Mediterranean rapid warming drives abrupt runoff decline in South China around 2002

South China is located in humid region. Decadal Abrupt Changes (DACs) in regional hydroclimate significantly impact water resources and ecosystem stability. This study investigated a pronounced DAC in summer runoff over South China around 2002 with moving t-test technique, characterized by an abrupt transition to reduced runoff. We explored the teleconnection mechanisms linking this hydrological shift with concurrent Mediterranean Sea surface temperature (SST) rapid warming using comprehensive observational analysis, Random Forest model, and the SPEEDY-Vegas coupled model, supplemented by 16 Atmospheric Model Intercomparison Project (AMIP) model validations. Results revealed a significant summer runoff decreased DAC around 2002 across the region. Concurrent Mediterranean SST exhibited a warming DAC, demonstrating a latent temporal synchronization. Random Forest analysis identified precipitation changes as the primary driver. The SPEEDY-Vegas model experiments successfully reproduced the observed runoff DAC when forced with realistic Mediterranean SST warming patterns. Both model and observational results revealed the physical mechanism: Mediterranean warming triggers an eastward-propagating atmospheric wave train that establishes an anomalous high-pressure system over East Asia, inducing regional moisture divergence and enhanced surface drying. AMIP model ensemble (16 models) further confirmed this teleconnection pathway. This circulation anomaly ultimately drives a reduction in regional moisture convergence, explaining the observed runoff decline. These findings demonstrate a teleconnection pathway through which Mediterranean warming modulates East Asian decadal hydroclimate via atmospheric wave dynamics and land-atmosphere feedbacks. • A decline Decadal Abrupt Change (DAC) in summer runoff occurred over South China around 2002, mainly driven by precipitation. • Concurrent Mediterranean Sea Surface Temperature (SST) DAC triggers the local atmospheric pattern shifts. • Numerical experiment shows Mediterranean warming triggers a wave train establishing anomalous high-pressure over East Asia.