Evaluation Of Water Cconservation Function Based On Distributed Hydrological Model

Forest is the important renewable resources in nature, it can adjust the climate, conserve water, clean air, etc., effectively improve the ecological environment. Forest vegetation can affect the hydrological process, change rainfall redistribution process, affect the soil moisture movement and so on, which will alleviate surface runoff, increase soil runoff and base flow. To a certain extent, it can play the peak clipping repair dry, control soil erosion, improve water quality and so on. Today, under the condition that the global water environment is in a sharp deterioration and water resources is gradually serious, water conservation function of forest is being more and more attention.In order to further understand the relationship between forest and water, and the process of redistribution of water in forest ecosystem, to understand the influence of the existence of forest on runoff and soil water content, quantitatively evaluate water conservation function of forest, so we can fully understand the value of forest ecosystem, protect, develop and utilize forest resources and water resources better. This paper simulated hydrological processes of Xinlin watershed in Daxinganling Mountain in2007and2008based on improved distributed hydrological model TerrainLab. Through the results of contrast between real land cover and assuming forest cover is zero, we analyzed the influence of the existence of large watershed forest on runoff and key parameters of water balance. On this basis, we calculated the amount of regulating runoff of forest in watershed (flood control ability of forest) and water conservation (water storage and water purification functions) and their economic value. The model was improved mainly on the following aspects:the solar radiation was spacially extended by considering factors of latitude, slope and aspect; the aerodynamic resistance for overstory, understory and moss layer were calculated by using the observation data of wind speed and the attenuation process inside the canopy; stomatal conductance was calculated by considering the influence of soil temperature.According to this study, some conclusions were followed by:(1) Three daily global solar radiation calculation model i.e. A-P, Thornton-Running and Liu Kequn model were analyzed using13weather station’s32years’ data from east of Inner Mongolia and three provinces in the northeast of China. After cross-validation analysis, mean absolute error(MAE) for each model was1.71,2.83and1.68MJ m-2day-1respectively, meaning that A-P and Liu Kequn model which use percentage of sunshine are much better than Thornton-Running model which doesn’t use percentage of sunshine.A-P, Thornton-Running and Liu Kequn model overvalued daily global solar radiation by12.2%,19.2%and9.9%respectively. Three models’ MAE for rainy days, non-sunshine days were greater than rainless days, sunshine days. Liu Kequn model played a good effect on the situation of non-sunshine, and its MAE and bias percentage was18.5%and.33.8%smaller than A-P model. The total radiation estimation results for cold seasons are better than warm seasons.(2)Water balance of model results was tested by using measured stream flow data at the outlet of the watershed. The error of water balance in2007and2008were1%and14.1%respectively. From the comparison between monthly measured runoff and simulated runoff we can see that the model had a good simulation effect in2007in which the rainfall changes smoothly, while the simulation error is bigger in2008in which the meteorological factors change complex.(3)The annual evapotranspiration in2007and2008is329.96mm and348.79mm, account for69%and56.3of precipitation respectively. The spatial distribution of evapotranspiration (ET) from June to August in2007and2008shows the spatial distribution of ET is uniform, and is affected less by topography. ET in June and July are intensity than ET in August.Among all the land cover, ET of coniferous forest is25.6%-28%lower than broad-leaved forest, ET of mixed forest has middle value.In the composition of broad-leaved forest, coniferous forest and mixed forest, canopy transpiration from unsaturated soil accounted for66%-73%of total amount of ET. Canopy transpiration of broad-leaved forest from saturated soil was larger than canopy evaporation, while coniferous forest and mixed forest acted contrary. ET from trees from broad-leaved forest, coniferous forest and mixed forest accounted for90%of the total ET, while the understory and soil and moss layer accounted for only4%-6%respectively.(4)The contrast between real land cover and assumed all grass cover situations showed that the existence of forest increased72%-83%of yearly ET, decreased50%-57%of the runoff, reduced the water table, slowed down the release of soil water content.(5) The regulating runoff was9.16×108m3and1.18×109m3in2007and2008respectively calculated based on the difference between forest and non-forest situations. The economic value for flood control was5.60billion yuan and7.21billion yuan, which is8665.6yuan per ha. and11414yuan per ha..(6) The amount of water conserved by forest in2007and2008based on canopy interception residual method was2.58×108m3and3.36×108m3respectively. The amount of water conserved by forest in2007and2008based on water balance method was8.53×108m3and1.05×109m3respectively. The total economic value of regulating runoff and water purification was6.85billion yuan and8.61billion yuan, which is10844.1yuan per ha. and13630.3yuan per ha..