Urbanization effects on heat waves characterized by high topographic relief in a typical mountainous urban region

Abstract

Understanding heat wave (HW) changes is essential for effective adaptation to global climate change and mitigation of disaster risks. However, urbanization effects on HW variations are rarely clarified in mountain areas. Taking Sichuan-Chongqing Region (SCR) of China as the study area, this study identified respective changes of HW intensity, frequency and occurrence time with Innovative Trend Analysis (ITA). Based on a dynamical classification of urban and rural stations using annual-varying land use, it innovatively distinguished urbanization effects (UE) on HW in different topographic locations. The results indicate that: (1) from 1970 to 2019, HW events became stronger, longer, and more frequent, with earlier commence and later termination, particularly at highly urbanized stations in middle-east of SCR; (2) In SCR, average urbanization effects respectively for HW magnitude (T_min, HWM and HWA), duration (HWL and HWD) and frequency (HWF) are 0.43 °C, 0.17 and 0.33 days per decade, which became more pronounced in steeper mountains; (3) with a greater topographic relief, the respective urban-rural contrasts of HW change trend and occurrence probability declined, which implies that stronger topographic gradients can partly modulate urbanization effects on HW. Such results unravel the multifaceted behaviors of HW evolution during urbanization in recent 50 years. Moreover, they quantitatively identify the role of topographic variations in urbanization effects on HW. They can provide valuable location-specific suggestion for sustainable urban planning and efficient climate disaster management.