Climate Change Impact on the Heat Index in India: Seasonal and Spatial Analysis Using CMIP6 Projections

This study investigates the climate change signal on mean and extreme temperatures in India, adding new insight by using the state-of-the-art CMIP6 projections to quantify the seasonal and spatial evolution of the Heat Index (HI) across India.; offering one of the first national-scale assessments combining temperature and humidity under Shared Socioeconomic Pathways (SSPs) scenarios. To assess the recent past climate change signal on those properties, ERA5 reanalysis data are used. CMIP6 models realistically reproduce historical warming patterns during winter (DJF) and pre-monsoon (MAM) seasons but tend to underestimate extreme summer (JJA) conditions. Results show a significant warming trend since 1980, characterized by an increased frequency of hot extremes, particularly during winter, with an increase of monthly hot anomalies of 2.15%. Then, future daily HI is calculated from mean temperature and relative humidity from CMIP6 global climate models (GCMs). Future projections indicate a substantial increase in both the frequency and persistence of dangerous HI levels across India, driven by rising temperatures and regionally variable humidity trends. By mid-21st century (2041–2070), the annual number of days with dangerously high HI values (27º and 32ºC) is projected to rise by more than 20 and 10 days, respectively, compared to 1971–2000. By the late century (2071–2100) under the SSP5-8.5 scenario, the HI will be above 27ºC (32ºC) during more than 75 (5) absolute days per year in JJA and more than 20 (1) days in MAM. Critical HI days will be highest in coastal regions in winter and more northern regions in summer, increasing towards northern latitudes with the emission scenario. These findings underscore the importance of region-specific adaptation strategies, as heat stress future anomalies will differ across India. Understanding these spatiotemporal patterns is critical for effective climate adaptation and public health policies aimed at mitigating the increasing risks associated with extreme heat events.