Close city-to-city collaboration on cloudburst management leads to historic New York investment

Last week, New York City Mayor Eric Adams announced the expansion of the city’s Cloudburst Program which includes clustered stormwater management projects in four flood-prone areas. This marks a major milestone for the city’s continued resiliency efforts to better prepare for intense rainfall events, like Hurricane Ida in 2021.

Supported with nearly $400 million in capital funds, these infrastructure projects aim to protect both residents and property in Corona Park and Kissena Park in Queens, Parkchester in the Bronx, and East New York in Brooklyn from future extreme weather caused by climate change.

“This $400 million investment in stormwater management projects cement New York City’s status as a national and global leader in green infrastructure and shows our commitment to protecting New Yorkers from disastrous floods,” said Mayor Adams.

This program expansion can benefit millions of New York citizens, improve local environments, and help reduce CO2 emissions. It represents a peak in a seven-year long city-to-city collaboration between Copenhagen and New York on climate resiliency and cloudburst management. Ramboll has played a prominent role in this collaboration.

The two cities started collaborating in 2012 in the wake of Hurricane Sandy’s damage. New York City strengthened its large-scale planning efforts to cope with cloudbursts. The city looked to sister cities which face similar challenges for inspiration and knowledge-exchange opportunities.

The year before, in 2011, Copenhagen was hit by a destructive downpour which caused approximately USD $1 billion in damages. This event kick-started the development of a flexible, universally adaptable approach to mitigating cloudbursts through a combination of grey and green solutions. The model also integrated urban planning, traffic, and hydraulic analyses with sound investment strategies to improve citizens’ quality of life.

Copenhagen’s cloudburst approach was created through a close collaboration between the City of Copenhagen and several consultancies. Ramboll was involved from the start of the model’s development and created the Cloudburst Masterplan based on the model which influenced New York City’s climate resilience development which influenced New York City’s climate resilience development.

The Copenhagen cloudburst approach was led by Lykke Leonardsen, Head of program for resilient and sustainable city solutions for the city of Copenhagen. Over the years, Leonardsen has met with members of the New York City Department of Environmental Protection (DEP) to exchange knowledge and experience.

Christian Nyerup Nielsen, Ramboll’s Global division director for water infrastructure and climate adaptation, and Trine Stausgaard Munk, the Global urbanism manager at Henning Larsen Architects, also joined many meetings to provide climate adaption expertise and experience.

In 2016, NYC DEP asked Ramboll to conduct a climate adaptation study and pilot project. The pilot project included a Cloudburst Master Plan for the South Jamaica Houses project in Queens. Inspired by the Copenhagen cloudburst approach, the study provided best-practice insights, an integrated planning framework, and conceptual designs for specific pilot projects in NYC.

Aligned with the Copenhagen approach, the new investments allow NYC DEP to install innovative and adaptive methods that absorb, store, and transfer stormwater to prevent flooding during a rainstorm. This includes incorporating grey and green infrastructure, as well as open spaces, to store excess stormwater. These resilience pilot projects incorporate various plans intended to mitigate future extreme weather events predicted to bring up to 5.842 cm (2.3 inches) of rainfall per hour, as well as fortify neighbourhoods against climate change.

Considering Mayor Adams’ investment announcement, Lykke Leonardsen is happy to see the full program being brought to life:

“With this initiative, New York City is taking a major step in flood-proofing the city. Copenhagen and New York have worked intensively together for the past seven years on developing this and it is fantastic to see it will now become a reality,” she says.

Christian Nyerup Nielsen, who was heading the cloudburst masterplan projects in both Copenhagen and New York City shares the happiness and emphasises that Lykke Leonardsen has been a great ambassador for the City of Copenhagen as well for the Danish water sector.

“It is so great to see how close collaboration and mutual inspiration between cities can foster new ideas. It has led to substantive investments addressing flood risks in a modern and sustainable way. Once all the projects are implemented, citizens in flood-prone areas will not only benefit from reduced damages but also from the newly created recreational areas,” he says.

Most recently, NYC DEP and Ramboll took a knowledge exchange tour of the Danish capital, sharing experience related to climate adaption during the IWA World Water Congress in September 2022. And according to Christian, there are still things that NYC can learn from Denmark:

“Firstly, New York City could be further inspired from the methods we use to gather, qualify, and not least share data among all stakeholders to ensure the evidence-based planning and design. Secondly, I think they could benefit from applying a multi-agency approach to planning and designing the solutions to optimise the efficiency and co-benefits. Thirdly, I would encourage the city to focus even more on the climate justice dimension and make strong business cases for the solutions to make sure that these plans will survive the political processes.”

Construction on the cloudburst projects in the four new neighbourhoods is expected to begin in 2025.