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Consider heat wave dangers as the onset of summer brings higher temperatures. As heat index over 105 creates extreme heat hazards, and precautions must be taken.
As high summer settles in over North America, we often have to deal with the weather extremes of heat waves and droughts. Although these are distinct events, heat waves do tend to occur when conditions are dry, and drought in summer is associated with high temperatures.
Heat waves and droughts also have the same meteorological parentage, an upper-level ridge of high pressure thousands of feet above the Earth’s surface. A ridge is a huge mound of warm air that effectively blocks storm systems from bringing precipitation. The air sinks, warming and drying as it descends to the ground, and few clouds block the sun’s hot rays. For heat waves, the ridge moves out in a matter of days. For droughts, the pattern is more permanent; often, one ridge may dissipate only to be replaced by another. This pattern can persist for months or even years.
Effects of Extreme Heat Hazards
The National Weather Service (NWS) defines a heat wave as a period of two or more abnormally and uncomfortably hot days.
Heat can be dangerous, even deadly. Death rates go up markedly during heat waves. Heat is the No. 1 cause of weather fatalities in the U.S. over the past 30 years, with more than 100 deaths per year attributed to excessively hot weather. Some groups are high-risk, including the elderly, people with underlying health conditions, and the impoverished.
In 2021, over 200 people in the country died due to heat waves. We don’t normally associate excessively hot weather with the Pacific Northwest, because ocean breezes usually keep temperatures on the pleasant side. This wasn’t the case in June last year, when an unprecedented heat wave smashed many all-time-high temperature records. Portland, Oregon, topped out at 116 degrees Fahrenheit, and Seattle, Washington, hit 108 degrees. Across the border in British Columbia, the town of Lytton recorded 121 degrees on June 29, setting a high-temperature record for the country of Canada. Hundreds died in British Columbia from excessive heat, and over 100 people died in Washington and Oregon, many in homes without air conditioners or fans. Washington’s heat wave is considered the deadliest weather-related disaster in the state’s history. Although the air aloft is dry during a heat wave, a region may experience higher humidity near the surface. Because humidity affects the rate of evaporation of sweat and its cooling effect on the body, meteorologists use the heat index to measure the “feels like” temperature. For example, if the air temperature is 90 degrees and the relative humidity is 60%, the human body will react like it’s 100 degrees. A heat index of 105 is considered dangerous. Effects on the body from excessive heat can range from painful cramps to possibly fatal heatstroke. To protect yourself, wear light-colored clothing made of breathable materials. Avoid strenuous activity during the hottest part of the day, typically the afternoon. If you must be active then, take frequent breaks in the shade, which can be 10 to 15 degrees cooler than in the sunshine. Hydrate with plenty of fluids rich in electrolytes. Be especially cautious if you’re taking medications, or are elderly or immunocompromised.
Heat waves can cause worse effects in cities due to a phenomenon known as the “urban heat island,” whereby building materials absorb the sun’s rays during the day and radiate their heat into the air, especially at night. Overnight temperatures in a city can be 10 degrees higher–or more–than in the surrounding suburbs or countryside.
Heat waves can usually be forecast days in advance. In the U.S., the NWS can issue an Excessive Heat Outlook 3 to 7 days in advance to give people time to prepare. An Excessive Heat Watch will be issued 1 to 3 days in advance, and a Heat Advisory is set 12 hours before the occurrence of dangerous conditions. The latter implies a maximum heat index of at least 100 degrees during the day, with nighttime temperatures exceeding 75 degrees for two or more nights. An Excessive Heat Warning is issued when the heat index is expected to rise to 105 degrees or higher during the day and nighttime air temperatures are expected to exceed 75 degrees for at least two days. (Note that these values will vary for different parts of the country.)
Fortunately, heat waves with excessive high temperatures are typically short-lived, especially in higher latitudes. The upper-level ridge tends to break down after a few days.
Dry as a Bone
A drought is defined by the NWS as “a deficiency of moisture that results in adverse impacts on people, animals, or vegetation over a sizable area.” Agricultural drought consists of a significant lack of water for crops or livestock and can develop in a few months. Hydrologic drought deals with reductions in the overall water supply and develops over a period of months or even years. Droughts can cause staggering monetary losses, especially for agriculture. According to the National Centers for Environmental Information, 29 separate drought events from 1980 to 2021 caused at least $1 billion in damage each in the U.S. The total combined cost to the country was $285.4 billion. The drought that gripped the western part of the country in 2021 cost an estimated $8.9 billion in damages. Although drought in the U.S., Canada, and other more industrialized nations hasn’t been directly responsible for deaths, crop failures have led to starvation in less developed countries around the world.
The current drought in the western U.S. began in 2000 and is now considered a “megadrought” that will last for decades. Researchers recently examined tree rings and determined that this is the worst drought in the West in at least 1,000 years.
Drought often sets the stage for wildfires, because of dried vegetation. This provides plenty of wildfire fuel and increases the chances of ignition. (See my article “Wildfire Behavior and Mitigation” for advice on how homeowners can protect their properties from wildfires.)
Dryness is seasonal in some locales; for example, during summer on the West Coast, and winter in Florida, especially the southern peninsula. In these regions, droughts develop when winter rains or summer thunderstorms don’t produce normal precipitation, or when the wet season is delayed or ends prematurely.
For other locations that typically experience consistent precipitation, drought conditions are sporadic and associated with the upper-level ridges described previously. Considering the size of North America and the magnitude of typical upper-level weather systems, drought will likely be occurring somewhere at any given time.
Over the years, the Drought Monitor has developed into the standard for quantifying drought severity. Experts synthesize a variety of numeric inputs and use their own expertise to come up with a representative value, the results of which are typically displayed in map form. The North American version can be found at Drought Monitor.
Although forecasts of future drought conditions are available, long-term weather patterns are notoriously difficult to forecast.
To lessen your household’s impact during a drought, you can buy high-efficiency washing machines and dishwashers, and only use them when they’re fully loaded. Install water-efficient showerheads and toilets in the bathroom, and take shorter showers. Don’t let the water run from the faucet while brushing your teeth or shaving. Find and fix any leaks. Outdoors, don’t wash your car, and limit the watering of plants and your lawn. If dry conditions are common in your area, consider using native drought-resistant vegetation or plant-free landscaping. Be sure to abide by water restrictions enacted by your local authorities.
Ed Brotak has taught college students about weather for more than 30 years, and led many of them to pursue careers in meteorology. He lives in Asheville, North Carolina, with his wife (also a meteorologist) and two daughters.