Soil moisture rapid transitions between dry and wet extremes in India, 1951-2024

Abstract

Soil moisture (SM) rapid transition categorized by the rapid swings between drought and wet phase has profound implications for agriculture and water resources. However, the drivers, impacts, and characteristics of the rapid transition in India have not been examined. Here, we use a well-calibrated hydrological model to simulate root-zone SM to identify rapid SM transitions in India for the 1951–2024 period. We show that rapid transition predominantly occurs during the monsoon season (June to September) in India with an average duration of two pentads. Soil moisture rapid transitions show a nonsignificant decreasing trend in transition duration and an increasing trend in intensity during 1951–2024. Most (more than 66%) of the large-scale rapid transitions are from drought to wet phase. Only two out of six homogeneous precipitation regions in India experienced equal numbers of drought-to-wet phase and wet phase-to-drought transitions, while the other four had more drought-to-wet phase transitions. Long dry spells/monsoon breaks during the monsoon season and positive air temperature anomalies rapidly deplete SM resulting in droughts. On the other hand, the sudden influx of moisture into the drought-affected region caused wet phases. The major country-level rapid transitions from wet phase to drought occurred during the monsoon seasons of 1972, 2009, and 2023; whereas transitions from drought to wet phase occurred in 2005, 1972, 1970, and 1962. Notably, 1972 experienced both types of rapid transitions, highlighting intraseasonal variability during the monsoon season.