Assessment of RegCM in simulating Indian summer monsoon drought and flood extremes

Abstract

This study evaluates the performance of the RegCM4.7 regional climate model in simulating extreme rainfall events, focusing on flood and drought years over India. A composite analysis of multiple drought and flood years was conducted to assess the fidelity of various cumulus parameterization schemes (CPSs) and land surface models in replicating the Indian Summer Monsoon (ISM) dynamics. Model validation against observed IMD datasets was carried out using Taylor diagrams, employing correlation coefficients, root mean square error, and standard deviation to identify optimal schemes. Among the tested configurations, Grell-based schemes, particularly Grell over Land and Tiedtke over Ocean and Grell over Land and Emanuel over Ocean, demonstrated improved agreement with observed rainfall patterns due to their advanced physical representations. The selected CPSs were further used to analyze atmospheric and surface processes, such as rainfall distribution, surface temperature, relative humidity, moisture flux, CAPE, wind stress, and vertical wind shear highlighting distinct differences in ISM behavior between flood and drought conditions. Results suggest that land–atmosphere interactions and convective processes play a crucial role in modulating monsoon variability. The study underscores the importance of selecting appropriate parameterization schemes for accurate climate simulations and offers insights into improving regional climate modeling for better flood and drought prediction.