The Hydrological Effect And Threshold Effect Of Impervious Area In Shanghai Over The Last50Years

The region of Shanghai is one of the highly urbanized areas in China, where therapid expanding of impervious surface as a result of rapid urbanization has changedthe hydrologic process observably. In this paper, a typical area of the rapidurbanization region–Shanghai was selected as the study area. Firstly, compared thedifference of L-THIA model simulated result between impervious area landscapeand land utilization landscape. And then, analyzed the variation of runoff and theresponse difference in different hydrologic period due to the rapid urbanization overthe last50years from impervious area perspective. In the end, further explored thethreshold effects between the impervious area and the current focus indicators ofwater environmental and heavy metals in surface sediment through regression model.Those results can provide useful support for environmental planning andmanagement.(1) Comparison of L-THIA model simulation in different Landscapeclassification system. Compared the runoff difference between impervious arealandscape and land utilization landscape simulated by L-THIA model, and test modelsuitability to ascertain the model parameter used in this paper. The results shows that,the relative differentiation of the average annual runoff between two landscapeclassification system is8.96%, the relative error of the average annual runoffbetween corrected result and real data is8.90%, and there were a very significantlinear correlation between the annual runoff simulation results.(2) The long-term hydrological effects and spatial differentiation of theimpervious area. Analyzed spatial pattern change of impervious area in1965~2010,and analyzed the variation of runoff and the response difference in differenthydrologic period. The results shows that, there was a linear relationship betweenimpervious area and runoff growth rate, and also in nine horton laws. In2010, The runoff increased31.33percent compared with1965, and the maximal average annualgrowth rate is1.73%which in the period of2000~2006. Under the sameurbanization condition, among the hydrological responses of annual runoff tourbanization, dry year was the most obvious, and wet year the weakest. Comparedwith the rainy season, the dry season hydrological response to the urbanization wasmore obvious.(3) Analysis of water environment threshold effect of the impervious area.Defined the hydrologic unit as the geographical buffer of water quality monitoringsections and sediment sampling point, explored the threshold effects between theimpervious area and the water environmental indicators and heavy metals in surfacesediment through regression model. The results shows that, there were the thresholdeffect between impervious area and surface water indicators including COD, TN, TP,NH3-N, Phenol,Oil, but didn’t the DO indicator, the threshold effect betweenimpervious area and heavy metals with their ecological risk were not existed. Theexponential model goodness of fit indicated that the impervious area threshold effecttent to unconspicuous as the urbanization level further increased. The risk indexaverage value was116.54, which indicated that the ecological risk of heavy metalsreached slight grade on the whole.