Assessing vegetation degradation in Loess Plateau by using potential vegetation index

The potential vegetation index determined by environmental conditions especially climate is the ideal baseline for assessing vegetation degradation based on remote sensing. After eliminating irrigated areas, This paper estimated the potential vegetation index by imitating upper borderline of scatter spots in the coordinates space of climate aridity index and remote sensing vegetation index. Then we assessed the vegetation degradation through comparing actual vegetation index with potential vegetation index. The climate aridity index is expressed by the ratio of Holdridge’s potential evapotranspiration and precipitation. The average value of SPOT VGT NDVI on July to September for many years is choosed as the vegetation index. As a result, potential vegetation index tends to saturation when aridity index is below 0.8. When aridity index is over 0.8, we can simulate potential vegetation index by a general index function. The degree of vegetation degradation takes on prominent spatial difference. On the whole, it is the most severe in the middle and the east of Gansu province and the south of Ningxia autonomous region.