In response to the global warming and increase in human activities over the ecologically fragile semi-desert areas, much of attention has been given to the desertification. Examining what degree of desertification has been occurring for last three decades over the Northeast Asia, we investigate interannual variations of vegetation from NOAA/AVHRR Normalized difference vegetation index (NDVI) for the 1982-2006 period and try to relate their variations to changes in climate variables (e.g., surface temperature and precipitation).

The linear trend of NDVI variation in the last 25 years during the growing season (April-October), shows that vegetation has been decreased in the northern portion of Mongolia, Siberia, some part of the northeast China, and Manchuria. However, the decreasing trend seems not to be statistically significant although decreased vegetation can be expected by the prevailed drought conditions after the mid-1990s. On the other hand, statistically significant trend of the vegetation increase has been occurred primarily in the semi-arid region (including Inner Mongolia), some part of the northeast China, and the high latitude regions north of 50°N.

From the relationships amongst NDVI, precipitation, and surface temperature, we find that the vegetation growth in the semi-arid region appears to be more sensitive to precipitation than temperature. The high latitude region mainly appears under conditions of abundant precipitation and low temperature, in which temperature probably is a limiting factor for the vegetation growth. The results also suggest the degree of coupling between vegetation and climate over East Asia.