Modelling Experiments On Impacts Of Three River Headwater Region's Changed Area On The Regional Climate

Impacts of Three River Source Region's changed area on the regional climate and environment, were studied and analyzed by using the latest Regional Climate Model (RegCM₃). Experiment was designed, to indicate the conclusion that RegCM₃ has the ability to simulate the climate of the Three River Source Region, in this way: The four times daily reanalysis data during the period of May to September in year 1995, offered by NCEP, was first used to initiate the Regional Climate Model, then the result of simulation was compared with the reanalysis data collected from ECMWF. There were three groups of experiment designed to study the influence of the growth and degradation of Three River Source Region's wetland on the climate of the studying region and the regions around. The first experiment is Controlled Experiment (A): run the model from 1st May, 1995 to 1st September, by using datasets of OISST, Topography, and Global Vegetation, offered by NOAA and US Geological Survey respectively. The second one was defined as Expanded Experiment(B) over Three River Source Region's wetland, as it just changed the Land Cover/Vegetation Classes over River Source Region from type 11—Semi-desert to type 14—Inland water. The final group is named as Miniature Experiment (C). It was done by substituting type 2, 9, 12, 13 and 14 of Land Cover/Vegetation Classes over River Source Region, which is Short grass, Tundra, Ice cap/glacier, Bog or marsh and Inland water respectively, with type 8—Desert, while keeping the other types unchanged. The comparing analysis indicated that: expansion and degradation of Three River Source Region's wetland can both impose impacts on Surface Temperature, Potential Height Field, Wind Field, and intensity of precipitation, as well as the vapor rate and containing water of soil. The main simulating results about the impacts imposed by increase or reduction of wetland area include the following:First, the average temperature in summer over Tibet Plateau falls down and precipitation decreases as the wetland areas increase. This can be explained by the fact that decreased surface reflective rate, increased thermal capacity, weakened sensitive heat flux and decreased heat on atmospheric turbulence, all resulted from the expansion of wetland, can lead the atmospheric temperature over this region to fall, and its rising movement to weaken, and then rise the geopotential height near the surface, as well, the rainfall reduce. The falling temperature over Tibet Plateau can further strengthen the cyclone circulation over the Plateau, which causes the precipitation over Yangtze River to decrease.Besides, changes caused by degradation of wetland are reverse to that of expansion. Obviously, the expansion and degradation of Three River Source Region's wetland impose great impact on the climate of the studying region and the regions around.