Hydrology And Water Quality Process Simulation Of Nanliu River Basin Based On The Fusion Of 3S And SWAT

Water resources are an indispensable resource for human survival and development.Ensuring the sustainable use of water resources is an important prerequisite for achieving sustainable economic and social development.Under the influence of global climate change and human activities,the water cycle on the earth is constantly changing.Many regions are experiencing serious water crises,such as water shortages,water quality degradation,soil erosion,frequent droughts and floods,etc.,which have become the key to restricting regional sustainable development factor.Although the coastal area of Beibu Gulf of Guangxi has abundant water resources,its distribution is uneven during and inter-yearly.What is more serious is the water pollution and the deterioration of the water ecological environment.Water pollution in the basin has severely affected the ecological environment of the Beibu Gulf.This paper takes the Nanliu River basin,the largest river in the Beibu Gulf in Guangxi,as the research area.First,use a variety of mathematical statistical methods to analyze the characteristics of meteorological and hydrological changes in the basin;secondly,integrate 3S technology to construct a SWAT model to simulate runoff,sediment,ammonia nitrogen and total phosphorus in the Nanliu River basin to quantify the contribution of climate change and human activities;Finally,set up different climate scenarios to simulate the response of hydrology and water quality to climate change.The main research contents and conclusions are as follows:(1)Analysis of meteorological and hydrological characteristics of Nanliu River basin.From 1961 to 2016,the multi-year average precipitation in the whole basin was1747.8mm,and there was no significant trend in precipitation overall.The average temperature of the basin for many years is 22.23?,the overall temperature is increasing,and the average temperature increase rate is 0.02?/a.The temperature increase is mainly based on the annual average minimum temperature increase,with strong low temperature warming and weak high temperature warming.The distribution of runoff and silt at Changle Station in the basin is uneven from year to year.The multi-year average coefficient of variation of runoff is 0.33,and the maximum value of the coefficient of variation in the 00s is 0.45,and the inter-annual runoff fluctuates the most;the period of the largest fluctuation of inter-annual sediment volume is the 1980,and the maximum value of the variation coefficient of sediment volume during this period is 0.63.In addition,the distribution of runoff and sediment volume during the year is dominated by the summer half year(April to September),and the summer half year runoff and sediment volume accounted for 77.01%and 89.5%of the total respectively.In terms of the time trend,the Mann-kendall and double cumulative curve method were used to test the time series of runoff and sediment.The runoff showed an insignificant downward trend(a rate of 100 million m~3/a).The sediment abruptly changed in 1988.The study period showed a significant downward trend(reduction rate was 12,800 t/a).Taking 1988 as the boundary,the study period is divided into two periods:the base period(1966-1988)and the impact period(1989-2016).The annual mean values of runoff and sediment in the latter period decrease to At 7.9%and 43.5%,the amount of sediment transported dropped significantly.(2)SWAT model construction and hydrological simulation.Based on Arc GIS geographic information software,using elevation,soil and land use data and weather-driven data,the SWAT model of the Nanliu River Basin was established,and the model results were calibrated(1966-1980)and verified(1981-1988).The periodic determination coefficient(R~2)of runoff rate is 0.94,the Nash coefficient(NS)is 0.91,the verification period determination coefficient(R~2)is 0.93,the Nash coefficient(NS)is 0.92,and the relative error is 3.6%;The periodic determination coefficient(R~2)of the sediment rate is 0.88,the Nash coefficient(NS)is0.87,the verification period determination coefficient(R~2)is 0.88,the Nash coefficient(NS)is 0.86,and the relative error is-1.5%;The R~2 and NS of the runoff simulation calibration and verification period are both greater than 0.9,and the accuracy is excellent;the sediment simulation calibration and verification period R~2 and NS are both greater than 0.8,and the accuracy is good,indicating that the SWAT model has good applicability in the study area.Use the calibrated model to simulate the runoff and sediment during the impact period(1989-2016)to quantify the impact of climate change,land use,and direct human activities on the runoff and sediment.The contribution rates of climate change,land use and direct human activities to runoff changes were 46.4%,3.1%,and 50.5%,respectively,and the contribution rates to sediment transport changes were 46.9%,11.8%,and 41.3%,respectively.Runoff and sediment are mainly affected by climate change and direct human activities,and the impact of land use changes is relatively small.(3)Simulation of pollution load in Nanliu River basin and analysis of temporal and spatial characteristics.In terms of time trends,ammonia nitrogen and total phosphorus increase and decrease with runoff during the flood season(April to September)and non-flood season(10-March of the following year),and the total monthly load of ammonia nitrogen and total phosphorus increases-decreases-Increased fluctuation is positively correlated with runoff.Spatially,ammonia nitrogen and total phosphorus migrate along the main stream distribution.As time goes by,the upstream load decreases,and the downstream load increases cumulatively.Calculating the annual average discharge of ammonia nitrogen and total phosphorus,the maximum load of ammonia nitrogen and total phosphorus in the sub-catchment located at the downstream outlet is 1,585.37t/a and 1145.9t/a,respectively.The main stream load is greater than the tributary river load.(4)Estimation of the impact of different climate scenarios on hydrology and water quality.Set a variety of different climate change scenarios(temperature increase/decrease1?,precipitation increase/decrease 10%)to simulate the hydrological and water quality response of the Nanliujiang Basin under different scenarios.Based on the SWAT model that has been built,using scenario assumptions,nine scenarios with different climatic conditions are set up.Under the scenario where other conditions remain unchanged,the climate data of 9 different climatic conditions are input,and the change rate of runoff under different combinations of precipitation and temperature conditions is obtained.When the temperature remains the same and the precipitation increases/decreases by 10%,the runoff change rates are 18.95%and-18.33%,sediment change rates are 23.5%and-22.1%,ammonia nitrogen change rates are 7.6%and12.6%,and total phosphorus change rates are-9%and-12.9%,respectively.When the precipitation is unchanged and the temperature is increased or decreased by 1?,the change rate of runoff is only-1.86%and 1.95%,respectively,the change rate of sediment is-1.1%,1.2%,and the change rate of ammonia nitrogen is-0.2%,-2.2%,the change rate of total phosphorus was 1.4%and 2.1%respectively.Comparing the law of change rate,it is concluded that the changes of runoff,sediment,ammonia nitrogen and total phosphorus are positively correlated with precipitation,and weakly negatively correlated with temperature.And changes in precipitation have a greater more significant impact on hydrology and water quality than changes in temperature have on flow.