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» Nouakchott, Mauritania
 

Not too long ago, Nouakchott, Mauritania, was a small fishing town. It became the country’s capital in 1958, shortly before Mauritania became independent. The town rapidly bloomed into a huge metropolis.

During a long series of drought years in the 1970s, thousands of rural families moved to Nouakchott in search of a better life. Refugees displaced by the Western Sahara War, which started in the mid-1970s, added to the city’s growth.

From small fishing town to rapidly expanding national capital, Nouakchott is surrounded by shifting sand dunes from the north and east, threatened by sea level rise from the west, and facing rising salty groundwater from below. Sand, salt, and water simultaneously threaten to damage the city from all sides. That’s why monitoring the region with Earth-observing satellites will be important for its future.

Map of the featured area.

Nouakchott was a small fishing village for hundreds of years. As recently as 1950, it had only about 200 residents. Drought throughout the 1970s brought migrants to the city, and its population swelled to about 150,000 in 1980. It now has around 900,000 people, and its urbanized area has changed from 5 km2 in 1965 to 150 km2 in 2016.

A 1965 close-up of Nouakchott from the Corona satellite shows the extent of the city at that time. Since then, the city’s expansion has been horizontal, spreading outward. Much of city’s urban growth occurs in informal settlements, which can be seen in the later Landsat images in the varying patterns of urban areas. Streets go in multiple directions and sprawl unevenly across the desert from the city’s center.

This may be against conventional wisdom, but this growing city in the desert is at high risk for flooding. The city is mostly below sea level and vulnerable to rising groundwater levels, seawater intrusions, porous soils, sand extractions, and heavy rains in low-lying areas.

In recent years, the number of rainy days has been increasing. The biggest problem is that a large amount of rain can fall in a short period of time. Since the groundwater level is high, and the type of soil there is not very good at absorbing even a small amount of rain water, rain cannot infiltrate into the ground. These factors lead to a city at high risk. In fact, heavy rains in August 2013 caused flooding in Nouakchott and south-central Mauritania.

Nouakchott is surrounded by a succession of sand dune belts, some of which are highly mobile and can reach 20 m high.

North and east of the city, a green belt was established between 1975 and 1990. Various trees and grasses were planted to curb sand encroachment. Evidence of this effort is seen in Landsat images, where the green belt actually appears red. Landsat’s ability to see various infrared wavelengths of light allows us to more easily differentiate actively growing vegetation from the urban areas and open desert. This vegetation appears red in these images because of Landsat’s near-infrared imaging capability, which reveals actively growing vegetation.

This green belt has changed recently because of the city’s expansion. From 2000–2007, a new project extended the plantings around the city. During this project, 800 ha of inland dunes were stabilized with various trees and grasses.

Nouakchott’s airport is visible as the straight diagonal line near the city’s center in the images in the other subsections. Over the time series of images, the airport became surrounded by the urban growth.

A new larger airport, Nouakchott-Oumtounsy (NKC), opened in June 2016. In the 2013 image, the airport is still under construction, and in 2011, there is no sign of it. Located about 20 km north of the old airport, and about 17 km north of the northern extent of the city, this new airport will accommodate even more growth.

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