A meta-analysis of the regional extreme rainfall events in the Indian sub-continent during the southwest monsoon period

Abstract

The present review focuses on extreme rainfall events (EREs) over the Indian subcontinent during the southwest monsoon period. The evolution of ERE studies across India concentrates mainly on the regional characteristics that have influenced these events during the past decade. It evolved slowly by accounting for different indices to represent extremes, understanding causative mechanisms, and improving their forecasting. There are many methods for estimating EREs, each suited to various objectives. Rather than seeking a perfect method, the studies may adopt methodologies based on the purpose and scope. Moreover, EREs impose severe socioeconomic impacts on India, with heavy burdens on communities and resources. Factors such as low-pressure systems, Indian Ocean warming, and circulation shifts contribute to these extremes. Northwest India has seen a significant rise in ERE frequency and intensity in recent decades due to enhanced convective instability and moisture transport by various climate drivers. In contrast, Northeast India shows a decline in EREs driven by synoptic systems. EREs in the Himalayas are more complex and influenced by tropical and extratropical drivers. Regions like Kerala and the northeastern states face frequent ERE-linked flooding, while the Western Ghats show a declining trend. The ERE in the different regions show different dynamics due to their heating structure, moisture availability, and atmospheric instability factors. Thus, regional ERE forecasting is complex, but combining numerical models with machine learning can enhance accuracy and reliability. Future projections indicate a significant increase in regional EREs, but uncertainties persist due to models' biases. The findings underscore the need for improved modeling strategies and targeted policy measures to mitigate the adverse impacts of future EREs. This review offers insights into India's current state and research prospects, highlighting critical areas for further investigation and enhanced forecasting.

Keywords: Extreme rainfall events; Future projections of extremes; Regional and topographical features; Socio-economic influences; Southwest monsoon.