Simulation Of Hydrological Effects Of Vegetation Evolution In Basin

The headstream of one river is a key ecological function area. Vegetation in one basin is evolution as time past by, and the vegetation is vital element to influence the eco-hydrological effects in a basin. Meijiang is the 1st level branch of Ganjiang river. Meijiang river basin located in semi-tropic humid area, the vegetation, climate and hydrology has typical characters. The vegetation is the basin has changed tremendously in the last few decades caused by human activities. By now, the environment and ecology health is a key part to people's life and has big influence on keeping a sustainable way of our society. Environmental issues are becoming a more and more hot spot in the researching working. At present, the problem attracted more and more attention and researching. This paper do some research in Meijiang basin to discuss the hydrological effects caused by vegetation evolution directed by local residents.Using two distributed hydrological model, SWAT and Topmodel, under the assistant of geographical information system (GIS), we simulate the eco-hydrological effects of vegetation change in Meijiang basin in the last two decades. The change of runoff and flux process were simulated and we expect to the results can give some suggests to the management of the river watershed. Firstly, the paper discussed the application scope of the two distributed hydrological model and the researches already done by those two models, finding that the two model are very suited for the simulation in Meijiang basin partly because of the watershed topography and partly because the affluent rainfall climate in the watershed. Then we collected the basic geography data the models need, processing in the ArcGis and other GIS software, estimating some missing climate data in other software. After that we run the models and change its parameters to get reasonable results. These parameters was collected and analyzed for latter simulations.The change of annual runoff from 1987 to 2000 caused by vegetation changing was simulated in SWAT model; the conflux speed and flux process changing form was simulated in the Topmodel. Setting two simulation scenarios for different model, we put different parameters in different years into the SWAT and put five unvaried parameters into topmodel then the simulation can exclude the climate variation and land use and land cover change in the scenarios. Results showed as follow: the annual runoff from 1987to 2000 has increased about 14%; but the flux process was changing apparently. We simulated 7 times floodwater in the basin from 1995 to 2000 from SWAT, then using Topmodel to simulating the same floodwater process,founding the trend line of flux process from Topmodel simulation and SWAT simulation have some regulate tendency. Vegetation changing in the Meijiang basin has not changed the hydrological effects ,the conflux speed and peak discharge were not like before. The reason why the runoff has increased and the conflux speed and conflux process has slowed was discussed by forest hydrology theory. Forest grew rapidly in land cover area and in its better quality, that cause runoff increased. However, at the same time the grass land was changing into other land use and land cover, the great effect of grass land on postpone to the conflux speed was lost, so the conflux speed in some time of the floodwater simulation was not as others, nevertheless its reverse. At last of the paper discussed some skills needed in using the simulation results to other parts of hydrological effects of vegetation evolution, the relation between input parameters and the simulation results and the disadvantage in data processing of the remote sensing image.