Uncertain seas: probabilistic modeling of future coastal flood zones

Abstract

Future sea-level rise will likely expand the inland extent of storm surge inundation and, in turn, increase the vulnerability of the people, properties and economies of coastal communities. Modeling future storm surge inundation enhanced by sea-level rise uses numerous data sources with inherent uncertainties. There is uncertainty in (1) hydrodynamic storm surge models, (2) future sea-level rise projections, and (3) topographic digital elevation models representing the height of the coastal land surface. This study implemented a Monte Carlo approach to incorporate the uncertainties of these data sources and model the future 1% flood zone extent in the Tottenville neighborhood of New York City (NYC) in a probabilistic, geographical information science (GIS) framework. Generated spatiotemporal statistical products indicate a range of possible future flood zone extents that results from the uncertainties of the data sources and from the terrain itself. Small changes in the modeled land and water heights within the estimated uncertainties of the data sources results in larger uncertainty in the future flood zone extent in low-lying areas with smaller terrain slope. An interactive web map, UncertainSeas. com, visualizes these statistical products and can inform coastal management policies to reduce the vulnerability of Tottenville, NYC to future coastal inundation.

Inundation Exposure Assessment for Majuro Atoll, Republic of the Marshall Islands Using A High-Accuracy Digital Elevation Model

“…There is a rich heritage of treating elevation error probabilistically [52,[55][56][57], and the method has been successfully applied and its advantages demonstrated in numerous recent sea-level rise and inundation assessment studies [21,46,49,53,[58][59][60][61][62]. For users of an assessment conducted with the probabilistic method, the stated probability indicates the likelihood, or chance, that the mapped area will be impacted at the specified increased water level, for example a 68% chance (or at least 68 times out of 100) that the area will be inundated.…”

Sensitivity of Flood Hazard and Damage to Modelling Approaches

“…Many low-lying areas that are sensitive to coastal flooding during storm events will be overwhelmed with just 25 cm of sea-level rise along the California coastline; in combination with a 1:100 year storm event this could cause substantial flooding that would impact 150,000 residents and cause up to $30 billion damage [92]. Future sea-level rise will increase 'tail waters' and reduce the rate at which low-lying coastal and estuarine areas are able to drain floodwater, increasing the likelihood of further inundation from subsequent storm or rainfall events [93]. Extreme events can cause initial damage from flooding, but lack of drainage, potentially exacerbated by subsequent events, can cause knock-on effects to impact economic sectors in relation to closure of ports and harbours or disruption of transport of goods, and critical services (e.g., power, water, and communications), essential for public safety.…”

Housing Market Value Impairment from Future Sea-level Rise Inundation

“…In addition to the discount rate assumption, our housing market impairment analysis makes a series of simplifying assumptions: First, we assume that once a property is inundated by SLR, the value of the property falls to zero, which is an assumption in line with previous research (Bernstein et al, 2019). In reality, additional flood risks from nuisance flooding or enhanced storm surge would also erode economic value well before terminal impairment from SLR inundation (Amante, 2019;Ghanbari et al, 2019;Beltrán et al, 2019). Second, our approach assumes no foresight on the part of homeowners, who would likely begin to discount property values well before terminal impairment or might take steps to protect their properties (e.g., by erecting protective flood walls).…”

“…Accurate, high-resolution DEMs are needed to both delineate areas with low elevations below a projected sea-level and to determine hydrologic connectivity. Natural terrain features (e.g., gullies, hills) and man-made terrain features (e.g., culverts, levees) can enhance or impede the flow of water and affect flooding at inland elevations (Li et al, 2009;Poulter and Halpin, 2008;Gesch, 2009;Zhang et al, 2013;Amante, 2019). The spatial resolution of the DEM is an important factor in coastal flood modeling, as it determines the ability to resolve these terrain features (e.g., gullies, hills, culverts, and levees) that can affect hydrologic connectivity.…”

“…As sea-levels slowly rise, these locations will likely face increased nuisance flooding (Moftakhari et al, 2015;Sweet et al, 2017), enhanced storm surge inundation (Amante, 2019), and permanent change of coastlines. In extreme cases, some coastal areas may experience out-migration, and city planners may need to implement policies to facilitate population departure (Wrathall et al, 2019).…”