NDVI-indicated decline in desertification in China in the past two decades

In this study, we explore the trend in desertification in China from 1982 to 1999 by investigating the changes in area and normalized difference vegetation index (NDVI) of arid and semiarid regions, using NDVI time series data sets and climatic variables. We use Thornthwaite moisture index (I-m) to define the arid and semiarid region as I-m <= -40 and -40 < I-m <= -20, respectively. Rainy season NDVI (May to October NDVI) increased in most areas of arid and semiarid regions over the past two decades, accounting for 72.3% and 88.2% of total area of arid and semiarid regions, respectively. Compared to that in the early 1980s, the area of arid and semiarid regions decreased by 23 x 10(4) km(2) (6.9%) and 7 x 10(4) km(2) (7.9%) by the end of the 1990s, suggesting a reversal of desertification processes in these two climate regions. Transformation from warm-arid to warm-wet climate and weakened disturbance from human activities may be the major causes of this declined trend.