Assessing Changes in Characteristics of Hot Extremes Over India in a Warming Environment and their Driving Mechanisms

Change in hot extremes is one of the accepted evidence and also a global indicator of an anthropogenic climate change, which has serious environmental and economic impacts. In the present study, the India Meteorological Department gridded temperature data is used to characterize hot extremes over India in terms of frequency and intensity. Results provide compelling evidence that large parts of India, except the Indo-Gangetic plains, have experienced more occurrences of hot days (upsurge by 24.7%) having higher temperatures in the recent period (1976-2018), compared to the past (1951-1975), which suggests a shift in climate. Strong positive geopotential height anomalies at 500 hPa over the northern parts of India, which dynamically produces subsidence and clear sky conditions along with reduced precipitable water and depleted soil moisture are identified to be the crucial factors responsible for an increase of hot extremes in recent decades. Furthermore, the preceding December-February Nino-3.4 sea surface temperature (SST) anomalies are strongly connected with hot days frequency and the mechanism for the lag of several months is related to 3-4 months delayed response of Indian Ocean SSTs to El Nino/Southern Oscillation. Thus, post-Nino hot extremes over India can be potentially anticipated in advance and this will help society to prepare for such extremes.