| Taking Qinhuai River Basin for study, RS and GIS technology was used to extract impervious surface and land use information in the study area. Variation characteristic of spatial pattern of urbanization since1988was studied in Qinhuai River Basin. Hydrological response of long-term runoff and short-term flood to impervious surface in Qinhuai River Basin was studied quantitatively and qualitatively here, using the HEC-HMS distributed hydrological model. Besides, for a given impervious rate, hydrological effects of different spatial pattern of impervious surface were discussed, revealing the intrinsic link between urbanization and runoff process. Based on the prediction of future landuse scenarios for Qinhuai River Basin, the long-term hydrological effects in the future was analyzed. All above could support decision for city construction, allocation of land use and water resource, flood control and disaster reduction in this area. This paper was supported by the National Natural Science Foundation of China (40730635), Public Projects of Ministry of Water Resources (200701024),"Study of impact of urbanization in Yangtze River Delta on river systems and hydrological processes"-"Study of impact of urbanization in Qinhuai River Basin on the hydrological processes".Research in this paper focused on the following three aspects:1Extraction of impervious surface for study area with multi-temporal, multi-source remote sensing images was implemented in this paper. Using Landsat and CBERS images as two data sources, each pixel was dealt as a mixture of vegetation, high-and low-albedo and bare soil, impervious surface was extracted with linear spectral mixture model, landuse information was determined with supervised classification method. It was analyzed that change of spatial pattern of urbanization in the Qinhuai River Basin since1988. Based on the trends of landuse in study area from2003to2006, the future landuse information in2009,2012and2018was predicted with the CA-Markov model. On this basis, urbanization scenarios in Qinhuai River Basin were built with gradually expanding impervious surface, while other landuse types remaining unchanged; spatial pattern scenarios of urbanization were built for the following study.2A distributed hydrological model named HEC-HMS was built for Qinhuai River Basin. According to the theory and characteristics of HEC-HMS system, appropriate modules were selected for the study area including precipitation, evapotransporation, runoff, transforming and baseflow. The required driving data and initial parameters were obtained in help of combination of GIS and RS technologies. And then HEC-HMS model should be calibrated and validated, giving a scientific method for the analysis of long-term and flooding hydrological effects of urbanization in the watershed.3The hydrological effects of urbanization were simulated through scenario analysis method which revealed the relationship of urbanization and long-term/flood hydrological effects in Qinhuai River Basin.(1) Analysis of the long-term hydrological impact of urbanization:keeping meteorological conditions fixed, the daily runoff process was simulated under different urbanization scenarios, and statistics of annual runoff for long-term was analyzed which showed the relationship between change of annual runoff and landuse type, especially the impervious surface. Impervious rate of3.4%in1988increased to31.4%in2018, the annual average runoff depth of the basin has increased by6.8%. Meanwhile annual runoff was simulated under the same urbanization scenarios but different conditions of precipitation, it could be concluded that the hydrological impact of urbanization on annual runoff depth of typical hydrological years was as following order: dry years> average year> wet year. This indicated that among the hydrological responses of annual runoff to urbanization, dry year was the most obvious, and wet year the weakest. Statistics of dry season, wet season runoff of long term and the typical years, the hydrological response of dry season to the urbanization was more obvious.(2) Analysis of the short-term hydrological impact of urbanization:the impact of urbanization on storm flood was studied through simulation of flood process under different urbanizatioin scenarios. The simulation results showed that under the same precipitation condition, both peak flow and flood volume increased, and flood with smaller scale increased more obviously; for a given flood, the change rate of flood volume were more obvious than the change rate of peak flow.(3) Hydrological effects of spatial pattern of urban space in Qinhuai River Basin. Four scenarios of different spatial patterns were built with ArcGIS by locating urban area in the upper reaches, the lower reaches, the periphery, and each sub basins of the whole basin, while keeping the impervious rate of the whole Qinhuai River Basin unchanged. Long term runoff and some flood events were simulated under the same meteorological condition but different scenarios of urban area. And the results of simulation showed that both long term runoff and flood events had hydrological response to different spatial patterns of urban area. The spatial pattern of urban area bringing the largest change on runoff was when the impervious surface was located in the upper reaches, then in the periphery, next in each sub basin, and the last in lower reaches. When the spatial pattern of urban area was relatively consistent, the degree of linear fit in changing rate of runoff depth and impervious rate was much better than that of real case of urban distribution. |
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