East Asia: Water surpluses forecast to diminish in Yangtze Basin, increase in Pearl

September 19, 2016

The Big Picture
The 12-month forecast map for East Asia ending May 2017 (below) shows a complex patchwork of water anomalies. Deficits are forecast for: South Korea, and across the Yellow Sea from the Shandong Peninsula westward to the Tibetan Plateau; northeastern Inner Mongolia; eastern Yunnan into western Guangxi; and Taiwan. Water surpluses are forecast along the Yellow River and along the middle and lower reaches of the Yangtze River in China; and in Hokkaido, Japan. Both deficits and surpluses are forecast in Mongolia and western regions of China including the Tibetan Plateau.

Impacts
Musan and Hoeryong, along North Korea's far northern border with China near Russia, suffered extensive damage from flooding on the Tumen River. Heavy rainfall produced what was described as the worst flooding ever in the region and left 133 people dead, 395 missing, 107,000 homeless, 9,000 public buildings and 35,000 homes damaged, and 16,000 hectares (39,537 acres) of farmland inundated. North Hamgyong Province received up to 32cm (12.6 inches) of rain within 4 days.

In China's renowned wine region of Ningxia Helan Mountain East heavy rain and flooding along the Yellow River destroyed 133 hectares (329 acres) of vineyards with estimated damages of 225 million RMB (US$34 million).

Southwest of Ningxia, drought in Gansu Province has affected 413,000 hectares (1,020,545 acres) of farm land, primarily corn and potatoes, according to the Gansu Agricultural and Animal Husbandry Bureau, with losses estimated at 3.62 billion yuan (US$542.16 million).

Many rivers in Hokkaido, Japan overflowed their banks as rainfall swept away bridges, stranded residents on rooftops, and left three people missing. The Sorachi, Memuro, Pekerebetsu, and Nubinai Rivers were all affected, with floodwaters 60 meters deep in the town of Memuro.

Forecast Breakdown
The 3-month maps (below) show the evolving conditions in more detail. Most noticeable in the September through November map compared with the prior three months is the shrinking extent of water surpluses in the Yangtze Basin and the increase in the extent of deficits just north, from the Shandong Peninsula westward to the Tibetan Plateau. Between these, an area with both deficits and surpluses is forecast to expand, though an isolated dot near Shanghai stands out in red, indicating a forecast of extreme (20 to 40 years) deficit. Less noticeable but noteworthy, is an increase in the extent of moderate (5 to 10 years) surpluses forecast to the south, in the Pearl River Basin.

Elsewhere in the region, deficits are forecast September through November in: Taiwan, South Korea, southern North Korea, and northern Inner Mongolia. Surpluses are forecast for much of Hokkaido, Japan, and along Honshu from Tokyo north. Both deficits and surpluses are forecast throughout Mongolia.

From December through February surpluses along the Yellow, Yangtze, and Pearl Rivers will continue to shrink, as will aforementioned surpluses in Japan. Water deficits are forecast to persist in Northeast China, the Korean Peninsula, Taiwan, and a wide area from Shandong to the Tibetan Plateau. Mongolia and a vast area of western China will continue to transition to both deficits and surpluses, shown in pink and purple tones.

(It should be noted that forecast skill declines with longer lead times.)