Abstract
Substantial changes in land use and land cover dynamics have occurred during the last several decades in western China, which include deforestation, desert expansion and intensified land use due primarily to an increasing population, industrialization and agricultural development. These changes have had great impact on ecosystem functions at both local and regional scales. The Gobi Desert area near Zhangye City, Gansu Province, P.R. China has been blamed for the frequent occurrence of dust and sand storms in remote areas such as the Beijing and HuaBei regions. A study was conducted to quantify the land cover dynamics using remotely sensed images from the Landsat MSS, TM and ETM+ sensors for the region near Zhangye city within the Heihe River watershed. The regional landscape ecology for 1977, 1989 and 2002 was quantified using both traditional classification techniques as well as the continuous field method, the latter being a measure of land degradation severity. These remote sensing products were used to quantify the magnitude of the land use and land cover changes over 25 years. The results indicate that agricultural areas increased from 6% to 15% due to increased human activities. At the same time, other land use areas decreased because of conversion into agriculture lands. Land degradation in the region was obvious as evidenced by the increase in lower vegetative areas (0 to 10% fractional vegetation cover) and disappearance of high vegetative areas (90% or more). One of the most noticeable changes is that Zhangye city expanded rapidly during the last 25 years and practically doubled its urban territory.
