Abstract:

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.