Extreme Heat

High temperature records in the United States have set records in recent years, nearly 106,000 daily temperature records tied or broken. The ten warmest years in the 143-year record have all occurred since 2010, with the last nine years (2014–2022) ranking as the nine warmest years on record.

Heat waves turning into heat domes have become an annual occurrence over the past decade, with the frequency of high heat days and the peak temperature on those days both increasing year over year across the United States. A heat dome occurs when the atmosphere traps hot ocean air like a lid or cap. This happens when strong, high-pressure atmospheric conditions combine with influences from La Nina, creating vast areas of sweltering heat that gets trapped under the high-pressure dome.

What is Extreme Heat?

Extreme heat is defined as either:

• A period of high heat and humidity with temperatures above 90 degrees for at least two to three days (Department of Homeland Security).
• A summertime temperature that is much hotter and/or humid than average. Because some places are hotter than others, this depends on what’s considered average for a particular location at that time of year. 

When heat and humidity are too high for sweat to evaporate from the skin - the body's natural cooling mechanism - a condition known as wet bulb occurs. If the temperature and humidity both exceed 95 degrees, wet bulb conditions can be fatal for even physically fit individuals. Climate forecasts indicate wet bulb threats will expand rapidly by 2053.

Damages to Critical Infrastructure Sectors from Extreme Heat

Extreme heat threatens critical infrastructure across the country. High heat events can impact infrastructure sectors such as transportation when roadways, runways, and railways begin to buckle, with secondary impacts across all sectors from heat-related power outages and health threats to the general population. 

Additional impacts include:

• Power lines become less efficient from overheating effects like drooping and load shedding capacity can be overwhelmed as transformers degrade or become damaged. 
• Concrete degradation from direct sunlight and heat can cause cracks, dimpling of the material, expansion within the structure which allows moisture to infiltrate and break down the stability of the foundation/support. 
• Overheating of materials can permeate buildings and cause greater energy needs for cooling, dangerous internal heat levels during power outages, and degraded refrigerant abilities. 
• Cast iron cannot bend or stretch and will crack to relieve stresses of a weld if there is no preheat event. 
• The loss of cooling abilities at datacenters and end offices could result in power loss as sites will have to shut down or reduce operations to prevent overheating with threats to server bays and equipment storage. 
• Crop decay and increased livestock mortality rates are expected due to worsening heat.  
• Snowpacks have begun to melt earlier and form later as winter shortens causing earlier blooms and out of cycle harvest periods along with reduced water storage capabilities.  
• Local dams, levees, and other water retention structures could see loss in efficiency as cracks, breaks, and elevation shifts from subsidence expand across regions from the stressors of heat and overpulling.