[Dynamic assessment of grassland degradation in Naqu of northern Tibet].

Based on the past years vegetation cover, annual maximal grass yield and June-September mean modified soil-adjusted vegetation index (MSAVI) that were inversely deduced from the 10-day composite data of NOAA/AVHRR channels 1 and 2 and NDVI in 1982-2000, this paper analyzed the recent 20 years dynamics of grassland desertification in Naqu of northern Tibet. The results showed that in recent 20 years, the area of degraded grassland in Naqu was averagely 43.1% of the total land area. It was decreased in the former ten years while increased in the latter ten years, but overall, had a decreasing trend. The degraded area was larger in west part of Naqu than in its other regions. Among the eight climatic factors including temperature, precipitation, potential evapotranspiration, vapor pressure, wind velocity, sunshine hour, ratio of precipitation to evapotranspiration, and ratio of temperature to precipitation, the most remarkable factor affecting the dynamic of grassland degradation was the potential evapotranspiration.