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Abstract: Land use change has significant impacts on hydrologic processes at the watershed level. This paper combines an empirical land use change model and an event-scale, rainfall-runoff model to quantify the impacts of potential land use change on the storm-runoff generation in the Xitiaoxi basin upstream of Taihu Lake watershed. The HEC–HMS rainfall-runoff model is calibrated and validated for 7 storm events in the study area, and the results show good consistency between the simulated and measured hydrographs at the outlet of the basin with Nash–Sutcliff efficiency ranging from 75% to 95%. Then two future land use scenarios for the year 2050 are forecasted using the CLUE-s model based on the land use of 2002: (1) scenario A with an increase in urban area from 9.2% to 17% of the entire watershed and (2) scenario B with an increase from 9.2% to 14%. Finally, the calibrated HEC–HMS model is applied for these future land use scenarios under designed storms with different recurrence intervals to assess the potential land use impacts on the storm-runoff generation. The results indicate that the future land use scenarios are projected to increase the total runoff as well as the peak discharge, and that the magnitude of increment relates to the expansion rate of built-up area. In the case of rainstorms with recurrence intervals of 10, 50 and 100 years, the simulated peak discharges increase by 3.8%, 2.6% and 2.3% under scenario A, and by 2.8%, 1.9% and 1.7% under scenario B, respectively; while the total runoff is projected to increase by 4.7%, 3.4% and 3.0% under scenario A, and by 3.3%, 2.5% and 2.1% under scenario B. It can be concluded that the sensitivity of hydrologic response to land use change tends to increase as the recurrence interval of rainfall events decreases. Additionally, remarkable spatial variations of the land use changes and its impacts can be observed at the subbasin level, and the most sensitive subbasin is closeby the city. The results of this paper can provide useful support for land use planning and management, and the methods applied here have proved a useful tool for land use impact studies. [Copyright &y& Elsevier]

Abstract: Severe pollution in Lake Taihu in the lower reach of the Yangtze River has led to the need to evaluate transport pathways and the overall water balance of the catchment. This paper describes the development of a grid-based spatially distributed hydrological model for integrated simulations of surface runoff and groundwater flow at catchment scales. Surface water flow is modeled based on rainfall-runoff transformation and stream flow routing, while the saturated groundwater is modeled by MODFLOW-2005. Surface water flow is coupled to the groundwater flow regime through the soil layer. Relatively simple equations are used to describe the soil storage and soil water percolation. These equations are computationally inexpensive and overcome some of the limitations in existing models for coupled simulation of surface and subsurface domains, such as either multiple soil layer data are needed in the vertical direction or numerical difficulties are encountered in dealing with the high non-linearity of the equations representing the variably-saturated subsurface. The model was verified against the V-catchment benchmark problem and was compared to existing models to demonstrate its accuracy and capability. The model was applied to Xitiaoxi catchment of Lake Taihu watershed. The accuracy of the model was satisfactory with daily and monthly efficiencies of 0.80 and 0.92, respectively for stream discharge comparison, and an absolute error of 0.144m for groundwater level comparison. The model indicated that for Xitiaoxi catchment, a percentage of 37.4% of rainfall transferred to surface overland flow, and a percentage of 16% infiltrated as groundwater recharge, of which 81% returns to rivers as base flow and the rest is lost to the system via evapotranspiration. The model can be used as an alternative to more complex methods to assess impacts of land use or/and climate changes on water resources availability, and the interactions between surface and subsurface flow domains. [Copyright &y& Elsevier]