Climate Proof Cities - Policy Summary

All cities in the Netherlands, large and small, are vulnerable to the effects of climate change. The degree of vulnerability varies considerably within urban areas. This means that making cities more climate proof can be done most efficiently by taking many relatively small and local measures. Many of these can be carried out simultaneously with major repairs or renovations. This does require collaboration with many and various parties.

These are the most important findings of the Climate Proof Cities (CPC) research programme. This programme has yielded much insight in making Dutch cities climate proof, with a focus on heat stress and flooding due to heavy rainfall. The programme was carried out by a consortium of ten universities and knowledge institutes that worked together for four years with municipalities, water boards and the national government to provide answers to knowledge questions from practice.

The urban climate is changing
Climate change leads to more heat waves, more frequent heavy rainfall events, and more periods of drought. If cities do not prepare for this, it will influence people’s health, quality of life in city districts, comfort in houses and buildings, and productivity, leading to economic problems.

The high percentage of paved area in the city, combined with the increasing chances of heavy rainfall, can lead to greater material and financial damage through traffic disruptions, problems with infrastructure and the expense of calling in emergency services. The thresholds for flooding in the urban environment have stayed the same or even decreased in recent years, and flooding is a recurring problem in some districts. More summery and tropical days are also expected in the future. Without an explosive increase in air conditioning in buildings, this will lead to much higher temperatures in a vast proportion of Dutch housing. Heat stress can lead to illness and increased mortality among sensitive sections of the population, such as the elderly and the chronically ill, but also to decreased productivity and sleeping disorders.

Both large and small cities are vulnerable
During heatwaves, it is warmer in every city in the Netherlands, large or small, than it is in the surrounding area. This heat island effect is clearly noticeable and can reach a difference of more than 7 ˚C, especially in the evening. Because of climate change, the number of days with heat stress in the city can increase substantially. Heavy rainfall can also hit any city.

Vulnerability varies greatly within the city
A striking conclusion of the CPC research is that within the urban area, there is great spatial variation in vulnerability, depending on the properties of the district and the building and the distribution of sensitive persons and objects. Exposure to heat and flooding, for instance, is mainly determined by the amount of paved area and the density of buildings in an area. Overheating in buildings strongly depends on the presence of sun blinds and degree of insulation. Information about exposure, combined with the locations of sensitive groups (for instance, the elderly) and of objects (such as switch boxes and houses with cellars), forms the basis for identifying areas that need attention.

Adapting to climate change is a matter of the combined effects of relatively small, local measures
Because vulnerability to the effects of the climate is determined locally, the choice of measures is also dependent on the local context. The input of generic measures for a whole city is less effective. A wide variety of adjustment measures exists, ranging from influencing the urban climate or the urban water system (for instance, collecting and storing rain water, creating a cooler layout of streets and squares), adapting buildings and infrastructure (e.g. installing doorsteps), changing human behavior and increasing acceptance of discomfort and preventing damage when an extreme event does take place (such as care for the elderly). Various adjustment measures contribute to easing problems with flooding, heat and drought at the same time, and an integral approach to these three problems is preferred. Rain water from wetter periods could for instance be stored underground and used to combat dryness, and, through evaporation, heat. Many measures have a positive effect on other policy themes, such as migration and biodiversity, and/or contribute to the improvement of the general living conditions in buildings and in public spaces. The CPC research has provided a number of new and sometimes startling insights about the effectivity of measures:

  • Traditional green roofs, without restricted discharge measures, are hardly effective for both the indoor climate, the outdoor climate and the temporary storage of extreme rainfall
  • The cooling effect of the surface water in the city is not unequivocal: bodies of water can even contribute to the warming of the city; large bodies of water, depending on their orientation in terms of the direction of the wind, can have a cooling effect.
  • Insulating buildings without paying attention to protection against sunshine can lead to more heat problems in hot summers

Planting deciduous trees with large crowns, and more generally adding green elements in private and public spaces leads to better thermal comfort and lessens problems caused by extreme rainfall.

Many measures can easily be integrated into other policy, but require interdisciplinary collaboration
Many measures require collaboration between different parties: the departments within a municipality, water boards, home owners, sometimes businesses. However, integration of climate adaptation in other sectors is not self-evident. Institutional entrepreneurs can help to connect different goals and ensure widely supported solutions for urban development and realising cost savings simultaneously. Making cities climate proof should be an integral part of decision-making for all sorts of parties interested in the urban environment. Only when authorities, citizens and private parties realise a climate proof city requires combined effort, will there be a basis for success.

Now is the time to define the areas for special attention and to develop a strategy, and in the execution, join in with larger renovation and restructuring projects
The climate is changing slowly but steadily. Because investments that are currently being made in the urban environment, for instance in renovations or new construction projects, will result in buildings and infrastructures that will still exist in roughly fifty years, it is important to determine already whether adjustments to a future climate can be made. More and more studies, both international and national, show that the costs of adjustments made now are limited compared to the damage that can be caused in one day due to extreme weather conditions.

Because becoming climate proof requires a long-term plan, it is important to clarify already which measures should be applied in which areas. In policy terms this is known as a climate stress test and a climate adaptation strategy. The execution can subsequently take place in phases in the next decennia by joining in with regular maintenance and renovations, so that costs are limited. Identifying these windows of opportunity for planning and executing adaptation measures gives a time plan for implementation. Missing opportunities for including adaptation measures during large transformations can lead to greater costs later.

Read further in the Final report Climate Proof Cities 2010-2014