High-Resolution Land Surface Modeling of Hydrological Changes Over the Sanjiangyuan Region in the Eastern Tibetan Plateau: 2. Impact of Climate and Land Cover Change

Known as the China Water Tower, the Sanjiangyuan region over the eastern Tibetan Plateau experienced significant hydrological changes during the past few decades, potentially affecting the security of food, energy, and water over the downstream areas. Previous studies attributed the hydrological changes to global warming or land cover change, and obtained contrary conclusions on the dominant drivers. Here we show that natural climate change is mainly responsible for most hydrological changes (except low flows) over the Sanjiangyuan region, followed by the anthropogenic climate change, while land cover contributed the least. The newly developed Conjunctive Surface-Subsurface Process version 2 land surface model that was evaluated comprehensively in the first part of this series was used to conduct a set of high-resolution simulations driven by Coupled Model Intercomparison Project phase 5 detection and attribution experiment outputs with natural or anthropogenic forcings. By using an integrated hydroclimate attribution framework, anthropogenic climate change was found to cause significant ground temperature warming and soil frozen period shortening. However, significant decreasing trends in annual mean streamflow and high flows over the Yellow River headwater region and the terrestrial water storage averaged over the Sanjiangyuan region were mainly caused by natural climate change, with contribution by 57-97%. The contributions from land cover change are less than 11%. This study suggests that adaptations are more important than mitigations for the water resource management over the Sanjiangyuan and its downstream regions, because natural climate change outweighed human-induced climate change in the headwater region.