Land use and tsunami hazards in the Pacific Northwest

Science Center Objects

Tsunamis have the potential to cause considerable damage to communities along the U.S. Pacific Northwest coastline. As coastal communities expand over time, the potential societal impact of tsunami inundation changes.

To understand how community exposure to tsunami hazards may change in coming decades, we projected future development (i.e. urban, residential, and rural), households, and residents over a 50-year period (2011–2061) along the Washington, Oregon, and northern California coasts.

 

Study map for showing communities in the Pacific Northwest from projecting community changes in hazard exposure paper

Study area map including 2011 NLCD and the incorporated cities, Indian Reservations (IR), and counties in the U.S. Pacific Northwest with land in tsunami-hazard zones associated with Cascadia subduction zone earthquakes (Credit: Benjamin M. Sleeter, USGS. Public domain.)

Project Description

The objective of this paper is to characterize and compare community changes in population exposure to tsunami hazards between current patterns of development and projected growth. To demonstrate this approach, we focus on coastal counties and communities in the U.S. Pacific Northwest (PNW) that are threatened by local tsunamis associated with a Cascadia subduction zone (CSZ) earthquake, which last occurred in 1700 A.D. Cascadia Region Earthquake Workgroup.

Methods

We created a spatially explicit, land use/land cover, state-and-transition simulation model to project future developed land use based on historical development trends. We then compared our development projection results to tsunami-hazard zones associated with a Cascadia subduction zone (CSZ) earthquake. Changes in tsunami-hazard exposure by 2061 were estimated for 50 incorporated cities, 7 tribal reservations, and 17 counties relative to current (2011) estimates. Across the region, 2061 population exposure in tsunami-hazard zones was projected to increase by 3880 households and 6940 residents.

Findings and Results

The top ten communities with highest population exposure to CSZ-related tsunamis in 2011 are projected to remain the areas with the highest population exposure by 2061. The largest net population increases in tsunami-hazard zones were projected in the unincorporated portions of several counties, including Skagit, Coos, and Humboldt. Land-change simulation modeling of projected future development serves as an exploratory tool aimed at helping local governments understand the hazard-exposure implications of community growth and to include this knowledge in risk-reduction planning.

Bar graphs showing the net change in developed land, households, and population

(Credit: Benjamin Sleeter, USGS. Public domain.)

Graph of projected change in residents by community

(Credit: Benjamin Sleeter, USGS. Public domain.)

Above: Bar graphs showing the net change in developed land (thousands of hectares), households (thousands of units),

and population (thousands of persons) for (a) the entire study area, and (b) for land in tsunami-hazard zones for Washington,

Oregon, and California. Error bars represent the minimum and maximum estimates across 50 Monte Carlo realizations.

Right: Mean estimated number of additional residents in tsunami-hazard zones in 2061 and percentage increase in exposure

relative to 2010 by county.

For more information visit the Land Use and Climate Change Team website.