CMIP6 Simulations of Compound Hot Days and Nights over Interior Peninsular Region of India

Interior Peninsular region of India (IPI) witnesses a rise in extreme heat events driven by its unique topography, regional climate change and human-induced emissions, resulting in increased death rates. The IPI covers the states, Maharashtra, Telangana, Chhattisgarh, Odisha, Andhra Pradesh, Karnataka, Tamil Nadu. The study analyzes historical (1955–2014) and projected (2015–2100) occurrences of hot days (HDs), hot nights (HNs) and compound hot days and nights (CHDNs) during the summer months (March, April and May) in the IPI region. The analysis utilizes gridded datasets of maximum (Tmax) and minimum (Tmin) surface air temperatures from the India Meteorological Department (IMD) and the Coupled Model Intercomparison Project—Phase 6 (CMIP6) Global climate models (GCMs). The frequency and length of CHDNs during the summer months were analysed with the historical Tmax and Tmin datasets of observations as well as CMIP6 multi-model mean. The future projections of CHDNs were also analysed under two socio-economic pathways (SSP2-4.5 and SSP5-8.5). During the historical period (1955–2014), IMD observations recorded average number of ~ 7 HDs, ~ 7 HNs and ~ 5 CHDNs per year. Future projections for the near-term (2021–2040), mid-term (2041–2060) and far-term (2081–2100) indicate significant rise under both SSP2-4.5 (Middle of the Road) and SSP5-8.5 (Fossil-fuelled Development) scenarios. By the end of the twenty-first century, the mean change in the number of HDs, HNs and CHDNs with respect to historical observations of IMD is expected to rise by ~ 5, ~ 7 and ~ 7 in the near-term; ~ 9, ~ 8 and ~ 11 in the mid-term; and ~ 14, ~ 17 and ~ 20 in the far-term under SSP2-4.5 scenario. Similarly, Under SSP5-8.5, the expected rise is ~ 6, ~ 9 and ~ 11 in the near-term; ~ 10, ~ 11 and ~ 13 in the mid-term; and ~ 18, ~ 20 and ~ 24 in the far-term. Relative humidity (RH) was also analyzed during HDs, HNs and CHDNs. It was observed that the average RH during CHDNs lies in between the average RH of HDs and HNs. These findings emphasize the alarming trend of rising temperatures during days and nights and there is an urgent need for climate action to reduce the adverse impacts on public health, agriculture, and ecosystems.