Driving Factor Analysis Of Wetland Evolution In Dunhuang Xihu National Nature Reserve

The wetland has a crucial value to the ecosystem in the arid inland area. The evolution of wetland connected closely with the circumjacent natural and social development. Studying the law of wetland’s evolution and analyzing the driving method are beneficial to the protection of the wetland system and social development. The peripheral area could hold a sustainable development only when the wetland keeps a certain scale. In the recent years, the wetland has been degenerated in most arid areas which was caused by both natural and anthropic factors. The global warming also aggravated the degradation of wetland. As a result, to study the contribution of each driving factor to the evolution of wetland and to judge the tendency of the wetland evolution are meaningful to both the protection of the ecosystem and the social development.In this study, based on the natural and humane driving factors and the remote sensing data, the evolution of wetland was studied. The analysis is composed of the law and tendency of wetland evolution and the contribution of each driving factor. To give an example, the wetland of Dunhuang Xihu National Nature Reserve is analyzed in the study and the main conclusions are as follows:This paper mainly puts focus on the Dunhuang Xihu National Nature Reserve in Northwest Gansu. The area of surface water distribution in not freeze-up period and years of wetland area are interpreted with the help of remote sensing images. The result of the analysis of the distribution of water area in one year reveals that the source of water of the wetland is the overflow of the spring water and there is a good relationship between the distribution of the water area and the change of the groundwater level. In the spring, because of the low temperature and evaporation intensity, the groundwater can hold a relative high level and area of the surface water is big. The evaporation gets higher and the overflow of spring water becomes less, and the area surface water changes to a small area. The groundwater upraises gradually in the autumn and the area surface water extends slowly. The study of the years’ wetland evolution shows that the wetland area decreased from 17200 hectares to 9900 hectares from 1980 to 2013. The wetland evolution has a tendency of fragmentation. And as a result of the development of the city located in the east of the wetland, the wetland also shows a trend of shift to the southwest.To analyze the influence of each factor to the wetland evolution, this study firstly analyzes the relationship between natural and humane driving factor and the wetland evolution. The result shows that among the natural factors, the increase of temperature will aggravate the degeneration of wetland. The change of the runoff doesn’t have a significant effect to it. The change of area of the glaciers will affect the groundwater recharge of wetland. The snow changes the runoff of the upstream by melting to water. The declining of groundwater level, the main natural driving factor, can intensify the deterioration of wetland. The humane factors also have a negative influence to the wetland evolution. The increase of population and GDP make the need of water resource of society larger and larger. The augment of plantation increases the extraction of groundwater of irrigation.In the natural driving factors, the change of ice and snowmelt water is very important. In this research, the relationship between glacier change and climate variation is analyzed and the result shows there is a good relationship between the glacier change and the runoff. The snowmelt runoff is modeled by the SRM model. Considering the importance of snow cover data to the model, the pi theory is used to build the function between snow cover change and climate factors. Then, the snow cover data is calculated and is used in the SRM model. The result reveals that the simulation precision increased from 0.84 to 0.92 which indicates that the PI theory can be used in the SRM model.The wetland evolution and the change of each factor are calculated by the projection pursuit model. The result of the project vector shows that the area of agriculture, ground water level, the area of glaciers and population are more important among all the factors. The result of the best projection value indicates that the wetland shrank rapidly in 25 years and degenerated seriously in 7 years from 1980 to 2013.Taking consideration of the compression of the agriculture in the future, the tendency of wetland’s evolution is also predicted by the gray model. The result shows that the wetland degeneration would become slower in the future if the plantation can decrease to 24.1 thousand hectare. The prediction shows that the wetland area will decrease to 9212 hectares and the sand and gobi zone will increase slightly.