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Adaptation option

Using water to cope with heat waves in cities

Investments in water supply services and infrastructures can help cities in their efforts to become more resilient to the negative effects of global warming and of heat waves. These measures can consist in different packages of grey interventions such as: 

  • Building, repairing and maintaining fountains for drinking and cooling 
  • Cooling by water spray (fountains and recreational water features, such as splash pads and spray parks) 
  • Cooling by wetting streets 

Repairing historic drinking fountains and installing new ones creates more opportunities for people experiencing the negative effects of heat in the city. They can use water for drinking when feeling thirsty or they can use water to cool down. The use of water for cooling effects decreases the air temperature by evaporation, absorption of heat and transport of heat. The cooling effect of flowing water is greater than that of water that is standing still, due to the process of mixing flowing water with air and transport of heat. A water spray from a fountain has an even greater cooling effect because of the large contact surface of the water and air, which stimulates evaporation. Cooling effect by evaporation also occurs when water spray is in contact with the skin, decreasing body temperature. Fountains and recreational water features can also have positive social effects as they enhance the attractiveness of public spaces. For example, the city government of Budapest has revived its “Cooling programme”, setting up cooling islands and drinking fountains to protect residents and guests from prolonged exposure to high temperatures. All drinking fountains in Budapest can be easily found through an online map available at the municipal website. Fountains are also commonly enjoyed by people and they serve as meeting places. 

Wetting of streets also has a cooling effect on the surrounding environment. Wetting is best done in the morning and afternoon in direct sunlight. This technique is historically common in Mediterranean cities, but it has become common practice in summer throughout Europe. Experiments in Paris revealed that pavement-watering is an effective method for limiting maximum daily heat stress, but watering streets should target the area to which pedestrians are most exposed, i.e. the sidewalk (Hendel et al. 2016). 

There is an evident trade-off between the implementation of above-mentioned cooling solutions and water consumption. Therefore, the options mentioned above cannot be implemented in situations of water scarcity. Indeed, there is a huge need for cities to adopt sustainable cooling strategies that do not cause additional pressure on valuable water resource.  

For this reason, it is highly recommended that cities, using water features to manage heatwaves, adopt all precautions to minimise water consumption. This can be achieved by: 

  • integrating water use with green infrastructure options that provide cooling through the shading effect and microclimate offered by vegetation, tree canopy cover and urban water bodies in densely built urban areas with high proportion of paved soil. Climate-resilient tree species are especially suitable to this scope (see also the option Green spaces and corridors in urban areas 
  • making use of innovative design for the construction of drinking water fountains, minimizing water consumption (systems to avoid permanent water flowing) 
  • maximising the adoption of closed water cycle for not drinking purposes. Rainwater or domestic and municipal wastewater may be re-used for cooling (e.g. wetting of streets), after proper treatment (see Water re-use option). 

Planning and design of sustainable water uses for cooling can benefit from being combined  with water sensitive urban design (WSUD). 

Additional Details
Reference information

Adaptation Details

IPCC categories

Structural and physical: Engineering and built environment options, Structural and physical: Technological options

Stakeholder participation

As with any kind of urban planning, stakeholder participation is important for successful planning, design and implementation of these measures. As some urban cooling systems are complex, they need cross-sectoral collaboration and expertise from different disciplines. The private sector and local businesses can be relevant participants and can be involved in planning or covering costs of implementation. Neighbourhoods with low socio-economic status and vulnerable groups may suffer disproportionately more during heat waves as their living environment may be less green and cool than in wealthier neighbourhoods. Specific attention is needed to ensure that cooling infrastructure is developed in a socially just way in cities. Proactive outreach and meaningful involvement is necessary to ensure that targeted communities participate in urban cooling planning. Equal access to outdoor cooling options (cooling centres, parks) is crucial in effectively adapting against extreme heat, especially for the elderly population.  

Success and Limiting Factors

Strong commitment from the city leadership and support from the local Mayor interested in the adaptation agenda can be a key driver for sustainable solutions. Holistic planning as a part of other urban planning, mapping of social vulnerability and placing new systems based on holistic analyses will enhance the social and environmental sustainability of cooling systems. The measures should be included in the city planning instruments and in particular in its Adaptation Plan. The success significantly depends on the level of integration with other measures, e.g. waste-water reuse for watering gardens, to save clean water to be used for this measure. If not integrated in a broader water management plan, this measure could lead to an increase in water consumption, which would be unsustainable during droughts and heat waves. Another problem is that sustainable cooling is a cross-sectoral effort that requires collaboration between sectors and disciplines. Very often there are no clear “owners” of the measure, or no one takes responsibility for it. One important limiting factor is the lack of information on sustainable urban cooling practices, including heat-resilient urban design and the lack of available tools to support the implementation of this option. The role of education, training and sharing experiences is crucial, especially for policymakers and professionals, to ensure that norms, practices and standards, designs and plans are aligned with the technical possibilities and appropriate measures for sustainable urban cooling. Inter-departmental collaboration is needed for successful planning and implementation. 

Costs and Benefits

Direct costs can vary substantially depending on the solution. For example, the cost of using water to cool streets is low compared to complex solutions combining nature-based solutions with engineering-driven techniques (e.g. different combinations of shading, evaporation and ventilation around water bodies and mist nozzles to increase cooling effect). Extending water supply services are low cost activities. Fountains require regular monitoring and maintenance for the water quality, filters and spray nozzles. Costs can increase in situations of water scarcity and conflicting demands for water resources, with other uses and users. Cooling cities by using water can provide many benefits though, most importantly for improved wellbeing and health, especially for the elderly. Installing new drinking fountains can also have an environmental benefit, since citizens and city guests are encouraged to refill reusable bottles with tap water, instead of buying new plastic water bottles. 

There is no strong regulation for sustainable urban cooling by using water in the EU or EU member states. Local governments (municipalities) are responsible for city water and climate adaptation planning, including measures extending water supply services like (drinking) fountains and wetting techniques. 

Implementation Time

Implementation time is dependent on solutions and can vary from a few months up to a few years depending on the complexity and size of the system constructed. Local cooling systems based on man-made systems such as fountains or water showers do not take so long to complete once the decision to construct them has been made. Implementation time can be longer (several years) if these solutions are integrated in a plan that also includes more complex blue-green infrastructure such as restoration of urban brooks or developing networks of cooling places at the city scale. 

Life Time

As they are part of the built environment, established cooling systems such as fountains are usually long lasting, over 10 years. On the contrary, other cooling systems such as wetting streets or spraying public open spaces have short term effects, and require repeated implementation, when needed. 

Reference information

Published in Climate-ADAPT Aug 30 2016   -   Last Modified in Climate-ADAPT Dec 12 2023

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