NYC Flood Map - Exploratory Data Analysis

In keeping with the three topics we outlined last week:
1. Flood Maps’ “Grey Area”
We investigate the differences between proposed and existing flood maps - what makes these places difference? How are they the same? What would change if new flood maps were adopted?
This chart shows when buildings within two versions of the NYC flood zones were constructed or renovated. The red bars represent buildings that are currently in the flood zone , while the blue bars represent building that are outside of the flood zone, but would be included in the currently proposed flood boundaries. Most striking here is that buildings in the flood zone were generally renovated more recently (perhaps to comply with flood codes) than buildings outside of the flood zones. If these preliminary flood zones are accepted, there would be a significant set of buildings constructed in the early 20th century that may need to be renovated. This data comes from a ProPublica database of buildings damaged by Sandy, matched with administrative records of building construction. Flood zones are spatially joined in postGIS based on overlapping area, and analysis is done in SQL and R.

We also look at differences in income between those in the flood zone, those in the proposed flood zones, and those out of the flood zones.
We find that those in the flood zone have slightly higher incomes than those outside of the flood zone, though more analysis may be worthwhile here to control for other factors that impact home prices and median income. This data comes from the census, which was spatially joined to flood zones and graphed in R.

2. Sandy - How wrong were the flood maps? Why were they wrong? Would things have been different if they weren’t so wrong?
Here we look at the impact of Sandy on building in the flood zone and buildings outside of the flood zone, assessing the quality and impact of flood maps that grossly underpredicted damage.
The chart above measures buildings that were damaged in hurricane Sandy, showing the degree of damage and splitting data based on whether the building lay within the 2007 flood zone (which were active at the time of Sandy), the proposed 2015 flood zone, or out of a flood zone entirely. One immediately striking note is the more buildings outside of the 2007 flood zone were damaged by Sandy than buildings inside the flood zone. Expectedly, the damage was generally more severe within the 2007 flood zone than elsewhere, where nearly 40 percent of damaged buildings saw major damage or destruction. Most of the buildings damaged outside of the 2007 and 2015 flood zones saw only slight damage, though more than 5,000 buildings outside of the currently proposed zones were damaged. The data displayed here was collected by ProPublica, which analyzed damage reports collected by FEMA and the City of New York. This was joined to current and proposed flood zone in PostGIS and analyzed in R.

3. What are the factors that influence the use and creation of flood maps?
Finally, we dig into the neighborhoods that would be most impacted by changing flood zones, asking both what will happen to these places, and also how might residents make their voices heard.

Proposed flood map:
Looking closely at Tribeca in particular, one can see a significant difference in the estimated extent of the floodplain versus the reality. Tribeca property values are likely some of the highest in NYC, and it is in the interest of property owners to be able to market and sell buildings that are out of the likely flooding zone (and probably, in turn, pay less in flood insurance).
The current area marked by FEMA as .2% annual chance flood hazard, or 1% annual chance flood with average depth less than one foot falls about five-seven full blocks short of the intersection clearly flooded during Hurricane Sandy (it spread both N and S at the intersection of Lafayette and Canal, whereas the FEMA boundaries only spread N and S at Broadway and Canal). This is one area where lobbying and independently contracted flood maps may have played a role in redrawing the boundaries of FEMA’s special flood hazard areas.

Interviews for Next Week

  1. Klaus H. Jacob, Special Research Scientist, Lamont-Doherty Earth Observatory
    Klaus is very familiar with climate projections in NYC (he serves on the NYC Climate Panel) and is often quoted as source in articles related to climate projections and sea level rise in NYC. He is generally of the opinion that the climate projections are too mild if anything and is a strong voice for bold action for NYC to adapt

  2. Thaddeus Pawlowski
    Thaddeus Pawlowski is an urban designer who has been working at the forefront of adapting cities to climate change. Working in New York City government since the early 2000s, he has sought to integrate adaptation and resilience into the long term development patterns of the city through the design of projects, policies and programs. After Hurricane Sandy, he worked with the NYC Mayor's Office on setting up disaster recovery programs and worked with communities to navigate the complex regulatory programmatic, regulatory and design landscape of recovery and resilience. He has a Masters in Architecture from University of Pennsylvania and was a 2015 Loeb Fellow at Harvard University. He is also the co-director of the soon to be announced Center for Resilient Cities and Landscapes along with Kate Orff here at GSAPP

  3. Deborah Morris - Executive Director of Resiliency Planning, Policy, and Acquisitions at NYC Dept. of Housing Preservation and Development.
    Strong believer in NYC's policy that New York does NOT turn its back to the water. Would be interesting person to talk to about city policies regarding waterfront planning, increased coastal resiliency measures for buildings and housing, and the Build It Back Program.

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