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Tech Tool for Mapping Urban Flood Risk

October 28, 2021
Urban flooding is a growing concern in cities like New York. Connecting the Dots provides a 3D visualization of how neighborhoods could be impacted by floods and a mapping application that charts the risks. edenpictures/Flickr

Cities around the world are ramping up their efforts to combat the impacts of climate change, and New York is at the forefront of this movement. From ambitious coastal protection projects to the creation of the Climate Resiliency Design Guidelines for every stage of the building lifecycle the city is taking a proactive approach to protect its 578 miles of shoreline and vulnerable coastal neighborhoods. While many of these strategies are geared toward individual buildings, imagine being able to plan for the resiliency of an entire community. A new web-based mapping tool can help do just that.

Connecting the Dots is application software that seeks to raise awareness of how climate change and sea-level rise can have an effect on New York City. Developed as part of my participation in the 2020 UN Local Pathways Fellowship Program, it consists of two components: a 3D visualization of how buildings, streets and entire communities could be impacted by flooding, and a web-based mapping application that aims to support place-based planning by providing information on current and future flood risk, city hazard mitigation projects, land use and development trends.

The dire need for greater resiliency became apparent this past summer when the National Weather Service issued its first-ever flash flood emergency warning for New York City because of heavy rains from Hurricane Ida. Unlike coastal and riverine flooding, urban flooding is a lesser-recognized—and underestimated—threat. While it can be caused by natural disasters, like Hurricanes Ida or Sandy, urban flooding more frequently occurs when significant rainfall overwhelms local stormwater drainage capacity. Therefore, neighborhoods with crumbling or inadequate infrastructure are more prone to flooding. It also tends to affect those who are less likely to be covered by flood insurance.

One of the lessons learned in the aftermath of 2012’s Hurricane Sandy was the need for a holistic approach to resilience. Even businesses with the foresight to protect their properties against natural disasters still took a hit to operations from damage to critical infrastructure and supply chain disruption. The city’s long-term strategic plan, OneNYC 2050, has set forth sustainable development goals and initiatives to address such climate-related challenges. It includes empowering property owners, policymakers and local communities to work together to develop place-based programs to improve resilience.

Connecting the Dots uses the city’s stormwater flood maps developed earlier this year as part of its stormwater resiliency plans. The goal of the app is to better communicate the risk by making the data more accessible to the public so they can take appropriate action. Property owners located in areas with high risk of urban flooding, for instance, should consider mitigation measures to prevent wet basements and sewer backups when a heavy precipitation event is forecasted.

The web app combines the flood hazard data with information from the New York City Hazard Mitigation actions plan and city development layers. The mitigation actions/projects are color coded by category, such as coastal natural resource protection, infrastructure project, prevention and policy and property protection. A pop-up of each project provides a short description, project timeline leading agencies and other relevant details (see figure 1).

Figure 1

I performed a trend analysis using New York City Department of Buildings incomplete/ongoing projects data. As shown in figure 2, red areas are projected hot spots for real estate and housing development for the near term. The map shows a rise in waterfront development and the distribution of the city resilience projects within these fast-growing neighborhoods. Connecting the Dots is designed for New Yorkers who don’t necessarily want to be climate change experts but want to still be able to plan for its impact. Here’s how it works: A property owner in the East Village, for example, can use the map to find out if its building is located within the current or future floodplain. In addition, it can see that the East Side Coastal Resiliency (ESCR) project targets reducing flood risk on Manhattan’s East Side. The project is currently under construction with an expected completion date in 2026. Connect the Dots notes that ESCR is designed to protect against the 2050s 100-year storm (8-9 feet above the existing ground elevation). Hence, the property owner will need to provide interim flood protection while ESCR is under construction and decide whether to invest in additional preventative measures beyond those provided by ESCR. With more and readily accessible information, property owners can optimize their investment in climate-smart adaptation measures and actively engage in community planning.

Figure 2

Sometimes small actions have the power to make a difference to an entire community. By educating the public about flood risk, we hope to incentivize people to protect their assets and to become actively engaged in resilience planning. Future iterations of the tool may include information sharing, which could facilitate a more active dialog between public agencies and local stakeholders. It could serve as a forum for everything from connecting property owners interested in supporting a community-wide flood resilience programs to informing residents of buildings willing to provide shelter during severe climate events. It’s all about connecting the individual dots to make New York City more resilient.

- Barbara Gao, Resilience Engineer, New York