Increasing amounts of rainfall and more powerful cloudbursts caused by climate change are posing a challenge to the city of Copenhagen. The city has worked for years to reduce overflows from the city's combined sewer system to improve conditions in the city's water areas. This has led to major environmental improvements in the city's water areas and, since 2002, swimming has been possible in the port of Copenhagen.

If action is not taken soon to reduce the climate impact, there is a risk that the environmental improvements the city has achieved over the last decades will be lost. Furthermore, there will be major damage and financial losses as a result of the more frequent cloudbursts of the future.

The climate adaptation plan and the cloudburst plan integrate the management of both everyday rain and cloudbursts in the development and transformation of the city in a way that is both economically and environmentally sustainable, so the city becomes climate-proof and able to withstand climate change 100 years into the future.

The work began with the City Council's approval of the climate adaptation plan in 2011 and the cloudburst plan in 2012. Both plans were strategic plans which formed the basis for an implementation plan for climate adaptation of Copenhagen. Implementation of the plan was decided by the city council in 2015, with an expected implementation period until 2035. 

Implementation of the plan is well underway and 11 major surface projects and 2 major cloudburst tunnels have been constructed. 60 surface projects of 300 are under development. The surface projects have added more green recreational areas to the urban areas and increased biodiversity. In one of the projects, 75% of the former grey surfaces have been transformed into green areas. 

A socio-economic method has been developed for determining the amount of rainwater that needs to be managed in order to become climate resilient. This includes a method for assessing the current risk of damage during cloudbursts and the projected risk of damage over the next 100 years as a result of climate change. 

To support this, descriptions of solution topologies have been developed for surface solutions. These typologies have been used to develop a comprehensive plan for climate proofing the whole city. An assessment has also been made of the need for greening the city as a way to improve the urban environment. 

The design for the master plans includes a concept for detailed analysis of sub-areas with the goal of creating a greener city with more recreational areas and increased biodiversity. So far, 9 major surface projects have been implemented, with 66 more in the design and planning phase. These projects will be carried out in synergy with other projects to achieve the goals of the master plan.

The lead agency for the project is the City of Copenhagen in collaboration with the utility company HOFOR. The total cost of implementing the plan is estimated at 1.7 billion euros. Costs are divided between water tax (approx. 1.3 billion EUR), municipal tax (0.13 billion EUR) and private investments (approx. 0.3 billion EUR). So far, approx. 0.7 bio. EUR is invested in the projects.

The key to success in the cloudburst management plan is the many partnerships that contribute to the realization of the projects. Citizens are engaged in the development of the projects. There are workshops, working groups and many other ways of engaging the local community, which creates a strong feeling of ownership. It is also important to engage the local community in the development of projects to increase their knowledge of local rainwater solutions and how they can be linked to local development. The same goes for private land and house owners. Additionally, in developing the plan, the implementation team collaborated with many different departments in the municipality.

One of the major challenges was financing the implementation of the plan. This was overcome by successfully lobbying for a change in the law, which allowed the City to develop the projects in collaboration with the utility company. The utility company charges water tariffs, which in turn helped to finance the implementation.

One obstacle to the development of multifunctional urban space solutions is the potential for water damage. To solve this, water is only retained at the surface for a short period of time, so that damage to plants, unwanted contact with water, or problems with mosquitos can be avoided.

Implementation of Copenhagen's climate adaptation and cloudburst planned has required the collaboration of different departments of the City Council and experts in the climate and scientific sectors.  Implementing the plan throughout the municipality has solved some major challenges including the establishment of green areas in socially disadvantaged urban areas. Based on this experience, the Council has decided to restructure some departments in the municipality and now planning, design and construction are in one unit. 

Future plans that include the use of nature-based solutions for climate adaptation projects are being developed with a view to climate-proofing the city and creating more green spaces that increase social cohesion between citizens. Additionally, citizens benefit from the plan by protecting their properties from cloudbursts and making the district greener and more attractive.  

The City of Copenhagen has developed a full concept for climate adaptation of a metropolitan area, including methods for risk assessment, socio-economic analysis, development of solution typologies, forms of financing, master plans and organization of work. The data collected is available to everyone and is published on the City’s website. The City is also entering into partnerships with other cities to further develop climate adaptation initiatives.