LAUSR

Recent heat waves have been a matter of serious concern for India because of potential impacts on agriculture, food security and socio-economic progress. This study examines the trends and variability in frequency, duration and intensity of hot episodes during three time periods (1951-2013, 1981-2013 and 1998-2013) by defining heat waves based on the percentile of maximum, minimum and mean temperatures. The study also explores heat waves and their relationships with hydroclimatic variables, such as rainfall, terrestrial water storage (TWS), Palmer Drought Severity Index (PDSI), and sea surface temperature (SST). Results reveal that the number, frequency and duration of daytime heat waves increased considerably during the post-1980 dry and hot phase over a large area. The densely-populated and agriculturally dominated northern half of India stands out as a key region where the nighttime heat wave metrics reflected the most pronounced amplifications. Despite the recent warming hiatus in India and other parts of the world, we find that both daytime and nighttime extreme measures have undergone substantial changes during or in the year following a dry year since 2002, with the probability distribution functions (PDFs) manifesting a hotter-than-normal climate during 1998-2013. This study shows that a few months preceding the 2010 record-breaking heat wave in Russia, India experienced the largest hot episode in the country's history. Interestingly, both these mega events are comparable in terms of their evolution and amplification. These findings emphasize the importance of planning for strategies in the context of the rising co-occurrence of dry and hot events.