陕西榆林地区植被退化与沙漠化趋势分析

Vegetation degradation and desertification in Yulin area of Shaanxi Province

以陕西榆林地区MODIS I_(NDV)(2000—2015年)和气温降水(2000—2014年)数据为基础,结合混合像元分解模型、线性趋势法、相关系数等方法,分析了植被覆盖度变化、植被退化、沙漠化过程和气候的驱动作用.结果表明,榆林地区植被覆盖度呈显著的线性增加趋势,年递增率为2.29%,增加速率呈现出自南而北、自东向西的递减过程.植被退化以变化不明显和改善为主,占区域总面积的99%以上,重度、中度和轻度退化范围主要局限在行政中心城区及其附近区域.沙漠化过程分为两个阶段,2000—2013年重度沙漠化面积大幅减少,中度、轻度和潜在沙漠化面积缓慢减少,而非沙漠化面积大幅增加;2013年之后,非沙漠化面积减少,而重度、中度、轻度和潜在沙漠化面积增加.空间分布上,榆林西部、西南部县区是轻度以上沙漠化主要分布区域,2000—2013年该区域出现逆沙漠化过程,但2013之后又出现沙漠化趋势,应加强监测,应对其未来可能变化.榆林地区F_(VC)与气温呈负相关关系,与降水呈正相关关系,即在全球气候变暖过程中,随着气温的升高,该区域植被可能朝着恶化的方向发展,而降水的不确定性增大,又使得该区域植被在未来具有很大的波动性和不确定性.总体上,榆林地区2000—2013年植被覆盖度增加,植被退化减少,出现逆沙漠化过程,但2013年之后出现相反情况,需加强监测.

Vegetation degradation and desertification, as well as their relationship with climate change were analyzed by the index of fraction of vegetation cover（Fro）, based on MODIS /NDV （2000--2015）, temperature, and precipitation（2000--2014） data, as well as the method of mixed pixei decomposition model, linear trend analysis, and correlatio show the following. Fvc has a linear growth from the south to the north, and from the n analysis in Yulin, Shaanxi trend with the rate of 2.29 %, Province, China. The results east to the west. Vegetation which shows degradation a decreased trend is divided into 5 types, which includ improved and not significant changed accounting for 99%, and severe, moderate and mild degradation accounting for 1% which mainly distributed in urban neighbor area. Desertification is divided into2 stages, 2000--2013 and 2013--2015. In the former stage, severe desertification is decrease largely, and moderate, mild and potential desertification is also decrease slowly, while non-desertification is increase largely. In the latter stage, mild, moderate and severe desertification distributed in the west and southwest counties, where had a contrary process between the former and the latter stage. Negative correlation is between Fvc and temperature, while positive correlation between Fw and precipitation. By global climate warming, vegetation would be worsen with temperature increase and precipitation uncertainty. Overall, during 2000-2013, the area of vegetation degradation and desertification decreased, hut during 20013--2015, it showed a contrary process, which need more monitoring on vegetation change.