North America heat wave 2021

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Temperature deviation on June 29, 2021 compared to the average of that day in the period 2014-2020 (in degrees Celsius )

The North America 2021 heat wave is a sustained extreme heat wave that will affect much of the Pacific Northwest and Western Canada . In particular, it hit western Nevada , northern California , Oregon , Washington, and Idaho in the United States, as well as British Columbia, and in the later phase Alberta , Saskatchewan , Yukon, and the Northwest Territories in Canada. At the same time there were an unusually high number of lightning strikes and increased forest fires.

The heat wave is considered a millennium event and is described by scientists, weather services and the media as unprecedented in the known history of the region. It performed at the end of June, and thus unusually early in the summer . The maximum temperatures were reached around June 25th to 30th and clearly broke numerous regional temperature records. The heat wave was compounded by the ongoing drought in Northwest America. Global warming has also been identified as an important facilitating and reinforcing factor , without whose assistance a heat wave of this intensity would hardly have been conceivable.

In the second week of July, extreme heat reappeared on the west coast of the United States, particularly in California, Nevada, and Arizona .

causes

500 mb map of the high and low pressure areas in North America on June 28, 2021, 11:00 UTC

Heat build-up

The extreme temperatures in the region were triggered by an atmospheric blockage of a high pressure area and the resulting heat build-up (“heat bell”). Rising warm air is pushed back down by the high pressure area, so that temperatures continue to rise. The heat dome was the strongest ever observed in this region. Due to the particularly long days at the end of June, among other things, the temperatures rose extraordinarily.

The interaction between the jet stream and a tropical storm in the Pacific is also discussed as a further favorable factor . The tropical storm near Japan caused a meandering turbulence in the jet stream. On the way to North America, the Atmospheric Rossby Wave intensified until it finally broke, creating a stationary high pressure area over Northwest America, while at the same time a low pressure area lay off the coast. The air pressure gradient between the two pushed cool ocean air away from the coast to the west and warm air towards the coast. Over the Rocky Mountains and the Cascade Mountains , the air also warmed up further down the slope due to the increasing air pressure. The east wind thus had an intensifying effect.

dryness

Drought Monitor USA, June 22
Predicted temperatures ( degrees Fahrenheit ) for Washington on June 28, 2021

Another factor was the prevailing drought . 81% of the American West suffered a severe to exceptional drought in late June; the first time ever that this value was over 80%. 55% of the area even experienced an extreme or extraordinary drought at the time of the heat wave. This enormous drought favored the rise in temperature: when it is drought, less water can evaporate from the soil, the air thus remains drier and dry air is heated significantly more than moist air by the same amount of energy. Research shows that global warming made this drought worse as higher temperatures dry out the soil more. This is the mechanism by which the heat wave in turn worsens the drought. In addition, the high pressure area that triggered the heat wave meant that any rain clouds were deflected.

Global warming

The heat wave was significantly influenced by global warming, which has already led to a global temperature increase of 1.2 ° C compared to the pre-industrial era. According to Omar Baddour, who heads the Climate Monitoring and Policy Department at the World Meteorological Organization , as greenhouse gas concentrations rise, heat waves become more frequent and intense, start earlier, end later, and have a greater impact on human health . Nikos Christidis of the Met Office said that without man-made climate change it would have been nearly impossible to reach temperatures this high in June, as the probability of such occurrences under natural circumstances would be one in a few tens of thousands.

Atmospheric wind bands such as the jet stream are influenced by climate change and contribute to the development of extreme temperatures. An increased incidence of heat waves in the USA has already been identified. In the 1960s, there were an average of two heat waves per year, whereas the number tripled to six heat waves per year by the 2010s. The size of the regions affected by the heat waves has also expanded by an average of 50 percent in the Northern Hemisphere , according to a study by several American universities based on data from the past 38 years .

An attribution study published on July 7, 2021 came to the conclusion that the heat wave with these maximum temperatures in the region of 45–52ºN, 119–123ºW would have been almost impossible without man-made climate change. Accordingly, the temperatures were so far outside of historical observational data that it was difficult to quantify how rare the event was. As the most realistic value, the study states that such a heat wave would only occur once every 1000 years in the current climate. In addition, man-made climate change made the occurrence of this heat wave at least 150 times more likely. The heat wave due to climate change was also 2 ° C hotter than an otherwise identical heat wave that would have occurred at the beginning of the industrial revolution. If the heat wave had taken place under conditions of a world warmer by 2 ° C compared to the pre-industrial era, which could have been reached as early as the early 2040s (this is an increase of 0.8 ° C compared to 2020), then the heat wave would have been another degree turned out hotter than observed. In such a world, a heat wave like the one that occurred in 2021 would then repeat itself every five to ten years instead of about every 1000 years. According to a study by climatologist Michael E. Mann , global warming increases the probability of heat waves and extreme rain occurring by around 50 percent by the year 2100, as shown by jet stream simulations.

Temperature records

Land temperatures on June 29th as measured by Sentinel-3 radiometers - these are different from air temperatures and reached a maximum of 69 ° C in Washington state

Even before the start of the heat wave, weather models predicted exceptionally high temperatures, which indicated the arrival of a historic heat wave .

The heat wave resulted in some of the highest temperatures ever recorded, including the highest temperature ever recorded in Canada. It also affected inland areas of central and southern California and northwestern and southern Nevada, although temperatures weren't as extreme compared to regions further north. Temperatures were reached in several places that exceeded the previous temperature records despite z. Some of the records, dating back more than 100 years, were exceeded by several degrees Celsius, which is extraordinary from a meteorological point of view. In a number of cities, the previous temperature records were surpassed by 5 ° C and more, including Portland with 46.6 ° C. In Olympia and Quillayute, the previous records were exceeded by approx. 6 ° C, Salem was even 9 ° C above its previous temperature record.

Weather historian Christopher Burt said the heat wave was "the most abnormal regional extreme heat event that has occurred anywhere on earth since temperature records began." Maximiliano Herrera, a scientist who researches weather records, wrote that there was no global comparison for the heat wave. There is an "endless waterfall of records that would be shattered". In one week, more all-time heat records were broken by more than 5 ° C than in the more than 84 years since there have been global temperature records.

According to Copernicus , June 2021 was also the hottest June in North America since satellite data collection began. The month was 1.2 ° C above the monthly average for the years 1991 to 2020 or more than 2 ° C above the pre-industrial period.

Canada

Among other things, the Canadian temperature record was broken in Lytton in British Columbia for three days in a row. After the record of 45 ° C that had existed since 1937 was clearly exceeded at 46.6 ° C, the thermometer rose to 47.9 ° C the following day and finally reached 49.5 ° C on June 29th. The temperature was thus higher than ever in Europe , South America , large parts of the USA with the exception of the desert regions in the southwest, or cities such as Sydney and Las Vegas . Only in 26 countries in the world have higher temperatures ever occurred. Usually the maximum temperatures in Lytton in June are around 25 degrees Celsius, in July the long-term average daily maximum temperature is 24.3 ° C. Without human influence on the climate, such a temperature deviation would statistically only occur at intervals of a few thousand to around ten thousand years.

In addition, on June 30, 2021, Fort Smith , which is north of the 60th parallel , reached 103 degrees Fahrenheit (about 39.5 ° C). This is the highest temperature ever recorded this far north.

United States

New temperature records were also set in many other regions of the northwestern United States. In Northern California , Oregon , Washington and Idaho alone , around 175 new heat records were set between June 25 and 30. In Oregon values ​​of well beyond 40 ° C were measured. Seattle , Portland and a multitude of other US cities never reached temperatures measured there before; sometimes the values ​​were above 46 ° C. In Salem , at 47.2 ° C, the highest temperature since records began at the end of the 19th century was reached.

In the second phase, extreme heat again occurred on the west coast of the USA from July 9, 2021. Among other things, 130 degrees Fahrenheit were measured in Death Valley (approx. 54.4 ° C). Only twice, in 1931 in Tunisia and in 1913 also in Death Valley, were higher temperatures recorded on earth. Both measurements are scientifically controversial, so that the temperature measured on that day could have set the record for the highest temperature reliably determined to date. The highest reliably determined temperature to date was 129.9 degrees Fahrenheit (54.4 ° C) and was also set up in Death Valley on August 16, 2020. In addition, on July 10th, the highest daily minimum temperature in North America was measured at 42.0 ° C. Only once before was a higher minimum temperature recorded worldwide of 42.6 ° C: June 26, 2018 in Oman .

Palm Springs in southern California set a new all-time record at 49 ° C, while Las Vegas set its temperature record at 47 ° C.

consequences

Deaths

The heat wave caused numerous deaths; i.a. At least 719 people died suddenly in British Columbia within a week, about three times the average (as of July 2, 2021). In the previous three to five years, there had been only three heat-related deaths in the province. In Vancouver alone , 69 people had died of the heat as of June 30th. At least 95 heat deaths were reported in Oregon as of July 3, and around 30 more in neighboring Washington state.

A particular problem was that the heat dome kept temperatures very high even at night, which prolonged the heat stress for the affected population. It is expected that the excess mortality caused by the heat wave will in all probability be much higher than initial estimates suggest.

Even before the heat wave, heat led the statistics of weather-related causes of death in the United States.

Ecological consequences

As a result of the heat wave, there was also damage to the fauna and flora . Among other things, the heat wave resulted in the death of large numbers of marine life such as clams , mussels , sea slugs and starfish in the tidal areas of the coast . These are basically adapted to the retreat of the water and can withstand temperatures of almost 40 ° C for short periods of time at low tide . However, due to the heat wave, they were sometimes exposed to temperatures of over 50 ° C, with the high temperatures sometimes lasting over six hours. A marine biologist from the University of British Columbia calculated from projections of dead animals found that the heat wave in the Salish Sea area could have killed more than a billion animals. This also has an impact on the water quality , as mussels filter the water.

Power outages and infrastructure damage

Repair work on a heat-damaged section of Interstate 5 , Washington

In the region hit by the heat wave, several power outages were reported due to the overloading of the power grid due to the increased use of air conditioning and fans. Portland trams stopped operating because power cables stretched and sagged in the heat. In order to avoid the collapse of the power supply, the electricity suppliers in some regions have switched off the electricity as a precaution.

In Edmonton in the province of Alberta , it was so hot, that dozens pavements made of concrete so strongly stretched that they aufwölbten itself. In total, the city registered 57 such cases as of July 3.

Forest fires

Lava Fire , California, June 30, 2021
California forest fire, June 28, 2021

Due to the enormous heat, the risk of forest fires was very high, so that hundreds of wildfires broke out in both the USA and Canada. As of July 12, more than one million hectares of land were burned in the two states .

United States

Fires broke out in about a dozen US states; in California, inter alia the so-called lava fire , which had already destroyed 7,000 hectares of forest by July 1st. US President Joe Biden said the 2021 wildfire risk was "more serious than ever," and warned that the season could get worse than the 2020 wildfire season , when California saw the biggest fires on record. In California alone, where soil moisture had already dropped to a level at the beginning of July that would otherwise not be reached until the end of August, thousands of people had to be evacuated at times and several buildings were destroyed. On July 12, more than 60 fires burned, including a dozen major California forest fires, one of which also threatened Yosemite National Park . The power supply in Oregon and California was also threatened, as a fire endangered important high-voltage lines. Two firefighters working with aerial observation were killed in a plane crash in Arizona.

Canada

Large-scale forest fires also broke out in British Columbia, and the overheating engines of the fire-fighting helicopters made fighting them even more difficult. As of June 30, the “Sparks fire” was estimated at around 200 km², the “Mckay Creek” fire at 60 km². Another fire at Pink Mountain at that time had a size of 48 km². As of July 4, there were more than 180 wildfires in British Columbia alone, of which 86 had ignited in just two days. On July 13th there were already more than 300 fires. Lytton , which had set the Canadian temperature record the day before , was also destroyed by flames . Due to the speed with which the fires spread, the village had to be evacuated within minutes. Several residents are still missing. 90% of the place was destroyed, including the entire town center. Two people are said to have died in the flames.

As a result of the extensive forest fires, pyrocumulonimbus clouds (fire clouds) formed, which reached a height of 16.8 km. This enabled them to reach the stratosphere , which is very unusual and has only been observed in the most severe fires (for example the 2019/2020 bush fires in Australia ). These clouds led to heavy, almost precipitation-free thunderstorms with a lot of lightning , which in turn very likely caused further forest fires. Of the more than 180 wildfires that burned in British Columbia on July 4th, 70% were classified as likely caused by lightning strikes by the Forest Fire Department. In western Canada, more than 700,000 lightning bolts occurred in 15 hours on June 30 and July 1, of which more than 100,000 hit the ground. This is about 5% of the amount of lightning that would otherwise occur in Canada over the course of a year. Most of these lightning bolts were triggered by pyrocumulonimbus clouds created as a result of the forest fires. These clouds can be so extensive and high that they produce their own local weather . Neal Lareau, professor of atmospheric science who studies weather phenomena caused by forest fires, said this could be the largest occurrence of these clouds that he has ever seen.

The Canadian military sent a unit to the area to support the fire department.

Web links

Commons : North America Heat Wave 2021  - Image Collection

Individual evidence

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