The largest lake is so dry that China is digging deep to water crops

BEIJING — With China’s largest freshwater lake reduced to just 25% of its usual size due to a severe drought, work crews are digging trenches to allow water to flow into one of the country’s key rice regions.

The dramatic decline of Lake Poyang in landlocked southeastern Jiangxi province would otherwise have shut down irrigation channels to nearby farmlands. The crews, who use excavators to dig trenches, only work after dark because of the extreme heat during the day, the official Xinhua News Agency reported.

A severe heat wave wreaks havoc in much of southern China. High temperatures have sparked mountain fires that have forced the evacuation of 1,500 people in the Southwest, and factories have been ordered to cut production as hydroelectric plants cut production during droughts. The extreme heat and drought have wilted crops and shrunken rivers, including the giant Yangtze, disrupting freight traffic.

Fed by China’s major rivers, Poyang Lake averages about 3,500 square kilometers (1,400 square miles) in peak season, but has shrunk to just 737 square kilometers (285 square miles) due to the recent drought.

As determined by the water level, the lake officially entered this year’s dry season on August 6, earlier than at any time since the start of registration in 1951. Hydrological surveys for that time are incomplete, although it appears that the lake is on or around the lowest state level in recent history.

In addition to providing water for agriculture and other uses, the lake is an important stopover for migratory birds that migrate south for the winter.

China is more used to tackling the opposite problem: seasonal rains that cause landslides and flooding every summer. Two years ago, villages and fields of rice, cotton, corn and beans around Poyang Lake were inundated after torrential rains.

This year, much of western and central China has seen days with temperatures exceeding 40 degrees Celsius (104 Fahrenheit) in heat waves that started earlier and last longer than usual.

The heat is likely linked to human-induced climate change, though scientists have yet to do the complex calculations and computer simulations to say for sure.

“The heat is certainly record-breaking, and certainly exacerbated by human-induced climate change,” said Maarten van Aalst, director of the Red Cross Red Crescent Climate Center in the Netherlands. “Drought is always a little more complex.”

The “truly mind-boggling temperatures roasting China” are linked to a stuck jet stream — the airflow that moves weather systems around the world — said Jennifer Francis, a climate scientist at the Woodwell Climate Research Center in Falmouth, Massachusetts.

She said an elongated area of ​​relatively high atmospheric pressure parked over western Russia is responsible for this year’s heatwaves from both China and Europe. In the case of China, the high pressure prevents cool air masses and precipitation from entering the area.

“When hot, dry conditions get stuck, the soil dries out and warms up more easily, further reinforcing the overhead dome,” Francis said.

In the hard-hit city of Chongqing, some shopping malls have been ordered to open only from 4 to 9 p.m. to conserve energy. Residents have sought respite in the coolness of World War II air raid shelters.

This reflects the situation in Europe and elsewhere in the Northern Hemisphere, where high temperatures negatively affect public health, food production and the environment.

———

Science writer Seth Borenstein of Associated Press in Washington, DC, contributed to this report.

———

See more of AP’s climate coverage at: