A Geospatial Assessment of Flood Vulnerability Reduction by Freshwater Wetlands-A Benefit Indicators Approach

Abstract

Flooding is among the most common and costly natural disasters in the United States. Flood impacts have been on the rise as flood mitigating habitats are lost, development places more people and infrastructure potentially at risk, and changing rainfall results in altered flood frequency. Across the nation, communities are recognizing the value of flood mitigating habitats and employing green infrastructure alternatives, including restoring some of those ecosystems, as a way to increase resilience. However, communities may under value green infrastructure, because they do not recognize the current benefits of risk reduction they receive from existing ecosystems or the potential benefits they could receive through restoration. Freshwater wetlands have long been recognized as one of the ecosystems that can reduce flood damages by attenuating surface water. Small-scale community studies can capture the flood-reduction benefits from existing or potentially restored wetlands. However, scalability and transferability are limits for these high resolution and data intensive studies. This paper details the development of a nationally consistent dataset and a set of high-resolution indicators characterizing where people benefit from reduced flood risk through existing wetlands. We demonstrate how this dataset can be used at different scales (regional or local) to rapidly assess flood-reduction benefits. At a local scale we use other national scale indicators (CRSI, SoVI) to gauge community resilience and recoverability to choose Harris County, Texas as our focus. Analysis of the Gulf Coast region and Harris County, Texas identifies communities with both wetland restoration potential and the greatest flood-prone population that could benefit from that restoration. We show how maps of these indicators can be used to set wetland protection and restoration priorities.

Keywords: benefit indicators; flooding; geospatial; resilience; wetlands.

FIGURE 1 |

Workflow used to characterize catchment attributes using (A) landscape input datasets. Catchments were characterized by landscape attributes either (B) as a percent of catchment area, for wetlands, or (C) as a total after being overlaid with a flood-prone-area, for flood-prone population.

FIGURE 2 |

Example of how upstream/downstream catchment metrics were calculated from catchment attributes.

FIGURE 3 |

Map of catchment percent wetlands in the contiguous United States. Catchment values range from 0.00 to 1.00. The US border is used to show where the NWI dataset stops, indicating catchments outside that border include areas of missing data.

FIGURE 4 |

Maps of population in flood-prone areas using FEMA (A) and EnviroAtlas (B) flood zone extents. Colors for the number of people in flood prone areas within each catchment use a consistent scale across the two maps to facilitate comparisons.

FIGURE 5 |

Map of HUC-8 percent wetland quartiles (A) scaled nationally, with the Gulf of Mexico region highlighted in brown (B) scaled to the Gulf of Mexico region with the TX 12a sub-region highlighted in tan, and (C) an expanded highlight showing the HUC-8 watersheds within the TX 12a sub-region.

FIGURE 6 |

Map of HUC-8 population in USEPA flood-prone area quartiles (A) scaled nationally, with the Gulf of Mexico region highlighted in brown (B) scaled to the Gulf of Mexico region with the TX 12a sub-region highlighted in tan, and (C) an expanded highlight showing the HUC-8 watersheds within the TX 12a sub-region.

FIGURE 7 |

Map of Texas 12a sub-region catchment percent in NWI wetlands quartile. This map also shows NHDPlus reaches with a stream order greater than two in blue.

FIGURE 8 |

Map of Texas 12a sub-region catchment percent flood-prone area quartiles (A) using USEPA flood model, or (B) using FEMA A flood zones.

FIGURE 9 |

Map of Texas 12a sub-region catchment quartiles for (A) population (B) flood-prone population using USEPA flood model, and (C) flood-prone population within 4 km downstream. Each map uses colors based on quartiles of values for all catchments shown on the map.

FIGURE 10 |

(A) Map of TX 12a sub-region catchments prioritized for conservation and restoration based on percent wetlands and flood-prone population within 4 km downstream (USEPA). (B) Map inset focused on outline of Harris County (FIPS 48201).