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Sea level rise in deltas

What is an urban delta?

More than half of the world's population lives in cities and this number is expected to increase over the next years. (United Nations, s.d.) In the future, 70% of the world's population will live in urban deltas (Bijlsma et al., 2018).

But what exactly are deltas and urban deltas?

Deltas are areas where a river often flows with several branches into another body of water. This may be the sea or a lake, but it may also be another river. Thus, a delta is actually an outlet where an exchange of water and sediment takes place. (Micalizio & Evers, 2013). Deltas are usually recognised by their shape, namely that of the Greek capital delta. However, not all deltas have the characteristic shape of a triangle. (Delta, s.d.) The name delta was invented by the Greek historian Herodotus when he was studying the Nile and found that it resembled the capital delta.

Besides the term delta, the term urban delta is also used. These are deltas inhabited by large numbers of the population and can therefore actually be regarded as urban areas. Areas around deltas are attractive to live in for several reasons. Firstly, there is a lot of fertile soil present, which makes it possible to grow crops well. Secondly, because of the presence of the river, there are good transport routes, such as transport by water. Furthermore, there is a lot of trade and, of course, fishing. Nevertheless, the urban deltas also face increasing problems.

The Niger and the Elbe delta are two deltas in different parts of the world, but are facing the same threat: Sea level rise.

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Sea level rise

Sea level rise is an increase in the level of the world's oceans due to the effects of global warming (National Geographic Society, 2019). The global mean sea level is rising and accelerating, mainly due to the melting of glaciers and ice sheets. Observations show that the sea level has been rising since 1901 and that the rate of sea level rise is increasing. In the period 1901-1990 it was still 1.4 mm per year-1 and in the period 1993-2015 it was already 3.6 mm yr-1. (Oppenheimer et al., 2019)

Sea level rise is not the same worldwide and differs regionally. Due to thermal expansion, ocean dynamics and loss of land ice, there are deviations of about 30%. Therefore, it is important to look at what exactly is going on in terms of sea level rise for both deltas.

The delta's

Niger delta

The Niger Delta is the delta of the Niger River. The Niger River is one of the largest rivers in Africa and flows through the countries of Guinea, Mali, Niger, Benin and Nigeria. The Niger Delta is located in Nigeria and discharges into the Gulf of Guinea and the Atlantic Ocean. The Niger Delta is located in one of the most densely populated areas of Africa and is often seen as the heartbeat of West Africa (WWF, 1986).

Elbe estuary

The Elbe delta is the delta of the River Elbe. In reality, it is not a delta but an estuary. The River Elbe originates from the Czech Republic, and flows through Germany and finally discharges into the North Sea at Hamburg. The river is an important means of transport for shipping.

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