干旱区生态环境知识资源中心

Several sandstorms invading the capital of China in recent years cause many concerns to the issues of grassland ecosystem degradation in arid and semiarid grassland region of north China. Actually the degradation can be viewed as the decrease of primary productivity in the grassland. This provides the possibility to monitoring the degradation using satellite remote sensing technology. In the study we present our experiences in conducting the monitoring of grassland ecosystem degradation in north China. Using the EOS/MODIS data, we develop an applicable method for the monitoring on the basis of net primary productivity (NPP). We assume that there is always a turf without degradation in the area of the same hydrothermal condition and type of grassland. We then use the NPP of the turf to determine the level of degradation in this area. The grassland region in north China can be divided into a number of small sub-regions for the determination and the division of sub-regions can be done according to the types of grassland. As far as every sub-region is concerned, we take the max NPP as the base line to determine the degradation of other pixels in the sub-region. The degradation can be graded into five levels: serious degradation, high degradation, medium degradation, light degradation and non-degradation. Finally we apply the method to analyze the spatial characteristics of grassland degradation in north China in the year 2005. The results show that the situation of grassland degradation in north China is very serious. 95.57% of the grassland in north China has suffered from deterioration to various levels, among which serious degradation, high degradation, medium degradation and light degradation account for 41.06%, 33.52%, 11.72% and 9.28% of the total, respectively.