Extreme heat is any period when the temperatures are well above the usual level. Because this level is relative to the area, this means that extreme heat events may occur anywhere in Placer County, even though temperatures in the valley regions will almost always be the hottest. Extreme heat conditions can also compound the effects of other hazards, such as drought and wildfire, and can contribute to increases in tree mortality. Extreme heat can also affect agriculture in Placer County. During times of high heat, low humidity, and winds, electrical utilities can issue a Public Safety Power Shutdown (PSPS) for the County.
Extreme heat events are dangerous because people exposed to extreme heat can suffer a number of heat-related illnesses, including heat cramps, heat exhaustion, and (most severely) heat stroke. Very high temperatures can harm plants and animals that are not well adapted to them—wild ecosystems as well as farm crops and livestock. Extreme heat can increase the temperature of water in lakes, streams, creeks, and other water bodies, especially during drought events when water levels are lower.
Indirectly, extreme heat puts more stress on power lines, causing them to run less efficiently. The heat also causes more demand for electricity (usually to run air conditioning units), and in combination with the stress on the power lines, may lead to brownouts and blackouts.
Extreme Heat often results in the highest number of annual deaths among all weather-related hazards. In most of the United States, extreme heat is defined as a long period (2 to 3 days) of high heat and humidity with temperatures above 90 degrees. In extreme heat, evaporation is slowed and the body must work extra hard to maintain a normal temperature. This can lead to death by overworking the human body. Remember that:
Extreme heat can occur quickly and without warning.
Older adults, children, and sick or overweight individuals are at greater risk from extreme heat.
Humidity increases the feeling of heat as measured by a heat index.