Optimization Model Based Analysis Of Hydrological Effects Of Land Use

The paper selected the upper Han Jiang basin as the study area and established SWAT database and SWAT Model based on the DEM data, hydrological data, soil data, weather data and land use/land cover data,which are collected from the relevant departments and field investigation. And this paper made sensitivity analysis and calibration of SWAT model, and verified the applicability of the model in the upper Hanjiang basin.Then the study set up scenarios of LUCC,analyzed the hydrological effects under different case of LUCC and set up the optimized mode of LUCC for upper Han Jiang basin:LUCC optimized mode for ecological protection and LUCC optimized mode for farmland protection. At finally analysis of hydrological effects under optimized modes of LUCC. The main conclusions as follows:(1) According to the sensitivity analysis of SWAT model, the main sensitive parameters which effects the hydrological processes of upper Han Jiang basin are Cn2,Esco,Surlag,Canmx, Sol_Awc,Gwqmn,Revapmn,Ch_K2,Sol_K,Alpha_Bf,Ch_N2.(2)From the process of correcting SWAT mode of upper Han Jiang basin,the paper get, calibration:Shi quan station,R2=0.894,Ens=0.844;Chang Qiangpu station,R2=0.851,Ens=0.819; Gao tan station, R2=0.837,Ens=0.843,Verification:Shi quan station,R2=0.843, Ens=0.824; Chang Qiangpu station,R2=0.792,Ens=0.79,Gao tan station,R2=0.837,Ens=0.8. R2=0.837. R2and Ens of calibration and Verification are both greater than75%, indicating that the simulation of SWAT mode are better and the model suited for upper Han Jiang basin on hydrological analysis of LUCC.(3) The simulation results from LUCC scenario are as follows:①Forest and grass have the ability of conservation of water and soil, and the ability of forest on conservation of water and soil are stronger than grass. And the evaporation ability of farmland is less than forest, but is greater than the grass.②The influese of land use/land cover on flowout has a certain seasonal characteristic. The monthly flowout would reduce in flood period and ofter flood period it has a sudden decline if the study area is full of forest or after the conversion of cropland to forest,which implys forest have water conservation decrease flood peak function. The monthly flowout in dry season will have a little increase if the study area is full of forest or after the conversion of cropland to forest,which would protect the reservoir located in the lower reaches.③The evaporation trend after the conversion of grass to farmland is different from other land use scenarios. There is a sudden increase of evaporation in July and October, which contribute to the farming methods of two crops a year in upper Han Jiang basin.④There is a positive correlation between the sediment flowout. The function of forest and grass on conserving water and soi is not a simple sum relationship, but a complex process.⑤The terrain factor could impact the function of different types land use on conserving water and soi. The conserving water and soi function of gentle slope is stronger than steep slope when the study area implementes policy of returning farmland to forest. The conserving water and soi function of gentle slope is weaker than steep slope when the study area has the conversion of cropland to forest. (4)The paper set up the optimized mode of LUCC for upper Han Jiang basin: optimized mode LUCC for ecological protection and optimized LUCC mode for farmland protection, based on hydrological effects analysis of the LUCC scenarios for upper Han Jiang basin.. LUCC of optimized mode for ecological protection(optimized mode1):slope15-25,altitude below800meter farmland convert to grass; slope15°-25°,altitude above800meter farmland convert to forest; slope above25°farmland convert to forest. LUCC of optimized mode for farmland protection (optimized mode2):slope15-25,altitude800-1200meter farmland convert to grass; slope15°-25°,altitude above1200meter farmland convert to forest; slope above25°farmland convert to forest.①The flowout and related uneven distribution coefficient for the a year of optimized mode1and optimized mode2both decreased,indicating that flowout distribution of optimized modes gradually become uniform. The rangeability of uneven distribution coefficient of optimized mode1is bigger than optimized mode1.How flowout distributed in a year is by the LUCC function of conserving water and soil. The minimum of optimized mode1conservation index is0.098and the maximum0.197, which can imply the conservation capacity the optimization mode1has reached over-qualified and is in good condition. The minimum of optimized mode1conservation Index is0.82and the maximum is0.129, indicating that the optimized mode2conserving capacity has reached middle level.②The potential evapotranspiration is much larger than the actual evaporation in. upper Han Jiang basin. The potential evaporation of optimized modes are both reducing. The potential evapotranspiration rangeability of optimized mode1is-0.94%, optimized mode2is0.48%. The actual evaporation of optimized modes are increasing. The actual evaporation rangeability of optimized mode1is1.92%, optimized mode2is1.22%. The impact of land use change on the actual evaporation is greater than the potential evaporation.③The sediment of optimized mode are decreasing to achieve the purpose of keeping soil.The ability of optimized mode1on conservation of and soil are stronger than optimized mode2. But the realizaition of optimized mode2are higher than optimized model.(5) The paper evaluate the optimized mode by marketing value method, the marketing value of LUCC of optimized mode for ecological protection is730million. the marketing value of LUCC optimized mode is LUCC of optimized mode for farmland protection (optimized mode2).