Among NYC's corporations owning  stock of affordable rental housing are Hope and Ascendant. Hope’s Property Management Department services and Ascendant Neighborhood Development (the former referred to as HOPE and the latter referred to as AND from now onward) are two community-based not-for-profit affordable housing organization based in East Harlem. The two organizations are part of a larger coalition of CDCs, called the Northern Manhattan Coalition (NMC), which in total represents 157 affordable rental properties. Both organizations advocate for the preservation of affordable housing in New York City, "as rapid increases in market-rate residential and commercial development propel speculation, drive up rents, and encourage tenant harassment and displacement" (AND website). Just 22 percent of rental units in New York City are affordable to households whose annual income is below $30,000. Both organizations also work to strengthening the neighborhood's social fabric by assisting in the growth and success of local businesses, by assisting residents to enhance their lives and incomes, and by sponsoring community programs.
 
HOPE owns over 1,300 affordable apartments in more than 78 buildings throughout Central and East Harlem (Community District 10 and 11). AND owns over 628 apartments in 28 buildings.  During a meeting at the New School both Hope and Ascendant, expressed the need for evidence-based mapping to understand the exposure to flooding to their properties. Following a meeting with Hope, one of the main problems seems to be ‘blue sky flooding’, the type of flooding occurring without stormy weather and influenced by high tides at seas, high ground water table and surface elevation. There is anecdotal evidence that this type of flooding affects basements, which are recurrently flooded, but for which Hope has very little funding for left over after what goes towards regular building maintenance. Moreover, Hope has been receiving a number of violations from ConEd, NYC's energy company, because as flooding affects basements, officers cannot access gas and water readings  stored there. Because of these violations, HOPE has been unable to close housing retrofitting deals with for-profit-banks they partner with. At the same time HOPE has been an early adopter of green infrastructure, like green rooftops and gardens, thanks to funding made available by the city. However, green rooftops address a different problem: they slow down excess rainfall but they do not slow down water coming from below, or from coastal storm surges. 
Initially this study was going to access data on occurrence of inland flooding in basements from the building manager service SiteCompli. This website contains information about the violations that both organization incur year round since 2012. A close inspection of the data revealed that violations are filed for issues such as "sewer backup" but no further explanation is given about whether the violation was filed because inspectors could not access the basement due to flooding. The number of complaints  related to sewer backup was also too small to warrant visualization through GIS mapping (36 complaint between 2010 and 2018). The fact remains that, so far, violations descriptions are not capturing important information about whether the violation is issued as a result of the inability of inspectors to access the basement due to flooding.  Therefore we based our analysis on coastal flooding alone but we recommend Hope and Ascendant Property managers to produce a protocol for collecting more accurate descriptions of violations occurring as  consequence of flooding. In the long term, we see a need for quantifying the hidden recurrent costs due to basement flooding, adding to the burden of regular housing maintenance costs.  

A Framing for Flood Vulnerability in New York City

This project aims at a large scale mapping of the vulnerability to coastal flooding of both Hope and Ascendant properties. GIS is used for this purpose. GIS and remote sensing are critical tools for analyzing, preparing for, mitigating, and responding to natural and human-induced disasters, including from flooding events \cite{Huang_2009}\cite{Strobl_2012}. Geo-spatial technologies are used to estimate the risk of occurrence of a disaster based on physical and/or social dimensions. These two dimensions are brought together in the concept of risk, which is a function of a hazard, the exposure to it and social vulnerability, defined below after \citet{Rosenzweig,Ka_mierczak_2011}.  Although there may be many variables influencing exposure to floods, here I refer to exposure as the susceptibility of people, properties and systems to being affected by an environmental related hazard \cite{Cutter_2005,Cutter_2012}, which in this case is understood to be the current and projected floodplain in Central and East Harlem, New York City. We furthermore consider as elements of exposure the number of affordable housing buildings and their topographical elevation.  In terms of socio-economic vulnerability, we considered three variables that can compound the threat of CDCs housing units to present and coastal flooding in East Harlem. In East Harlem the percentage of people living below the federal poverty level is slightly higher (22%) than the mean for the whole city of New York (20.5%, U.S. Census, 2010), and research shows that people living in poverty and who are socially marginalized have reduced capacity for self-protection in terms of mitigating flood hazards at home pre-event, evacuating  in response to flooding, or returning home or to employment in the aftermath of a flooding event, accessing social protection such as flood insurance, hazard mitigation infrastructure, emergency response information and assistance \cite{Collins_2009,Collins_2012,Elliott_2006,Maldonado_2015}
The second variable of socio-economic vulnerability is related to the benefits and drawbacks of urban rezoning plans. Changes in land use zoning and floor area ratio (FAR) permits can have important impacts on neighborhoods’ populations by increasing property costs  and influencing housing careers, skewing access to services and utilities, affecting the distribution of parks and public space. Rezoning can lead to increased density and waste water pumping needs These impacts can lead to the progressive displacement of low-income socioeconomic groups but also of certain land-uses such as industrial land uses and manufacturing \cite{Curran_2007}. The changing of  land uses can imply the loss of economic stability for working-class communities \cite{Wolf_Powers_2005} and their ability to equally access opportunities and privileges in society.  In this study we pay attention to the urban blocks interested by the East Harlem Rezoning Plan approved by the New York City Council in 2017, and which is expected to result in a net increase of approximately 3,500 dwelling units, a substantial proportion of which are expected to be affordable. However, this portion may be allotted to for profit developers instead of CDCs, who can guarantee to keep the rent to a level of affordability in line with the needs of the poorest segments of society. There is reason to believe that the East Harlem Rezoning will just hand over more of the affordable housing stock into the hands of property developers, reframing what affordability means by potentially increasing the density of market rate housing or changing the ways in which local people can afford the amenities in their neighborhood. This is troubling for two reasons: the share of severely burdened renters, among the  921,000  renter households in New York City remains steady at 22% \cite{commission2018}. At the same time, over the past decade or so, New York city housing has been shifting in favor of more middle and high priced rentals, in a glaring erosion to the inventory of rent regulated housing \cite{stringer2018}.
The third variable of socio-economic vulnerability is represented by the date of expiration of the affordable rent subsidy. In exchange for a government subsidy, privately owned, publicly subsidized rental housing corporations agree to keep units affordable to low- and moderate-income households for a set number of years, typically 30 years. After a regulatory agreement expires, however, owners can begin to rent their units at market rates. This, however would not be possible for corporations like Hope and Ascendant, whose mission is to provide and maintain affordable housing. Hope and Ascendant, apply for subsidies, at the federal level, to the U.S. Department of Housing and Urban Development (HUD) and the city level, to the NYC Housing and Preservation (HPD). We account the subsidy expiration as a possible socio-economic vulnerability because, should the subsidy fail to be renewed the tenants risk rent spikes or evictions. According to a 2016 analysis by the NYU Furman Center, by 2020, the regulatory agreements governing of 157 federally subsidized residential properties in New York City are set to expire. Over the following decade, an additional 593 will follow suit \cite{center2016}.
 
This large scale mapping project aimed to answers the following questions: 
  1. How many Hope and Ascendant properties are in the current and future floodplain?
  2. How do Hope and Ascendant buildings compare with the rest of the buildings in Central and East Harlem?
  3. What is the average elevation of flooded and not flooded BBL under different flood scenarios?
  4. Where are high or low socio-economic vulnerability clusters located within East Harlem?