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Click on the icons below to learn more about the hazards detailed in the 2020 Maui HMP.
Extreme heat is generally defined as temperatures that hover 10 degrees or more above the average high temperature for the region and last for an extended period. A heat wave may occur when temperatures hover 10 degrees or more above the average high temperature for the region and last for an extended period. The actual temperature threshold depends on norms for the region.
Extreme heat events are usually a result of both high temperatures and high relative humidity. (Relative humidity refers to the amount of moisture in the air.) The higher the relative humidity or the more moisture in the air, the less likely that evaporation will take place. This becomes significant when high relative humidity is coupled with soaring temperatures. On hot days, the human body relies on the evaporation of perspiration or sweat to cool and regulate the body’s internal temperature. Sweating does nothing to cool the body unless the water is removed by evaporation. When the relative humidity is high, then the evaporation process is hindered, robbing the body of its ability to cool itself.
NOAA’s NWS devised the Heat Index as a mechanism to better inform the public of heat dangers. The Heat Index Chart uses air temperature and humidity to determine the heat index apparent temperature. In addition, information regarding the health dangers by temperature range is presented.
Some populations, such as the elderly and young, are more susceptible to heat danger than other segments of the population.
In Maui County, an Excessive Heat Advisory is issued by the NWS for elevations at or below 3,000 feet when daytime heat indices of 105°F or greater and nighttime heat index values of 80°F or greater are expected for at least two consecutive days.
Heat disorders are illnesses caused by prolonged exposure to hot temperatures and are characterized by the body’s inability to shed excess heat. These disorders develop when the heat gain exceeds the level the body can remove or if the body cannot compensate for fluids and salt lost through perspiration. In either case, the body loses its ability to regulate its internal temperature. All heat disorders share one common feature: the individual has been overexposed to heat, or over exercised for their age and physical condition on a hot day. The following describes the symptoms associated with the different heat disorders.
Sunburn: Sunburn is characterized by redness and pain of skin exposed too long to the sun without proper protection. In severe cases it can cause swelling, blisters, fever and headaches. It can significantly retard the skin’s ability to shed excess heat.
Heat Cramps: Heat cramps are characterized by heavy sweating and painful spasms, usually in the muscles of the legs and possibly the abdomen. The loss of fluid through perspiration leaves the body.
Heat Exhaustion: Heat exhaustion is characterized by heavy sweating, weakness, nausea, exhaustion, dizziness and faintness. Breathing may become rapid and shallow and the pulse weak. The skin may appear cool, moist and pale. Blood flow to the skin increases, causing blood flow to decrease to the vital organs. This results in a mild form of shock. If not treated, the victim’s condition will worsen.
Heat Stroke (Sunstroke): Heat stroke is a life-threatening condition characterized by a high body temperature (106°F or higher). The skin appears to be dry and flushed with very little perspiration present. The individual may become mentally confused and aggressive. The pulse is rapid and strong. There is a possibility that the individual will faint or slip unconscious. If the body is not cooled quickly, then brain damage and death may result.
Studies indicate that, all things being equal, the severity of heat disorders tend to increase with age. Heat cramps in a 17-year-old may be heat exhaustion in someone 40 and heat stroke in a person over 60. Elderly persons, small children, chronic invalids, those on certain medications and persons with weight or alcohol problems are particularly susceptible to heat reactions.
The entire county is impacted by extreme heat events. Warmer, drier locations within the county (such as leeward areas) may be higher risk for extreme heat events than windward locations within the county, or areas at high elevations.
Average maximum temperatures in Maui County range from the mid-80s throughout the year. Record highs were hotter, ranging from the low-90s in the winter months to the upper-90s in the summer months. Such temperatures can be extremely dangerous to human health.
Past extreme heat events were gleaned from the NCEI Storm Events Database, which reported no historic extreme heat events for Maui County. However, Maui County experiences temperatures in the 80s and 90s regularly, and historic extreme heat events have occurred. Most notable was the recent heat wave in 2019. The heat wave set records from spring through early fall. From mid-August to mid- September, Hawai’i experienced record-breaking heat for 29 out of 30 days. From April to October, 84 heat records were tied or broken in Maui County, and July saw the highest energy demand in Maui County in a decade. Further, it is likely that Extreme Heat events have impacted Maui County that have not been reported.
Extent of extreme heat can be defined with record highs and the NWS Heat Index. The record temperature at the Kahului Airport monitoring station is 97°F, occurring in 1994, 2015, and 2019. This temperature reaches the extreme danger level (Figure 81) of the NWS Heat Index Chart when combined with relative humidity levels over 65%, which are common in Maui County. Higher temperatures are possible, especially as warming trends are projected to occur with climate change.
The extent of extreme heat events can also be measured in terms of loss of human life, or by economic costs imposed by property, crop, and infrastructure loss. No deaths or damages have been reported due to extreme heat events in Maui County.
Future Probability
While temperatures in most of Maui County are relatively consistent year-round (not prone to temperature extremes), Maui County regularly experiences temperatures in the “danger” category on the NWS Heat Index Chart (upper 80s and 90s considering Maui’s relative humidity). Further, it is likely that record temperatures and frequency of heat events will increase due to climate change as temperatures warm. Community planning areas with higher elevations and dense vegetation are less likely to experience extreme heat events, whereas urban areas at lower elevations, such as the central valley, are more likely to experience extreme heat.
As the extreme heat hazard is atmospheric and does not have a geographic boundary, all current and future populations and structures, including critical facilities, are considered at risk.
Buildings and Infrastructure: Extreme heat events generally have limited impact on buildings. However, in some rare cases extreme heat can cause structures to collapse or buckle. Similarly, extreme heat events generally have minimal impact on infrastructure. Power consumption for air-conditioned environments could increase and thus stress utility infrastructure, resulting in blackouts or brownouts.
Health and Safety: Maui County is vulnerable to extreme heat, particularly in the summer months. Urban areas are exposed more acutely to the dangers of extreme heat due to the urban heat island effect. While all populations are considered vulnerable to extreme heat, certain populations may be more vulnerable to the effects of extreme heat. Groups particularly vulnerable to extreme heat include the following: 1) Older adults who do not adjust as quickly to changes in temperature. Older adults are also more likely to be on medications or have chronic illnesses that affect the body’s ability to regulate its temperature. 2) Infants and children, who rely on others to keep them cool and hydrated. 3) Athletes, who may be more likely to exercise and become dehydrated during extreme heat events. 4) Outdoor workers, who have more exposure to extreme heat and are more likely to become dehydrated. 5) Households without air conditioning available at home. 6) Visitors who are not adjusted to warmer climates may be at a higher risk to adverse heat impacts, or may not recognize symptoms associated with heat exhaustion or heat stroke.
Aside from the heat-induced health impacts described above, extreme heat negatively impacts air quality by increasing the amount of ground-level ozone (or smog). Worsened air quality can aggravate existing respiratory illnesses, and long-term exposure can result in decreased lung function. Extreme heat can degrade water quality by heating water bodies directly or heating runoff that drains into larger basins.
Economic Impacts: Generally, economic impacts due to extreme heat are minimal. It is possible that indirect losses due to business interruption in the case of a power outage during an extreme heat event. Extreme heat waves may negatively impact tourism. Economic impacts expected from warming caused by climate change are further described below.
Climate Change Impacts: According to the Fourth National Climate Assessment, annual average temperatures in Hawai’i will increase by 2-3°F by the mid-21st century and 5-6°F by the late-21st century under a high emissions scenario (representative concentration pathway (RCP) 8.5).127 This warming trend means that extreme heat events in Maui County are expected to become more frequent and more intense.
Significant increases in extreme heat events could have severe health impacts, especially for vulnerable populations such as the elderly, young, outdoor workers, and impoverished households. An increase in extreme heat days could also contribute to more frequent and severe droughts and wildfires, as baseflow in streams decreases and evaporation increases. In addition, warming has the potential to cause economic and environmental impacts within Maui County. According to the Fourth National Climate Assessment, coral reefs contribute an estimated $477 million to the local economy every year in Hawai’i. Under projected warming, all nearshore coral reefs in Hawai‘i will experience annual bleaching before 2050.
