Runoff reconstructions and future projections indicate highly variable water supply from Pacific Rim water towers

Anthropogenic climate change affects regional hydrological cycles and poses significant challenges to the sustainable supply of freshwater. The Central China water tower (CCWT) is the key source region feeding the Yangtze and Yellow Rivers, and its runoff is indispensable for the surrounding mega-city clusters. Here we present a reconstruction of CCWT runoff depth back to 1595 CE, based on a new dendrochronological network including 100 tree-ring chronologies and an ensemble averaging approach that combines multiple regression models. Comparison of this reconstruction with similar records from six water tower regions along the Pacific Rim (Mongolian Plateau, Tibetan Plateau, Great Dividing Range, Southern and Northern Rocky Mountains, Andes Mountains) revealed that the CCWT provide the most stable water supply, while the Tibetan Plateau to be most susceptible to extreme runoff events. Twenty-first century projections indicate generally increasing runoff across most Pacific Rim water towers, whereas the Northern Rocky Mountains are projected to decline substantially. We attribute the differences in runoff variability and projected trends across Pacific Rim water towers to their distinct geographies and synoptic climatic conditions. The long-term runoff reconstructions and projected changes highlighted in this study provide insights for adaptive management strategies in China and all other regions relying on supply from mountain water towers.