A green roof in Fukuoka, Japan. © Shutterstock
Cities take up less than three percent of the land area, but they harbour more than half of the population – and this figure is only growing. One important issue is how to keep cities liveable in the future. ‘Climate models show that extremes will increase. Dealing with this will require adjusting, for example in the field of water management’, says Huub Rijnaarts, professor of Environment and Water Technology, who will speak on the subject during the Science Café tomorrow.
One extreme that we will face in the Netherlands, but also in the rest of Western Europe, is increasingly heavy showers, while it may also become dryer during spring and summer. As cities hold more heat, the warm, rising air could lead to more heavy showers, says Rijnaarts. ‘This is comparable to the emergence of hurricanes above warm oceans. The exact process is being studied by the Meteorology group in Wageningen.’
Dutch cities are still designed for the rainfall of decades past.
Huub Rijnaarts, professor of Environment and Water Technology
Many cities experience flooding when hit by heavy rain, and the hardened surfaces impede the water’s easy spread. Rijnaarts: ‘Dutch cities are still designed for the rainfall of decades past.’ In times of heavy rainfall, is it important to have a space to store the water, Rijnaarts explains. ‘Nature could be of help, for example through the placement of additional parks, green verges, and by equipping houses and business premises with green roofs.’ This ecological approach can be combined with technology. A good example is the application developed by the Amsterdam Institute for Advanced Metropolitan Solutions (AMS), co-founded by WUR, in collaboration with the Wageningen professors Bert Holtslag and Remko Uijlenhoet: this application accurately tracks the location of rainfall down to street level. The water company can then see where the rainfall was the heaviest and take measures to ensure that damages are limited in case of heavy rain.
In the current situation, our sewage is treated and subsequently flushed into the sea. This requires a lot of energy and isn’t sustainable.
Huub Rijnaarts
According to Rijnaarts, it is also important to improve the water quality, so that water can be recycled more easily. ‘In the current situation, our sewage is treated and subsequently flushed into the sea. This requires a lot of energy and isn’t sustainable. We are working on new technologies to create closed loops and recycle water.’ He is thinking of loops in which city sewage is recycled for the industry or agriculture and then brought back into the city. To achieve this, it is vital to remove all salt, medicine and pesticide residues from the water.
The studies are not merely focused on the Netherlands, but also on countries such as India or Vietnam. ‘Those countries encounter some of the same problems we do in the Netherlands. For example, in the Mekong Delta, there is a shortage of fresh water during periods of draught, and salt water flows in from the sea when the river water levels are low; the latter is detrimental to the supplies of drinking water, water flora and fauna and the agriculture.’ In other parts of the world, like China, cities are expanded or started. Rijnaarts: ‘Those could be designed with a green and sustainable approach from the start. But there are also opportunities to make the cities gradually greener in the Netherlands and Europe. Collaboration between the various fields of knowledge and practice is very important to achieve this.’
The Science Café ‘Sustainable City Concepts’ will be held on Thursday 30 November in Café Loburg. The evening will start with live music at 19:45, and the speakers will start around 20:15. Visit this page for further information.