A Study of Recent Changes in Moisture Flux Patterns Over India: Implications for Indian Summer Monsoon Rainfall

Abstract

This study examines the changes in the linear trends of the precipitable water content (PWC) associated with the Indian summer monsoon rainfall using the ERA-5 datasets. The study period of 63 years (1959–2021) is divided into two time periods P1: 1959–2001 and P2: 2002–2021. In the recent period (P2), we observe a significant rise in the statistically significant linear trend of the mean JJAS PWC leading to a significant positive difference of P2 − P1 over most of India. This change is found to be largest in the middle troposphere, where the rotational component of the moisture flux is strengthened in P2 relative to P1. This modulation is attributed to the non-uniform rate of change of tropospheric air temperature in the lower and middle troposphere in P2 from the rising land–ocean thermal contrast. This results in stabilising the atmosphere. Consequently, we also observe an increase in the fraction of stratiform precipitation in P2 relative to P1. This increase in stratiform precipitation is associated with enhanced mid-atmospheric diabatic heating and mid-tropospheric southwesterly moisture flux, which enhances PWC in P2 compared to P1.