Tucked away beneath courts for playing the bowling game pétanque, its entrance part-concealed by hanging plants, lies a cavernous concrete tank for collecting floodwater.
The underground tank in Barcelona's northern Horta district is the size of 19 Olympic swimming pools, and three or four times a year it partly fills up during heavy rains, siphoning off water that might otherwise flood the city.
The retained water is then pumped to a treatment plant, and ultimately re-used for cleaning streets and irrigating gardens.
Completed in 2011, the storage tank is one of 13 around Barcelona – but more are planned as the city prepares for climate change, which is expected to bring less rainfall but in more intense bouts.
Around the world, cities threatened by increasingly severe floods and droughts are looking for ways to cope – a particular challenge when urban space for solutions is often limited.
In compact Barcelona, Spain, Horta's water tank hosts a park on its roof, an added attraction for people living nearby.
Katie Vines, head of adaptation research for the C40 Cities Climate Leadership Group, says a big innovation in boosting resilience to disasters and climate change is to combine those efforts with other improvements for local communities.
"The value of something not happening is very difficult to monetize, and so you have to create projects and programs whereby there are immediate as well as long-term benefits," she said.
That could mean enhancing biodiversity by restoring wetlands, building urban drainage in a way that makes streetscapes more pleasant, or mitigating urban heat by planting trees or gardens atop buildings.
In New York City, for example, an initiative to paint black roofs with a white coating that reflects heat and cools building interiors has provided training for job seekers, Vines said.
United Nations and development bank officials have argued for more than 10 years that investing $1 in ways to protect people and assets saves between $4 and $7 in losses from disasters.
The trouble is that the evidence base for that assertion has always been "flaky" and is rarely questioned, according to Tom Mitchell, head of the climate and environment program at the London-based Overseas Development Institute (ODI).
In addition, it has failed to get much traction in finance ministries, especially in poorer developing countries, he said.
"Presenting a cost-benefit analysis on a hypothesis or a scenario is not something that gets ministers of finance with very pressed public budgets interested," Mitchell told the Thomson Reuters Foundation. "They'd rather spend on something that brings them a bounce in terms of the votes they might win, and that tends to be focused on things like health, education, and infrastructure."
A better approach is to highlight the short-term wins from investing in measures to prevent disasters, Mitchell said. Economic, social, and environmental benefits can help convince businesses they have "safe spaces" for their money, he added.
New research to be presented by the ODI and other experts at a global conference on reducing the risk of disasters in Japan this month argues that investing in resilience can support economic growth and bring other dividends, besides lowering disaster losses.
In the case of Barcelona, which has won international recognition for its efforts, a three-day power blackout in 2007, caused by a fire at an electricity sub-station, was the impetus for change after the city was left struggling to provide basic services.
"The loss of energy affected many things. Without electricity, we didn't have elevators or water pumps," said Manuel Valdés, deputy manager of infrastructure and urban coordination for the Barcelona City Council.
Since then, the authorities and the private sector have introduced a system that alerts energy, water, communications, and waste management service companies to problems and activates joint contingency plans, he told a recent conference on urban resilience in the city.
Bogotá's risky slopes
In the Colombian capital Bogotá, meanwhile, the city and its partners are working to cut disaster risk and make life better for residents by turning a landslide-prone area in the south into a protected park.
Some residents of Ciudad Bolívar remember how houses were crushed in landslides that began in 1997, partly as a result of quarrying and unplanned settlements. Some 3,300 families were given financial help to move off the unstable land.
Now in the grassy 73-hectare (180 acre) Altos de la Estancia park, paths snake past wooden terraces planted with bushes, flowers, and trees. There are water-filtering systems, a community farm, and a retaining wall decorated with graffiti by local youths.
The city has a plan to make similar use of 114 hillside sites where people are at risk. Duván Hernán López of Bogotá's Institute for Risk Management and Climate Change (IDIGER) said the goal is to make these areas part of the urban landscape, and to stop them being resettled.
The city has set up a special council to manage disaster risk and climate impacts, as well as a new fund to pay for projects. It receives 0.5 percent of the city's revenues.
For Han Admiraal, chair of the International Tunneling Association's Committee on Underground Space (ITACUS), the biggest threat to cities is "to look at every challenge ... as a separate issue. "You can solve a lot of these things at once. You can integrate mass transport systems with water management, and you can also think about energy," he said by telephone.
Jakarta, Indonesia, and Bangkok, Thailand, for example, have plans to build underground tunnels with two to three levels that can be used to carry vehicles or floodwater as needed, on the model of Kuala Lumpur, Malaysia's 9.7 km (5.6 mile) Stormwater Management and Road Tunnel (SMART).
While big engineering schemes like these are expensive, Malaysian officials have said the government's 2 billion ringgit ($551 million) investment in SMART was largely recovered in just three years by a toll fee and avoided losses from flash floods.
Rising real estate prices in better-protected central districts may be another financial positive, Admiraal said.
"It often creates a lot of value above ground, and if you factor that in these are very sensible business solutions rather than huge costly projects," he said.
(Reporting by Megan Rowling; editing by Laurie Goering)
• This article is part of a Thomson Reuters Foundation series on preventing disasters, ahead of a conference to adopt a new global action plan to reduce the risks of disasters in Sendai, Japan, in mid-March.