Study On The Response Mechanism Of Hvdrological Processes In The Typical Watershed Of The Lower Nu River Under Changing Environment

The mountainous hydrological processes in the lower Nujiang River basin has undergone complex changes,resulted by its climate change,land use and cover change,hydraulic engineering construction,and other human activities.It is critical to reveal and quantify the effects of climate change and human activities on the hydrological processes in the river basin.Mengboluo River basin,which locates in the lower Nu River basin,was chosed as the case area.In the study,I applied comprehensively the hydrological statistics methods to clarify the temporal and spatial characteristics of key meteorological(temperature and precipitation)and hydrological features(runoff,sediment)in the basin,to improve the SWAT model’s surface runoff module,and compare the applicability of different models in the study area.Based on the"reconstruction land cover and climate scenario",the revised SWAT model was used to estimate the contribution of the major drivers that affect the runoff and sediment.At last,the response mechanism of hydrology process to climate change and human activities was discussed.The main contents and results of this study are as follows;The analysis of temperature,precipitation,runoff,and sediment variation trends and change points in the basin showed that in the past 50 years,the temperature in the basin has increased significantly,and the increase rate was 0.27℃/10a.The precipitation trend in the basin was not so significant.The runoff at Kejie station was reduced significantly and the rate of reduction was 0.48×10 m3/10a.The sediment transport showed a significant decrease trend,and after 2002,the amount of sediment transported at Kejie Station abruptly reduced by about 83%from the previous period.The original SWAT,the improved SWAT-Rλ and SWAT-TVGM models were constructed for Mengboluo River basin to simulate the stream flow and the sediment load.The Nash efficiency coefficient(NSE)of SWAT-RX and SWAT-TVGM model during the calibtration and validation in runoff simulations was above 0.8,which was higher than the original model with NSE value of 0.75.SWAT-Rλ and SWAT-TVGM models had an NSE higher than 0.75 on sediment simulation.The improved model SWAT-Rλ considered the influence of the topography slope of the river basin,which is suitable for the hydrological simulation in the mountainous basin.Based on the "reconstructed land cover and climate scenario",the improved model SWAT-RX was used to quantitatively identify the contribution of climate change,land use and cover change,and other human activities influence on runoff and sediment at Kejie station.The results show that the effects of climate change,LUCC,and other human activity on runoff and sediment load were inconsistent.Human activities have more impact on sediment than on runoff.Around 2002,climate change was the dominant factor affecting runoff changes,and it contributes about 55.9%of runoff reduction.Human activities had larger impact on the reduction of sediment load,its contribution rate was about 78.4%,where LUCC contributed 19.8%,and other human activities contributed 58.6%.This study provides a new scientific reference to revel the hydrological response on environment change and to promote ecological protection in Nu River basin;it also provides a reference case for the study on surface hydrological process in the remote mountainous basin.