Delta Life 8

DELTARES, OCTOBER 2017 27 REGIONAL SEA- LEVEL RISE: ON OUR COASTLINE, TOO? Why doesn't the sea level rise at the same rate around the globe? Three millimetres a year. That is the average sea- level rise. Regional differences have different causes. Due tomovements in the Earth's crust, some parts of the earth, such as the Himalayas, rise faster than others. Others, such as the Mississippi Delta, are subsiding. Melting ice also has an effect: areas that were covered by heavy ice during the Ice Age, such as Scandinavia and Canada, are still rising back to their previous height. Another cause is gravity: the mass of an ice cap attracts water. When the ice melts, the water rises slower locally than further away. Ocean currents and storms cause temporary rises and falls in the sea level. In addition, there are other human influences in alongside the greenhouse effect. For example, if people living on coasts pump up water, the land subsides. Howdoes a region know if the local sea level is rising faster than average? By making their own measurements or by using satellite databases like those of NASA and data fromscientific literature. Unfortunately, data about important processes such as land subsidence and human influences have not yet been brought together into a single global model. That can result in inaccurate predictions. To improve models and forecasts, we need a dataset with data fromall over the world. Deltares is working with others to produce a global dataset of this kind and we are involved in the development of an app tomake those data public. If the level is indeed rising faster than average, what can be done? First of all, when planningmeasures that regions already intend to implement, it is important not to adopt the average global increase as an assumption but to work with the regional predictions that are available. This makes it possible to introduce reinforcements in a highly targeted way, to plan new residential areas intelligently in places where levels increase relatively little, and even to build floating cities in some places. Residents could also use regional predictions to take sea-level rise into account more by buying homes in areas that are less affected. Poorer countries have fewer options. Here, knowledge from countries such as the Netherlands can be helpful in terms of selecting the smartest solutions. More information: fedor.baart@deltares.nl marc.hijma@deltares.nl The sea level isn't rising at the same rate everywhere. For example, in New York, the water will have risen ten centimetres more than the average in eighty years from now. Deltares is working on a global, public database with regional differences. But first: how do these differences come about? BY ANDREA FORZONI IMAGE ISTOCK