Abstract:

Urbanization has increased the risk of urban flood. Quantitative research of urban rainfall-runoff process, can provide a scientific basis for the scientific planning and management of the city. In this paper, the land use/cover data and urban functional zones within Beijing five-ring areas were classified with the aid of GIS and RS technology. The SCS-CN method, as a traditional empirical model in the fields such as surface hydrology, was selected for simulating the surface runoff potentials within different urban functional zones in this study. Meanwhile, we analyzed the distribution of the surface runoff under different return periods of precipitation. Then the index of Moran's I was used to recognize the "hot spots" and "cool spots" of surface runoff in Beijing five-ring areas. The result showed that, the distribution configuration of surface runoff experienced a remarkable difference under different return periods of precipitation. The area of high runoff potential regions increased from 18.90% to 54.74% across the whole five-ring areas when seeing 1-year and 100-year return periods of precipitation respectively. Due to the difference and diversity of the impervious surface rate, runoff risks differed significantly from each other across different urban functional zones. For example, the highest risk of runoff generation was captured in the commercial zone by the hydrological model, with an average of 24.76 mm under 1-year return period of precipitation. The preserved zones, on the other hand, had the lowest risks of runoff generation (7.36 mm). Furthermore, the potential risk of runoff depth became similar to the increase in precipitation return-period. Finally, the spatial cluster of various runoff risk zones was captured by using spatial autocorrelation analysis method. In general, runoff risk zones experienced a circular pattern, which decreased from the central to the peripheral region. In most cases, the commercial and residential zones located in the core area of the city were prone to higher runoff generation and risks. Large parks and natural green areas, on the other hand, can help to minimize the flooding risk, and thus can be treated as the low-risk zones. These zones are mainly situated within the fourth to fifth-ring road areas of Beijing city. In order to remit the flooding hazard, city administrators should take account of the distribution of runoff risk area and rainfall-runoff characteristics of various urban functional zones before the relevant regulations were formulated. And also the ecological advantage within the city should be made full use of to solve the urban flooding hazard.

Key words: SCS-CN model, urban function zones, Moran’s I, runoff risk