Sea level is rising

A large part of the world population is living in cities at the coast. Coastal cities with a population of more than 1 million inhabitants occur on the coasts of all continents, except the Arctic regions of North America, Europe and Russia. Coastal cities with more than 10 million inhabitants are mainly found in Asia. Between 2020 and 2070, the population of coastal cities is projected to grow.

A large part of the population in these coastal cities is exposed to the risk of coastal flooding, and this risk is increasing. Even if we succeed in strongly mitigating climate change, sea level is projected to rise by about 0.5 to 1 metre between now and 2150. It is more likely that sea levels will have risen even further by then.

The land of deltas is subsiding

At the same time, the land of many urbanised deltas is subsiding. It is the relative sea level rise – the sum of absolute sea level rise and subsidence – that determines coastal flood risk. In fact, in many deltas around the world, subsidence is much greater than absolute sea level rise, and in many deltas in Asia even more than 20 centimetres per year.

Sediments no longer reach the deltas

These deltas can only keep up with relative sea level rise if large amounts of sediments are transported from the river catchments to the river deltas. However, this is no longer the case. About two-thirds of the river sediments that used to be transported to these deltas no longer reach these deltas because they settle behind dams in the upstream parts of the rivers.

A triple threat

The combined effect of sea level rise and land subsidence requires more river sediments than ever if the deltas are to keep up with sea level rise. However, less and less sediments reach these deltas because of all the dams in upstream river reaches. The future of our deltas is at stake.

Geography of Coastal Water Challenges

In 2023, The Netherlands Environmental Assessment Agency published The Geography of Future Water Challenges, an overview of global challenges on water- and climate-related issues. This publication was presented at the UN 2023 Water Conference in 2023. Part of this publication focuses on deltas and coasts, in particular the pollution of coastal seas and the future of deltas and small island states in view of sea level rise, land subsidence and dams that retain most river sediments. The shortread The Geography of Future Coastal Water Challenges presents these results in beautifully designed and easy-to-understand infographics.