East-west coastal asymmetry in the summertime near surface wind speed and its projected change in future climate over the Indian region

Abstract

The behaviors of various meteorological parameters during 1981–2010 are investigated to obtain any asymmetric variability of summertime near surface wind over Indian coastal boundaries. No significant changes were obtained in the trends of surface pressure, surface relative humidity, 2-metre temperature and surface precipitation; although, near surface wind speed is found to have significantly declined on the eastern coast with respect to the western coast during this period. Summertime surface wind speed on the eastern coast have decreased from 3.5 to 2.5ms−1 (7 to 5knots) whereas 4.5 to 4ms−1 (9 to 8knots) during the last three decades (statistical significance level~95%). A decrease in the atmospheric instability may serve as the potential reason for the suppression of severe convective occurrences manifested by a parallel decrease in surface wind speeds over these regions. The local heating up of middle atmosphere (300–500hPa pressure level) due to increased humidity and the difference in net heat flux over Arabian Sea and Bay of Bengal due to the variance of temperature gradient (1000–925hPa) along the coastal boundaries might be responsible for this climatic disparity between the coastal regions of India since the last three decades. Summertime near surface wind speed projections for Indian sub-continent based on 7 best climate models, for RCP8.5 scenarios, has been calculated to show a mean increase by ~10–15% on the eastern coast (Eastern Ghats), ~1–2% on the western coasts (Western Ghats), ~1–5% decrease in the Indo-Gangetic Basin and ~3% decrease in the Gangetic West Bengal and adjoining Bangladesh.