Charleston County, SC flood risk and hazards

Charleston County in the state and national rankings

National placement for Charleston County is #33 of 3,232, with an expected annual loss estimate of about $499.8 million. The county ranks #1 of 46 in South Carolina and accounts for 16.7% of state loss. The modeled $499.8 million annual average does not predict the loss in any single year. The next higher national total is about $517.3 million, in Honolulu County, HI. The next lower national total is about $494.6 million, in Hillsborough County, FL. Within the state list, Horry County, SC has the next lower estimate: about $290.4 million. That puts the estimates about $209.4 million apart, with 9.7% of state loss in the comparison county.

South Carolina county comparisons

Charleston County hazard estimates

Hurricane

With about $281.3 million in modeled expected annual loss from hurricanes, the county ranks #6 of 2,485 in the national comparison. At 56.3% of the county’s modeled loss, the hazard places #1 of 46 statewide; FEMA assigns a Very High rating, matching 47 US counties, including 5 in South Carolina, for this hazard.

Earthquake

With about $118.0 million in modeled expected annual loss from earthquakes, the county ranks #38 of 3,232 in the national comparison. Its 23.6% share of total loss comes with a state loss rank of #1 of 46; FEMA assigns a Relatively High rating; the Relatively High label covers 1 state county and 53 nationally for earthquakes.

Riverine Flood

The national loss rank for riverine flooding is #287 of 3,232, based on about $44.2 million in modeled expected annual loss. Its 8.8% share of total loss comes with a state loss rank of #6 of 46; FEMA assigns a Relatively Moderate rating; the Relatively Moderate label covers 17 state counties and 639 nationally for riverine flooding.

Coastal Flood

At about $35.6 million, the modeled expected annual loss from coastal flooding ranks first among 588 US counties. At 7.1% of the county’s modeled loss, the hazard places #1 of 14 statewide; FEMA assigns a Very High rating; the same rating for coastal flooding covers 1 South Carolina county and 29 across the US.

Cold Wave

The national loss rank for cold waves is #318 of 3,232, based on about $6.6 million in modeled expected annual loss. Its 1.3% share of total loss comes with a state loss rank of #7 of 46; FEMA assigns a Relatively Moderate rating; the same rating for cold waves covers 20 South Carolina counties and 746 across the US.

Wildfire

For wildfires, about $3.1 million in expected annual loss puts the county #169 of 3,144 across the US. This hazard makes up 0.6% of the total; FEMA assigns a Relatively Moderate rating, and its loss ranks #1 of 46 in South Carolina; the Relatively Moderate label covers 5 state counties and 274 nationally for wildfires.

For hurricanes, modeled loss is about $163.3 million above earthquakes, leaving 32.7 percentage points between their county shares. The loss estimate for earthquakes exceeds riverine flooding by about $73.8 million, equivalent to 14.8 percentage points of total loss. For riverine flooding, modeled loss is about $8.6 million above coastal flooding, leaving 1.7 percentage points between their county shares. About $29.0 million separates coastal flooding from cold waves in the local estimates, equivalent to 5.8 percentage points of county loss. The loss estimate for cold waves exceeds wildfires by about $3.5 million, equivalent to 0.7 percentage points of total loss.

Population and recorded values

Charleston County covers about 1,372 square miles, with 407,722 residents in FEMA data. About $96.54 billion is the building value amount in FEMA’s record. About $28.8 million is the agricultural value amount in FEMA’s record. Total modeled loss averages about $1,226 per resident annually, compared with about $584 statewide. Its 8.0% share of state residents sits alongside 16.7% of of annual loss. The county contains 8.5% of the building value recorded across South Carolina. The county holds density position 6 of 46 in South Carolina, using FEMA’s recorded population and area. The population-to-area ratio is about 297 residents per square mile; statewide it is about 158. At 407,722 residents, the county compares with the South Carolina county median of about 59,530. The county’s national shares are 0.1% for population and 0.3% for modeled loss. For comparison, the US modeled loss average is about $459 per resident; the county figure is about $1,226. The six hazards described above together make up 97.8% of modeled loss, about $488.8 million annually. The balance outside those six estimates is about $11.0 million, or 2.2% of total loss. The county’s number 7 hazard by dollar loss is tornadoes: about $3.0 million, with a state rank of #20 of 46. With 0.6% of county loss, this hazard has national placement #755 of 3,225. The estimate for heat waves ranks #8 of 46 in South Carolina: about $2.0 million annually, in local position 8. Nationally, this estimate places #450 of 3,202; its share of the county’s modeled loss is 0.4%.

FEMA labels and risk score

Charleston County has a FEMA risk index score of about 98.6, ranking #44 of 3,144 nationally. Among 46 South Carolina counties, 4 receive the same Relatively High label for risk index. FEMA labels expected annual loss as Relatively High, matching 4 county records across South Carolina. Among 46 South Carolina counties, 6 receive the same Relatively Low label for social vulnerability. For community resilience, FEMA assigns Very High; 1 county in South Carolina has that label. Its risk score ranks #1 of 46 within South Carolina, while its loss total ranks #1 of 46. This combination, Relatively Low for vulnerability and Very High for resilience, occurs in 1 counties in South Carolina. Of the modeled loss among these 1 counties, 100.0% belongs here; the group holds 16.7% statewide. With a score of about 98.2, Horry County, SC ranks #2 of 46 statewide, immediately below this county. FEMA gives that county a Relatively High risk index label, alongside 9.7% of the state loss total. Nationally, 632 counties carry the same Relatively Low social vulnerability label, covering 30.0% of FEMA’s recorded population. Nationally, 629 counties carry the same Very High community resilience label, covering 27.2% of FEMA’s recorded population. The county’s Very High group contains 2 hazards: coastal flooding, hurricanes. The county’s Relatively High group contains 3 hazards: earthquakes, ice storms, lightning. Across the county’s hazard ratings, 7 carry Relatively Moderate: cold waves, heat waves, riverine flooding, strong wind, tornadoes, wildfires, winter weather. The county’s Relatively Low group contains 2 hazards: drought, hail. The local Very Low hazard group contains 1 entries: landslides.