East Asia: Yangtze water surpluses will retreat

26 May 2020

THE BIG PICTURE
The 12-month forecast for East Asia through January 2021 indicates surpluses in the Pearl River Basin (Zhujiang River) in South China that will be severe to exceptional in Hunan near the border with Guangxi.

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Widespread surpluses of varying intensity are forecast in the upper portion of the Yellow River Basin (Huang River). Severe surpluses will follow the path of the Tongtian River as it flows south from Qinghai through the western border of Sichuan. Surpluses will be exceptional in western Tibet (Xizang) and along much of the Yarlung River (Brahmaputra River). Northeast China can also expect some pockets of surplus varying in intensity and some pockets of moderate deficit in far northern Inner Mongolia.

Exceptional deficits will form a vast band across much of the breadth of Xinjiang in western China beginning in the Taklimakan Desert and connecting to deficits of equal intensity in western Inner Mongolia, continuing well into Mongolia. Some conditions of both deficit and surplus (pink/purple) are also expected in Xinjiang as transitions occur.

On the Korean Peninsula, a few scattered, small pockets of deficit are forecast in North Korea, including moderate anomalies around Pyongyang. In Japan, moderate deficits are forecast in southeastern Honshu from Osaka reaching almost to Tokyo.

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

The forecast through July indicates that surpluses in the Yangtze River Basin will retreat as conditions return to normal. Severe surpluses will persist along the path of the Lower Yellow River and surpluses of varying intensity in the vast expanse of the river’s upper watershed. Surpluses will shrink and downgrade considerably in the Pearl River Basin leaving moderate anomalies primarily in Guangxi. Widespread surpluses in Northeast China will also shrink considerably. Extreme to exceptional surpluses will persist in western Tibet and along the Yarlung River.

ISciences_East_Asia_Composite_Adjusted_202002-202101_3mo_twitter.png

Deficits will shrink and downgrade in Mongolia, and deficits of varying intensity will persist from Xinjiang through western Inner Mongolia and will include exceptional anomalies as well as transitional conditions. Exceptional deficits in southern Yunnan will disappear and conditions in Taiwan will normalize, transitioning from moderate deficit. Nearly normal conditions are also forecast for much of the Korean Peninsula and Japan. Some moderate deficits will persist near Pyongyang and will emerge south of Seoul. Moderate to extreme deficits are expected to emerge in Hokkaido.

From August through October, conditions in many regions of East Asia will normalize though anomalies are forecast, primarily in western China. Moderate surpluses are forecast in the Upper Yellow River Basin and intense surpluses will persist in western Tibet and along the Yarlung River. Deficits will shrink and downgrade in Xinjiang and some moderate deficits will persist in western Inner Mongolia and emerge in far northeastern Inner Mongolia. Moderate to severe deficits will emerge in southern Yunnan and mild to moderate deficits from central Sichuan through western Guizhou. Moderate surpluses are expected to emerge in eastern Taiwan and along South Korea’s central east coast. In Japan, deficits will nearly disappear in Hokkaido but moderate deficits will emerge in southeastern Honshu from Osaka reaching nearly to Tokyo.

The forecast for the final three months – November through January – indicates that widespread deficits will emerge in the Lower and Middle Yangtze Basin, dipping south into the western portion of the Pearl River Basin where anomalies may be intense. Moderate deficits will emerge around the Bohai Sea, on the Korean Peninsula, and in Japan. In western China, anomalies are expected to persist in a pattern similar to the forecast for August through October with an increase in mild to moderate deficits in southern Mongolia and across the border into China.

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

IMPACTS
Pounding rains in the sprawling metropolis of Guangzhou in southern China along the Pearl River (Zhujiang River) collapsed the canopy of a large hotel after nearly ten inches fell in just 24 hours. Waist-high floodwaters swept vehicles through city streets and inundated train stations. Intense rainfall was recorded throughout the region including Dongguan, Huizhou, and Shanwei, with almost 100 stations reported daily rainfall above 200 mm (7.87 inches) and 5 reporting between 363 to 402 mm (14 to 15.8 inches).

In the nearby province of Guangxi, the local police force was called in to carry out emergency rescue operations as flooding made many roads impassable in Baise (Bose), a mining town near the border with Vietnam. In Guilin City to the northeast a printing factory flooded, trapping several workers.

In mid-May, the water level in the Gaoping River Weir serving the 2.5 million residents of Kaohsiung City in southern Taiwan dropped to its lowest level in 21 years. Authorities instituted water rationing by lowering water pressure during peak hours. Seasonal rainfall is expected to alleviate drought conditions.

Mongolia broke its all-time temperature record for April on the 30th of the month when Ekhiyn-Golhit Oasis in the Gobi Desert hit 36 degrees Celsius (96.8 degrees Fahrenheit).

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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