How urban land expansion alters terrain in mountainous and hilly areas: An empirical study in China

• Terrain alteration induced by urban land expansion in China is assessed. • Terrain altered the most in China’s Southwest, Southeast, and Loess Plateau regions. • Contributions of different urban functional zones to terrain alteration is quantified. • Specific strategies should focus on mitigating the impacts in ecologically sensitive areas. Large-scale urban land expansion in mountainous and hilly areas (UEMH) has significantly altered the terrain in many Chinese cities, leading to various environmental and urban challenges. Despite its importance, there is limited nation-scale research that reveals the amount and the spatial variations of UEMH-induced terrain alteration. This research integrates the Global Annual Urban Dynamics dataset, the Global Basic Landform Unit dataset, the TanDEM-X DEM Change Map (DCM) dataset, Baidu Points-of-Interest (POI), and other auxiliary datasets to conduct a comprehensive analysis of terrain alteration induced by UEMH in China from 2012 to 2020. The results indicate that the country-wide UEMH-induced terrain alteration reached approximately 13 billion m³, which is about 100 times the volume of Hangzhou West Lake, and terrain alteration volume in over 300 counties exceeded 10 million m³. The Southwest and Southeast regions, which are ecologically sensitive and critical, feature the greatest alteration in terms of area and volume. The most significant terrain alteration in terms of intensity is observed in the Southwest and Hengduan Mountain Area. Additionally, there are significant spatial variations in the contributions of different urban functional zones to terrain alteration. Our findings indicate that urban land expansion in mountains and hills has significantly altered terrain in some regions of China, necessitating customized urban planning strategies for better managing mountainous urban land expansion and governance policies to address the geological, ecological, and urban development challenges.