Research On Hydrological Effects Of Land Use Changes In Nansihu Basin

The research is based on National Natural Science Foundation, named as study on basin-oriented hydrological effects of urbanization and urban sustainable development. Nansihu basin is selected as subject to study the mechanism and evolution between land use changes and natural water cycle, for providing decisions of water environmental protection and watershed land use management.Agricultural and construction land are in dominant position of land use structure in Nansihu basin from 1987 to 2014, and the development of construction land is rapid. The land use changes are mainly reflected in conversion of forest land, grassland and agricultural land into construction land in the two stages of 1987~2000 and 2000~2014. The change of the latter stage is significant. For natural environment factors, construction land changes are significant, while the land use structure is in elevation of 0~100 m, NDVI of 0.44~0.568 and river buffer of 0~6 km. For administrative divisions and river basins, the land use changes are most prominent in Zaozhuang, Tengzhou, Jining and Heze which are located in Panlong River basin, Cheng River basin, Guangfu River and Liangji River basin, Zhuzhaoxin River basin respectively. Factors such as population growth, economic development and policies of land use management are the main reasons of land use changes.SWAT distributed mechanism hydrologic model is used to simulate the watershed hydrological processes of Nansihu basin. The results show: with the influence of land use changes, annual runoff depth, base flow and evapotranspiration is increased by 0.57%,-1.49%, 0.07%; 0.99%,-7.88%, 0.53% in the two stages. Under different conditions of rainfall, the strongest response of three hydrological parameters to land use changes happenes in dry years, the next happenes in normal years, and the weakest happenes in flood years. The monthly runoff depth is increasing, while monthly base flow is decresing. But monthly evapotranspiration is not stable, such as decreasing from July to August, increasing in the rest months. As well, three hydrological parameters changes of the latter stage are significantly higher than the previous stage.Rainfall has a pattern that the south and north is high and the middle is low, and runoff depth, base flow also has the same pattern in space. Due to the rapid development of construction land in Heze, Cao, Tengzhou, Zaozhuang, runoff depth is increasing and base flow is decreasing significantly in Zhuzhaoxin River basin, Dongyu River basin, Cheng River basin, Panlong River basin. For evapotranspiration, it is increasing prominently in lake districts, and decreasing significantly in peripheral places.The decreasing forest land, grassland and increasing construction land has positive influence on runoff depth, and has negative on base flow and evapotranspiration. Responses of three hydrological parameters are different because of different land use types and range in different river basins. The ecological consequences of urban development should be especially concerned about the midstream in Panlong River basin and downstream in Zhuzhaoxin River basin in the future, because hydrological sensitivity is higher.