Understanding Heat Extremes with Hot Days and Warm Nights Across India

Abstract. India is experiencing a significant intensification of heat extremes, with both hot days and warm nights becoming more frequent and severe in recent years. Studying these evolving patterns is crucial for understanding regional climate trends and addressing the growing vulnerabilities. This study focuses on the temporal trends in heat extremes by analysing the increase in the frequency of very hot days and very warm nights across Indian districts. By comparing data from a baseline period (2003–2012) to a recent period (2019–2023), the research aims to capture the evolving spatial patterns of heat extremes and assess their implications for vulnerable populations. The analysis was conducted using MODIS Aqua Land Surface Temperature (LST) daily products available on Google Earth Engine. The study derived thresholds for very hot days (90th percentile of daytime LST) and very warm nights (90th percentile of nighttime LST) based on the baseline period. These thresholds were applied to the recent period to quantify the increasing frequency of very hot days and warm nights across all districts. Temporal and spatial variations in the frequency of very hot days and warm nights were analysed to identify emerging hotspots and trends. The analysis reveals a significant increase in heat extremes across India, with both hot days and warm nights becoming more frequent and intense in recent years. These patterns highlight the complex thermal dynamics shaped by topography, urbanisation, and atmospheric processes, emphasising the need for targeted adaptation and mitigation measures. This study comprehensively assesses the temporal and spatial trends in heat extremes across India with a scientific foundation for targeted heat mitigation strategies and evidence-based policy-making for planning, agricultural strategies, and disaster management. Mapping heat extremes provides a robust foundation for designing policies.