Long-term Change in Summer Water Vapor Transport over South China in Recent Decades

Abstract

This article investigated the long-term variation of the boreal summer (JJA) moisture circulation over South China (SC). The total precipitable water (TPW) and moisture convergence over SC have increased obviously, such trend is not a local phenomenon, but the result of large-scale circulation anomaly. In the past few decades, the water vapor transport from southern hemisphere and subtropical western Pacific is strengthened, while the northward transport over East Asia is weakened, leading enhanced moisture convergence over the Philippines and adjacent region. The net flux of SC shows no significant shift in the end of the 1970s which is widely acknowl-edged as “climate shift”, but ascends remarkably after the early 1990s. This doesn't mean the moisture circulation over SC experiences no variation with the ''climate shift''. In fact, the relationship between total net flux with budgets of four boundaries had been modified in the end of the 1970s. The correlation of the net flux is highly negative with the budget of north boundary, and positive with the budget of west and east boundaries before 1979/80, but only highly positive with the budget of south boundary after 1979/80.
This modification is closely related to the north-south migration of western Pacific subtropical high (WPSH). Before 1979/80, the ridge of WPSH lies northward, resulting in stronger output of water vapor via the north boundary which may probably lead to the significant correlation between flux of north boundary and net flux. After 1979/80, the ridge of WPSH shifts southward, inducing stronger water vapor input through the south boundary, which is probably the causation of significant correlation between flux of south boundary and net flux.