50 years after a catastrophic flood in the Netherlands in 1953, climate change imposes new challenges on the Dutch, including more intense rainfall, rising sea levels, with the alarming increase of up to 2 centimeters per year in their rural areas and increase in temperature.
In the Dutch cities it is raining more frequently and more intensely, and they are simply not equipped to handle so much water, due to the intense urbanization that has reduced the infiltration zones of approximately 25% to 10%; runoff has increased from 10% to 55%; evaporation has been reduced from 40% to 30%; and the drainage system has no capacity to process any more water.
Being aware that a flood would have even bigger impacts today than 50 years ago, due to the increase in population, the Dutch have decided to opt for a spatial adaptation in their cities that follows the Delta Program. This programs is aimed at counting by 2050 with cities that are spatially planned, climate-proof and resilient to water to face the main effects of climate change: sea level rise, river overflows in winter, extreme rainfall in summer, droughts and heat.
Spatial Adaptation is only one of the three lines of action of the strategy to approach climate resilience, which also includes new flood protection standards (based on the impacts that a flood would have and not on the probability of flooding) and availability of water for economic activities and nature.
The implementation of the strategy began in 2015 by bringing together urban designers and hydrologists to map the points that are vulnerable to flooding in the city in case of heavy rain, taking as a reference 60 mm of rain per hour. The result in Amsterdam was the identification of 97 flood risk points, and 14 that required immediate intervention. This mapping has allowed knowing how water flows through the city and dividing the city into hydrological entities to monitor the behavior of the rain and prioritize urban works and the maintenance of the drainage system.
Based on the decision that the expansion of the drainage system is not an option, due to the high financial cost, the Dutch have introduced a combination of measures that seek to create “sponge cities”. Such cities are resilient and climate-proof and have the capacity to absorb as much water as possible in the case of heavy rainfall, reducing the pressure on the drainage system.
Water sensitive urban design to be resilient and climate-proof has played a very important role in containing water caused by intense rainfall. Multipurpose urban spaces have been designed that function as play areas, squares or parking lots, but in the presence of rain they turn into water tanks. Rainwater storage levels range from domestic storage in barrels to large areas such as the Watersquare Benthemplein in Rotterdam, a 9,500 cubic meters play area that has 3 areas that become retention ponds in the presence of heavy rain; or the Underground water storage in Kruisplein with a storage capacity of 2,300 cubic meters; and the Museumpark car park with a storage capacity of 10,000 cubic meters.
Green roofs have also played a very important role, which has even created competition with solar cells. Amsterdam has 4,000 square meters of green roofs, most of them built during 2016, but the Dakaker, in Rotterdam, is still the prime example, as it was the first green roof built in Europe, with an area of one thousand meters and an absorption capacity of up to 60,000 liters.
This article is from Raquel Vargas from the National Water Commission. The content of this article is the sole responsibility of the author.