陕北黄土高原丘陵沟壑区植被覆盖变化及其对气候的响应

Vegetation Change and Its Response to Climate in the Hill and Ravine Region of the Loess Plateau in Northern Shaanxi

利用1982～2007年GIMMS、SPOTVEGETATION两种NDVI数据集和气候资料对陕北黄土高原丘陵沟壑区植被覆盖变化趋势及其与气候的关系进行了分析,结果显示:(1)近26年来该区的植被覆盖总体上处于上升趋势,大致经历了3个阶段:1982～1998年植被覆盖在波动中缓慢增加,1999～2001年植被覆盖处于一个相对的低谷,2003～2007年植被覆盖快速增加.(2)四季植被活动增强,以秋季NDVI增加最为显著;NDVI的年平均标准差在波动中逐年减小,高覆盖植被面积所占的比例在增加,植被覆盖状况趋于转好.(3)研究区内14个县(区)年平均NDVI线性倾向值都为正值,说明植被覆盖都在增加,但增加的显著性和幅度不同.(4)近26年来陕北黄土高原丘陵沟壑区年平均温度呈极显著(P<0.001)的上升趋势,年降水量具有减少的趋势;春季NDVI与温度之间存在着明显(P<0.10)正相关关系,夏季NDVI与温度之间存在着显著(P<0.05)负相关关系;夏季NDVI与降水量之间存在着极显著(P<0.01)正相关关系,同时夏季NDVI与春季降水量之间存在着显著(P<0.05)正相关关系,且夏季各月降水量对植被覆盖的影响具有滞后效应.研究表明,春季升温和退耕还林(草)生态建设工程是植被增加的主要原因,夏季水分状况是该区植被生长的制约因素.

The hill and ravine region of the Loess Plateau in Northern Shaanxi is the worst area of water and soil conservation in China. Vegetation plays a very important role to hold water and soil in this region. Inter-annual variation of vegetation coverage and its relationship with climate in the region between 1982 and 2007 were examined by using the monthly GIMMS （Global Inventory Modeling and Mapping Studies） and SPOT VEGETATION NDVI （Normalized Difference Vegetation Index） data and local meteorological records. Vegetation coverage of the region was generally improved in the past 26 years but with substantial variations,which had three phases that NDVI was （1） tardily increasing in 1982-1998, （2） relative lowest values in 1999 - 2001, and （3） rapidly increasing 2003-2007. All seasons NDVI was increasing,and autumn NDVI increase was the most remarkable. Standard deviation of NDVI decreased year after year. Area of lower vegetation coverage decreased in contrast to the increase of higher vegetation coverage area. The annual temperature had a notable increase trend,and the annual precipitation had a decrease trend in the last 26 years. The spring NDVI showed positive correlation with the spring temperature. However, there was a significant negative correlation between the summer NDVI and summer temperature. The summer NDVI showed positive correlation with the summer and spring precipitation. The monthly precipitation was of deferred effect on monthly NDVI in summer. This implies that summer temperature increase and the project of replace farmland with meadow and forest were the main reason of increasing vegetation coverage. Summer water condition was the restrictive factor of vegetation. ~