Abstract: Climate change and human activities are two driving factors that have vital influence on vegetation growth capacity. Quantitative assessment of the relative impact of climate change and human activities on net primary productivity (NPP) in Beijing-Tianjin-Hebei (BTH) can significantly improve the understanding of driving mechanism and help the improvement of ecological environment. Based on NPP data derived from Carnegie-Ames-Stanford Approach (CASA) model and meteorological data from 2001 to 2020, the relative contributions of climate change and human activities to NPP in BTH were quantitatively assessed by the methods of trend analysis and “detrended regression residuals methods”. The results showed that: (1) 47.8% of total area in BTH exhibited significant restoration, while only 4.5% underwent significant degradation. The annual NPP in developed urban agglomeration except Beijing decreased faster compared with other regions, while the middle of Zhangjiakou was the area with the fastest increase in annual NPP. (2) The climate change and human activities drove the NPP variation jointly as important forces in BTH and both induced a rapid increasing trend in the most areas. The spatial average influence of climate change on NPP variability was 1.5gC·m−2·y−1, while the impact of human activities was 2.4gC·m−2·y−1. (3) The contributions of climate and human activities accounted for 25.8% and 74.2% respectively to the significant increase of NPP in BTH in the past 20 years. The regions where the contribution rates of climate change were more than 80%, were mainly distributed in the northwest of Zhangjiakou and east of Cangzhou which covered 1.3% of the total areas. While there were 22.1% regions of BTH where the contributions of human activities were over 80% in the southwest of Zhangjiakou, Chengde, the south of Cangzhou and Hengshui. (4) The significant degeneration of vegetation was mainly induced by human activities whose contribution rats reached 94.9%. The results indicate that the human activities should be more focused on the ecological construction of vegetation restoration in BTH.

Key words: NPP, Climate change, Human activities, Detrended regression residuals methods, Beijing-Tianjin- Hebei