Colum/ Light, air, and space and Dutch summers/ Heatstress and flooding/ NL/ July 2021
Light, air and space and Dutch summers
The Netherlands had a beautiful maritime climate according to the Köppen climate classification system with a moderate maritime climate (type Cfb) with relatively mild winters, mild summers and precipitation throughout the year. The layout of Dutch towns and villages from the 1930s onwards is mainly based on this climate. The city builders soon came up with the principles of ‘het nieuwe bouwen’: meaning light, air and space. This was partly a response to the sometimes overcrowded neighbourhoods in the old town. In the Netherlands, the sun has plenty of space in the city and the facades of houses consist of a lot of glass. When the sun shines, it should be used as much as possible.
Climate adaptation due to more extreme weather
But that idea seems outdated. The temperature is rising, according to all KNMI climate scenarios. Heat waves will become more frequent in the future and the number of hours of so-called heat stress could double by 2050. This directly affects the health of the population. An extension of the growing and flowering season is also associated with more pollen in the air and with it an increase in respiratory allergies. According to the most recent KNMI ’14 climate scenarios, we will have more extreme weather in the future. Especially in the summer months the chance of extreme showers increases. The research indicates that with one degree increase in temperature, the amount of precipitation per hour during the most extreme showers increases by about fourteen percent. In other words, the heavy showers will increase in intensity and amount of precipitation (more millimeters of rain per hour), and possibly also fall over a larger area. The number of days with extreme precipitation has doubled compared to 1950. (source KNMI) The weather is becoming more extreme with more heat waves and heat stress in the summer and flooding due to heavy showers. The new buzz words are: heat island, heat stress, heat director, climate adaptation, downpour, flooding, water-retardant greenstrips, rainproof, dry farming, mulching, cooled areas, water supply, CO2-neutral and national heat plan. More extreme weather requires adjustment of our behaviour and our environment. This not only has consequences for the entire urban fabric, but especially for the immediate living environment. For people with a reasonable condition, heat stress will mean little more than a reduced feeling of comfort. But for the elderly, small children and people with heart problems, the consequences can be serious. A long heat wave leads to significantly more deaths. There is reason to take into account the increasing number of very hot days when designing the space in the broadest sense with regard to the health of residents.
Comfortable in winter and cool in summer
The emphasis for designing the immediate living environment is shifting to an environment that is focused on climate comfort. The principles of ‘het nieuwe bouwen’, meaning light, air and space, are expanded with possibilities to adapt to the changing climate. This means a comfortably heated house in winter and cool in summer, with very low energy costs and CO2-neutral. The living environment is designed in such a way that flooding is prevented. Rainwater is infiltrated as much as possible into the healthy ‘sponge’ soil in the urban environment, which serves as a water reserve for trees, shrubs and plants. Which provides much-needed cooling in their neighbourhood during heat stress. One tree donates the cooling that is comparable to ten air conditioners.
Planting trees is the most effective measure. Trees provide cooling by evaporating water and thereby dissipating the heat. In addition, they provide shade. Fortunately, trees are not the only way to combat heat stress. Green is generally good, grass also absorbs heat. But when there’s a heat wave, deep roots allow trees to continue evaporating from groundwater longer than grass, which quickly dries up. More green roofs and more grass instead of pavement is part of the solution. Water bodies provide cooling during the day. The disadvantage of this is that water retains heat in the evening, so that the net effect is not so great. Especially during a longer heat wave, the water stores heat, so that the city remains warm for a long time in the evening or after the heat wave. A fountain, on the other hand, does provide cooling. (source WUR) Insulation is always a good solution for the built environment. A well-insulated home retains heat in winter and keeps heat out in summer. The door should not be opened and you should ensure that the sun stays out. You can take sun protection measures on the outside of the house, such as: sunblind’s, shutters, deciduous trees or green roofs. Apply summer night ventilation. If it gets cooler outside than inside, open windows together. A vertical channel creates a pull in the house. Open a window at the bottom and top of the house for vertical draft.
More heavy rain showers in combination with thunderstorms and gusts of wind can cause a lot of nuisance and even cause damage and injury. Harvests can fail due to extreme rainfall, hail and heavy gusts of wind. This affects many people and leads to economic damage. With targeted and timely weather warnings, measures can be taken to reduce or prevent injury, damage and nuisance. Cities and municipalities have the excess paving in their urban network unpaved. Unpaving is a policy goal that is becoming increasingly important, because it allows more rainwater to filter into the soil. That should prevent drought. In Belgium 15% of the soil is paved and therefore covered by buildings, roads and parking lots. A large part of this is paved with stones and asphalt. When soil is paved with tiles, asphalt, concrete or the like, water flows directly into the sewers and cannot penetrate into the soil. This causes a shortage of groundwater, so drought and heat stress. That is why more and more cities and municipalities are urging residents to unpaving and lay out gardens and terraces with permeable materials. The soil needs to be turned back into a sponge that retains the water and releases it slowly when it dries. This is how we make the city climate-robust.
Healthy soil is important to reap the benefits of greening. Without a healthy soil, greenery cannot flourish, less water is retained by plants and in the ground, and rainwater does not sink into the soil as easily. Whether a soil is healthy depends on the chemical, biological and physical composition of the soil. The advantages of an unpaved surface with good quality greenery far outweigh a greater degree of maintenance of a paved surface: less flooding, less heat, a healthier soil, the groundwater is replenished, no dried out soil, fewer foundation problems due to drying soil, more biodiversity and better air quality. (source Amsterdam Rainproof)
By creating lowered, vegetated strips next to paved surfaces, rainwater flows down to these strips, where the water is temporarily retained and slowly sinks into the ground. When considering these water-retardant green areas, the groundwater level and the soil type must be taken into account. The permeability of the soil is maintained through rooting of plants and biological soil activity.
Heat stress and flooding
The Dutch living environment after the 1930s is spacious. So there are many opportunities here to make them climate-robust in a simple way. Greening and planting trees in combination with home modifications ensure a cool house in the summer and a comfortable home in the winter. Flooding can be prevented by filtering rainwater into a healthy soil that acts as a sponge. With water-retardant green strips, excess rainwater can be infiltrated into the subsoil.