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.人为气候变化影响区域水文循环，对淡水的可持续供给构成严峻挑战。华中水塔（Central China Water Tower, CCWT）是长江与黄河的关键源区，其径流对周边超大城市群而言不可或缺。本研究基于包含100个树轮年表的全新树木年代学网络，以及结合多种回归模型的集合平均方法，重建了可追溯至公元1595年的华中水塔径流深度序列。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、南北落基山脉、安第斯山脉）的同类径流记录进行对比后发现，华中水塔的供水稳定性最高，而青藏高原最易遭受极端径流事件的影响。21世纪的气候预估结果显示，环太平洋多数水塔区域的径流将整体呈增加趋势，而北落基山脉的径流则预计会大幅下降。本研究将环太平洋各水塔区域径流变异性与预估趋势的差异，归因于它们各自独特的地理环境与天气尺度气候条件。本研究中呈现的长期径流重建序列与预估变化，可为中国以及所有依赖山地水塔供水的区域提供自适应管理策略的参考依据。