King County, WA flood risk and natural hazards

King County in the state and national rankings

At about $1.68 billion, modeled expected annual loss in King County ranks #10 of 3,232 across the US. Its share of Washington modeled loss is 35.8%, with a state rank of #1 of 39. About $1.68 billion is the modeled yearly average over the long run, rather than a one-year prediction. Alameda County, CA ranks immediately above it, with about $1.88 billion in modeled annual loss. The next lower national total is about $1.54 billion, in San Diego County, CA. Within the state list, Pierce County, WA has the next lower estimate: about $531.9 million. Its 11.3% state loss share accompanies an estimate about $1.15 billion away from this county’s total.

Washington county comparisons

King County hazard estimates

Earthquake

With about $1.21 billion in modeled expected annual loss from earthquakes, the county ranks #3 of 3,232 in the national comparison. At 72.3% of the county’s modeled loss, the hazard places #1 of 39 statewide; FEMA assigns a Very High rating; the Very High label covers 1 state county and 8 nationally for earthquakes.

Riverine Flood

The national loss rank for riverine flooding is #11 of 3,232, based on about $416.9 million in modeled expected annual loss. In Washington, this estimate ranks #1 of 39 and represents 24.8% of the county’s modeled loss; FEMA assigns a Very High rating, matching 26 US counties, including 1 in Washington, for this hazard.

Heat Wave

The national loss rank for heat waves is #46 of 3,202, based on about $18.9 million in modeled expected annual loss. This hazard makes up 1.1% of the total; FEMA assigns a Relatively High rating, and its loss ranks #1 of 39 in Washington; for heat waves, 3 state counties and 98 US counties share that label.

Avalanche

With about $11.1 million in modeled expected annual loss from avalanches, the county ranks #6 of 684 in the national comparison. Its 0.7% share of total loss comes with a state loss rank of #1 of 37; FEMA assigns a Very High rating; for avalanches, 6 state counties and 37 US counties share that label.

Tsunami

The national loss rank for tsunamis is #36 of 119, based on about $6.3 million in modeled expected annual loss. At 0.4% of the county’s modeled loss, the hazard places #4 of 15 statewide; FEMA assigns a Relatively Low rating, matching 14 US counties, including 4 in Washington, for this hazard.

Tornado

With about $3.5 million in modeled expected annual loss from tornadoes, the county ranks #650 of 3,225 in the national comparison. This hazard makes up 0.2% of the total; FEMA assigns a Relatively Moderate rating, and its loss ranks #1 of 39 in Washington; the same rating for tornadoes covers 1 Washington county and 796 across the US.

The loss estimate for earthquakes exceeds riverine flooding by about $797.8 million, equivalent to 47.5 percentage points of total loss. For riverine flooding, modeled loss is about $398.0 million above heat waves, leaving 23.7 percentage points between their county shares. For heat waves, modeled loss is about $7.8 million above avalanches, leaving 0.5 percentage points between their county shares. The loss estimate for avalanches exceeds tsunamis by about $4.8 million, equivalent to 0.3 percentage points of total loss. About $2.7 million separates tsunamis from tornadoes in the local estimates, equivalent to 0.2 percentage points of county loss.

Population and recorded values

King County covers about 2,331 square miles, with 2,268,178 residents in FEMA data. About $527.74 billion is the building value amount in FEMA’s record. For agricultural value, the source records about $174.4 million. Per resident, the modeled annual amount is about $741; the Washington average is about $609. Its 29.5% share of state residents sits alongside 35.8% of of annual loss. The county contains 32.1% of the building value recorded across Washington. Its population density ranks 1 within 39 Washington counties that have both area and population estimates. Those recorded totals give about 973 residents per square mile, versus about 107 across Washington. The median county population in Washington is about 65,689, compared with 2,268,178 locally. The county’s national shares are 0.7% for population and 1.1% for modeled loss. The county’s about $741 per resident compares with about $459 nationally in modeled annual loss. The six hazards described above together make up 99.5% of modeled loss, about $1.67 billion annually. The balance outside those six estimates is about $8.9 million, or 0.5% of total loss. The county’s number 7 hazard by dollar loss is volcanic activity: about $1.9 million, with a state rank of #4 of 31. This 0.1% slice of county loss ranks #7 of 360 across US counties. The estimate for landslides ranks #4 of 39 in Washington: about $1.7 million annually, in local position 8. With 0.1% of county loss, this hazard has national placement #75 of 3,222.

FEMA labels and risk score

King County has a FEMA risk index score of about 99.7, ranking #11 of 3,144 nationally. The risk index rating is Very High, a label shared by 1 of 39 Washington counties. Among 39 Washington counties, 1 receives the same Very High label for expected annual loss. FEMA labels social vulnerability as Very Low, matching 8 county records across Washington. The community resilience rating is Very High, a label shared by 3 of 39 Washington counties. Its risk score ranks #1 of 39 within Washington, while its loss total ranks #1 of 39. The Very Low vulnerability and Very High resilience pairing appears in 1 Washington counties. Of the modeled loss among these 1 counties, 100.0% belongs here; the group holds 35.8% statewide. The adjacent state score below this county belongs to Pierce County, WA: about 98.5, ranked #2 of 39. That comparison county holds a Relatively High risk index rating and 11.3% of Washington modeled annual loss. The Very Low category for social vulnerability includes 625 US counties and 23.7% of recorded US residents. The Very High category for community resilience includes 629 US counties and 27.2% of recorded US residents. Across the county’s hazard ratings, 3 carry Very High: avalanches, earthquakes, riverine flooding. Across the county’s hazard ratings, 5 carry Relatively High: heat waves, ice storms, landslides, volcanic activity, winter weather. FEMA assigns Relatively Moderate to 3 hazards here, covering coastal flooding, lightning, tornadoes. The county’s Relatively Low group contains 3 hazards: cold waves, tsunamis, wildfires. The local Very Low hazard group contains 3 entries: drought, hail, strong wind.