EHF based Heatwave Identification and its Impact on Urban Heat Island Intensity: A Case Study of an Indian City

Abstract. In the Indian subcontinent, the heatwaves occur mainly during the summer months from April to June. This heatwave becomes more severe when accompanied by higher summer temperatures in the country. Excess Heat Factor (EHF) is a metric used to identify heatwaves. This study identifies the heatwave using EHF and its relationship with UHI intensity in pre, post, and during heatwave event. The results show a heatwave event in the area from 10-16 June 2023 with positive EHF values. The values range from 0.433087-5.277442 during the heatwave event. To establish the link between the positive EHF value and UHI intensity, the variation of UHI intensity is monitored using MODIS data. The findings indicated that during the heatwave event, the UHI intensity and its extent grew with an increase in temperature of 2°C in the daytime and slight changes in the nighttime. This result is also validated by plotting the variation of UHI intensity using ERA-5 Land data on the grid point of the weather station (29.5°N, 79.5°E), which ranges between 0.504764 – 0.633209 during the pre-heatwave event. The intensity value kept on increasing as the heatwave event approached and reached the maximum magnitude of 0.70384 during the heatwave event. As the event finishes, intensity values decrease to 0.147939 post heatwave event. The findings provide an understanding of localized interaction of UHI intensity and the heatwave which is identified using the EHF factor.