The origins and physical drivers of moisture transport anomalies during monsoon season droughts in the Yangtze River Valley

Abstract

The Yangtze River Valley (YRV) experienced four monsoon season droughts (MSDs) that occurred in the monsoon season, i.e., July–September) from 1950 to 2022, causing severe losses to the society and economy. However, the sources and physical drivers of moisture deficits linked to these MSDs are unclear. Using a land-atmosphere water balance framework, we found that the atmospheric moisture deficits over the YRV during MSDs stem from reduced precipitation and elevated evapotranspiration, with the reduction in the precipitation component contributed by advected moisture explaining 92.7% of the total precipitation decrease. From a Lagrangian perspective, moisture deficits over the YRV during MSDs mainly arise from weakened moisture supply along the moisture transport channels from the northern Indian Ocean, the South China Sea, and the northwestern Pacific Ocean, with event-specific moisture source regions and anomalous circulation patterns governing the deficits. The decreased moisture transport to YRV is dominated by the atmospheric dynamic process associated with the wind changes (86.5% of moisture deficits), especially for the wind divergence process (68.7%). This dynamic-linked moisture transport decreases with –0.24×10 −5 kg·m −2 ·s −1 per decade during 1950–2022, suggesting a rising occurrence risk of MSDs. This calls for proactive management to address potential drought risks and ensure sustainable water resources during the monsoon season in YRV.