干旱对华北地区植被变化的影响

Drought impacts on vegetation changes in North China

利用中分辨率成像光谱仪(moderate-resolution imaging spectroradiometer,MODIS)归一化植被指数(normalized difference vegetation index,NDVI)数据产品和气象站点的帕尔默干旱指数(the palmer drought severity index,PDSI)数据,分析了2001—2013年华北地区及3个主要地表覆盖类型区植被变化的时空特征和干旱的变化特征,并以不同时间尺度分析了干旱对植被变化的影响.结果表明:1)华北地区植被NDVI空间分布差异较大,NDVI总体上呈东南高、西北低的分布特点.2001—2013年,华北地区植被活动呈增强的趋势,其中秋季植被活动的增强趋势最明显.2)2001—2013年,华北地区的干旱总体上有所减轻,其中秋季干旱减轻的趋势最明显.3)华北地区植被年际变化与干旱有显著的正相关关系,干旱对植被生长状态有较大影响.北部草原区和中部落叶阔叶林带的植被年际变化与干旱的正相关性显著;而南部农作物区不显著,干旱对农作物生长状态影响较不明显.4)在季节尺度上,华北地区夏季植被变化与干旱的正相关性最为显著,夏季植被生长状态最容易受到干旱的影响;以16d的植被数据分析表明,NDVI距平值更适合表征华北地区植被生长状态与干旱的关系.

The 13-year（2001-2013）time series of Moderate-resolution Imaging Spectroradiometer（MODIS）Normalized Difference Vegetation Index（NDVI）products and the Palmer Drought Severity Index（PDSI）calculated from meteorological station data were used to analyze spatial-temporal variations in NDVI,evolution characteristics of PDSI in North China and in three kinds of major land type areas.The multi-scale correlation between NDVI and PDSI was also calculated to explore drought impacts on vegetation changes.It was found that NDVI varied in different areas,with higher NDVI in southeast and center compared to northwest.From 2001-2013,vegetation activities in North China showed an increasing trend,and the increasing trend was most significant in the autumn.The annual average PDSI showed an increasing trend,especially in the autumn.There was a significant positive correlation between annual variation of vegetation and drought,and droughts had a strong influence on vegetation growth.Seasonally,apositive correlation between variation of vegetation and drought was the most significant in the summer.Vegetation growth was the most susceptible to drought in summer.Analysis of 16-day data showed that NDVI anomaly was more suitable than NDVI to characterize relationship between vegetation growth and drought in North China.