The Inland Niger Delta is the largest wetland in West Africa. It is spectacular in both its landscape diversity and dynamics. Water from the Niger River, which originates 900 km upstream in the Guinean Highlands, spreads out into a wide floodplain about 380 km long in central Mali. It has a very gentle gradient, dropping only 8 m over its entire length. The floodplain is a highly dynamic complex of wetlands, channels, islands and lakes that provides important habitat for fish, water birds, and other wildlife. The seasonal flooding also supports pasture and rice farming. The delta has provided livelihoods for people for millennia. Today, over 1 million people depend on the resources of the delta. About a quarter of the Delta’s population lives in cities like Djenné, Mopti, Niafounké, and Timbuktu.
In the recent geologic past, the Inland Delta area was once a huge lake, fed by the Upper Niger River. At some point in that wet period, the lake overflowed to the east through a breach. The interior lake was drained, although a number of small relic lakes remain.
The three Landsat images capture the dynamics of natural flooding as seen in May, September, and December 2015. The May image shows the extreme dryness of the land at the peak of the hot, dry season. The semi-permanent water bodies (dark blue and green) of the Delta stand out. Several major lakes have dried out since the early 1970s, most notably Lake Faguibine, whose arrowhead-shaped lakebed is clearly seen in the north. The low flood levels of the drier years are insufficient to reach many lakes and depressions. Flooding begins when the Niger and the Bani Rivers begin to rise. Starting in July, the Niger River rises about 4 m in 100 days. Peak level may even reach 6 m in the years of high rainfall (Zwarts and others, 2009). As the center image shows (above), by late September the natural flooding of the Inland Delta is well underway. Acting like a giant sponge, vast wetlands come to life. The southern Delta swells and greens first, while the northern Delta area experiences a two- to three- month delay in flooding. In the December image, the annual high water level has finally reached the northern Delta, while the southern Delta has already been drained of much of its water. Between the southern and northern floodplain, flooding permeates a total area of about 40,000 sq km. Numerous ephemeral lakes, along with the more permanent ones, like grapes on a vine, receive and store the floodwaters, releasing them gradually as the river level subsides.
Vast floating meadows of vegetation occupy the areas of deeper water, dominated by an aquatic grass species known locally as bourgou. During the flooding, bourgou, along with wild rice and other species, produce a considerable amount of habitat for fish and water birds and nutritious fodder for cattle during the dry season. As the water subsides in the dry season, the floodplain vegetation provides green pasture for the millions of cattle, sheep, and goats. Farmers cultivate rice, mainly in the southern Delta. They use a West African rice variety that grows well as the water rises. It is then harvested when the waters recede. This floodplain rice is more extensive than irrigated rice fields, which can also be found in the Inland Delta.
Flood forecasts will become increasingly important as the population grows and pressure on water resources increases. Water level measurements and satellite images help predict the onset of seasonal floods and help achieve food security. An early warning system will help predict drought and monitor food security. Data from both on the ground and satellites help manage water resources.