Study On Runoff Simulation And Its Response To Climate Change In Nanpan River Basin Based On SWAT Model

In the context of global warming,the runoff process of Nanpan River Basin may be affected by climate change,which may lead to water resources problems such as drought and flood disasters.In this paper,the upstream area of Tianshengqiao hydrology Station in Nanpan River Basin is selected as the research area.Based on the measured meteorological data in recent 32 years and hydrological data in recent 20years,the change regularity of meteorological and hydrological data is analyzed.At the same time,using the method of the SWAT model,build is suitable for the Nanpan River watershed hydrological model,and based on this model,rainfall and temperature as the main variable,by setting the 25 kinds of climate change,analyzed the sensitivity of the basin runoff to climate change in future,and then select 5 kinds of typical scene,the runoff change rule of years.The main conclusions are as follows:（1）The annual average annual precipitation in the Nanpan River Basin in recent 32years is about 965mm,and the trend of annual precipitation variation is not obvious and fluctuates greatly.The overall trend shows a slight increase,and the abrupt change of precipitation occurred in 2009.The distribution of precipitation in the year is not uniform,there are obvious seasons of drought and rain respectively,and the difference of average precipitation is great.The annual precipitation in dry season（Nov-April）accounted for 15.72%.The annual precipitation in rainy season（May-October）accounted for 84.28%.The annual average temperature was 17.0℃,the highest annual average temperature was 20.9℃,and the lowest annual average temperature was14.6℃.The annual average temperature showed an obvious increasing trend.（2）In recent 20 years,the annual runoff of Nanpan River showed a slightly decreasing trend,with the maximum value being 24.886 billion m3 in 1997,the minimum value being 5.892 billion m3 in 2011,and the average value being 16.294billion m3;The annual runoff distribution is very uneven,and the monthly runoff varies greatly.In flood season（May-October,corresponding to rainy season）,the annual runoff of Nanpan River accounted for 72.22%.The annual runoff reached its peak in July,which was 1311.15 m3/s,accounting for 28.8%of the annual runoff.April was the smallest,only 147.80 m3/s,accounting for 2.35%of the annual runoff.After September,the runoff gradually began to decrease.（3）Based on the existing data,the SWAT model was built step by step,and the measured data of Tiansheng Bridge station from 1996 to 2015 were used for model correction.The model had a good fit between simulated runoff and measured base flow during the rate period and verification period,and the evaluation indexes were satisfactory.Median interval:R²=0.77,E_ns=0.73;Validation period:R²=0.75,E_ns=0.72.The indexes meet the simulation requirements,and the AFOREMENTIONED SWAT model is suitable for Nanpan River Basin.（4）Based on the measured meteorological data in the last 32 years and hydrological data in the last 20 years,25 climate change scenarios are set according to the incremental scenario method and the future RCPs emission scenario model,which are precipitation change 0,±10%,±20%,and temperature change 0,±1,±2℃respectively.The established SWAT model was used to simulate the runoff response under different climate scenarios,and the sensitivity of runoff to precipitation and temperature changes was obtained.If the precipitation is kept constant,the runoff of Nanpan River will decrease by 2.48%and 7.46%when the temperature increases by 1℃and 2℃respectively.If the temperature drops by 1℃and 2℃,the runoff of Nanpan River will increase by 5.79%and 9.39%,respectively.If the temperature remains unchanged,the runoff of Nanpan River will increase by 8.36%and 14.74%when the precipitation increases by 10%and 20%,respectively.If the precipitation decreases by10%and 20%,the runoff of Nanpan River will decrease by 4.74%and 11.50%,respectively.Overall,from the annual scale,Nanpan River runoff is more sensitive to precipitation.Under the RCP4.5 emission scenario,the Nanpan River basin will be in the climate scenario with temperature rising by 2℃and precipitation increasing by 10%.According to the corresponding climate scenario simulated by the model,the runoff of The Nanpan River will decrease by 2.75%.From 2016 to 2050,the runoff of the Nanpan River will show a fluctuating trend of decline,and the runoff decline rate is about42.9m3/s·10a.Under the five typical scenarios,the monthly variation of runoff in each month of the year is as follows:the variation range of runoff from March to June and From September to December is greater than that of runoff from January to March and From June to September,which may be related to the difference of runoff volume and evapotranspiration in different seasons.