Multnomah County, OR flood risk and hazards

Multnomah County in the state and national rankings

At about $440.4 million, modeled expected annual loss in Multnomah County ranks #37 of 3,232 across the US. The county ranks #1 of 36 in Oregon and accounts for 17.4% of state loss. About $440.4 million is the modeled yearly average over the long run, rather than a one-year prediction. Hennepin County, MN ranks immediately above it, with about $456.4 million in modeled annual loss. San Juan Municipio, PR ranks immediately below it, with about $434.5 million in modeled annual loss. The nearest lower state total is about $270.3 million, recorded for Washington County, OR. Its 10.7% state loss share accompanies an estimate about $170.1 million away from this county’s total.

Oregon county comparisons

Multnomah County hazard estimates

Earthquake

For earthquakes, about $326.2 million in expected annual loss puts the county #16 of 3,232 across the US. At 74.1% of the county’s modeled loss, the hazard places #1 of 36 statewide; FEMA assigns a Relatively High rating, matching 53 US counties, including 6 in Oregon, for this hazard.

Riverine Flood

With about $91.2 million in modeled expected annual loss from riverine flooding, the county ranks #134 of 3,232 in the national comparison. Its 20.7% share of total loss comes with a state loss rank of #2 of 36; FEMA assigns a Relatively High rating; the same rating for riverine flooding covers 5 Oregon counties and 186 across the US.

Heat Wave

For heat waves, about $10.0 million in expected annual loss puts the county #91 of 3,202 across the US. In Oregon, this estimate ranks #2 of 36 and represents 2.3% of the county’s modeled loss; FEMA assigns a Relatively High rating; for heat waves, 2 state counties and 98 US counties share that label.

Cold Wave

The national loss rank for cold waves is #239 of 3,232, based on about $8.5 million in modeled expected annual loss. In Oregon, this estimate ranks #4 of 36 and represents 1.9% of the county’s modeled loss; FEMA assigns a Relatively High rating, matching 302 US counties, including 4 in Oregon, for this hazard.

Tornado

The national loss rank for tornadoes is #1,497 of 3,225, based on about $1.2 million in modeled expected annual loss. This hazard makes up 0.3% of the total; FEMA assigns a Relatively Low rating, and its loss ranks #2 of 36 in Oregon, matching 1,217 US counties, including 3 in Oregon, for this hazard.

Ice Storm

FEMA models about $1.2 million in expected annual loss from ice storms, placing the county #207 of 3,001 nationally. At 0.3% of the county’s modeled loss, the hazard places #3 of 36 statewide; FEMA assigns a Relatively High rating; the Relatively High label covers 8 state counties and 388 nationally for ice storms.

About $235.0 million separates earthquakes from riverine flooding in the local estimates, equivalent to 53.4 percentage points of county loss. The loss estimate for riverine flooding exceeds heat waves by about $81.2 million, equivalent to 18.4 percentage points of total loss. Between heat waves and cold waves, the modeled dollar gap is about $1.4 million; their shares differ by 0.3 percentage points. The loss estimate for cold waves exceeds tornadoes by about $7.3 million, equivalent to 1.7 percentage points of total loss. The loss estimate for tornadoes exceeds ice storms by about $25,000, equivalent to 0.0 percentage points of total loss.

Population and recorded values

Multnomah County covers about 470 square miles, with 814,167 residents in FEMA data. FEMA lists about $182.66 billion in building value. For agricultural value, the source records about $96.0 million. Total modeled loss averages about $541 per resident annually, compared with about $597 statewide. The county holds 19.3% of the state population, compared with 17.4% of modeled loss. Buildings account for 18.1% of recorded Oregon building value. Its population density ranks 1 within 36 Oregon counties that have both area and population estimates. Those recorded totals give about 1,733 residents per square mile, versus about 43 across Oregon. The median county population in Oregon is about 45,620, compared with 814,167 locally. Of FEMA’s US population, 0.2% lives here, alongside 0.3% of national modeled annual loss. The county’s about $541 per resident compares with about $459 nationally in modeled annual loss. About $438.3 million of annual loss falls within the six leading hazards, accounting for 99.5% of the total. The balance outside those six estimates is about $2.1 million, or 0.5% of total loss. About $925,000 places strong wind at number 7 in the local loss list and #6 of 36 within Oregon. This 0.2% slice of county loss ranks #901 of 3,225 across US counties. The estimate for winter weather ranks #7 of 36 in Oregon: about $309,000 annually, in local position 8. Its national loss rank is #436 of 3,230, and it represents 0.1% of the county’s modeled loss.

FEMA labels and risk score

Multnomah County has a FEMA risk index score of about 98.5, ranking #49 of 3,144 nationally. Among 36 Oregon counties, 6 receive the same Relatively High label for risk index. Among 36 Oregon counties, 4 receive the same Relatively High label for expected annual loss. The social vulnerability rating is Relatively Low, a label shared by 8 of 36 Oregon counties. The community resilience rating is Very High, a label shared by 2 of 36 Oregon counties. Within Oregon, the risk score places #1 of 36 and the dollar loss places #1 of 36. Within Oregon, 1 counties share both labels: Relatively Low vulnerability and Very High resilience. This county accounts for 100.0% of that group’s annual loss, while the group accounts for 17.4% across Oregon. Lane County, OR is next below it by state risk score, at about 96.4; that record ranks #2 of 36. Its share of statewide modeled loss is 8.8%; FEMA’s risk index label there is Relatively High. The Relatively Low category for social vulnerability includes 632 US counties and 30.0% of recorded US residents. The Very High category for community resilience includes 629 US counties and 27.2% of recorded US residents. FEMA assigns Relatively High to 6 hazards here, covering cold waves, earthquakes, heat waves, ice storms, riverine flooding, winter weather. Across the county’s hazard ratings, 3 carry Relatively Moderate: landslides, strong wind, volcanic activity. The local Relatively Low hazard group contains 4 entries: coastal flooding, lightning, tornadoes, wildfires. Across the county’s hazard ratings, 3 carry Very Low: avalanches, drought, hail.