Impacts of climate change and human activities on net primary productivity of vegetation in Ningxia, Northwest China.

This study aimed to quantitatively distinguish the contributions of climate change and human activities to net primary productivity (NPP). Based on meteorological observation data from 27 ground-based meteorological observation stations in Ningxia from 2000 to 2022 and Moderate Resolution Imaging Spectroradiometer (MODIS) data, we examined the spatiotemporal variations of potential net primary productivity (PNPP), actual net primary productivity (ANPP), and human-induced net primary productivity change (HNPP). The Thornthwaite Memorial model and the improved Carnegie-Ames-Stanford Approach (CASA) model, as well as Theil-Sen slope estimation, Mann-Kendall trend test, Hurst index, and partial correlation analysis were used. We quantitatively evaluated the relative effects of climate change and human activities on NPP by the residual method. From 2000 to 2022, both PNPP and ANPP in Ningxia exhibited increasing trends, with annual growth rates of 4.27 and 6.60 g C·m·a, respectively, while HNPP showed a fluctuating decreasing trend, with a reduction rate of 2.33 g C·m·a. Areas with increasing PNPP accounted for 94.4% of the study area, while the area with increasing ANPP covered 92.8%. Declining PNPP was primarily observed in the southeastern part of Shizuishan and the southern part of Yinchuan. The areas experiencing a decrease in ANPP were mainly distributed along the Yellow River. 66.5% area of Ningxia displayed a downtrend in HNPP, and human activities in most regions in the future. Precipitation was the dominant meteorological factor influencing ANPP variation, with 74.4% area of the region showing a significantly positive correlation between ANPP and annual precipitation. The influence of precipitation was greater than that of mean temperature, sunshine duration, and mean wind speed. The average relative contributions of climate change and human activities to NPP were 46.3% and 53.4%, respectively. In 62.1% of the total area, vegetation improvement was primarily driven by the combined effects of climate change and human activities, while 26.1% of the area experienced vegetation improvement mainly due to climate change. Vegetation degradation accounted for 7.2% of the total area, mainly driven by human activities or the combined effects of climate change and human activities. These findings would help reveal the mechanisms underlying the impacts of climate change and human activities on NPP, and thus offer scientific support for regional ecological construction and policy-making.