Intensification and spatial shifts of heatwave hotspot across India under climate and ENSO influences with health risk assessment

Heatwaves (HWs) in India have intensified significantly over the past two decades, with projections of further increase in frequency and duration. While global warming mitigation efforts are advancing, urgent local adaptation measures are required to minimize societal impacts. However, understanding regional climate risks has been limited. This study aims to address this gap by examining the intensification and spatial shifts of HW hotspots across India under the influence of climate change and the El Niño-Southern Oscillation (ENSO), along with a health risk assessment. A comprehensive archive of HWs using reanalysis-based daily maximum temperatures (Tmax) data for hot weather season has been constructed across India from 1981 to 2020. From 1981 to 2020, India’s average summer Tmax increased by 1.0 ± 0.12 °C, primarily driven by global warming, resulting in a higher frequency, duration, and extent of extreme HWs. Notably, the impact of El Niño has amplified this trend, with average summer Tmax increasing by 1.03 ± 0.44 °C, compared to a 0.77 ± 0.20 °C increase during Neutral ENSO conditions from the 1981–2000 period to the 2001–2020 period. A HW hotspot index (HHI) is introduced to identify the most vulnerable HW-prone regions, evaluated using satellite-based NDVI and LST data, indicating around 1.5 times increase in the spatial extent of HW hotspots between 1981–2000 and 2001–2020. Based on the HW health risk analysis, the central plains, the southeastern coast, parts of western India, and Gangetic West Bengal, along with certain areas in the central Indo-Gangetic Plain (IGP) region, were identified as the most at risk under the current scenario (2011–2020). This information enables informed decision-making and the implementation of measures for adaptation and mitigation.