“Seesaw Effect” of Northern Hemisphere Polar Vortex and Western Pacific Subtropical High on Cloud Water Resources in the North China Region

Reasonable exploration and utilization of cloud water resources (CWR) offer a key approach to addressing water security challenges. Using the 1° diagnostic cloud water resource dataset for China (CWR-DQ V1.0, 2000-2019) together with the Northern Hemisphere Polar Vortex Intensity Index (NHPVI), the Western Pacific Subtropical High Ridge Position Index (WPSHRP), and ERA5 reanalysis data, this study systematically investigates the spatiotemporal evolution of CWR over the North China Region (NCR) and its underlying dynamical mechanisms. Beyond the influence of complex mountainous terrain, a pronounced “seesaw effect” between the NHPVI and WPSHRP is found to regulate the spatiotemporal variability of CWR in this region. Correlation analysis reveals a strong synchronous negative correlation between CWR and NHPVI (-0.66), while the strongest positive correlation occurring when CWR leads by 2 months (0.58) and the strongest negative correlation when CWR lags by 5 months (-0.63). This seesaw pattern features a stronger WPSH coupled with a weaker PV in summer, favoring increased CWR, whereas the opposite configuration prevails in winter. The seesaw effect modulates CWR primarily through anomalous circulation: stronger and northward-shifted (weaker and southward-shifted) WPSH combined with a weaker (stronger) PV induces anomalous southeasterly (northwesterly) winds over NCR, favoring increased (decreased) regional CWR. A case study for 2010 further confirms this seesaw effect. Collectively, PV, WPSH, wind fields, and topography shape the dynamic framework modulating CWR spatiotemporal evolution in NCR. These findings advance the understanding of CWR variability and its driving mechanisms, offering scientific support for optimizing cloud seeding strategies to mitigate regional water scarcity.