“Seesaw Effect” of Polar Vortex and Western Pacific Subtropical High on Cloud Water Resources over North China

Reasonable exploration and utilization of cloud water resources (CWR) provide a key approach to solve water security challenges. Using the 1° × 1° diagnostic cloud water resource dataset for China (i.e., CWR-DQ V1.0, 2000–2019), alongside the Northern Hemisphere polar vortex intensity index (NHPVI), the western Pacific subtropical high ridge position index (WPSHRP), and the ERA5 reanalysis data, this study systematically investigates the spatiotemporal evolution of CWR over the North China Region (NCR) and associated underlying dynamical mechanisms. Beyond the influence of complex mountainous terrain, a pronounced “seesaw effect” between the NHPVI and WPSHRP is found to regulate CWR variability. Correlation analysis reveals a significant synchronous negative correlation between CWR and NHPVI (−0.66), with positive correlation being the maximum when CWR leads WPSHRP by 2 months (0.58), and negative correlation being the largest when CWR lags WPSHRP by 5 months (−0.63). A stronger western Pacific subtropical high (WPSH) coupled with a weaker polar vortex (PV) in summer favors higher CWR, whereas a weaker WPSH coupled with a stronger PV in winter leads to lower CWR. The seesaw effect acts via anomalous atmospheric circulations: a stronger and northward-shifted (weaker and southward-shifted) WPSH combined with a weaker (stronger) PV induces anomalous southeasterly (northwesterly) winds over the NCR, favoring higher (lower) regional CWR. A case study in 2010 further confirms this mechanism. Collectively, PV, WPSH, wind fields, and topography shape the dynamic framework modulating CWR spatiotemporal evolution over the NCR. These findings improve the understanding of CWR variability and its driving mechanisms, and support the optimization of cloud seeding strategies to relieve regional water scarcity.