Research on the cold-island effect with desertification process - Base on the QiTai oasis

Because of the special weather characteristic and the land surface properties, the field uniformity of the land surface in the arid area causes that the oasis is the cold source in its surroundings. It is the typical cold-island effect in oasis. But use the remote sensing means what to acquire is the land surface radiation temperature (brightness temperature). Therefore, withdraw the technique method of temperature information of thermal field in ground from the remote sensing and the research of the relation between the air temperatures with the brightness temperature, are important contents in cold-island effect research by the means of the remote sensing. The traditional temperature measurement by using the observation data from fixed stations can not reflect the land surface temperature correctly, so it is of great significance to supply the parameter of the ecological model and the climate model to recognize the interaction between the eco-system and the climate system .The remote sensing data have great capacity, strong objectivity and rich quantity. It is not seen much to make use of the remote sensing data to retrieve the ecological factors of the oasis in the arid area. This paper makes use of the thermal radiation recorded by the Band 6 of LANDSET TM/ETM in 1986, 1990, 1994, 1997, 1999and 2002 to deal with the land surface temperature in Qitai oasis and dynamically analyze the distribution characteristic and the influential factors of the surface temperature. Main conclusions are as follows: The Band 6 of TM satellite can nicely retrieve the distribution of the land surface temperature and can provide conveniences to study the thermodynamic energy in the oasis in arid area. The cold island effect is proved to exist in the oasis from the angle of remote sensing .The cold-island has an active significance to the oasis. In the arid area, the land surface thermal has a mutual relationship with the vegetation growing. The vegetation cover is influenced by several factors. The evolution process of Qitai oasis is analyzed by using the remote sensing images of 1986, 1990, 1994, 1997, 1999and 2002. It reveals that the artificial factor is the main driving force to accelerate and to slow the desert expansion. The cold island effect of the oasis is closely-related with the land surface circumstance, investigating from the open country, the region of lower planting cover, brightness temperature of its earth's surface is opposite and higher. But the city planting can reduce the thermal of the oasis obviously, living area of the city such as the down town of oasis turn down the thermal degree because of theirs planting. Present the black colors on the cold-island effect fig, because the tall tree inside the city covers obvious, opposite and peripheral farmland of the city area are still 4-6 lower with brightness temperature units. In 16 years studies, the area of cold-island effect are based on the mainly distributes in oasis, its variety scope is in accordance with the oasis set up the variety scope of the area basically. Activate the district along with the desert to expand continuously, and the desert activate the thermal field of the district also along with activate the district of the desert variety. The land surface soil moisture are asymmetry distribution, planting area and the water have higher humidity of the district than the desert or Salina area. The difference of the district of the soil degree of humidity resulted the variety precipitation in difference area, and also cause the of variety weather in oasis. Those are the key function to the oasis farm crop. In addition, because of the soil moisture affect the air humidity, and this also affect the person's living quantity level directly. The land use, the desert expansion and the environment change have close relationship. From 1986 to 2002, the desert in Qitai County expanded and the land use changed greatly. Because the desert expansion, the land use and the environment change has an interactive relationship, when we push to manage the desert, we must pay attention to harmonize the relationship among them to ensure the stability and the sustainable development of the oasis.