The Hutuo River is one of the important rivers in Hebei Province and Shanxi Province， and it plays an important role in the economic green development and ecological environment construction along the river. Based on MOD17A3 NPP data， the spatiotemporal evolution of vegetation NPP in the Hutuo River Basin was explored using Theil-Sen Median trend analysis， the Hurst index， and the coefficient of variation. Partial correlation and complex correlation analysis were used to explore the impact of hydro-thermal factors on vegetation NPP. Land transfer matrix， zoning statistics， and other methods were used to explore the impact of underlying surface factors on vegetation NPP. The study produced several important results： ① The vegetation NPP in the Hutuo River Basin showed an overall increase trend from 2003 to 2022， but its future trend mainly changes from increase to decrease. ② The partial correlation between vegetation NPP and temperature and precipitation is mainly nonsignificant positive， with only 42.74% of the basin being significantly correlated， and the main driving force for vegetation NPP changes in the Hutuo River Basin is precipitation. ③ Vegetation NPP increases with increase of elevation and terrain position and first increases and then decreases with increase of slope. The increase rate of vegetation NPP first increases and then decreases with increase of terrain level. The higher the elevation， the smaller the fluctuation of vegetation NPP， and the impact of slope and terrain position greater than 0.5 on the fluctuation of vegetation NPP is smaller. ④ The transition between grassland and cultivated land has the greatest impact on vegetation NPP in Hutuo River Basin. The total NPP of grassland is highest in the Ⅳ levels of terrain level （elevation of 1 000-1 500 m， slope of 15°-25°， and terrain position of 1.5-2.0）， while the NPP of cultivated land is the highest at the Ⅲ level of elevation （500-1 000 m）， Ⅰ level of slope （<5°）， and Ⅱ level of terrain position （0.5-1.0）. The results of this study not only demonstrate the spatiotemporal evolution characteristics of vegetation NPP in the Hutuo River Basin in recent years but also reflect the magnitude of forces exerted by hydro-thermal factors and underlying surface factors on NPP changes， thus providing theoretical references for the ecological environment construction and future development of this basin.
Yang et al. (Mon,) studied this question.