The Eastern China flood of June 2015 and its causes

Two record-breaking rainfalls in late June of 2015 led to widespread flooding in Eastern China, especially over the Yangtze River Delta, and this in turn led to huge economic losses. Analysis suggests that the El Nino-like sea surface temperature pattern during that month facilitated an intensified and southwestward-shifted western Pacific subtropical high and enhanced water vapor convergence along the Meiyu front, which provided a favorable environment for the occurrence of heavy rainfall over Eastern China. Meanwhile, two midlatitude troughs were successively formed over East Asia in the second half of the month as a consequence of the downstream energy dispersions of two midlatitude blockings. These configurations facilitated the southward intrusion of the extratropical high potential vorticity toward the Meiyu front. In this way, the ascent was enhanced along the Meiyu front over Eastern China, and the occurrence of heavy rainfalls was triggered. Moreover, a tropical intraseasonal active convection propagated northward and also contributed constructively to the heavy rainfall.