中国西北地区NPP变化及其对干旱的响应分析

为探究多年来中国西北地区NPP（植被净初级生产力）变化及其与干旱的关系，基于改进的MOD17A3数据，利用变化率分析、Mann-Kendall统计检验方法及GIS分析方法，对2000-2015年中国西北地区及其各省区NPP的地域分异规律及变化特征进行了研究；同时，利用PDSI（帕尔默干旱指数）与NPP数据实现了NPP对干旱的响应分析.结果表明:2000-2015年，中国西北地区NPP分布格局基本一致，整体上呈自西北向东南逐渐增加趋势，但各省区NPP的增幅不同，其中，以甘肃省的增幅最为明显，宁夏回族自治区和陕西省其次，青海省再次，新疆维吾尔自治区增幅最不明显.中国西北地区NPP增加区域主要分布于甘肃省、宁夏回族自治区南部及陕西省中北部，减少区域主要分布于新疆维吾尔自治区天山中段哈尔克山一带及陕西省中部.PDSI与NPP的相关性分析显示，中国西北地区81.71%区域的NPP与PDSI呈正相关；同时，NPP对PDSI变化响应结果显示，由于人为因素的影响，部分地区NPP与干旱程度变化呈现异向关系，说明人为因素开始成为中国西北地区NPP的重要影响因素.研究显示，2000-2015年中国西北地区NPP整体呈现增长态势，年增长速率约为0.59 g/m2，新疆维吾尔自治区天山中部及阿尔泰山一带NPP变化较为剧烈，多年NPP变化率均低于-20%；与此同时，干旱仍旧是制约中国西北地区NPP增长的主要因素. 

Change of NPP and Its Response to Drought in Northwest China

To explore the changes of NPP (vegetation net primary productivity) and its relationship with drought in northwest China from 2000 to 2015, the change rate analysis, Mann-Kendall statistical test and GIS spatial analysis methods were used to research the geographical differentiation and change characteristics of NPP based on improved MOD17A3 data. Meanwhile, the correlation between Palmer drought severity index (PDSI) and NPP was analyzed. The responses of NPP to PDSI changes were calculated spatially. The results showed that the distribution patterns of NPP in northwest China were basically consistent from 2000 to 2015 and NPP gradually increased from northwest to southeast. The NPP in northwest China showed an increasing trend overall but the increase degree of NPP was different in different provinces. The increase of NPP in Gansu Province was the highest, followed by Ningxia Hui Autonomous Region, Shaanxi Province and Qinghai Province, Xinjiang Uygur Autonomous Region was the lowest. NPP was mainly reduced in the Middle of the Tianshan Mountains, followed by central Shaanxi Province. The PDSI and NPP showed a positive correlation in 81.71% of the study area. The response of NPP to PDSI changes showed that the change trends of NPP were contrary to PDSI in some areas and revealed that human factor significantly influenced the NPP in northwest China. The annual NPP growth rate in northwest China was about 0.59 g/m². The NPP changed most severely in the central Tianshan Mountains and Altai Mountains with a change rate lower than -20%. Drought is still a main factor restricting NPP growth in northwest China.