Impacts of climate change and human activities on vegetation net primary productivity in the Huanghuaihai Plain

Vegetation net primary productivity (NPP) as an important indicator reflecting the response of vegetation ecosystems to climate change has been concerned by many countries around the world for a long time. Taking the Huanghuaihai Plain as the study area, this paper uses MODIS NPP from 2001 to 2022 and climate change and land use data during the same period, and employs trend analysis, partial correlation analysis and other methods to study the temporal and spatial changes of vegetation NPP in the study area. In addition, this study uses a multiple regression residual analysis method to study the relative contribution of climate change and human activities to the change of vegetation NPP in the Huanghuai Plain and further to determine the main drivers of vegetation NPP change. The results show that: (1) The average vegetation NPP in the Huanghuaihe Plain from 2001 to 2022 showed a fluctuating growth trend overall, increasing by 5.19 gC·m^-2·a^-1 per year. At the provincial scale, the provinces with the highest vegetation NPP in order from high to low are Henan Province, Shandong Province, Hebei Province, Beijing City, and Tianjin City, indicating that the spatial distribution of vegetation NPP in the study area generally shows a south-high-north-low pattern. (2) The trend of vegetation NPP change in the Huanghuaihe Plain is mainly an increasing trend. Among them, the extremely significant increase area accounts for 44.88% of the total study area. In addition, the trend of vegetation NPP change in Henan Province is mainly characterized by insignificant change, indicating that the vegetation NPP change in Henan Province is relatively small. (3) Vegetation NPP in the Huanghuaihai Plain is positively correlated with average temperature and precipitation. The comparison study on the magnitude of the correlation coefficient, the proportion of significant and extremely significant areas of the correlation, etc., indicates that precipitation is the main climate factor affecting the NPP of vegetation in the Huanghuaihai Plain. (4) The change of vegetation NPP in the study area is mainly affected by the combined effects of climate and human activities, followed by the main effects of human activities. At the provincial scale, the increase of vegetation NPP in Beijing and Shandong is mainly due to the combined effects of climate change and human activities, with the main effect being the combined effect. The increase of vegetation NPP in Tianjin and Hebei is mainly dominated by the combined effects of climate change and human activities, followed by the dominant effect of climate change. The increase of vegetation NPP in Henan is mainly dominated by the combined effects of climate change and human activities, followed by the dominant effect of human activities. Studying the spatial and temporal evolution of vegetation NPP in the Huanghuaihai Plain and revealing its main driving force can provide data support and assist decision-making for vegetation construction management and ecological safety warning in the study area.