Effect of water vapor transport and budget on precipitation in the Yangtze–Huang–Huai–Hai River Basin

Study region The Yangtze−Huang−Huai−Hai River basin (3.19 million km2) in China, which is vital for China's economic development. Study focus We employed the Eulerian method to identify the primary water vapor channels from 2005 to 2020, and the water vapor net budget over the basin was calculated. Additionally, the Lagrangian method was utilized to simulate water vapor transport trajectories across four seasons, with the aim of investigating the influence of changes in water vapor on precipitation. New hydrological insights for the region Utilizing both Eulerian and Lagrangian methods, the findings indicate that: (1) Precipitation in the basin experienced a downward trend of −3.5 mm·a−1 during 2005−2020, mainly in spring (−1.4 mm·a−1) and summer (−1.7 mm·a−1); (2) The water vapor net budget has a substantial downward trend (−0.9 kg·m−1·s−1·a−1), mainly in spring (−0.4 kg·m−1·s−1·a−1) and summer (−0.3 kg·m−1·s−1·a−1), which aligns with the declining trend of precipitation. (3) The Hybrid Single Particle Lagrangian Integrated Trajectory Model demonstrates that the decrease in long−distance water vapor transport trajectories impacts the basin’s water vapor channels. The decline in spring is predominantly influenced by the water vapor transport trajectories from Asia, Europe, and Africa−Arctic Ocean (−0.7 %·a−1), while the summer is mainly driven by the water vapor transport trajectory from the Indian Ocean−South China Sea (−0.3 %·a−1). This study improves the existing understanding of the hydrological cycle in the context of the basin, and offers a crucial scientific basis for water resource management and regulation.