Poyang Lake Extremes

Poyang Lake Extremes
Poyang Lake Extremes

Poyang Lake—China’s largest freshwater lake—routinely fluctuates in size between the winter and summer seasons. Between 2019 and 2020, however, water levels went from barely there to the highest on record.

These images, acquired with the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite, show the lake at its recent extreme low and high levels. The images are false color, using a combination of infrared and visible light (MODIS bands 7-2-1). Water appears black and navy blue; vegetation is bright green; clouds are white or cyan. This band combination makes it easier to see the boundary between water and land.

The left image was acquired on December 8, 2019. Winter is a dry time of year in eastern China, and the lake typically shrinks considerably. Pools of water mixed with patches of grass form important wetland habitat for migrating birds. But the yearly low water levels have been trending even lower, and in December 2019 they were the lowest in 60 years.

Human influences on the lake’s inflow and outflow of water—landscape change, dams, and sand mining—have contributed to the lake’s decline in recent years. Water levels in winter 2019-2020 were made even worse by a drought, with little rainfall since July 2019.

In June and July 2020, the pendulum swung to the other extreme. Since early June, unusually strong, stationary weather systems have produced frequent storms and heavy rainfall across the Yangtze River Basin. The early and intense start to the rainy season caused water levels to rise so that by July 13, Poyang Lake reached 22.6 meters—its highest level on record, and surpassing the previous record of 22.52 meters reached in 1998. The second MODIS image (above right) was acquired on July 14, 2020.

Flooding has been widespread and deadly in recent weeks. Beyond Poyang Lake, dozens of rivers across central and eastern China have reached record highs. But the worst of it has been in Jiangxi Province and around Poyang. Authorities declared a “red alert” for flooding at Poyang Lake and nearby populated areas, including Nanchang, the provincial capital and its largest city.

NASA Earth Observatory images by Lauren Dauphin, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview. Story by Kathryn Hansen.

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