Earthshots: Satellite Images of Environmental Change

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» Inland Delta of the Niger River, Mali

On the edge of the Sahara Desert lies one of the world’s most productive wetlands. The Inland Delta of the Niger River in Mali is a vast expanse of lakes, channels, and marshes. The Niger River divides into countless channels and forms the largest wetland in Western Africa. The river and wetland form an important water resource for Mali, a landlocked and generally dry country.

This delta floods seasonally from September to December, as rainfall from the river’s headwaters in the Guinea Highlands reaches the delta’s vast flat floodplain. The southern part of the delta is low-lying floodplain with expanses of wetland grasses and reeds. The northern part has sand ridges that emerge from the water during the flood season. The seasonal flooding supports fisheries, pasture, and rice farming. Over 1 million people depend on resources in the delta.

The Niger River is the third longest river in Africa. It begins in the highlands of Guinea, then flows 4,100 kilometers (2,550 miles) into the Atlantic Ocean in coastal Nigeria.

Map of the featured area.

In the flooded season, this part of Mali’s landscape stands out as bright green against the arid brown African Sahel. The Niger River and the Inland Delta have been an important water supply in the southern Sahara for thousands of years.

The river channels, lakes, swamps, and floodplains provide the main livelihoods in the delta: livestock, fishing, and farming. The delta is also a refuge for many migrating birds. After rice farming and livestock, fishing is the most important industry of the delta. The catch varies from year to year depending on water levels. An overall decrease in available water in the delta directly affects the population in this industry.

This series of images shows that the extent of the seasonal flood can vary. For example, 1984 was a low flood year, and the green extent in the image is smaller than it is for 1999. Another low water year was 2011. Exceptionally high floods can damage habitats and irrigation, but extremely low flows like those in 1984 can be disastrous. The loss of livestock caused by the lack of water one year can have long-lasting effects.

Two main threats to the region are inadequate water management and climate change. With growing water use and a predicted decrease in rain in the Sahel, the river flow of the Niger is expected to decline. The livelihoods of the delta’s people could be at risk.

Diverting upstream water for irrigation means less water for the delta. For example, the Fomi Dam in Guinea is being planned. The two countries are working on assessing the possible risks and benefits of the dam.

(Black stripes run through the 2011 image because of the Scan Line Corrector failure on Landsat 7 in May 2003.)

The Inland Niger Delta lies in the transition between a seasonally wet-and-dry climate in the south and a mostly dry climate at the edge of the Sahara. Therefore, the northern and southern parts of the delta have different characteristics.

The southern portion of the delta is a vast alluvial plain. The floodplains fill during the flood season. The water level rises between June and November. The water then flows north and the floodplains empty by early the next year.

The rainy season here begins in July and continues through October. The mean annual precipitation is 600 mm (23.6 inches).

(Black stripes run through the 2011 image because of the Scan Line Corrector failure on Landsat 7 in May 2003.)

In the northern portion of the delta, channels fill in between sand dunes during the flood season. Temporary lakes also fill during high floods. The water reaching these lakes is not returned to the river as flood waters recede.

The north receives far less precipitation than the southern portion. The mean annual precipitation there is just 200 mm (7.9 inches).

(Black stripes run through the 2011 image because of the Scan Line Corrector failure on Landsat 7 in May 2003.)

During the flood season, the delta can grow to 20,000 square kilometers (7,700 square miles). During the dry season, it can shrink to 3,900 square kilometers (1,500 square miles). The flatness of the delta region—it drops only 8 meters (26 feet) over its entire length—leads to this large spread of water.

In the images, dark blue to black areas represent open water. The water expands and then noticeably begins shrinking in December. Any bright green, which is actively growing vegetation, also begins to diminish by late December. Dark blotches in the June image are bare ground. And this is roughly what it will look like again the following June.

These 2014 images show a flood level that was close to average.

The busy port city Mopti is located at the confluence of the Niger and Bani Rivers. It is a crossroads of trade between the north and south.

Farming in this region relies on rainfed cereal crops. This makes farmers vulnerable to weather-related risks. They experience only one good harvest out of every three rainy seasons. To help residents plan for high or low water flood seasons, scientists are working on a greater understanding of the hydrology of the delta.

The Niger and Bani Rivers determine the flood extent each year. The water level in Akka, toward the northern part of the delta, can be reliably predicted from the combined flow of these rivers.

Flood forecasts will become increasingly important as the population grows and as 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.


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