Urbanization is a worldwide phenomenon, with population density continuing to grow and urban area to expand. Urban sprawl inevitably leads to non-urban land being converted to built-up areas, resulting in a significant increase in the proportion of impervious surfaces.
The process of urbanization can alter urban hydrological responses and negatively impact surface and downstream waters owing to the introduction of impervious surfaces, removal of deep rooted vegetation and alterations to the natural drainage network. Nowadays, increasing direct runoff caused by land use changes become a major challenge for urban ecological security.
Dr. LI Chunlin, researcher of Institute of Applied Ecology, CAS. They used a modified Soil Conservation Service Curve Number model to investigate the impact of urbanization on runoff. Many researches and practices in the last decades have shown that the impacts of urbanization on the hydrological cycle are strongly related to impervious surfaces, but few studies focus on the urban functional zones scale.
Urban functional zones are the largest elements of landscape planning related directly to functions such as dwellings, education, industry and commerce. Similar urban spatial structures, human activity types and urban functions of same UFZ result in similar hydrological characteristics. The UFZs were used as the suitable spatial scale for evaluating the hydrological impact. Meanwhile, the modified SCS-CN model they used is the Mishra and Singh (MS) model based on antecedent 5-day rainfall to estimate antecedent moisture. An improved composite CN method proposed by Fan (2013) was used to calculate composite CN.
The total direct runoff of the entire study area was 83.23 million m3, of which zone 4 contributed the most. The average direct runoff depth and direct runoff coefficient gradually decreased from zones 1 to 4. The area of significant hazard land was 77.5 km2, about 6.53% of the study area.
For different UFZs, the High-density residential zone had largest area of low hazard land (58.53 km2), and the Business zone had largest significant hazard proportion (21.19%). Correlation analysis showed that rainfall had the greatest impact on runoff depth (52.07%).
The study, entitled “Effects of urbanization on direct runoff characteristics in urban functional zones” has been published in Science of the Total Environment. The study is financially supported by the China National R&D Program and the National Natural Science Foundation of China.