Evaluates The Influence Of Vegetation Changes On Hydrological Processes In Typical Tatershed Of The Middle Reaches Of The Yellow River

The Yellow River basin is located in the arid and semi-arid areas in the north of China and its water resources are extremely scarce.The underlying surface of the middle reaches of the Yellow River has undergone the most drastic changes on account of the activities of returning farmland to forest and the forbidden in the past ten years.As a result,the area of forest and grass increases significantly and the runoff decreases sharply especially in tongguan,the head of the middle reaches of the Yellow River,where the Interval changes is so dramatic.The change of vegetation seriously affects the relationship between rainfall and runoff in this region that results in the change of river runoff.The mechanism of vegetation change under the influence of large-scale human activities on the hydrological process in the middle reaches of the Yellow River is the key to reveal the sharp decrease of runoff in the middle reaches of the Yellow River.This article that focuses on this key issue evaluates the influence of vegetation changes on hydrological processes in typical watershed of the middle reaches of the Yellow River and the main research contents and conclusions are as follows:The typical river basin in the middle reaches of the Yellow River as the research object carries out the work according to the overall thinking of remote sensing interpretation,runoff analysis,model simulation analysis and evaluation that aiming to evaluate the influence of vegetation change on the hydrological process in the middle reaches of the Yellow River.Analyzing the relationship between rainfall and runoff under different vegetation cover conditions and establishing a hydrological model suitable for the typical middle reaches of the Yellow River through remote sensing inversion of vegetation change process in the middle reaches of the Yellow River is significance for hydrological research.The hydrological process under different vegetation conditions in a typical watershed was simulated and the influence of vegetation change on the hydrological process was evaluated.(1)Vegetation changes in different periods of the Tuwei river basin and annual vegetation coverage changes in the basin from 2000 to 2013 were analyzed through remote sensing inversion,and the following conclusions were obtained:From 1978 to1990,the forest land and grassland area in the Tuwei River Basin increased,but the change range was less than 5%.In 1998-2010,the grassland area in the Tuwei River Basin increased significantly by 8%.The cultivated land and grassland are the dominant types of vegetation changes with the cultivated land decreased by 109 km~2and the grassland increased by 141.3 km~2from 1978 to 2010.From 2000 to 2013,the average annual EVI of the Tuwei River Basin increased year by year.The EVI average value of the January-March period was basically maintained at 0.07~0.08from the perspective of the year,which was in a low state and began to rise rapidly from April.It reached its highest value in August and it began to decline sharply in September.From November to December,the EVI fell to between 0.08 and 0.09.(2)The characteristics of rainfall runoff in the Tuwei River Basin were analyzed by measured data and remote sensing inversion vegetation coverage.The results show that:The runoff coefficient of the Tuwei River Basin in the past 10 years is 29%lower than the multi-year average rainfall runoff coefficient of 0.279.There are two variability points in the Tuwei River base flow sequence from 1956 to 2012,which were 1979 and 1996 respectively.With the increasing of vegetation cover,the runoff coefficient is significantly reduced by establishing the relationship between rainfall and runoff function under different vegetation conditions.The watershed will reduce water by 9778 m~3/km~2(measured)and 10203 m~3/km~2(natural)for every one percentage point increase in the EVI value of the Tuwei River Basin.(3)The distributed hydrological model and the LCM sub-rainfall runoff model were established and the model was validated according to the rainfall runoff characteristics of the Tuwei River Basin,which was verified by the runoff data,indicating the trend of the simulation using the distributed hydrological model and the sub-rainfall runoff model.As a result,the trend is well fitted and can better reflect the runoff process of the basin.(4)The distributed hydrological model was used to evaluate the annual runoff change of the tuwei river under the condition of vegetation change.When the climatic conditions in the 1970s were unchanged,the change of underlying surface in the1990s caused the decrease of runoff of 52 million m~3 without considering the influence of climate change.(5)The runoff simulation value was slightly larger than the measured value and the simulated runoff of the two scenarios LCM model was significantly lower than that of the 70s under the conditions of underlying surface in the 1970s based on the LCM model which used to simulate two different types of rainfall runoff.It shows the increase of forest and grass vegetation has significantly reduced the river basin production and discharge and the water reduction scenario 2 is more pronounced than scenario 1 under the two scenarios.