2001?2018年西北地区植被变化对气象干旱的响应

基于2001?2018年逐月的MODIS NDVI数据，以归一化植被指数（Normalized Difference Vegetation Index, NDVI）和植被状态指数（Vegetation Condition Index, VCI）作为植被生长状况指标，结合2001?2018年的月降水和月均温数据计算的标准化降水蒸散指数值，分析西北地区植被状况和气象干旱指数的变化趋势及其空间分布特征，以及多时间尺度下植被对气象干旱的响应。结果表明：2001?2018年西北地区植被的生长状况整体呈好转趋势，但空间分布上差异明显，东部植被改善状况高于中西部地区。近18 a西北地区5种不同时间尺度标准化降水蒸散指数（Standardized Precipitation Evapotranspiration Index，SPEI）均值整体上均呈增加趋势，表明干旱程度降低；空间上，干旱化趋势整体上表现为中西部高，东部低。植被生长状况在大部分区域均与SPEI呈现不同程度的正相关，总体表现为，西北地区东部植被对气象干旱的响应程度最高，西部次之，中部最低；不同植被类型中，草地对SPEI-12的响应最强，耕地次之，而林地的响应最弱；各植被类型在生长季的多数月份中对SPEI-3和SPEI-12的响应普遍较高。

Response of Vegetation Change to Meteorological Drought in Northwest China from 2001 to 2018

Northwest China is one of the regions with severe drought in China. Based on the monthly MODIS NDVI data from 2001 to 2018, the normal difference vegetation index NDVI and the vegetation condition index VCI were used as indicators of vegetation growth status, combined with the SPEI values calculated from the monthly precipitation and monthly mean temperature data from 2001 to 2018. Using the univariate linear regression trend analysis method and Pearson correlation coefficient to analyze the variation trend and spatial distribution characteristics of vegetation condition and meteorological drought in Northwest China, as well as the response of vegetation to meteorological drought in multiple time scales. The results showed that the growth of vegetation in Northwest China showed a trend of improvement in the period from 2001 to 2018, but the spatial distribution was significantly different. The improvement of vegetation in the eastern region was higher than that in the central and western regions. The average SPEI of the five different time scales in Northwest China all showed an overall increase trend in the past 18 years, indicating that the degree of drought decreased. In space, the overall trend of aridification was higher in the central and western regions and lower in the east. The vegetation growth status was positively correlated with SPEI in most areas. The overall performance showed that the vegetation in the eastern part of the Northwest China had the highest response to meteorological drought, followed by the western part and the middle part. Among the different vegetation types, the sensitivity of grassland to SPEI-12 was the strongest, followed by arable land, while the response of forest land was slower; the response of each vegetation type to SPEI-3 and SPEI-12 was generally higher in most months of the growing season.