Hydrologic responses to rapid urbanization for small and medium sized cities: a case study of Yiwu, China

Quantitative analysis of the impact of rapid urbanization on hydrologic cycle is important for optimizing water resources management. The rapid development of small- and medium-sized cities is one of the most significant characteristics of global urbanization today and in the future. This study, therefore, was to evaluate the impact of rapid urbanization on the hydrologic cycle in a typical medium urbanizing city (Yiwu in China) using the Soil and Water Assessment Tool (SWAT) model. For this purpose, scenario analyses with four land uses from different years (i.e., 1990, 1995, 2000, and 2005) were conducted. The hydrological outputs from the watershed with rapid urbanization were compared with those from the surrounding watersheds with less degree of urbanization. Observed monthly surface runoff data during 1972-1988 and 1989-1993 were used for model calibration and validation, respectively. The results showed that the rapid urbanization from 1980 to 2005 in Yiwu led to increased surface runoff and reduced groundwater recharge, evapotranspiration, and soil water storage. More obvious changes in hydrological components were usually observed near the urban areas and in rainy seasons. This study provided important information for managing the rapid urbanization of small- and medium-sized cities in developing countries.