Week 3: Flood Zone Analysis

This weeks assignment was to perform coastal flood zone analyses.  Specifically, we created a map of the District of Honolulu after a modeled 3ft and 6ft sea level rise (SLR) scenario, then analyzed the social impacts of the flooded area using demographic data from the US Census Bureau.  The map above shows the area flooded by a 6 ft sea level rise and the general population density in Census Tracts.  It was created by first demarcating the area that would be flooded using the Less Than tool with the original Raster DEM.  Then the depths were calculated by using the Minus tool between the new raster and the the original DEM.  The high population density near the coastline is noticeable in this map.  Below is a table of demographic data extracted from Census blocks (finer scale than Tracts).

Variable	Entire District	6ft SLR
		Flooded	Not Flooded
Total Population	953207	60005	893202
% White	20.85%	29.58%	20.26%
% Owner Occupied	56.77%	38.13%	58.02%
% 65 and Older	14.53%	17.04%	14.36%

The table shows demographic data for the areas flooded and not flooded by the simulated sea level rise of 6ft in Honolulu District, HI.  For comparison, there is demographic data for the entire Honolulu District.  This data is based on the 2010 U.S. Census.  All homes affected are located within close proximity to the coastal in Honolulu District. Clearly the populations affected by the 6ft SLR flood zone are different than the populations not affected by them.  Specifically, there is a greater proportion of persons 65 years and older and persons who describe themselves as “white” in the 3ft and 6ft SLR flood zones compared to the non-flooded zones.  Conversely there is a smaller proportion of owner occupied housing. 

These data can be examined in the context of social vulnerability.  While it is unclear that there is any social or political marginalization in this area due to racial disparity, areas in the United States with a high proportion of persons who describe themselves as “non-white” may be more vulnerable to environmental catastrophes (e.g. Hurricane Katrina; Cutter & Emrich 2006 as cited in Shephard 2012).  While the proportions described here for “white” persons is low compared to the national average, this is to be expected on a Hawaiian island to which “white” persons are secondary colonists.  The lower proportion of Owner Occupied housing in the flooded zones may be a result of seasonal/vocational visits by the owners, or some sort of rental-tenant situation.  This is important for social vulnerability because renters may not know local evacuation routes, or may not have access to personal vehicles for an evacuation situation.  Further, non-owner occupied housing is disproportionately uninsured, which could cause issues during flooding situations.  Lastly, the higher proportion of individuals 65 and older is significant because they may require assistance in an evacuation scenario, increasing their vulnerability to harm.

It should be noted that the 6ft flood zone affects a more racially diverse group of people than the 3ft flood zone.  This is observed in the decrease in the proportion of “white” persons affected from the 3ft to 6ft flood zone scenarios (from 36.79% to 29.58%).  It could be speculated that the greatest density of “white” persons is near the coast of Honolulu.