and vapour pressure deficit, contribute to flash drought development, it is unlikely that a single definition can fully capture their complexity. Nevertheless, it is essential to distinguish flash droughts—short-lived, rapid-intensifying events—from conventional droughts, which typically develop gradually and persist over longer timescales.  In this study, we propose a new definition of stand-alone flash drought based on rapid declines in soil moisture, independent of conventional drought classification. This approach enables the recognition of flash droughts as distinct events and underscores their unique characteristics. Using pentad-scale soil moisture data across India, we develop a simple yet robust framework to identify historical flash drought events that have contributed to a reduction in crop yield and vegetation cover, posing significant risks to the national economy. This approach enhances drought characterisation in a changing climate and supports more effective monitoring and impact assessment.