西南地区干旱时空变化及对植被NPP的影响

Spatio-Temporal Variations of Drought and Its Impact on Vegetation NPP in Southwest China

摘要:

利用气温、降水、归一化植被指数（NDVI）和净初级生产力（NPP）数据，通过计算温度条件指数（TCI）、植被状态指数（VCI）、植被健康指数（VHI）三种干旱指数，采用Theil-Sen中值趋势分析和Mann-Kendall检验方法，研究西南地区云南、贵州、广西三省1961—2023年干旱的时空变化特征，探究NPP与各干旱之间的关系，以及干旱和NPP变化的诱因。结果显示：（1）三种干旱指数TCI、VCI、VHI均呈现不同程度的上升趋势，尽管不同指数评价的区域干旱存在差异，但都表明在研究时期干旱逐渐缓解。（2）1982—2018年三省NPP整体水平为885.4 gC?m-2?a-1，整体增长趋势为2.053 gC?m-2?a-1，不同省份差异较大；NPP与TCI、VCI、VHI的响应表明，它们之间均有显著的相关性，其中VCI与NPP的相关性最好（r=0.687，p<0.01），表明VCI在指示干旱和反映NPP变化方面有较好效果。（3）综合相关分析和小波分析结果表明，区域干旱缓解是NPP增长的重要驱动因素；季风通过调节水汽输送过程，促进干旱逐步缓解。

Abstract:

Using temperature, precipitation, Normalized Difference Vegetation Index (NDVI) and Net Primary Productivity (NPP), three drought indices, namely the Temperature Condition Index (TCI), Vegetation Condition Index (VCI) and Vegetation Health Index (VHI), are calculated. The Theil-Sen median trend analysis and Mann-Kendall test methods were adopted to study the spatio-temporal variation characteristics of drought in the three provinces of Yunnan, Guizhou, and Guangxi in Southwest China from 1961 to 2023. The relationship between NPP and various droughts, as well as the causes of drought and NPP changes, were explored. The results show that: (1) The three drought indices, TCI, VCI, and VHI, all show upward trends of varying degrees. Although there are differences in the regional drought evaluated by different indices, they all show that the drought has gradually eased during the study period. (2) From 1982 to 2018, the overall NPP level in the three provinces was 885.4 gC?m-2?a-1, with an overall growth trend of 2.053 gC?m-2?a-1, and there were large differences among different provinces. The response of NPP to TCI, VCI, and VHI indicates that there are significant correlations among them. Among them, the correlation between VCI and NPP is the best (r=0.687, p<0.01), indicating that VCI has a good effect in indicating drought and reflecting NPP changes. (3) Comprehensive correlation analysis and wavelet analysis results indicate that regional drought mitigation is an important driver of NPP growth; the monsoon promotes gradual drought mitigation by regulating water vapor transport processes.