Understanding the hot season dynamics and variability across India

Abstract Climate change has a detrimental impact on human health due to increasing temperature extremes. It is undoubtedly true over India, where in recent decades a rise in the frequency and intensity of extreme events is witnessed. The present study primarily focuses on understanding the dynamics of the hot season over homogeneous regions of India. Using Canonical Correlation Analysis, five temperature homogeneous regions are defined. All regions showed a positive trend with less interannual variability, except Gangetic plains. The seasonal composites for extreme temperature years show that hot season over North India (NI) occurs mainly due to blocking high in upper atmospheres. Similarly, daily temperature anomalies for the heatwave days during hot years exhibit stationarity of such blocks centered over the region. Two global teleconnections have been found to be responsible for the NI seasonal anomaly, (i) a continuous anomalous low over Europe Granger cause anomalous high across the region, (ii) the subtropical jet stream and the polar jet stream help to maintain stationarity of anticyclonic blocks over the region. Sinking of air due to an upper atmospheric high over NI, causing adiabatic warming near the surface. Southern India mainly got heated due to warm air intrusion from northwest regions, contributing to anomalous low humidity over the southern coastal regions. This phenomenon blocks the transport of moisture from the adjacent ocean entering the region resulting in amplification of hotness due to moisture blocking, leading to an increased temperature anomaly.