| Land use/land cover change(LUCC) is the direct signal of human activities effect on the surface of the earth’s natural ecosystems,and is also the link of human social economic activities and natural ecological process. Urbanization is one of the most typical land use change process, because of the influence of the urbanization process, the water cycle mechanism of urban areas, including the process of rainfall, runoff and river all will be changed, and present the differences which is from the state of nature.The rising distribution ratio of impervious surface area is an important manifestation of urbanization, Impervious surfaces are the man-made materials,such as rooftopst, pavements, asphalted streets,squares, airports, parking lots. compared with the soil and vegetation, permeability of impervious surface is smaller. Along with the increased urban impervious surface, and a substantial reduction in the water permeability surface, natural runoff process gradually changes into runoff process of urban characteristics, leading to the increase in number of urban runoff, duration and intensity, increased the city flood control pressure, even caused the casualties and property lossesAsh River basin was selected as the study area,the data source are the Landsat TM images in 2000, 2006, 2010,2015. Using linear spectral mixture model in ENVI software to extract impervious surfaces percentage.The Arc Hydro Tools in ArcGIS was based on DEM and river network,which can divide Ash River basin into 63 subcatchments. Impervious surface percentage layer was overlaid with 63 subcatchments, which can obtain impervious surface percentage in each subcatchment.Analysis the change of impervious surfaces expansion of 16 years from 2000 to 2015. and the L-THIA model was used for simulation of runoff change caused by impervious surface expansion.Seted up different rainfall scenarios:four daily rainfall scenarios(low rainfall,moderate rainfall, high rainfall, heavy rainfall)and three years situations(dry years, normal years, wet years).simulated runoff changes in different years and different rainfall situations. Compared the impact of impervious surface expansion on daily and annual runoff.Results indicated that the 63 subcatchments showed different degrees of growth in 16 years. And impervious surface expansion is have a significant effect on runoff, in low rainfall scenario, compared with 2000, the increase proportion of daily runoff followed by 19.81% in 2006,56.34% in 2010 and 68.35% in 2015, with the increase of rainfall,the increase proportion decreased gradually,in heavy rainfall,the increase proportion dropped to 3.51%,15.22% and 16.41%.therefore,the daily runoff in low rainfall scenario is particularly affected by the impervious surface,with the increase of rainfall,affect reduced significantly; in terms of annual runoff, in dry years, compared with 2000, the increase proportion of annual runoff followed by 19.18% in 2006,56.11% in 2010 and 69.54% in 2015,in normal years,the increase proportion was 13.92%,45.87%and 53.30,in wet years,the increase proportion dropped to 10.02%,34.41% and 40.00%.From the perspective of the growth amplitude, the impervious surface expansion had a more significant impact on dry years than on normal years,and the influence of normal years is more significant than wet years. The L-THIA model used for simulation of runoff change caused by impervious surface expansion,which requires a small amount of parameters, operates simply and quickly, the precision of the simulation also meets the requirements,the result can provide a basis for strategic decisions in controlling urban water logging and flood hazards. |
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