Simulation Of Non-Point Source In Mi Shui Watershed Under Climate And Land Use Change

Under the background of climate change and the intensification of land use change caused by human activities,the spatial and temporal characteristics of precipitation and hydrological cycle in China have also undergone significant changes,bringing severe challenges to water resources and water ecological environment.Based on this,this paper studies on the topic of "simulation of non-point source pollution in the mi shui watershed under climate and land use change".The main work and achievements are as follows:(1)Linear trend method,ordered clustering method and Morlet wavelet analysis were used to study the evolution characteristics of Hydrometeorological elements in the watershed.The results show that the annual precipitation and annual runoff in the mi shui river basin have shown a non-significant increasing trend in the past 48 years,while the annual average temperature has shown a significant increasing trend;the annual rainfall time series has changed in 1993,the annual average temperature time series has changed in 1997,and the annual runoff time series has not changed;The first main periods of annual precipitation,annual average temperature and annual runoff are 30 a,6a and 32 a,respectively.The hurst index of annual rainfall,annual average temperature and annual runoff in the mi shui river basin is greater than 0.5,which indicates that all meteorological elements will show an increasing trend in the future.In spatial distribution,the annual average precipitation in the basin is more in the southeast and less in the northwest,while the annual average temperature in the basin is higher in the northwest and lower in the southeast.(2)Based on Arc GIS software,the change characteristics of land use types in the six periods of history in the mishui basin were analyzed.The results showed that woodland and cultivated land were the main land use types in the basin.During 1980-2015,the area of cultivated land,woodland and grassland showed a decreasing trend,while the area of water and urban land showed an increasing trend.The land use transfer in the basin from 1980 to 2000 wassimilar to that in 2000 to 2015,and the former was more extensive.(3)Based on the land use of 2015 and observed meteorological data of history,a SWAT model for simulating non-point source pollution in the mi shui basin was established,and the non-point source pollution load in the mi shui basin was simulated.The results show that the average annual load of ammonia nitrogen and total phosphorus is 3358.60 T and 475.63 t in the simulation period;the load of ammonia nitrogen and total phosphorus are similar in time and space,and the annual load is positively correlated with the annual rainfall,and the annual output load is basically consistent with the annual rainfall distribution;in the spatial distribution,the areas with high intensity of ammonia nitrogen and total phosphorus loss are mainly distributed in northwest of the basin,the drainage intensity in the northeast and south of the basin is lower.(4)The SWAT model with fixed utilization ratio and validation was used to simulate the non-point source pollution load under 25 climatic scenarios,5 land use scenarios and 4 climate-land use coupling scenarios.The response of non-point source pollution load to climate change,land use change and coupled climate and land use change was analyzed.The results show that the annual average ammonia nitrogen and total phosphorus loads are positively correlated with rainfall and temperature,and the simulation results of annual runoff,ammonia nitrogen and total phosphorus loads under different land use scenarios in different historical periods have little difference.In the future,the runoff of the basin will decrease slightly while the non-point source ammonia nitrogen and total phosphorus loads will be significantly reduced by implementing the measures of converting farmland to forestry.With the increasing trend of temperature and rainfall,the non-point source pollution load in the watershed will gradually increase.While strengthening land use management,watershed management departments should also pay attention to the impact of climate change on water environment.