Evolution Of Watershed Ecological Hydrology In Haihe Basin Mountainous Area

Haihe basin has a large population and many large or medium size cities. Impacting deeply by natural environment change and human activities, the shortage of water resources is more serious, coupled with groundwater overdraft and water pollution, that lead to a large regional water resources crisis and has been a serious threat to the sustainable development of regional social economy. In this context, this research set Haihe basin mountainous area as the study area, and watersheds as the study objects. Based on the hydrological, meteorological, land use, topography, and other data in 1957-2000, we analyzed the effects of climate change and human activities on regional water and sediment yield, discussed the effects of watershed shape, topography, rain, land-use on the watershed hydrological process like as runoff, sediment, low flow, high flow, water quality and so on, and emphatically study the effects of vegetation. The results showed as:(1) During the period of 1957 to 2000, the precipitation of study area showed a downward trend, but not obvious; the changes of temperature, potential evapotranspiration, land use were small; runoff and sediment had severe changes, and showed obvious downward trend, the annual runoff data had a sudden change in 1980, and the annual sediment data was in 1967; the high flow data showed obvious downward trend; the low flow data showed a upward trend, but the trend was not obvious.(2) The sensitivity coefficient of water yield to precipitation εp was about 3.51, the sensitivity coefficient of water yield to potential evapotranspiration εEp was about-2.51, the sensitivity coefficient of water yield to aridity index εφ was about-2.75, and these results showed that if the precipitation, potential evapotranspiration, aridity index increase 10%, the water yield would increase 35.1%, decrease 25.1%, decrease 27.5%, respectively. The absolutes value of sensitivity coefficient showed a negative relationship(Y=ax-o) with Q/P, and showed a positive relationship (Y=ax+b) with aridity index, and these results showed that basins with low streamflows would be more sensitive to climatic variation than basins with high streamflows.(3) For the changes of water yield, the contribution rate of climate change was 30.85%, while the contribution rate of human activities was 68.33%; for the changes of sediment yield, the contribution rate of climate change was 29.11%, while the contribution rate of human activities was 70.89%; these results showed that during the process of runoff or sediment change, the effects of human activities was larger, and its contribution rate could be about 70%, while the effects of climate change was smaller, it contribution rate only about 30%.(4) Among the impact factors of runoff and sediment, the effect of land use was larger than other factors; the contribution rate sorted by numerical size:land use (67.63%)> rain (16.92%)> topography (11.77%)> shape (3.68%); among the impact factors of sediment yield, the contribution rate sorted by numerical size:land use (45.32%)> topography (27.66%)> rain (19.62%)>> shape (7.41%).(5) Based on Zhang model, the simulation results of the effects of forest, grass, crop on water yield showed that, if the coverage increases 1%, the decrease of water yield by forest, grass, crop would increase 1.46mm,1.21mm,1.22mm; the effects of vegetation were larger in the wetter area,, and smaller in the higher area. Forest and grass had some effects on runoff and sediment, when the coverage of forest was more than 60%, or the coverage of forest-grass was more than 80%, the effects were obvious.(6) Among the impact factors of low flow or high flow, the contribution rate of topography and land use was larger, the sum of their contribution rate could be more than 70%. To some extent, forest, grass and crop could decrease high flow; for low flow, forest and grass could increase low flow, while crop and city construction would decrease low flow.(7) For water quality, whether total runoff, high flow or low flow, land use had a larger effect on water quality; and the contribution sum of forest, grass, crop and city construction could be 70%-90%.