| In recent years, the impact of land use changes on hydrologic process arouses broad attention, especially hydrologic.impact of increasing impervious area. Qinhuai River basin was choosed as the study area in this paper. Combined with Remote Sensing and Geographical Information System technology, the images were interpreted to analysis the spatio-temporal features of land use changes in Qinhuai River basin during1988-2009. The distributed hydrologic model of SWAT(the Soil and Water Assessment Tool) was used to simulate hydrologic response, analyzing the land use change on runoff, evaporation and peak flow. In this paper, the research focused on the following three aspects:(1) Land use changes were analysed. Historical land use maps were obtained from Landsat Thematic Mapper (TM) images and Enhanced Thematic Mapper Plus (ETM+) images. These imageries, combined with the existing land use map in2009and a single land use dynamic index K, revealed the Qinhuai River basin experienced conversion of approximately16%non-urban area to urban area between1988and2009, mainly from paddy fields and dry land.(2) The SWAT distributed hydrological model was built. With the help of RS, GIS, SPAW and data interpolation tools, the spatial pattern of topography, physical properties of soil, weather and other elements of the basin were described. Three nested distributed model were built, successfully dealing with bifurcation—a split in the flow in a channel. This also expanded the SWAT model application field. The whole basin was divided into42subbasins and nearly500hydrological response units to complete the watershed spatial discretization and parameterization. It also suggested SWAT model was suitable for the Qinhuai River basin.(3) Model parameters were calibrated and validated. Two methods were used in this paper, one was the conventional method, the runoff calibration was conducted for the period1988to1995, and the calibrated parameters were used for the period1996to2006to validate. The other method was dynamic parameter calibaration and verification. According to the different land uses, model parameters were calibrated separately, and relationships were established between impervious ratio and parameter values. Besides, parameters were verified in another land use map.Results showed that compared with the conventional method, the proposed method was more applicable. The relative error of the measured runoff volume and the simulation of runoff volume were reduced significantly, and the simulated runoff hydrograph were closer to the measured hydrograph.(4) Qualitative and quantitative analysis of hydrologic response to land use changes were made from the long time series of runoff and evaporation, the typical annual runoff and evaporation and impervious area expansion only. The results showed that①the Qinhuai River basin had a impervious rate threshold between6.6%-7.56%, when the ratio exceeded this value, the hydrological process would be impacted with urbanization. If the impervious ratio was less than the threshold, then the impact was not obvious. The average annual runoff depth, and the average annual evaporation were squadratic function with the impervious function.②With the same use scenarios under different precipitation, the change rates of hydrologic runoff depth were dry year>average year>wet year.③The hydrologic responses were verified mainly cased by the change of impervious surface. The future hydrologic response were predicted with the predicted land use map, when the impervious ratio reached23.83%in2012, the annual runoff depth was517.1mm, and evaporation was555.8mm. Compared with the simulated results in1988, when the impervious ratio reached31.47%in2018, the annual runoff depth was526.4mm, increasing by47.08%and evaporation was545.50mm, reduced by25.92%. |
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