Increasing Variability in Precipitation Impacts Alpine Rangeland Grazing Across Tibet

Increasing precipitation variability has been tightly coupled to livestock grazing through direct impacts on vegetation productivity in rangeland ecosystems. However, where and to what extent such impacts occur has not been quantified systematically at the regional scale; thus, adaptive grazing management is plagued by this knowledge gap. Hence, using 20 years of precipitation, rangeland productivity, and livestock density data across Tibet, we assessed long-term precipitation variability impacts on alpine rangeland grazing, specifically highlighting variations in intra- and inter-annual precipitation variability. We showed that the precipitation concentration index (PCI) and coefficient of variation in precipitation (CVP) both increased significantly across Tibet over the past two decades, especially in the western region. On the contrary, grazing intensity (GI) in most rangeland areas markedly declined over the same period. Moreover, we found that GI is highly responsive to PCI and CVP for the alpine steppe, but interestingly, only PCI is significantly associated with GI for the alpine meadow. Furthermore, the Granger causality test indicates an extremely significant causality between GI and PCI, further highlighting that PCI was a remarkable determinant of rangeland grazing over the last two decades. Notably, we statistically identified rangelands with higher precipitation variability that experienced intensive livestock grazing, specifically, GI responded positively to CVP and PCI. In conclusion, our findings provide novel support for the increasing precipitation variability impacts on rangeland grazing over time across Tibet, especially the intra-annual variation. Thus, we advocate the implementation of adaptive grazing management, such as excluding and minimizing grazing for the alpine rangeland ecosystem under higher precipitation variability.