Climatic Extreme in a High-Resolution Dataset over Densely Populated Cities of Middle Gangetic Plain, India

Abstract

The current study investigates the climatic extremes using high-resolution datasets over densely populated cities of the Middle Gangetic Plain, India. Extreme weather events significantly impact urban infrastructure, public health, and the economy, with these effects intensifying due to climate change. The Climpact2 package was used to analyse nine temperature-based and six precipitation-based indices from high-resolution Climate Hazards Center datasets (CHIRTS and CHIRPS) spanning from 1983 to 2016. The Mann–Kendall test and Sen’s slope estimator were employed to evaluate trends in extreme climatic events. Results reveal a significant increase in warm temperature indices and a decrease in cold temperature indices across most cities. Warm days (TX90P) increased up to 0.406% days/year over Bhagalpur, while warm nights (TN90P) increased by 0.509% days/year, indicating comparatively stronger nighttime warming. The Warm Spell Duration Indicator (WSDI) and Heatwave Frequency (HWF) also showed increasing trends, reaching 0.561 days/year and 0.548 days/year, respectively. In contrast, cool nights (TN10P) decreased significantly by − 0.489% days/year over Muzaffarpur, while the Cold Spell Duration Indicator (CSDI) declined by − 0.592 days/year, suggesting shorter and less frequent cold conditions. These trends indicate intensified urban warming and increasing thermal stress over the selected cities, particularly after 2005, possibly associated with rapid urban expansion, increasing built-up areas, urban heat island effects, and aerosol interactions. Precipitation indices exhibited mixed but statistically non-significant trends across the study region. Annual total wet-day precipitation (PRCPTOT) showed increasing tendencies over Muzaffarpur (2.887 mm/year) and Patna (2.087 mm/year), while maximum 5-day precipitation (RX5day) increased by 0.301 mm/year over Patna. However, the Simple Daily Intensity Index (SDII) generally exhibited decreasing trends across all cities, indicating reduced rainfall intensity in several urban locations. These heterogeneous precipitation patterns may be influenced by variations in urban morphology, land cover, topography, moisture availability, aerosol loading, and regional monsoon variability, leading to differing city-scale climatic responses. The findings further suggest that neighbouring cities sharing similar physiographic settings may still exhibit substantially different climatic behaviour due to variations in urban structure and local meteorological conditions. Overall, the study provides new insights into urban-scale climatic extremes over the Middle Gangetic Plain and highlights the urgent need for city-specific climate adaptation strategies, resilient urban planning, and improved infrastructure to minimise climate-related risks and support sustainable urban development.