Atmospheric moisture as a proxy for the ISMR variability and associated extreme weather events

P J Nair,H Varikoden,P C Pandey,A Chakraborty,P A Francis

doi:10.1088/1748-9326/abcfe0

Abstract

This study explores the potential of atmospheric moisture content, its transport and its divergence over the ocean and land as proxies for the variability of Indian summer monsoon rainfall (ISMR) for the period 1950–2019. The analyses using multiple linear regression reveal that the interannual and intraseasonal variability of ISMR and the mean ISMR is largely controlled by Arabian Sea moisture flux and Ganga river basin moisture content, and these parameters exhibit statistically significant high correlations in most regions. The regression model and the parameters are statistically significant and the model could explain rainfall variability of about 12%–50% in various regions. The model shows a false alarm rate (FAR) of 0.25–0.45 and a probability of detection (POD) of 0.43–0.50 for wet years in West Central, North West and North Central India. The FAR and POD are about 0.06–0.32 and 0.60–0.70, respectively for dry years in those regions. The model reproduces flood and drought years of about 32%–50% and 55%–70% in those regions. Also, the moisture indices could clearly identify the majority of wet and dry years that occurred during the period. The ISMR variability associated with moisture indices is unaffected by El Niño Southern Oscillation. Henceforth, this study demonstrates the significance of atmospheric moisture on regional rainfall distribution and suggests that these parameters can be used in both statistical and dynamical models to better predict monsoon and global precipitation.

Highlights

The hydrological cycle is an important natural process in which water reaches the atmosphere from water bodies through evaporation and plants through evapotranspiration, which eventually returns to the ground as precipitation
This study explores the potential of atmospheric moisture content, its transport and its divergence over the ocean and land as proxies for the variability of Indian summer monsoon rainfall (ISMR) for the period 1950–2019
The statistically significant correlation of JJAS rainfall with vertically integrated moisture flux (VIMF) and precipitable water content (PWC) is positive while that with vertically integrated moisture flux divergence (VIMFD) is negative in Peninsular India (PI), West Central India (WCI), North West India (NWI) and North Central India (NCI)

Summary

Introduction

The hydrological cycle is an important natural process in which water reaches the atmosphere from water bodies through evaporation and plants through evapotranspiration, which eventually returns to the ground as precipitation. The Hadley cell in the austral winter supplies the water vapor required for the boreal summer. Precipitation in the northern hemisphere during boreal summer is made available by moisture in the austral winter, in tropical regions (Peixoto and Oort 1983). In India, there are two main rainy seasons: the southwest (June through September—JJAS) and northeast (October through December—OND) monsoons. The southwest monsoon is the major rainy season bringing moist air from the oceans to the Indian subcontinent, known as the Indian Summer. During this season, moisture transport is regulated by southwest winds followed by the cross-equatorial flow that normally decides the strength of moisture transport and the nature of the ISM to some extent (Ramesh Kumar et al 1999)

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Conclusion