East Asia: Water surplus will persist in Yellow, Yangtze, & NE China

21 November 2020

THE BIG PICTURE
The 12-month forecast for East Asia through July 2021 indicates widespread, intense surpluses in the Yellow (Huang He) and Yangtze River Basins. Conditions will include exceptional anomalies in Gansu and much of the Ordos Loop in the Yellow River Basin, and severe to extreme surpluses in the lower and middle areas of the basin.

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In the Yangtze region, exceptional surpluses will dominate much of the path of the river itself and many regions in the river’s upper basin, dipping south into the Pearl River Basin between the Hongshui and Rong tributaries. Between the Yellow and the Yangtze, moderate to extreme surpluses are expected.

Northeast China can expect widespread extreme to exceptional surpluses, and surpluses are expected on the Liaodong Peninsula in the northern Bohai Sea reaching well into Liaoning Province.

In southern and southeastern China, nearly normal conditions are forecast but intense deficits are expected in coastal Fujian and Taiwan, and moderate deficits in northern Guangdong. Southern Guangdong can expect intense surpluses as can nearby Hainan. Surpluses are also forecast in Yunnan.

In Tibet (Xizang), intense deficits are forecast in the west, and surpluses or transitional conditions in the remainder of its extent. In China’s vast northwest, surpluses are expected in northern Xinjiang Province, intense deficits and transitional conditions in the Taklimakan Desert, and moderate to severe deficits in the northeastern region of the province leading to exceptional deficits in northern Gansu.

Moderate deficits are forecast in the south-central region of Mongolia, reaching greater intensity in the center. Surpluses are forecast in the nation’s eastern and western thirds. Intense surpluses and transitional conditions are expected in North Korea, and moderate surpluses along with transitions in South Korea.

In Japan, deficits are predicted for Hokkaido and pockets of central and southern Honshu and Shikoku. Moderate surpluses are forecast for Kyushu.

FORECAST BREAKDOWN
The 3-month time series maps below show the evolving conditions in more detail.

The forecast through January 2021 indicates that surpluses will remain widespread in the Yellow and Yangtze River Watersheds. However, the overall extent of exceptional anomalies will shrink somewhat, as will the extent of anomalies south of the Yangtze. Exceptional surpluses will persist between the Hongshui and Rong Rivers, tributaries of the Pearl River in the south. Surpluses will remain widespread and intense in Northeast China and will increase in southern China in Guangxi, coastal Guangdong, and Hainan. Deficits will increase in northwestern China in Xinjiang and northern Gansu, and also in coastal southeastern China, and will intensify in Taiwan. Deficits will increase substantially in southern Mongolia though many areas will be in transition. On the Korean Peninsula, surpluses will persist in the north, remaining intense as areas of transition increase. Transitional conditions are forecast in the south. Surpluses will retreat from Japan, and many pockets of moderate deficit are forecast.

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From February through April 2021, surpluses in the Yellow River Watershed will downgrade slightly and will shrink and downgrade in the Yangtze region, retreating from the Lower Yangtze Basin. In China’s Northeast, however, surpluses will remain widespread and intense though the extent of exceptional anomalies will shrink slightly. Deficits will downgrade in Xinjiang and northern Gansu, becoming mild overall. Moderate deficits will increase in coastal southeastern China and deficits in Taiwan will downgrade, becoming moderate. Deficits are expected to emerge in South Korea while surpluses in North Korea shrink and moderate. In Japan, moderate deficits will persist, intensifying in some small pockets of Honshu. Surpluses will increase in Hokkaido as deficits shrink.

The forecast for the final three months – May through July 2021 – indicates normal conditions in many parts of the region with intense surpluses in the Yellow River Watershed through the base of the Ordos Loop, and in Northeast China. Moderate surpluses are forecast in Yunnan, and surpluses of greater intensity in western Tibet. Deficits are forecast in Fujian, eastern Tibet, and northwestern China.

Please note that WSIM forecast skill declines with longer lead times.

IMPACTS
Through September, 21 large-scale floods have washed over China this year, the most in nearly 25 years. Torrential rainfall driven by a series of typhoons flattened corn crops in Northeast China’s Heilongjiang Province, leading commodity experts to predict a 20 percent drop in the region’s corn output this year compared to last. Heilongjiang leads China in corn output, contributing 15 percent to the nation’s total.

Water levels in Taiwan’s largest reservoir, Zengwen Reservoir, are at just 23 percent of capacity as of mid-November, compared to 77 percent at this time last year. Reservoirs in central and southern areas are at one-third capacity. To conserved diminished supplies, authorities have reduced or cut off allocations for the second rice crop, reserving it for household or industrial use. Land-based cloud-seeding efforts have also been attempted to alleviate drought conditions.

Warm temperatures and low snowfall in Japan during early 2020 created conditions leading to low SWE, snow water equivalent, in many areas of the country, according to one recent study. The study points to the possibility of future conditions of even lower SWE if high temperatures and reduced snowfall occur simultaneously.

NOTE ON ADMINISTRATIVE BOUNDARIES
There are numerous regions around the world where country borders are contested. ISciences depicts country boundaries on these maps solely to provide some geographic context. The boundaries are nominal, not legal, descriptions of each entity. The use of these boundaries does not imply any judgement on the legal status of any territory, or any endorsement or acceptance of disputed boundaries on the part of ISciences or our data providers.

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