Effects Of Land Use And Land Cover Change On Environmental Hydrology In The Center Urban Area Of Shanghai

Land use and land cover change (LUCC) research was one of advance and hot area of the global change researches. Fast development of urbanization lead to continuous expansion of city size, and high-intensity human activity changed land use and land cover type greatly. Hydrology process was changed dramaticly by the second nature setup in city which was different to nature ground surface. So hydrology response to LUCC caused by human activity became a better research subject. Baesd on the cross subjects of environmental science, ecology and hydrology, revolved around two points (hydrology effects due to LUCC and runoff pollution reduceing), both theoretical and practical aspects related to environmental hydrology effects due to LUCC in the center urban of Shanghai were discussed, and an optimum adjustable strategy of land use and land cover type in city was rebuilt based on the conception of ecological drains. The main research conclusions of this paper were summarized as follows:(1) During rescent 50 years in center urban of Shanghai, the main land use types changed from water (include farm field), urban residential area and road to urban residential area, industrial land and green area. The decreasing of area diffence among different land use types resulted land use structure became more equilibria. The typical case study showed that because the human activity, there were great differentiation in the process of LUCC in small urban catchment. The differentiation would cause profound effects on urban surface hydrology. The reason of ecological services failed down greatly was water area disappearing largely, which was caused by economic development, urban construction and population growth..(2) On the research viewes of river system change, soil water content and water holding capacity, soil stable infiltration rates and rainfall-runoff process, hydrology effects due to LUCC were discussed. The results were showed as follows:â‘  In the past 50 years, a large number of rivers disappeared centrally during several phases, which was casued by human activity, that lead to river system structure destroyed greatly. High urbanization lessened the branching ratio, which resulted to an abnormal fractal dimension. The total river storage capacity reduced over 70 % compare with the storage capacity of 50 years ago, so the ability of water storage capacity was greatly weakened and flood prevention pressure was also increased in the center urban of Shanghai.â‘¡ Land use and land cover type, and land elevatioin affected soil water content and water holding capacity effectively. Water content and water holding capacity of soil with vegetation cover were greater than those without cover, and sunken green space has better storage capacity than high elevatioin and general elevatioin green space.â‘¢ Land use type, land vegetation cover type and soil surface crust affected soil stable infiltration rates significantly.â‘£ LUCC impact rainfall-runoff process deeply, fast urbanization process resulted an increasing tendency in runoff coefficient. Taking two adjacent small urban catchments as a study case, there were significant differences in the change of land use type between the two catchments in the urbanization process because of the different land use structure in small scale area, which caused the variation of runoff storage capacity between the two drainage systems. The green space had significant storage effect on city runoff. Adding 10 % green space land would result considerable effects of runoff storage and increase time-lag between precipitation and runoff flood reaching time.⑤ Sunken green space and multifunction green-water space compound system were some of the useful ecological drains facility with powerful rainwater capacity, which had good environmental hydrology effects through storing and infiltrating more rainwater. Under general case, with area ratio from 10% to 30%, sunken depth from 0.10 m to 0.30 m and soil stable infiltration rate from 5.0×10^-7 to 5.0×10^-5 m/s, sunken green space can store and infiltrate one hour continues precipitation at three years rainfall recurrence interval. Based on the analysis of the secular precipitation, soil stable infiltration rate and present urban green open space area in the center urban of Shanghai, sunked green space could be built in proper areas of center urban and developing urbanization area. Through the calculation, it was got that green-water space compound system had fine rainwater capacity.(3) There existed significant temporal and spatial variation in rainfall-runoff non-point pollution in center urban of Shanghai, TSS and COD_Cr were the main pollution of rainfall-runoff. The significant first flush phenomenon resulted in great impact deterioration of the quality of urban receiving water. The experiments of inside and outside with different land use and land cover typies showed that urban green open space had notable effect on decreasing contaminant of runoff. Inside experiment showed that a soil aquifer treatment with or without vegetation cover, the average COD_Cr, NH₃-N and TP remove rate of low, middle and high pollutant concentrations were 35.27 %, 60.12 % and 65.37 %, respectively. Those influencing factors to pollutant remove rate were land cover, pollutant concentration, thickness of soil layer and hydraulic retention time. Outside experiment showed the average COD_Cr, NH₃-N and TP remove rate of representative green open space were 52.21%, 48.98 % and 47.35%, respectively. Comparing to those of inside experiment, COD_Cr romove rate increased about 20%, romove rates of NH₃-N and TP decreased about 10 % and 16 %, respectively. Because of the short hydraulic retention time, the main pollutant remove mechanics was related to mechanical filtering and physical absorption by soil, and micro-biological degradation could be ignored, so the pollutant remove rate model could agree with first reaction kinetics model. Experiments also showed that pollutant remove rate decreases with increasing of rainfall intensity.(4) Depending on advanced experiences of rainwater resource utilization and management of Germany, USA and Japan, ecological drains conception was structured through two aspects, which were zero growth of rainfall-runoff and runoff pollutant decrease. In order to realize optimal urban hydrologic cycle, the ecological drains conception required increasing runoff infiltration and decreasing runoff pollutant through engineering technical facilities and non-engineering management measures. Based on optimal urban land use and land cover type, best management practices of ecological drains were formed through decreasing runoff and remove pollutand. Four inspirations of set up urban rainwater resource utilization and management system were gained. The first is to establish nationwide law and rule to guarantee rainwater resource use, the second is to support development of rainwater resource utilization technology to promoting use of rainwater resource, the third is to use establish economic adjust and control means to motivate rainwater resource use, the fourth is to establish uniform specialized functional management department to norm rainwater resource utilization.