The importance of permafrost in the steady and fast increase in net primary production of the grassland on the Qinghai–Tibet Plateau

•We selected Tibetan Plateau to examine net primary production during 2000–2018.•The NPP in permafrost region had a steadier and faster increasing rate.•Soil water and temperature were the main reasons for NPP changes.•The NPP values will show greater interannual changes in the future. Permafrost affects soil water and soil temperature regimes; however, its effects on net primary production (NPP) remain unknown. Here, we examined temporal-spatial changes in grassland NPP during 2000–2018 in permafrost and permafrost-free areas on the Qinghai–Tibetan Plateau using the random forest (RF) and radial basis function artificial neural network (RBF-ANN). Our results indicated that the areas that showed increasing, decreasing, and non-significant trends for NPP accounted for 13.88%, 1.90%, and 84.22% of the permafrost area, respectively. For the permafrost-free areas, these NPP trends accounted for 22.25%, 2.68%, and 75.07% of the permafrost-free area, respectively. The mean NPP in the permafrost regions showed a faster and steadier (1.520 g C/m2/yr, p