Just a few decades ago, most cities in Denmark regarded rainwater as something to dispose of and hide in sewers – not as the valuable resource it actually is. Today the situation is quite different, as water is now recognised as an asset with enormous potential to enhance the daily lives of city
dwellers. This also makes investments in climate change adaptation projects easier to justify to the public. While choosing an integrated approach may initially be more complex, as it involves a broad range of environmental, economic, and social strategies, it is often more cost-efficient from an overall societal perspective.

Creating the liveable city

While there is no global definition of what makes a city ‘liveable’, various international rankings of the world’s most liveable cities typically consider factors related to dimensions such as safety, healthcare, economic and educational resources, infrastructure, culture, and environment. The best cities manage to create synergies between these dimensions. When nature-based solutions (NbS) are designed correctly, they can serve multiple functions beyond rainwater management and thereby play a key role in creating ‘the liveable city’. This is also in line with the International Water Association’s ‘Principles for Water-Wise Cities’ which among otherthings focus on Water Sensitive Urban Design that not only reduces the risk of flooding, but also enhances liveability though the presence of ‘visible water’ in urban design. The key is long-term planning, as many projects are built to last for decades, or even longer. When deciding upon which  projects to implement, city planners and other decision makers need to consider what kind of city they want to have in fifty years from now, as decisions made today will have a significant impact on the city’s urban structure for years to come. At the same time, there is a dawning understanding that the existing, expert-based service and the passive citizen role is no longer adequate. Broad stakeholder collaboration and involvement is needed.When creating liveable cities, three consecutive challenges need to be addressed:

• How do we create climate-resilient societies in practice and utilise the potentials to strengthen the sustainable transformation of urban and rural areas?
• How do we develop new types of interaction with the citizens?
• How can we work innovatively with climate adaption and develop new professional skills and approaches to planning?

Estimating the economic value of NbS by thinking of the multiple uses of rainwater, it is possible to create synergies from investments. In many cases, surface solutions with multiple functions are actually cheaper due to lower construction costs. However, assigning economic value to green or dual-purpose solutions and the positive spillover effects from these compared to traditional basins or sewerage system expansions can sometimes be difficult.

In Denmark, there are no national guidelines for calculating the benefits and added values of green solutions that involve NbS elements with multipurpose functions. However, two different tools have been developed for this purpose. The first tool is a method for comparing expenses for
building ‘grey’ vs. ‘green’ solutions. The calculations in this method include the various types of costs (such as project planning, construction work, maintenance etc.), the frequency of each cost, who the cost bearer is and if there are any associated risks. Finally, it also takes into account parameters such as the durability of the solution, the environmental effect(s), aesthetic and recreational aspects as well as possible synergies with other planned construction projects.

The second tool is called ‘SPLASH’ (in Danish: PLASK) and has been made available free of charge by the Danish Environmental Protection Agency to help calculate the socio-economic consequences of specific climate adaptation measures in a local area. SPLASH calculates the size of investments needed to guard against a given rain event and reveals the economic gains from each suggested action on a long-term basis (e.g., the reduced costs of flooding damages). The value of positive spillover effects such as increased green areas, reduced water consumption and increased CO2 absorption etc. is also included. Both tools are available online (in Danish only) and can be used by Danish urban water managers to help them plan and prioritise their efforts.