流域植被水文效应的动态模拟

为了揭示森林植被水文效应的动态变化过程，将简化的简单生物圈模型与动态植被模型和流域地形指数水文模型相耦合进行长江上游梭磨河流域植被及其水文效应的动态模拟。结果表明：植被覆盖和叶面积指数的增加使植被蒸腾和冠层截留蒸发增加而使土壤蒸发减小，植被的水文效应取决于蒸发分量中这两个相反方向变化的净效应。流域主要由草地和灌木覆盖时流域总蒸发大于裸地和林地。与裸地相比较，当单位叶面积指数截留能力取值0.1 mm时，森林减小了流域总蒸发，但当单位叶面积指数截留能力取值0.2 mm时，森林增加了流域总蒸发。森林的水文效应对冠层截留能力敏感，冠层截留能力存在一个控制森林水文效应从减小总蒸发变为增加总蒸发的转折点。植被的水文效应是随时间变化的，对于给定的植被类型其叶面积指数是决定其水文效应的关键因子。

DYNAMIC SIMULATIONS OF HYDROLOGICAL EFFECT OFVEGETATION OVER A BASIN

In order to reveal the dynamic process of hydrological effects of vegetation，top model and a dynamic vegetation model were incorporated into the land surface model simplified simple Biosphere Model.The coupled model was employed to perform dynamic simulations of vegetation and its hydrological effects over the Suomo basin in the upper reaches of the Yangtze River.Simulation results show that as vegetation cover and leaf area index within the basin increase makes vegetation transpiration and canopy interception evaporation increase and soil evaporation decreases.The net effect of these two opposite changes in evaporation components will determine vegetation whether to increase or reduce runoff of the basin.When basin is mainly occupied by grass or shrub,the total evaporation of the basin will be higher than the evaporation from bare soil and forest covered land.When the interception capacity of unit leaf area index is set to be 0.01 mm,forest will reduce the total evaporation of the basin,while the interception capacity of unit leaf area index is set to be 0.02 mm,forest will increase the total evaporation of the basin compared with evaporation from bare soil.The hydrological effect of forest is sensitive to the canopy interception capacity which has a tipping point to control transitions of effects of forest on hydrology from reducing total evaporation to increasing total evaporation.For a certain type of vegetation,its hydrological effect changes with time,and its leaf area index is crucial factor to determine its hydrological effect.