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A severe heatwave across the basin of China's longest river, caused by a larger than usual Western Pacific subtropical high, has now lasted more than two months, slashing hydropower supplies and drying out large expanses of arable land.

A "special case" of high pressure from the West Pacific subtropical high, stretching across much of Asia, is likely to be the cause of the extreme heat, said Cai Wenju, climate researcher with CSIRO, Australia's national scientific research institute.

The heavy storms over the Yangtze River Basin are the result of a western Pacific subtropical high, a pressure system that every summer carries warm air from south to north.

This pattern, in turn, is associated with a greatly expanded subtropical high pressure system over much of the US at the moment, with the jet stream pushed well to the north.

Kottlowski continued, "The temps are not nearly as warm as they were last year, and also the upper air pattern looks slightly different... than last year, so that could have an impact as to where that subtropical high, that big high pressure area that helps guide tropical storms, sets up."