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.

人为气候变化会扰动区域水文循环，对淡水可持续供给带来显著挑战。华中水塔（Central China water tower, CCWT）是长江与黄河的关键补给源区，其径流对周边特大城市群不可或缺。本研究依托包含100条树轮年表（tree-ring chronologies）的全新树轮年代学网络（dendrochronological network），结合多元回归模型（multiple regression models）集合平均方法（ensemble averaging approach），重建了公元1595年以来的华中水塔径流深度（runoff depth）序列。将该重建序列与环太平洋沿岸6个水塔区域（蒙古高原、青藏高原、大分水岭山脉、南北落基山脉、安第斯山脉）的同类径流记录对比后发现，华中水塔的供水稳定性最优，而青藏高原最易受到极端径流事件的影响。21世纪径流预估结果显示，多数环太平洋水塔的径流总体呈增加趋势，而北落基山脉的径流预计将大幅下降。研究团队将环太平洋各水塔间径流变率与预估趋势的差异，归因于其各自独特的地理环境与天气气候条件。本研究提出的长期径流重建成果与预估变化，可为中国及所有依赖山地水塔供水的地区制定适应性管理策略提供科学参考。