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Overall Resilience Metrics

The climate in Fairfax County is becoming warmer, wetter, and weirder. Extreme heat, flooding, severe storms, and other changing hazards repeatedly impact our neighborhoods, infrastructure, services, and natural resources. The good news is that there is a lot we can do to adapt and boost our resilience to these conditions! Resilient Fairfax is Fairfax County’s climate adaptation and resilience plan and program.  Data and metrics help us track conditions and progress.

This page highlights data and metrics for the topic of climate resilience overall. For detailed information on Resilient Fairfax, please see the Resilient Fairfax page.

three charts side by side showing the average temperature by yar, number of flash floods and numbers of thunderstorm wind events by year, showcasing the warmer wetter and weirder conditions in the county

The figure above summarizes the “warmer, wetter, weirder” conditions in Fairfax County in recent decades. For additional details on this data, please scroll down to the “warmer,” “wetter,” and “weirder” sections below.

Resilient Fairfax Map Viewer

Use the Resilient Fairfax Interactive Map Viewer interactive map to see various heat and flooding hazards, and how those hazards overlap with buildings, utilities, public services, natural resources, and more. The sections below walk through specific hazards.

This map will be updated as data becomes available. Please click this link to see a video explaining how to use this map.

Resilient Fairfax Strategies

The Resilient Fairfax Plan includes 48 strategies, 18 of which are prioritized (denoted with a black star). The plan includes implementation actions to guide the county in completing these strategies. The status of these actions for each strategy are summarized in the figure below. (Last updated December 2023).

The status bars shown here are based on the number of implementation actions complete for each strategy. For example, if there are 5 implementation actions for a strategy, and 1 is complete, the status bar is at 20%. Some actions are much larger than others. Action status bars are not a measurement of outcomes or results. For example, completing 50% of implementation actions from the plan for “Green Infrastructure” does not mean that 50% of the county has adequate green infrastructure. Progress on these strategies and actions is detailed in the 2023 Progress Report and additional highlights on progress can be found in the 2024 Climate Action Progress and Highlights report. Please email ResilientFairfax@fairfaxcounty.gov with any questions.

To view an ADA accessible version of this graphic, click here.

Key Metrics

The county tracks dozens of climate resilience metrics, based on the Key Performance Indicators from the Resilient Fairfax plan. A few key metrics are shown in the graphic below. Some resilience metrics have a goal of decreasing, while others have a goal of increasing.

In terms of flooding, people often think of floodplains, but in Fairfax County we have both riverine (floodplain) and urban flooding. There are very few structures (0.9% of buildings) in floodplains in Fairfax County, and nearly all of those are insurable buildings (99%) that have flood insurance, because it is a requirement for a federally backed mortgage. (Data is based on the 2010 FEMA FIRM). Outside of floodplains, there are larger flooding issues in the form of urban and flash flooding. Urban flooding is a larger issue. When we look at buildings at potential risk of flooding in Fairfax County, 28% are in floodplains, while the remaining 72% are vulnerable to potential urban flooding. (The data shown here is based on DPWES’ Analyzing Flood Risk Story Map.)

The county is addressing these flooding issues through a combination of policy updates, capital projects, and community services. Staff are conducting research to update stormwater design standards and are also continuously completing capital projects to resolve known flooding issues. In terms of community services, the Conservation Assistance Program continues its success, and the Flood Mitigation Assistance Program (FMAP) was newly launched in July 2024. FMAP has a goal of approximately 100 projects per year, which would mean approximately 500 projects by 2030. Less than one year into the program, 35 FMAP applications have been approved to date, or 7% of the 2030 milestone.

For heat, the county provides Cooling Centers, cooling programs, tree planting, and more. 78% of Urban Heat Islands in Fairfax County have Cooling Centers nearby, thanks to the county’s updated Cooling Center services. “Nearby” is defined as having a Cooling Center either within the same Census Tract as the UHI or in a directly adjacent Census Tract. In terms of air conditioning access at home, there are continued opportunities for progress. An estimated 5% of Virginia households may lack air conditioning equipment, according to a 2020 survey by EIA. This translates to 20,793 households in Fairfax County. Since that survey, 153 households (<1% of households in need) have received assistance with air conditioning equipment (not to be confused with bill payment assistance) through county programs (Cooling Assistance or AC Rescue).

For storm resilience, there are also opportunities for enhanced resilience using back-up power sources. Of the 312 county government facilities on the county’s Continuity of Operations list, 17 facilities, or 5.5%, have generators.

To view an ADA accessible version of this graphic, click here.

Warmer

Temperature Trends:

Extreme Heat Days:

“Extreme heat” is defined by FEMA and CDC as “period of high heat and humidity with temperatures above 90F for at least 2-3 days.” High temperatures are especially dangerous when combined with humidity, which limits our ability to cool ourselves naturally by sweating.

In the past (1976-2005), Fairfax County averaged 25 days per year above 90°F. Today (1991-2020), that average has increased to 29 days per year.
By mid-century (2035-2064), Fairfax County is projected to have an average of 69 days per year above 90°F, and,
By the end of the century (2070-2099), 101 days per year, or approximately the whole summer, above 90°F.

Urban Heat Island Effect:

While extreme heat affects all of us, it affects neighborhoods in “urban heat islands” more. Urban Heat Islands are areas of the county that remain hotter because they have more asphalt, densely-built buildings, roadways, and other infrastructure that retain heat. In contrast, rural areas with more green space and forests stay much cooler. The map above shows the real average land surface temperatures during the day for the summers of 2013-2020. (Land surface temperatures are different from air temperatures). The areas in red have hotter land surface temperatures than the areas in blue. To see an interactive version of this map, please see the Resilient Fairfax Map Viewer. Fairfax County partnered with NASA DEVELOP to obtain these land surface satellite data. For more information on the satellite data, please see the NASA DEVELOP – Fairfax County Urban Heat Island Study. For detailed data on impacts of extreme heat, and specific populations and assets that are exposed to the Urban Heat Island effect, please see the Vulnerability and Risk Assessment. For information on what the county is doing to adapt and boost resilience to changing conditions including heat, please see the Resilient Fairfax Plan.

Wetter

Precipitation Intensity:

In Fairfax County, the intensity of precipitation has increased (i.e., it is raining harder than it used to). While the total amount of rain the county receives per year has been fairly consistent*, we are receiving this rain in heavier, shorter downpours and flash flood events. This intense rain causes flooding because our infrastructure and natural systems are not designed to handle such high volumes all at once. The Department of Public Works and Environmental Services (DPWES) is the primary agency responsible for stormwater management. For more information, please see Stormwater Management.

*The total quantity of precipitation received by the county per year has increased slightly. However, the bigger change is the increase in intensity of precipitation.

The figure below shows the number of flash flood events in Fairfax County between 1996 and 2024, as tracked by the National Oceanic and Atmospheric Administration (NOAA) National Centers for Environmental Information Storm Events Database. There is wide variation in these events, but they are generally increasing in frequency over time.

We measure precipitation by intensity, duration, and frequency (or “IDF curves”). As can be seen in the chart below, using data from MARISA, the IDF curve for our area is shifting. The historic IDF curve is the lower line shown in red. The projected IDF curve is the higher line, shown in blue. This means that it is raining harder than it used to.

Flooding Types:

Fairfax County experiences a few different types of flooding. The map shown above, which is from the Resilient Fairfax Vulnerability and Risk Assessment, shows different types of flooding in Fairfax County.

Floodplain or riverine flooding occurs when water bodies overflow onto their banks. Approximately 2,215 buildings (or 0.9% of buildings) in Fairfax County are in FEMA Special Flood Hazard Area (“100 year”) floodplains. Floodplains in the map are shown in yellow.
Coastal flooding in Fairfax County refers to flooding of the Potomac River and associated tidal water bodies as a result of sea level rise, high tide, storm surge, or a combination thereof. Approximately 699 buildings (or 0.3% of buildings) are vulnerable to coastal flooding in Fairfax County. Coastal flooding in the map is shown in red. In this map, “SLR” refers to projected sea level rise of 1 foot and 3 feet, respectively. “Cat 1&2” and “Cat 3&4” refers to Category 1, 2, 3, and 4 storm surges that could push water onshore.
Urban or pluvial flooding occurs when heavy rain overwhelms stormwater management systems, pools in low-lying areas (sumps), cannot sink into the ground, or is blocked from reaching waterways (overland relief paths blocked). The exact number of structures vulnerable to urban flooding in Fairfax County varies by storm and type but is consistently higher than those vulnerable to floodplain flooding. As of 2021, over 97% of flooding-related service requests were not in floodplains. (See Resilient Fairfax Vulnerability and Risk Assessment). Potential urban flooding of various types is shown in the map and graph in blue.

Sea Level Rise and the Potomac River:

“Coastal flooding” in Fairfax County refers to flooding of the Potomac River and associated water bodies due to tidal flooding, sea level rise, coastal storm surge, or a combination of all three. Tides are measured with tide gauges. The nearest tide gauge is located in Washington DC. Since 1920, this area has already experienced an increase in sea level rise of 0.135 inches per year, or 13.56 inches over the past century. This water level is projected to increase by an additional 1 to 3.5 feet by 2050. There are approximately 699 buildings in Fairfax County that are vulnerable to this projected coastal flooding.

The figure below shows an example of a few neighborhoods that are especially vulnerable to flooding of the Potomac River (New Alexandria, Belle Haven, and Westgrove). From left to right, the images show existing conditions, additional projected sea level rise of 1 foot, additional projected sea level rise of 3 feet, and coastal storm surge (where the water goes if a severe tropical storm or hurricane pushes it on shore). These images are taken from the Resilient Fairfax Interactive Map Viewer.

Weirder

Storm Intensity and Frequency:

Storms are more frequent and intense than they used to be. The National Oceanic and Atmospheric Administration (NOAA) tracks the occurrence of storms and other significant weather phenomena “having sufficient intensity to cause loss of life, injuries, significant property damage, and/or disruption to commerce.” NOAA’s data for Fairfax County shows that we have seen an increase in the number of storm events per year and the number of days per year with storm events and storm-related property damage. (Please Power BI visual below). NOAA’s database goes back to the 1950s; however, methodology for tracking storm data changed in 1996 to include more storm types. Therefore, to avoid blending the increase in storm events with the increase in types of storms that are tracked, only data with consistent methodology are shown here (1996 and beyond).

One of the storm types that has been continuously tracked since the 1950s is “thunderstorm wind.” As can be seen in the chart below, in Fairfax County, the number of days per year with “thunderstorm wind” events severe enough to be tracked by NOAA has increased notably between 1950 and 2022. While much of this increase is due to a change in the storm events themselves, it is possible that a portion of this increase is due to improvements in storm tracking and reporting. For questions about the raw data, please contact NOAA.

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Department Resources

Related Resources

Overall Resilience Metrics

Resilient Fairfax Map Viewer

Resilient Fairfax Strategies

Key Metrics

Warmer

Temperature Trends:

Extreme Heat Days:

Urban Heat Island Effect:

Wetter

Precipitation Intensity:

Flooding Types:

Sea Level Rise and the Potomac River:

Weirder

Storm Intensity and Frequency:

Sector-Specific Metrics

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