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Risks from Concurrent Heatwaves and Power Outages

Modern weather forecasts reference “normal” weather conditions. Forecasters routinely issue statements like “…we’ll see temperatures a few degrees below normal …” or “… April has been wetter than normal …”. While we may often take these statements for granted, where do the “normal” values come from?

Temperatures Seem Warmer

In the USA, weather data is collected by the National Oceanic and Atmospheric Administration (NOAA). Data for some regions goes back as far as 1895. Each decade, NOAA revises normal values for temperature, precipitation, and other weather characteristics. The revised numbers are based on averages for the last several decades, and the newest assessment was recently released. NOAA’s announcement contains links to interactive charts showing changes in weather characteristics across the USA as well as a tool for seeing conditions in specific regions, states, counties, and cities.

Some interesting comparisons:

• From 1895 to 2020, mean temperatures across the USA increased at a rate of +1.55°F per Century. Maximum temperatures increased by +1.38°F per Century.

• From 1942 to 2020, temperatures in Olympia, Washington (an area with temperate conditions), have risen at a rate of +0.5°F per Century. Maximum temperatures increased by +1.3°F per Century.

• In San Diego, California (an area of warmer arid conditions), the rate of change from 1940 to 2020 was +5.9°F per Century. Maximum temperatures increased by +6.0°F per Century.

Plotting temperature and precipitation trends for your area of interest makes for worthwhile reading. Our informal sampling suggests that temperatures are rising, the east is getting wetter, and the west is becoming drier.

Big Weather-Related Outages Seem More Common

Interestingly, the United States Energy Information Administration issued an assessment of US outages in June of 2020. It reviews data from 2013 through 2018, and concludes that, excluding major events (snowstorms, hurricanes , floods, heatwaves, etc.), US electricity customers have experienced a relatively steady amount of downtime, ranging from 106 to 118 minutes per year. However, it found that outages from these types of major events over the same time period were twice as long in 2017 and 2018 as previous years. Events since then, such as outages from California Wildfires and the recent Texas Freeze, seem consistent with this finding.

Another source also claims that big outages are increasing. The annual number of electrical grid failure events lasting at least one hour and impacting 50,000 or more utility customers increased by more than 60 percent over the last five-year reporting period. As interesting as that seems, it was not the major thrust of the study in which it was published …

So What Happens to People if a Major Outage Occurs During a Major Heat Wave?

The outage information above appeared in a study entitled Compound Climate and Infrastructure Events: How Electrical Grid Failure Alters Heat Wave Risk, which was published in the scientific journal Environmental Science and Technology on April 30, 2021. It noted that 46% of these blackout events occur between May and September. In the Northern Hemisphere, that’s when heat risks are greatest.

More importantly, the study evaluated and compared the effects of a hypothetical, concurrent, five-day heat wave and power outage event on the US cities of Atlanta, Georgia; Detroit, Michigan; and Phoenix, Arizona. For each locale, this study:

• reviewed the occurrence and magnitude of outages
• evaluated the occurrence and magnitude of heatwaves
• estimated the impacts of city-wide blackouts during these heatwaves on indoor air temperatures by using models for:
- regional climate
- building energy, including indoor air temperatures
- prevalence of air-conditioning systems

The results were sobering. The simulations predicted that concurrent heat wave and grid failure events of recent intensity and duration would produce indoor temperatures that expose between 68 and 100 percent of these urban populations to an elevated risk of heat exhaustion and/or heat stroke. Other interesting points:

• Temperatures inside single-family homes reach 4°C higher than temperatures inside apartment buildings.
• Lack of air conditioning disproportionately affects lower income households.
• Public cooling centers in these cities can accommodate only 1 to 2 percent of their residents. None of the cities required backup power for their cooling centers.
• Heat/outage risks like those for cities under study are a growing issue for the US as a whole.

You can read an abstract of the study here. A New York Times article summarizes the study here. The New York Times followed up and learned that only a collective subset of the cooling facilities in these cities have backup generators. (Interestingly, Detroit officials said they could deploy portable generators to shelters that needed them. For more information about this type of solution, review NEC Requirement for Permanent Manual Switching Means.) But none of this addresses the heat risks for the many residents that lack cooling or backup power.

The Takeaway

If the trends identified by these sources continue, the juxtaposition of climate developments with outage trends could raise the risk of "negative health outcomes" for people in affected areas. These risks could warrant measures that exceed existing code requirements for providing backup power. The issue would challenge not only public policy, but also the facility designers, power professionals, and facility managers that must consider risks posed by extreme events and conditions.

The timing and nature of any collective response could take multiple forms. At the simplest level, the issue is one more reason why critical backup power never seemed so critical.

End Notes

1. National Oceanic and Atmospheric Administration, U.S. Department of Commerce. The new U.S. Climate Normals are here. What do they tell us about climate change? May 4, 2021. https://www.noaa.gov/news/new-us-climate-normals-are-here-what-do-they-tell-us-about-climate-change. Accessed May 29, 2021.

2. National Centers for Environmental Information, National Oceanic and Atmospheric Administration, U.S. Department of Commerce. Climate at a Glance - National Time Series. May 2021. https://www.ncdc.noaa.gov/cag/national/time-series/110/tavg/ann/12/1895-2021?base_prd=true&begbaseyear=1901&endbaseyear=2000&trend=true&trend_base=100&begtrendyear=1895&endtrendyear=2021. Accessed May 29, 2021.

3. Ibid. Climate at a Glance: City Time Series. May 2021. https://www.ncdc.noaa.gov/cag/

4. Ibid. https://www.ncdc.noaa.gov/cag/city/time-series/USW00023188/tavg/12/12/1895-2021?base_prd=true&begbaseyear=1901&endbaseyear=2000&trend=true&trend_base=100&begtrendyear=1895&endtrendyear=2021&_sm_au_=iVVq0RkT7NDsr4THJ6F3jKH7c2fV2. Accessed May 29, 2021.

5. U.S. Energy Information Administration. U.S. customers experienced an average of nearly six hours of power interruptions in 2018. Jun 1, 2020. https://www.eia.gov/todayinenergy/detail.php?id=43915#. May 29, 2021.

6. B. Stone, E. van Mallen, M. Rajput, et al. Compound Climate and Infrastructure Events: How Electrical Grid Failure Alters Heat Wave Risk. Environmental Science & Technology, 55, 10, 6957-6964. April 30, 2021.

7. ACS Publications. How Electrical Grid Failure Alters Heat Wave Risk. April 30, 2021. https://pubs.acs.org/doi/10.1021/acs.est.1c00024. Accessed May 29, 2021.

8. New York Times. A New, Deadly Risk for Cities in Summer: Power Failures During Heat Waves. May 3, 2021. https://www.nytimes.com/2021/05/03/climate/heat-climate-health-risks.html. Accessed May 29, 2021.