Study On Land Use Change And Impact On Runoff In Wuding River Basin

The Wuding River Basin locates Shaanxi and Inner Mongolia province,and flows into the Yellow River from Qingjian county of Yulin city,located in the Loess Plateau,with a fragile ecological environment,complex land use and transfer conditions,and no longer shows an obvious"decreased of cultivated land and increase of woodland and grassland"trend.The surface changed because of the human activies,and it effects the water resources.This study clarified the land use change patterns from 2005 to 2030,and used the SWAT as a tool to clarify the impact of different land use change on runoff and water yield under the influence of human activities,aiming to providing some advices for the Wuding River Basin.The Wuding River Basin is the study area.Based on the annual-scale data of precipitation,average/maximum/minimum temperature,actual evaporation and runoff,using the moving average method,linear regression method and Mann-Kendall mutation test methods,analyzing the trend and sudden change of the hydro-meteorological elements.The calculation equation of monthly-scale runoff reduction is established.The parameters are optimized by the SCE-AU algorithm,and the monthly natural runoff from 2006 to 2018 is calculated.Based on the multi-period land use from2005 to 2020 Data and used the CA-Markov model,predict land use data in 2025 and2030,aiming to establish four land use change modes(hereinafter referred to as C1-C4)with the 2005 data as the base period to analyze their area and spatial change characteristics.SWAT is established using the meteorological data,and the parameters are calibrated through SWAT-CUP to verify the applicability of the model.Four experimental schemes are designed,and the built SWAT is used to analyze the impact of C1-C4 on the monthly scale,annual scale,and runoff in sub-watersheds,and the impact of different land use types on water yield.The main conclusions are as follows:(1)The average rainfall in the watershed shows an insignificant downward trend,and the TMX、TMP、TMN shows a significant upward trend,and both of them have mutation points.From 1970 to 2018,the whole basin shows a trend of drying and warming;from 2006 to 2018,it shows a trend of warming and wetting.From 1960 to1990,the flow of Baijiachuan Station shows a significant downward trend,and from2006 to 2018,it shows a significant upward trendm,the multi-year average water volume decreased by 39.71%compared with 1960 to 1990.From 1970 to 1990 and from 2006 to 2018,the monthly average reduction water volume are 0.11 million、0.52million m~3.(2)The Wuding River Basin is dominated by grassland,cultivated land and unused land,accounting for more than 90%;the upstream is dominated by grassland and unused land,while the downstream is dominated by cultivated land and forest land;residential land is distributed on both sides of the river.In C1-C4,the residential land has the most severe positive change,and the unused land has the most severe negative change;C2 has the most severe change in C1-C4.In C1-C4,the conversion of cultivated land and unused land to residential land of different scales mainly occurred in Yulin City,the central part of Jingbian County and the northern part of Hengshan County;the conversion of grassland,woodland and unused land of different scales into cultivated land occurred in Yulin City and Jingbian County;unused land of different scales is converted into grassland,and it is transferred in a point-like manner in the watershed.(3)There are 15 types of soil in the basin,the top three are transitional red sandy soil,calcareous red sandy soil,and calcareous prototype soil 2,accounting for 62.7%in total.The study area is divided into 18 sub-basins and 372 HRUs.A total of 17parameters are selected for sensitivity analysis,and the NO.1 parameter is the SCS runoff curve number,indicating that the watershed runoff is most easily affected by land use,soil and other underlying surface conditions.Both R~2 and NSE are above 0.8,and PBIAS values are all around 0,indicating that the constructed SWAT model is suitable for the Wuding River Basin.(4)Analysis of△Q and△R under C1-C4:(1)The order of the total increasing flow isΔQ2>ΔQ4>ΔQ3>ΔQ1>0,indicating that C1-C4 all increase the runoff in the basin,and the total change ofΔR2 is 0.274 billion m~3,indicating that C2 has the greatest promotion effect;(2)C1-C4 all increase the runoff depth in flood season/non-flood season,and it has a greater impact on water volume in flood season;(3)The order of the total increasing runoff depth from January to December isΔR2>ΔR3>ΔR1>ΔR4>0,the total change ofΔR2 is 0.92mm,indicating that C2 has the greatest promotion effect;(4)C1-C4 all make the annual distribution of runoff more uneven,and the influence of C2 and C4 is greater among C1-C4;(5)The order of the total increasing runoff depth above Hengshan is R2>ΔR4>ΔR3≈ΔR1>0,indicating that C1-C4 all promote the increase of runoff in the above Hengshan area,and C2 has the greatest promotion effect,and the promotion in the water volume between Hengshan and Baijiachuan by C3 is greater than C1;(6)The order of the variation range of runoff depth in the subs is△P4>△P3>△P2>△P1.C1-C4 all play a negative role in NO.16sub at runoff,while play a positive role in No.3 sub at runoff.Analysis of water yield under C1-C4:(1)The contribution rate of land use type to WYLD is ranked as residential land>arable land≈grassland>unused land,indicating that although the area of residential land is small,it has a huge impact on WYLD;(2)In C1-C4,The WYLD is positively correlated with the residential,and negatively correlated with grassland,forest,cultivated,and unused land.