1981-2001年中国西北干旱区NDVI变化分析

Change of NDVI based on NOAA image in northwest arid area of China in 1981-2001

采用1981-2001年连续21年的NOAA/AVHRR的NDVI植被覆盖指数,空间分辨率为8km×8 km,时间分辨率是"准半月",分析了中国西北干旱区四个地区(新疆的南疆地区、北疆地区、甘肃内蒙古河西走廊地区和青海柴达木地区)1981-2001年连续21年的NDVI变化。结果显示:1981-2001年中国西北干旱区四个地区的NDVI虽然普遍不高(小于0.3),但是其在新疆的南、北疆处于增大的趋势,北疆1991-2001年的平均NDVI值比1981-1990年的平均值增加了2.48%,南疆的相应增幅较大为8.95%;甘肃内蒙古河西走廊地区的NDVI值年际变化不明显;青海的柴达木地区NDVI值则有减小的趋势,其1991-2001年的平均NDVI值比1981-1990年的平均值减少了2.76%。新疆植被覆盖的增加可能与大面积开荒等人为活动以及这一段时间新疆地区"增温"和"增湿"的自然气候变化有关,而青海柴达木地区植被覆盖的减少则可能存在更复杂的自然和人类活动等多方面的驱动因素。

The Change of vegetal index can reveal the evolvement of environment. Long-term quantitative analysis of vegetal distribution and change can illustrate the reason of environment change. Based on the continuous NOAA/ AVHRR data with the spatial resolution of 8 km × 8 km and the temporal resolution of half-month （ University of Maryland Global Land Cover Facility Data Distribution） between the years 1981 and 2001, by means of some image software such as ENVI 4.0, IDL6.0 and ArcGis, this paper develops the data sets of NDVI for analyzing and discussing the moving average change of annual NDVI in northwest arid area of China including the south and the north of Xinjiang, the Hexi Corridor of Gansu ＆ Inner Mongolia and the Qaidam basin of 2001 in order to find out the true reason that causes the change of environment in Qinghai continuously from 1981 to northwest arid area of China. The results are as follows： First, the whole NDVI value of 1991 -2001 in northwest arid area of China is not high（ less than 0.3 ）, but the annual NDVI value of Xinjiang is in the increasing trend. At the Hexi Corridor of Gansu ＆ Inner Mongolia, the NDVI value changes little. While at the Qaidam basin of Qinghai the NDVI value is in reducing. Second, the change of average NDVI in ten year scale is near to its annual change in northwest arid area from 1981 to 2001. Its average NDVI of 1991 -2001 is 2.48% higher than that of 1981 - 1990 in north Xinjiang and 8.95% higher than that in south Xinjiang. But its decade change is not very obvious at the Hexi Corridor of Gansu ＆ Inner Mongolia in 1981 - 2001. Synchronously there is a decreasing extent of 2.76% compared the average NDVI of 1991 -2001 with that of 1981 - 1990 at the Qaidam basin of. Qinghai. And the opening-up of wasteland by human and the ＂warming＂ ＆ ＂wetting＂ of climate contribute to the increase of NDVI value in Xinjiang. However, perhaps more intricate driving factors from both nature and human being lead to the decrease of NDVI value at the Qaidam basin of Qinghai.