New York City Flood Risk and Climate Justice

Scientist anticipate a much higher probability of major flooding events in NYC over the next century

Were you here in New York City during Hurricane Sandy? While many of us have been fortunate enough to move on unscathed, for some, impacts linger.

Nearly 1 and 16 Americans — or 20m people — inhabit the greater New York metropolitan area. In 2012, Hurricane Sandy hit New York City causing 44 deaths and $19B in estimated economic damages as 14 ft. high storm surges covered 17% of the city’s land. [1]

Studies suggests that climate change will increase the probability and propensity of coastal storm events. [2] Given the dense population and strong economic activity in this region, further risks of flooding — from either storms, sea-level rise, intensified precipitation, or any combination thereof — threaten to once again uproot lives and result in severe consequences.

The experience of Sandy as well as continued scientific evidence of human-induced global warming has driven New York City to plan and invest in resiliency projects. Yet the question remains — are we doing enough to protect future generations and those in coastal communities in an equitable fashion?

The issue of coastal flooding in urban cities is not limited to New York City, but will be faced by cities across the globe. The UN estimates that 40% of the world’s population currently lives within 60 miles off the coast, 37% in coastal communities, and 10% in areas just less than 10 meters above sea level.

Historically, New York City has seen sea level rise at nearly double the global trend rate. Source: New York City Panel on Climate Change

The connection between climate and water resources cannot be denied, and a few dynamics are particularly noteworthy. The interactions that apply to New York City flood risk as a result of human-induced global warming include the following:

1) Impact on melting ice and related feedback loops (e.g. albedo)

2) Thermal expansion

3) Increased extreme weather events / precipitation

The first two phenomenon — melting ice and thermal expansion — are the primary drivers of sea-level rise. While there is some uncertainty within scientific forecasts due to the potential acceleration of impacts from feedback loops, high end projections over the next century approach 6 feet!

The albedo effect, for example, is one of those feedback loop uncertainties. Albedo describes the propensity of a surface to reflect light (and heat) back into space. Surface albedo will be reduced as ice caps and glaciers melt, resulting in more heat being absorbed by the earth, contributing to more warming and quickening the pace of those melting ice caps — and the cycle thus continues.

Beyond the melting of land-based ice, thermal expansion also plays a role in sea-level rise. In simple terms, this phenomenon describes the natural expansion of water as it warms. In this context, oceans absorb ~90% of the increased atmospheric heat caused by human-induced global warming. [3]

Projections for sea level rise in New York City at the low end follow a linear trend line, and at the high end represent 5.7x the increase from 1900–2013 — suggesting major implications for city planners and resilient infrastructure development and maintenance. Source: New York City Panel on Climate Change 2015 Report.

Changes in the frequency of extreme temperature, particular that of intense precipitation will also contribute to increased risks of coastal flooding. There is a relationship between atmospheric capacity to store water vapor, temperature, and the intensity and frequency of rainfall.

Put simply, the higher the temperature, the more capacity the atmosphere has for storing water vapor, which leads to more frequent and intense periods of precipitation.

There is an important relationship between temperature, the saturation of water vapor, and intensity and frequency of rainfall. Further warming drives the expectation for increased humidly in the New York City region and will increase the likelihood of extreme precipitation events. Source: New York Panel on Climate Change Report, 2019.

Scientist anticipate a much higher probability of major flooding events over the next century. Source: New York Panel on Climate Change Report, 2015.

Climate Justice and Way Forward

Just as on the global scale, climate impacts will affect those who contribute to climate change the least. The top 10% richest people produce half of global carbon emissions, while the poorest half contribute only 10%. [4]

While companies are just beginning to disclose their respective carbon footprints, they have certainly not yet fully priced those costs into their operating structures. In many ways, government funded resiliency projects, directly paid for by NYC taxpayers, represent a wealth transfer as citizens pay the environmental costs of company impacts on climate change.

Further, low-income groups may be particularly vulnerable to the increases in flood insurance costs. Globally, there are many scenarios where those who contribute the least to climate will be the most severely impacted. Let’s re-write the script in the name of climate justice!

[1] Lower Manhattan Climate Resilience Study. March 2019. Mayor’s Office of Recovery & Resiliency

[2] New York City Panel on Climate Change Report, 2019.

[3] National Ocean Service

[4] Extreme Carbon Inequality. 2015. Oxfam