Understanding the Decadal variability of Indian summer extreme precipitation and its recent westward shift using a GEV-based approach

The present study investigates the decadal variation of summer monsoon extreme precipitation over India for the period 1901 to 2020 using the Generalised Extreme Value (GEV) distribution. The analysis focuses on the spatial and temporal variation of annual maximum rainfall (Yearmax), assessing the evolution of GEV parameters- shape (ξ), location (µ) and scale (σ) – over the three climatological epochs. GEV distribution effectively captures the patterns of extreme rainfall and provides further insights into the frequency, intensity, and duration through its parameters. Comparison with the earlier decades reveals a significant anomalous increase in the increases of extreme precipitation in the recent decades over west-central India, where rainfall extreme values have risen from 78 mm (1900–1940) to 88 mm (1980–2020), while a decrease has been observed in east-central India. The rise in extreme rainfall in west-central India is attributed to broader climate change feedback, such as persistent warming of SST over the Arabian Sea, an increase in land-sea contrast, anomalous stronger winds, enhanced moisture transport, westward shifts in monsoon circulation, local convective amplification due to changes in land surface, and broader climate change feedback. Conversely, the anomalous decline in extreme rainfall over east-central India is correlated with the weaker SST anomalies in the Bay of Bengal, reduced anomalous westerly winds, and fewer intense low-pressure systems. The study presents a comprehensive analysis of the bimodal distribution of extreme rainfall in recent decades, with the backdrop of recent factors related to climate change. These analyses are helpful for improving forecasts and developing effective mitigation strategies for the present scenario of extreme weather conditions.