Understanding spatiotemporal variability of drought in recent decades and its drivers over identified homogeneous regions of India

Drought is a recurring hydroclimatic extreme whose frequency and intensity have increased over India in recent decades, with a detrimental effect on regional water resources. This study addresses the spatiotemporal variability of drought and its plausible mechanism over India from 1951 to 2018. Firstly, six drought-homogeneous regions are adequately ascertained by applying rotated empirical orthogonal function analysis using the Standardized Precipitation Evapotranspiration Index that captures most of the reported drought and regional hydroclimatic patterns. For the study period, a drying trend is witnessed across the regions though not significant, whereas in recent decades, northeast India (NEI) and some parts of the Indo-Gangetic plain (IGP) exhibit higher drought frequency. This anomalous drying is attributed to a weakening of the monsoon circulation and accelerated warming caused by changes in the land-use pattern. The interplay between El Niño Southern Oscillation and the Indian Ocean Dipole largely affects drought's interannual variability, which shows a modified response in recent decades. However, the long-term decadal drought pattern is found to be strongly teleconnected with a newly discovered Southern Atlantic Oscillation (SAO) index, which reveals a statistically quite significant relationship (>50%) with drought variability. The positive phase of the SAO index is generally associated with drought across the regions except for IGP and NEI. Despite the recent overall wetting trend, drought frequency has enhanced over most of the regions, modulating the regional hydrological cycle.