Interactive Mechanism Between Vegetation And Hydrology In Lancang River Basin Under The Background Of Environmental Change

The Lancang River is located in southwestern China, across Qinghai, Tibet, andYunnan. Lancang River is an important cross-border river in China, whose lowerreaches was called Mekong river. Lancang River is rich in water resource, but not bewell developed and utilizated for the complex terrain and the low levels of socialeconomic. The difference of natural conditions between north and south of LancangRiver Basin is great, especially the vegetation. Under the influence of climate changeand human activities, the vegetation and the hydrological processes are undergoingprofound change. In order to meet the demand of social economy in the future, thewater resources of Lancang river need to be further developed. At the same time, theecological resources of vegetation need protections. To meet the growing need ofwater resource without prejudice the functions of ecological environment protection,it is a prerequisite to identify the interaction mechanism between the hydrologicalprocesses and the vegetation processes.The eco-hydrological numerical simulation technology, remote sensingtechnology and geographic information system were used in this study. Under theguidance of eco-hydrological simulation technology framework, the numericalsimulation model of vegetation hydrological interaction process on Lancang Riverbasin was established based on the CLM-DGVM model and WEP model. Throughdebugging and checking, the model achieved a good simulation results in bothvegetation process and hydrological process. On the basis of the vegetationhydrological model, the historical process of vegetation and hydrologic weresimulated. More simulation has been performed in the hypothesis of the extremeclimate change. Through comparative analysis to the simulation result, the interactionof vegetation and hydrological process were introduced, the main research results areas follows:（1） The temporal and spatial distribution of the vegetation and hydrologicalfactors are consistent in the Lancang river basin. The annual variability of the factors is small. There is no clear pattern between the vegetation and hydrological factors.Seasonal change of the factors is significant during the year. Each factor shows highervalue in the summer. From May to October, the precipitation and runoff accounted formore than80%of all year. In north area, each element shows lower value than southarea. The differences are greater in winter than summer.（2） In Lancang River basin, the interaction law of vegetation and hydrologicalfactors was reflected on the scale of month. All the factors passed the0.01level ofcorrelation tests. From April to August, higher precipitation and temperature increasethe photosynthesis. The hydrological factors perform positive effect on vegetation.The growth of vegetation promoted the rise of evaporation, and also improved thewater holding capacity of the soil. Water sinks into the River was relatively small. Therise of runoff lags behind the rise of precipitation. Rainfall and temperature dropduring September to November. In the same time, vegetation leaves decline. The soilwater holding capacity decreased, and the water permeate into rivers through theunderground runoff. Because of the groundwater recharge, runoff drop lag inprecipitation. The profile of runoff also lags behind the precipitation month.（3） Three factors, atmospheric CO₂concentration, temperature and precipitationwere selected to describe the increase in greenhouse gas emissions, climate warmingand drought-flood events. Simulation results show that elevation of the three factorsin a range promoting positive effect on vegetation, but excessive rise will causevegetation decline. Reduction of precipitation will make the rest of the vegetationhydrological elements decrease. When many factors change at the same time, thethree factors impact the remaining vegetation hydrological factors according to thelaw: impact weight precipitation> temperature>CO₂. In a certain threshold valuerange, high temperature and rainy environment is more advantageous to the growth ofvegetation.