People do not often consider cities to be an ecosystem. Yet when I saw a hedgehog rummage around the streets of city-center Amsterdam I realised that that really is what a city is, not unlike a dune area or a forest. A collection of flora and fauna delicately balanced and living off each other and with each other. A city is, perhaps, an entirely man-made ecosystem, in which we have control over even the smallest of details. Is it, then, not strange that we treat a city vastly different from a forest. Plants and trees have value and so do animals, not only for recreation, but also for productivity and regulation of extremes. All around the world we are noticing that urban areas are struggling with pests, heatwaves and floods. It is widely accepted by policymakers that vegetation, greenery and parks will counteract many of these problems. There is, however, difficulty in this as building more parks takes up a lot of space and would require tearing down many (monumental) residential buildings. For cities like Amsterdam, however, there could be an easy solution. It should become common policy in Dutch cities that 60% of back- and front-yards should be covered in vegetation. There are a number of great advantages to such a “tile taxing”, I will discuss these concisely.
Decreasing urban heat islands
Urban heat islands are caused by the heat uptake retention of concrete and other building materials to a much greater extent than for example water or vegetation. These urban heat islands account for sometimes up to a few degrees extra warming in certain areas of cities, causing higher risk of strokes and other health hazards, especially to the vulnerable parts of the population such as the elderly, disabled and young children. Parks have been shown to decrease the urban heat island effect and even a singular tree already makes a difference. They do this not only by providing shade, which is a more minor factor than one may expect, but also by less heat uptake and increased heat regulation through evaporation of moisture that was present in the vegetation. If tiles would be replaced by vegetation in all backyards it would create a similar effect.
Retention basins for Heavy rainfall and drought
Flooding due to heavy rainfall already occurs a few times each year and in future climate scenarios this will only become worse. Weather extremes will become more frequent and both drought and heavy precipitation events will become less exception and more the rule each summer. This leads to great challenges in future city planning where heavier precipitation events may cause serious harm to infrastructure and people if flooding would occur regularly. One effective way to counteract flooding is to build retention basins. Retention basins are designated areas that can absorb water and delay the time it takes the water to reach the sewage system. Something that functions brilliantly as retention basins are parks and vegetation covered gardens. The plants ensure more initial evapotranspiration, causing a lower influx of rainwater and delay the time it takes the water to reach the surface. Once the water has arrived here it is partly soaked up by the soil and retained there. This process greatly reduces the stress on the sewage system and damages on infrastructure due to flooding. In case of drought quite the opposite occurs where the foliage cover reduces evapotranspiration causing more water to be retained in the soil. As well as the vegetation providing the cooling mentioned earlier.
Increased biodiversity
Biodiversity is often relatively low in cities. However, indigenous species such as hedgehogs, hares and foxes, as well as smaller species such as frogs, toads and newt could easily return to urban areas if larger portions were covered in vegetation. Not to mention insects (notably bees) and birds. This would not only help control pests such as mosquitoes, flies and mice but would also increase overall human happiness. As it has been shown that being exposed to nature increases happiness in people.
Discussion and conclusion
Apart from the aforementioned reasons to ensure more greenery in urban gardens some other things include improved production, as company buildings next to parks are shown to be 10% more productive than those not exposed to vegetation. And increased real estate prices, since property in greener (yet otherwise identical) areas is more valuable.
Arguments against tile taxing would be that it would be too time consuming for some hard-working people to take care of a green garden and that tiling a garden reduces maintenance cost and time. Solutions to this can be found however, both in community- and municipality-provided aid. The possibility of exemption in case of inability and education on low-effort green gardens that require little maintenance, but function nonetheless.
Tile Taxing would reap a great many benefits and aid in climate-proofing cities for the future. While keeping a garden green and flourishing may require some effort of people who do not have the time or do not wish to put in the effort, it is of great importance to cities to ensure that there is enough vegetation cover. And solutions to this problem can easily be found through aid, exemption or education. While there are still some practical issues that need to be resolved such as the occasion of smaller backyards that are used as storage for bikes or other materials, solutions to this are easily introduced.
Additional reading:
KWR 2014: Risico’s van klimaatverandering voor de drinkwatersector
KNMI’14-klimaatscenario’s http://www.klimaatscenarios.nl/brochures/images/Brochure_KNMI14_NL_2015.pdf
Enhancing Resilience of urban ecosystems through green infrastructure
Energy, Climate & Sustainability 