Opposite trends in heat waves and cold waves over India

Extreme weather events have become remarkably more evident in recent decades. Heat waves and cold waves are anomalous weather events resulting from excessive heat and cold conditions, respectively, in the near-surface atmosphere. They may last from a few days to a few weeks, depending on the geography and climatology of the region. In this study, we have used the India Meteorological Department (IMD) daily maximum and minimum temperature data over the period from 1970 to 2019 to investigate the decadal variability and trends in the frequency of heat waves and cold waves over the four broad climatic zones of India. We found opposite trends in the heat wave and cold wave events over India. The frequency of the occurrence of heat waves increased by about 0.6 events per decade, while cold waves decreased by about 0.4 events per decade. Although most of northwest India is highly vulnerable to heat wave conditions, central peninsular India is also experiencing frequent heat waves in the recent decade. Concurrently, the average duration of cold waves decreased over montane, arid and semi-arid, and tropical wet and dry climate zones. But, cold wave events frequency showed an increasing trend over the subtropical humid climatic zone of India. When compared to IMD observations, the CMIP6 models generally failed to capture the observed spatial features in the heat wave frequency trend and cold wave frequency trend. This suggests that CMIP6 model output data should be used cautiously to predict future changes in the heat wave and cold wave events frequency. This emphasizes the need for an improved process-level understanding of these extreme events.