Challenges

Bo02 Hammarby Sjöstad, Stockholm, Sweden © atelier GROENBLAUW, Madeleine d’Ersu

Challenges

Themes

Climate change

Most scientists and policy-makers accept climate change as a fact. In the case of the Netherlands, the widely-accepted, most probable changes in this century are an average sea level rise of 85 centimetres, coastal erosion, wetter and warmer winters with expected higher river discharges, drier or wetter and warmer summers, more precipitation in shorter periods and heavier showers. The increase in intensity of summer showers will occur mostly in the coastal areas, winter showers will occur particularly in the Rhine River catchment area. The prediction for the coming century is that sea level rise will accelerate. River floods will occur more often due to heavier precipitation of longer duration. Sea level rise will increase the water level in rivers, causing salt intrusion to the inland areas close to the coast. [Bakel et al., 2008]

Schematic overview of the four KNMI’14 climate scenarios. © Klein Tank et al., 2015

The changing climate in the Netherlands

In an interview in the ‘Watervakblad’ (a Dutch magazine for water professionals) of June/July 2011, Rob van Doorland of the KNMI (the Dutch Meterological Institute) states that the largest increase in rainfall over the last thirty years has occurred in the Dutch coastal area. This increase is due to higher water temperatures in the North Sea. Every degree of increase in water temperature causes a precipitation increase of 15%. A prime example of this effect occurred in August 2006, when the sea water temperature was 2°C higher than normal while 30% more rain fell than usual. The heavy showers occur only when the prevailing wind is from the sea and the upper atmosphere is colder. Sewage system capacity was insufficient and street flooding occurred. The KNMI is developing computer models to assist with water management decisions. The air temperature in the Netherlands is rising twice as fast as the world average: 1.5°C between 1950 and 2008 as compared to 0.7°C for the rest of the world. These higher temperatures can be explained by an increase in westerly winds in winter and spring, carrying milder air masses. In the summer the wind blows more often from the east, bringing with it warmer air masses. Besides the increase in precipitation in the Rhine River catchment area in winter – which causes higher water levels – and heavier showers in the summer, increasing periods of drought are also a problem. This causes lower water levels in rivers and thus salt intrusion to river mouths and estuaries. In the summer of 2003, we saw the consequences of hot, dry summers. That summer fresh water from the IJsselmeer had to be pumped to the low-lying coastal areas to counter the salt intrusion through the river mouths. In the same year river water could almost not be used as cooling water for power plants due to the combination of low water levels and higher than normal water temperatures. In 2003 the ‘peat’ dike in Wilnis collapsed because it had dried out. Sea level rise, which is caused by a rise in sea water temperatures and the melting of the polar ice caps, causes further salt intrusion, with consequences for agriculture and nature. [Watervakblad, 2011]

Average precipitation per winter semester © KNMI/Alterra

Average precipitation per summer semester. The maps are based on an automatic interpolation of climate data of individual weather stations without additional knowledge. The displayed local variations may also be determined by the interpolation technique used and the location of the measuring stations. © KNMI/Alterra

Land subsidence

The Netherlands is essentially one large delta. The Rhine, Ems, Meuse and Scheldt rivers flow into the North Sea here. In a “natural” delta without dikes (levies) and dams, overland flooding from the rivers and the sea would deposit sediments (clay and sand) which would raise the level of the land (even in the case of sea level rise). Due to human interference this process doesn’t occur anymore in the Netherlands. About 1000 years ago, the inhabitants of the delta started constructing dikes to reclaim agricultural land. Additionally, peat was extracted for fuel from the wetlands behind the dunes, creating lakes that were metres deep. From the 17th century on, these lakes were drained to create polders. This caused a subsidence of the ground water level, and thus land subsidence due to soil settling and soil oxidation. As a consequence the water levels in the polders had to be lowered which caused more land subsidence and so on. This has resulted in the ground level in the western part of the Netherlands subsiding several metres since the Middle Ages, a process which continues until this day.

Almost two-thirds of the Netherlands would flood regularly without the presence of dunes, dikes and dams. A large majority of Dutch citizens live below sea level in or near the areas of the largest economic value. The risk of flooding can be controlled by raising dike levels but also by accepting the consequences of any flooding during planning by building on local land mounds (so-called ‘terpen’). There can be more variation in the flood risks and land use of a given area. For example, we can more easily accept the flooding of recreational areas than of residential areas. [Brinke et al., 2008]

Desiccation

In addition to periods with a surplus of water, problems concerning droughts due to longer periods without precipitation and rapid discharge are becoming more noticeable. This has consequences for flora and fauna and requires a different way of managing urban green space and use of different species of plants, but can also cause damage to the foundations of buildings. Water managers are confronted not only with climate change, but other challenges as well, such as scarcity of drinking water sources due to salinisation and droughts. Increased use of drinking water will likely lead to an increase in sewage water volume and higher costs for sanitation.

Surface water pollution and droughts will have large effects on flora and fauna. Moreover, floods will occur due to rapid discharge of rain water and decreased buffer capacity of urban areas and rivers. [Pötz et al., 2009]

Dyke breach in Wilnis (The Netherlands) during the dry summer of 2003 © Waternet / Albert Jan Perier

Awareness

Urban citizens have lost their awareness of water because water and its cycles have become less noticeable since the second half of the last century. Rain water is nowadays discharged through underground sewage systems, and city canals have been covered or filled in. The transportation of drinking water over large distances and the treatment of sewage water outside the cities, the decreased importance of waterways for transport, and the low cost of drinking water have all contributed to a further decrease in the awareness of the importance of water. Less awareness leads to less commitment and the waste of natural resources, potential qualities and ecological values. The water cycle is just one example of this problem. Centralisation of water management is reaching its limits, and there is therefore rising interest in alternatives for urban water management with regard to developed areas. Recently there has also been renewed interest in ecological values and the quality of experiencing urban water and nature. Only when we again give water and nature a valuable place in our cities will they also have a prominent place in our consciousness. Or do they first need to become more prominent in our consciousness before they re-appear in our cities as the spiritual bearer and origin of all life? Through the effects of climate change, water and nature are literally reclaiming the position robbed of them in the last century.

Literature