| The mountain area of north Hebei province is water source of Panjiankou reservoir andMiyun reservoir, which play important roles in providing water to Beijing and Tianjinrespectively. In recent years, the amount of water in two reservoirs has becoming less and less.Many previous researches showed that changes of land use resulted from human activitieshindered runoff production, which resulted in water shortage downstream. Therefore,optimizing land use structure in mountain area of north Hebei province is a good measure toincrease runoff entering two reservoirs, so that resolving water shortage in Beijing andTianjin.Dongbeigou watershed, standing for the mountain area of north Hebei province, is agood research area. This paper taking the Dongbeigou Watershed as a case study, on the basisof field investigation, remote sensing data and social economic surveying data discusses theinteractions between land use, soil erosion and water consumption. Firstly, Revised UniversalSoil Loss Equation (RUSLE) supported by GIS was used to get soil loss amount of differentland use types. Then Penman-Monteith formula was applied to calculate referenceevapotranspiration which would be revised through soil and vegetation data to obtainecological water requirement of different land uses．Based on the above research results, theoptimized land use structures were obtained under different objective functions by means ofmultiple objective programming. Through the programming in MATLAB and GIS approaches,the space optimization distribution map of Dongbeigou was obtained.(1)The land use structure in Dongbeigou watershed has undergone obvious change from1990to2009. Overall change characteristic was land use type with low coverage convertingto land use type with high coverage. Woodland increased from38.56%in1990to55.83%in2009, compared to grassland decreased from29.53%to18.92%, unused land decreased from17.11%to13.64%, cultivated land decreased to3.49%.(2)The change of land use influence on soil erosion, whose intensity weakened obviously.The annual average soil erosion modulus decreased from5136.13t/(km~2·a) in1990to1823.30t/(km~2·a) in2009. In2009,The soil erosion happening in unused land was serious with annual average soil erosion modulus5342.97t/(km~2·a) compared with361.69t/(km~2·a)soil erosion modulus in woodland. Different land use types have various soil erosionintensities. Consequently, conversion between land uses would influence on soil erosionintensity in watershed.(3)Vegetation ecological water requirement increased obviously, leading to thedecrease of water resources transferring downstream. The watershed suitable ecological waterrequirement was399.42mm in2009, compared with254.92mm in1990. Watershedecological water requirement increased with improvement of vegetation coverage. Land usetype with higher vegetation coverage requires more water resources.(4)According to watershed development and downstream requirement for waterresources, the paper set3scenarios (minimum soil erosion, minimum ecological waterrequirement, maximum economic benefits) to single-objectively optimize land use. Land useoptimization results under3scenarios had big diversity and conflicts. And different land usewould bring different ecological and economic effects. Optimization results taking theminimum soil erosion as an objective function is large forest and bush land area; Optimizationresults taking the minimum ecological water requirement as an objective function is largeopen forest land and grassland area; Optimization results taking the maximum economicbenefits as an objective function is large economic forest area. Watershed ecological waterrequirement is668.57×10~4m~3under the minimum ecological water requirement land useoptimization,105.75×10~4m~3less than that in2009. Under the minimum soil erosion land useoptimization watershed ecological water requirement is740.65×10~4m~3,33.66×10~4m~3morethan that in2009and soil loss amount is9054t less than that in2009. Under the maximumeconomic benefits land use optimization, watershed ecological water requirement is898.07×10~4m~3,123.76×10~4m~3more than that in2009, and soil loss amount is6390t less thanthat in2009. However, economic incomes are157.78×10~4yuan more than that in2009.(5)Based on single-objective optimization, the paper combines soil erosion andecological water requirement to carry out ecological transferring water multi-objective landuse optimization. Likewise, the paper combines soil erosion, ecological water requirementand economic benefits to carry out comprehensive objective multi-objective land useoptimization. Two multi-objective land use optimizations have the same characteristic thedecrease of woodland and increase of grassland compared land use in2009. Undercomprehensive objective multi-objective land use optimization, forest land area is larger andforest and bush land and open forest land is smaller compared to results under ecologicaltransferring water multi-objective land use optimization. Under comprehensive objectivemulti-objective land use optimization, watershed ecological water requirement is 757.08×10~4m~3, only17.23×10~4m~3less than that in2009and soil loss and economic incomeimproves. While watershed ecological water requirement is704.61×10~4m~3,69.70×10~4m~3lessthan that in2009, and economic incomes are77.16×10~4yuan less than that in2009.(6)The most optimum land use is ecological transferring water multi-objective land useoptimization results. Carry out payments for water provision service scheme to compensateeconomic loss in Dongbeigou watershed. Ecological transferring water multi-objective landuse optimization results are as follows: cultivated land115ha, forest land and shrub land300ha, open forest land473ha, economic forest land86.5ha, grassland with high coverage594.6ha, grassland with medium and low coverage51.6ha, unused land234.5ha. Thepayments amount is between77.16×10~4yuan and157.78×10~4yuan. |
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