An Inland Delta Flooded

An Inland Delta Flooded
An Inland Delta Flooded

Drought is a perennial problem in the semi-arid Sahel region of Africa. But in 2020, in Mali and other countries in West Africa, excessive rainfall has been the problem at times. Exceptionally heavy summer rains pushed seasonal floods on the Niger River and its inland delta to destructive levels.

After intense rains fell in July and August in the Guinea Highlands and overloaded many streams and rivers, it took several weeks for flood waters to work their way through the vast inland delta in central Mali. When the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite captured a natural-color image on October 29, 2020, water had spread widely across the nearly flat delta, which was once a lake bottom. Standing water appears black. Many flooded areas appear green because bourgou grass, rice, and other plants grow in the shallow flood waters. For comparison, the other image shows the dry landscape in May 2020, before the rains.

In late October, floodwaters reached their peak height at Mopti, a town at the confluence of the Niger and Bani Rivers. Water levels in the delta were recorded at 670 centimeters (22 feet) on October 26 and remained at that level until November 2, according to Mali’s National Directorate of Water Resources. That tied the peak water levels from 2018, the highest since 1969.

After November 2, waters receded at Mopti even as they continued to rise at points downstream such as Akka and Diré. It typically takes water a full six months from falling in the Guinea Highlands to reach the ocean at the Niger Delta in Nigeria. People watch the timing of flooding closely because it affects when rice can be grown, when fish will be available to catch, and when pastures can be ready for grazing. Water levels were expected to be low enough in mid-December 2020 for the annual cattle crossing on the Niger River at Diafarabé. In the much anticipated event, nomadic herders drive cattle across the river toward rich grazing lands in the inland delta and are reunited with their families after months apart.

While seasonal floods are common in Mali, the severity of the floods this year caused widespread damage. The United Nations Office for the Coordination of Humanitarian Affairs estimates that 1,160 homes were destroyed by flooding.

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

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