High-Resolution Analysis of Severe Heat Wave Dynamics and Thermal Discomfort Across India

Abstract

The study explores variability and dynamical characteristics of heatwaves during March–June for 1990–2020 over India. Normalised T _max anomaly is used to identify different heatwave spells in vulnerable regions of North-central India (NCI) and Southeast coast of India (SECI) using India Meteorological Department (IMD, 1° × 1° resolution) observations, Indian Monsoon Data Assimilation and Analysis (IMDAA, 0.12° × 0.12°), and ECMWF Reanalysis v5 (ERA5, 0.25° × 0.25°). Results highlight that IMDAA exhibited a total 202 days (181 days) heatwaves duration in NCI (SECI) regions while ERA5 exhibited a total 132 days (89 days), respectively, compared with those of IMD (195 and 163 days). The primary heatwave periods for NCI (10 April to 20 June) and SECI region (1 May to 10 June) are well captured by IMDAA, unlike ERA5. The average length of the heatwave is 7.8, 7.5, and 7.76 days (8.15, 7.72, and 6.1 days) over NCI (SECI) in IMD, IMDAA, and ERA5, respectively. The high heat stress is more frequent in SECI than in the NCI region and is common during May–June (May only), as seen in IMDAA (ERA5). The middle to upper-level anticyclone over NCI is stronger than SECI during heatwaves. Heat advection with stronger 850-hPa north-westerlies (~10 ms⁻¹) abates sea breeze in the coastal region, aiding longer heatwaves in the SECI region. Ascending motion induced by surface heating is confined to the lower levels due to the subsidence by the upper-level anomalous anticyclone, stagnating higher temperatures in the lower atmosphere, depicting a heat dome. The surface temperatures are slightly higher in NCI (31°C–39°C) than in SECI (30°C–37°C). However, the double moist heat dome in SECI has witnessed higher heat stress conditions than NCI. Higher relative humidity in the SECI region is contributed by maritime winds from the Bay of Bengal and Arabian Sea, soil moisture, and so forth. The study highlights the value of atmospheric moisture in differentiating the study regions for heat stress conditions.