Intersecting Fluvial and Pluvial Inundation Estimates with
Sociodemographic Vulnerability to Quantify Household Risk in Urban Areas
Abstract
Methods to estimate compound flooding at the household level are largely
nonexistent outside of complex computational models. The exclusion of
topographic depressions, and therefore pluvial flooding, from leading
flood hazard maps is also underestimating potential exposure.
Furthermore, national level exploratory analyses have yet to capture
local variability in exposure and social vulnerability, which is
necessary for local stakeholders to identify the inequitable
distribution of flood risks. Using high resolution elevation data to
approximate event specific inundation from both pluvial and fluvial
sources, in conjunction with a localized social vulnerability index, we
created a methodology to estimate flood risk at the household level. Our
analysis uses the 2015 Memorial Day Flood in Austin, Texas as a case
study and proof of concept of our estimation methodology. We show that
the inclusion of pluvial flood sources increases inundation extents,
with 37% of the Census Block Groups in the study area experiencing
flooding from only pluvial sources. Furthermore, averaging flood depths,
and therefore exposure estimates, to geographical and cartographic
boundaries (e.g., Census Block Groups), masks household variability,
with 80% of the Census Block Groups in the study area having a
coefficient of variation around the mean flood depth exceeding 100%.
Comparing our pluvial flooding estimates to a 2D hydrodynamic
physical-based model, we classified household exposure accurately for
92% of the parcels. Our methodology can be used as a tool to estimate
the impacts of inland compound flooding on household risk in order to
provide a first estimate of storm specific risk.