Climate variability and heat wave dynamics in India: Insights from land- atmospheric interactions

Heat waves have emerged as one of the most severe and destructive meteorological phenomena, significantly threatening human health, agricultural productivity, and ecosystems due to their increasing frequency, duration, and intensity. In India, these extreme events predominantly occur during the pre-monsoon months (March to mid-June), with recent years (2016, 2019, 2022, and 2023) showing a clear intensification in their occurrence. This study aims to explore the dynamics of heat waves, synoptic conditions, surface land-atmosphere interactions, and regional variations in recent years across India, utilizing maximum temperature data from the India Meteorological Department (IMD) and heat wave indices to evaluate their intensity and impact. Analysis of maximum temperature data and heatwave indices highlights a notable rise in heatwave frequency and duration, particularly in northern and central India. The 2-meter (2 m) temperature anomaly in north, central, and southern India exceeded 2.5 degrees C, while the 925hPa temperature showed significant warming trends in north and northwest India. The analysis of the spatial distribution of the planetary boundary layer (PBL) and total cloud cover (TCC) indicates reduced cloud cover and an increased PBL, intensifying heat wave conditions across north and central regions. The warm air advection and sinking air in the descending limb of the Walker circulation ensured a stable and drier atmosphere, favoring heatwave conditions. Moreover, a persistent anticyclonic circulation and its associated high-pressure system enabled heat-trapping within the atmosphere, leading to prolonged and intensified heat wave conditions. The study indicates a shift in the position and strength of the subtropical jet stream (STJ) during these years, highlighting its significant role in developing and intensifying heat waves.