Oasis-Desert System And Its Land Surface Character

Oasis is a kind of special area adjacent to forested land. The process of oasification has improved the local environment and extended the living space of human being in arid and semiarid area. The area of desertification in the northwest of China accounting for nearly 95 percent, only 5 percent of these areas is oasis. Human activity is almost entirely concentrated in the area of oasis. Therefore whether the area of oasis will develop or decrease is important to the life of local residents. The environment which desert and oasis coexist is a complicated nonlinear system, interact with the boundary layer of the atmosphere, and further interact with the atmosphere circulation, then impact the global climate and environment. Therefore the environment which desert and oasis coexist how to develop deserves our investigation.In the thesis numerical model was used to analyze some coefficient which correlate to the maintain and develop of the oasis, The results showed that when the oasis scale becomes larger will help to maintain the oasis; when relative humidity of oasis is low, if there is sufficient soil moisture support for evaporation and transpiration, the oasis could be in a self-sustaining state; when the oasis scale becomes larger, the time required to reach quasi-steady state becomes longer, when the relative humidity of the oasis becomes greater, the time required to reach quasi-steady state becomes shorter. The data of observation is also used to analysis physical change feature of the land surface with different vegetation coverage in semi arid areas. The results showed that carbon dioxide density and sensible heat flux of Xinglong station is lower than that of SACOL station from 8:00-20:00 in July, August and September. Sensible heat flux and latent heat flux difference of SACOL station is much greater than Xinglong station in July. Latent heat flux of SACOL station decreasing in July 2007,2008 and 2009. The near surface temperature trends is opposite to water vapor density trends and carbon dioxide density trends. The change of near surface air temperature is more slowly than near-surface (2 cm soil depth) temperature. Soil temperature increases during the day, when the soil depth becomes deeper, the faster rise in temperature. Soil temperature decreases during the night, the fastest decline in near-surface temperature.