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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.

warmer wetter weirder graphs

Thie graphic 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 graphic 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. A detailed progress report for 2023 will be available in early 2024. 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 there are very few structures (0.9% of buildings) in floodplains in Fairfax County, and nearly all of those insurable buildings (99%) 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. (The data shown here is based on DPWES’ Analyzing Flood Risk Story Map.) In terms of heat, the county’s updated Cooling Centers are generally located in the right places, either within (26%) or adjacent to (78%) urban heat islands, where the temperatures are significantly hotter. However, there is room for continued improvement. In terms of storm resilience, there are opportunities to enhance the resilience of county facilities to power outages, to enable continued public service.

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. This map 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. For detailed data on populations and assets that are exposed to the Urban Heat Island effect, please see the Vulnerability and Risk Assessment.

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.

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.

flash flood events per year in fairfax county graph

This graph above shows the number of flash flood events in Fairfax County between 1993 and 2022, as tracked by the National Oceanic and Atmospheric Administration (NOAA) National Centers for Environmental Information Storm Events Database.

As can be seen in the graph, 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 graph above 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.

Office of Environmental and Energy Coordination

Alert: