2000—2019年中国西北地区植被覆盖变化及其影响因子

中国西北地区土地荒漠化问题严重，生态环境脆弱。厘清该地区植被覆盖时空变化特征及影响因子，对生态环境保护具有重要意义。基于MOD13A3数据，通过最大值合成法处理获得2000—2019年归一化差值植被指数（Normalized Difference Vegetation Index，NDVI）时序数据，采用趋势分析、Hurst指数法及地理探测器对研究区植被覆盖的时空变化特征及影响因子进行分析。结果表明：（1）2000—2019年，研究区植被覆盖整体呈增长趋势，NDVI年增长速率为0.0027（P<0.05），均值为0.252。空间分区年增长速率有差异，黄河流域片区（0.0062）>半干旱草原片区（0.0026）>内陆干旱片区（0.0018）。（2）研究区植被覆盖呈增长趋势的面积占55.77%，退化区域占3.76%，增长的土地利用类型以耕、林、草地为主。植被覆盖变化趋势具有持续性的区域面积占总面积的31.87%，其中持续性改善面积（17.04%）大于持续性退化面积（1.27%），黄河流域片区增长情况及持续性增长情况最优。（3）影响植被覆盖空间分布的主要因子按影响力依次为降水、气温、日照、相对湿度，但对各分区的影响程度略有差异。黄河流域片区、内陆干旱片区空间分布受降水影响最大，半干旱草原区受日照影响最大。（4）研究区植被覆盖变化以自然因子与人类活动共同驱动为主，自然因子对植被生长的促进作用大于人类活动，且自然因子对植被覆盖变化的贡献率更高。本研究结果可为评估气候变化背景下西北地区生态环境变化提供参考。

Vegetation coverage change and its influencing factors across the northwest region of China during 2000-2019

The problem of land desertification in northwest region of China is serious and the ecological environment is severe. It is of great significance to clarify the spatio-temporal variation characteristics and driving factors of vegetation cover in this area for ecological environment protection. In this study， MOD13A3 products in this area were used as the data source to obtain the NDVI sequence set from 2000 to 2019 through the maximum value synthesis method. Trend analysis， anomaly analysis， Hurst index， geographic detector， correlation analysis and residue analysis were used to analyze the spatiotemporal variation characteristics and impact factors of vegetation cover in the study area. The results showed that ：（1） In recent 20 years， the vegetation coverage in the study area showed an overall growth trend， with an increase rate of 0.0027·a^-1 and an average NDVI of 0.252. However， the growth rate of the Yellow River basin area （0.0062·a^-1） is higher than that of the semi-arid grassland area （0.0026·a^-1） and inland arid area （0.0018·a^-1）. （2） The vegetation coverage in the study area is on the rise， accounting for 55.77% of the total area， while the degraded area accounts for 3.76% of the total area. The increased land use types were mainly tillage， forest and grassland. The area with sustainable change trend of vegetation cover accounted for 31.87% of the total area， the sustainable improvement （17.04%） was greater than the sustainable degradation （1.27%）， and the growth and sustainable growth of the Yellow River basin area were the best. （3） The main contributing factors that affect the spatial distribution of vegetation cover are precipitation， temperature， sunshine and relative humidity in order of influence， but the influence degree of each sub-region is slightly different. The spatial distribution of arid areas in the Yellow River basin and inland is most affected by precipitation， and the semi-arid grassland is most affected by sunshine. （4） Vegetation cover changes is mainly driven by natural factors and human activities， and natural factors on the growth of vegetation role in promoting are greater than human activity， and natural factors on vegetation cover change in the rate of contribution are higher. The results of this study can provide reference for assessing the ecological environment change under the background of climate change in northwest China.