Heatwave

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A heat wave is in meteorology and climatology an unusually long period of consecutive unusually hot day. Somewhat weakened, one also speaks of heat waves for phases of abnormally high temperatures.

To define a heat wave

Map of the local temperature anomaly from summer 2003 to 1971–2000, as a measure of a heat wave

Heat waves as such are a relatively young field of research; in the past the focus was primarily on droughts . There is also no uniform definition of a heat wave. Typical modern approaches for quantifying a heat wave are structured as follows:

  • First, a certain threshold for the term abnormal heat is defined, either absolutely (e.g. using the term hot day , maximum daily temperature> 30 ° C) or using the temperature anomaly (threshold of a degree deviation from a more specific long-term mean temperature, e.g. the mean of the respective day or month of the last 30 years), or a frequency (e.g. standard deviation 95% percentile of such a tax base). Further criteria would be physiological values ​​such as perceived temperature or the heat index (a combination of temperature and air humidity).
  • Then criteria are selected for the length of time, the episode (about a minimum duration of three or five days; even if a single day below the heat threshold does not interrupt the heat wave) as well as the period in which one wants to speak of a heat wave at all (e.g. only the meteorological summer for temperate latitudes)
  • An affected area is determined from a meteorological analysis, within political boundaries, purely metrologically using stations, or a modeling grid - the definition range of the heat threshold and the area do not have to coincide (so the threshold could relate to individual measuring stations, the area on administrative units).
  • Criteria for the intensity of the heat wave are determined, for example the absolute highest temperature measured over the entire period, the mean maximum temperature over all measuring stations in the area, the maximum or mean anomaly, the annuality of the event, or the like.

This gives the following measures for the extent of a heat wave:

  • Duration
  • Geographical scope
  • Certain values ​​of intensity

A method of evaluation used for Central Europe goes back to the Czech meteorologist Jan Kysely , these days of the heat wave are called Kysely days :

“A heat wave is detected as soon as the maximum temperature exceeds 30 ° C for at least three days in a row and lasts as long as the mean maximum temperature remains above 30 ° C over the entire period and the maximum temperature does not fall below 25 ° C on any day . "

For heat waves - for example for the winter half-year - similar criteria with weaker limit values ​​are used.

The temporal and spatial dimensions can be related to each other, but an approach of how a local, short and violent heat wave would be compared with a long lasting and large-scale one, and that across different climatic regions, is very complex. These estimates of comparability across time series and regions of the world are currently in development in meteorology, weather medicine and climate impact research . The definitions for 'heat wave' can correlate with the establishment of certain severe weather warning levels.

Formation of heat waves

Heat waves have different causes depending on the region of the world. In winter, such situations lead either to an ingress of warm air and a thaw , or to a cold spell .

Mechanisms on the middle latitudes

Classic continental high over North America

The classic summer heat wave of the middle latitudes is caused by a high pressure area and heating by prolonged sunshine. For Central Europe, for example, thermal collapses are usually well-documented singularities (regularly occurring exceptions), such as the dog days in midsummer, but also in winter, for example, the Christmas thaw , they break down the phenological seasons of the vegetation.

Regular positions of the regions of origin of the air masses (west of Europe cold air, south warm air)

There are some largely regular permanent high pressure zones, such as the Azores high or the Siberia high , which always lead to summer heat. Abnormal heat waves can cause these if they move irregularly or if they are extremely strong: The Azores high can lie as far as Western Europe, and then have a particularly direct influence on the continent's weather (an example: late summer 1975 ). Or it is pushing the Atlantic lows excessively northwards, which leads to zonal heat in the entire Mediterranean area ( July 2015, second phase ). Because these highs are self-stabilizing, such heat waves can last for many weeks or an entire season, and can also lead to droughts . This effect is reinforced when high pressure bridges form between the highs, then these events also become quite large-scale.

Rossby waves of jet streams

An exception in the moderate latitudes is caused by a blockade : at certain intervals the jet stream changes into a particularly wavy shape, the westerly wind drift breaks off, the low pressure systems do not make any progress, and the highs in between remain stationary. This can lead to hot periods of one to several weeks. This shift of the polar front also leads to a strong heat exchange from the tropics to the polar regions and can also lead to abnormal heat in the higher north.

A cyclone (dynamic low) as a warm air pump: warm front and warm sector in front of the cold front

Another form of the middle latitudes are powerful low pressure systems (cyclones). These can then reach into the subtropics on their south-facing warm front , and in front of them pump enormous amounts of warm air to the north. These are short-term ingress of warm air up to a few days; such situations can also lead to heat waves in winter. Southwestern high-altitude currents in North African air are typical for Europe , often with Saharan dust events. A typical example is the summer of 2013 .

Rolling jet stream with extreme omegalage ( 2010 )

The combination of these situations can become extreme: If the high east and west of a blockade is flanked by strong lows, the omega position is created , according to the symbol , with a combination of blockage and southerly air currents, which increases the heat. The tropical nights are typical for this because there is no cooling at night due to increased radiation in normal high-pressure weather. In Europe, dry Saharan air or foehn effects in the Pyrenees and Alps result in a combination with abnormal drought, often eliminating the typical warmth thunderstorms that are otherwise characteristic of summer heat, which means that there is no further cooling factor. This was characteristic in the summers of the century in  2003 and 2015 (first and third phases) .

Global Mechanisms

Sea temperature anomaly July 2015 : El Niño in the Pacific: Heat waves on the North American west coast.

Another cause is fluctuations in the intensity and position of the warm oceanic currents , which fundamentally influences the positions of the centers of action and atmospheric currents. The best- known phenomenon of this type is the El Niño system, which can lead to heat waves on the west coasts of both Americas (and probably also affects the weather worldwide). Since this system shows certain regular recurrences ( El Niño-Southern Oscillation , ENSO), and other global weather relationships also occur in periods, extreme weather such as heat waves also show certain accumulation phases.

Influences of climate change

Frequency (vertical) to anomaly (horizontal) high summer temperatures in the northern hemisphere, mean 1951–1980 and last three decades: increase in median, decrease in frequency, increase in high anomaly (NASA-GISS)

That global warming regionally altered the frequency and duration of heat waves has the effect , is well established today. According to the forecasts of the Intergovernmental Panel on Climate Change, more hot and less cold temperature extremes will occur in connection with anthropogenic climate change , and heat waves will most likely occur more frequently and last longer. This has also been proven in numerous regional studies.

Ecological consequences

Abnormal drought during the 2015 European heat wave on the Upper Rhine

A drought can be associated with a heat wave , but it does not have to be, there are also humid, humid, rainy periods of heat.

Extremely low water levels cause considerable problems for shipping and the ecology of water bodies. Low water during heat waves with simultaneous slow flow movements also promotes fish deaths due to the lower oxygen content of the water .

Heat mortality

The following list gives the ten heat waves that are believed to have claimed the most deaths. It should be noted that this phenomenon has only been quantified in recent years: there is no clear definition of who is the victim of a heat anomaly. In contrast to those who were directly injured by storm or flood disasters, at most heat-related deaths from circulatory or heart failure are reported - for example, illnesses due to general weakening, accidents due to increased stress or even malnutrition victims due to subsequent crop failures due to an associated drought are not taken into account. Modern approaches calculate the victims purely statistically as an increase from the average natural mortality . The bases of calculation for the more recent events in Europe and other parts of the world are likely to be quite different. There is hardly any historical data and, in particular, comparability - for India, which has experienced four severe heat waves in the last 15 years alone, no figures at all on “regular” mortality should be available. Information on heat victims of individual events can vary greatly depending on the source and are generally to be viewed with reservation.

It is assumed that exposure to heat and ozone can intensify their combined effects.

According to a study published in 2017 in 27 European countries, an average of more than 28,000 people die each year in Europe as a result of heat waves, around 5,600 of them in Germany. In percentage terms, the highest death rates occur in Portugal, Spain and France. In Germany, too, deaths were slightly above the European average. Elderly people and those with previous illnesses are particularly affected. A further increase in mortality is expected in the future as a result of global warming.

region year Duration in
weeks		 T max Number of victims
Europe 2003 2 47 ° C 70,000
Russia 2010 8th > 40 ° C 55,000
Europe 2006 5 39 ° C 3,500
India 1998 10 50 ° C 2,500
India 2015 6th 49 ° C 2,500
USA, Canada 1936 2 44 ° C 1,700
United States 1980 ~ 10 45 ° C 1,300
Pakistan 2015 2 45 ° C 1,300
India 2003 3 50 ° C 1,200
India 2002 2 49 ° C 1,000
Greece, Turkey 1987 2 50 ° C 1,000
Source: Jeff Masters, as of June 2015 (figures rounded here); Duration and temperature of various sources

See also

Web links

Wiktionary: Heat wave  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. ↑ Christopher Polster: Northern Hemisphere Summer Heatwaves: An Overview and Case Studies. Bachelor thesis in the subject of meteorology, Johannes Gutenberg University Mainz, Institute for Atmospheric Physics, 2014, Chapter 3 Definition of a heat wave , p. 3 f ( PDF  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective . Please check the link according to the instructions and then remove this notice. , Uni-mainz.de, p. 11 f).@1@ 2Template: Toter Link / www.glk.uni-mainz.de  
  2. ^ George A. Meehl, More Intense, More Frequent, and Longer Lasting Heat Waves in the 21st Century . In: Science . 305, No. 5686, August 13, 2004, pp. 994-7. bibcode : 2004Sci ... 305..994M . doi : 10.1126 / science.1098704 . PMID 15310900 .
  3. ^ Peter J. Robinson: On the Definition of a Heat Wave . In: American Meteorological Society (Ed.): Journal of Applied Meteorology . 40, No. 4, April 2001, pp. 762-775. doi : 10.1175 / 1520-0450 (2001) 040 <0762: OTDOAH> 2.0.CO; 2 .
  4. ↑ In the USA: 90 ° F, cf. Heat wave ; Robert DeCourcy Ward: The Climates of the United States , 1925, pp. 383-395; online in American Meteorological Society: Glossary of Meteorology .
  5. ↑ a b This is how the Swedish weather service defines a 'heat wave' ( Värmebölja ) from 25 ° C; this is appropriate for the more northern latitudes and can also occur in winter; see. Värmebölja , Swedish Wikipedia.
  6. ↑ a b c Heat waves: 2015 was one of the most extreme years in measurement history. ZAMG Klimanews , August 13, 2015; Anomaly evaluation last section 2015 among the most unusual summers in measurement history; Definition of Kysely days quoted verbatim (end of article).
  7. ↑ For example in AEMET: Olas de calor en España desde 1975. Área de Climatología y Aplicaciones Operativas , undated [Update: 2015] ( PDF , aemet.es).
  8. ↑ a b c d e f Cf. Lukas Brunner , Gabriele C. Hegerl , Andrea K. Steiner : Connecting Atmospheric Blocking to European Temperature Extremes in Spring. In: Journal of Climate , January 2017, American Meteorological Society, doi : 10.1175 / JCLI-D-16-0518.1 ;
    Definition there (for studies of the spring period): 90% percentile of T max of the day to the average value of a 36-year comparison period with a 21-day moving average; hot spell day (WSD, Wärmewellentag ) when an entire 5 ° × 5 ° region on 6 consecutive days meets this criterion.
  9. ↑ PJ Robinson already emphasized the importance of perceived values ​​as a basis for assessment: On the definition of a heat wave. In: J. Appl. Meteorol 40 (4), 2001, pp. 762-775; Information on the upholstery: Summer heat waves ..., p. 3 (pdf p. 11).
  10. ↑ E.g. based on the Klima-Michel-Modell , cf. Website of the German Weather Service (DWD); Information on the upholstery: Summer heat waves ..., p. 3 (pdf p. 11).
  11. ^ According to the American National Weather Service (NWS), cf. NWS heat index ( memento of the original from July 12, 2015 in the Internet Archive ) Info: The @1@ 2Template: Webachiv / IABot / www.nws.noaa.gov archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. ; Information on the upholstery: Summer heat waves ..., p. 3 (pdf p. 11).
  12. ↑ See for example Swedish Meteorological Service: Värmebölja , smhi.se, accessed on July 11, 2015.
  13. ↑ Cf. AEMET: Olas de calor en España ... , Tercera etapa , p. 3.
  14. ↑ Cf. AEMET: Olas de calor en España ... , Primera etapa , p. 3.
  15. ↑ Cf. AEMET: Olas de calor en España… , Segunda etapa , p. 3: If 10% of the stations in the area measure abnormal heat, the day is considered the day of the heat wave.
  16. ↑ a b c Cf. AEMET: Olas de calor en España ... , Primera etapa , p. 4.
  17. ↑ A measure would be, for example, the sum of the area of ​​a degree day number, for example the sum of the anomalies over the days of the heat wave, corresponding to the heating degree days based on the temperature difference of the outside air temperature in relation to the desired room inside temperature. The corresponding cooling degree days are now an established measure of the general indoor climate heat exposure of a place or building: the anomaly of the actual cooling degree days in relation to the long-term mean would also be a measure for a single heat wave.
  18. ↑ Europe - (meteorologically) divided into two parts. DWD: Topic of the day , August 11, 2019.
  19. ↑ Andrew D. King, David J Karoly: Climate extremes in Europe at 1.5 and 2 degrees of global warming . In: Environmental Research Letters . tape 12 , 2017, p. 114031 , doi : 10.1088 / 1748-9326 / aa8e2c .
  20. ↑ IPCC: Fifth Assessment Report, Partial Report 1 (Scientific Basis) . Core messages (German summary) . 2014.
  21. ↑ For example:
    D. Oudin Åström, F. Bertil, R. Joacim: Heat wave impact on morbidity and mortality in the elderly population: a review of recent studies. In: Maturitas 69 (2), 2011, pp. 99-105.
    Jennifer F. Bobb, Roger D. Peng, Michelle L. Bell, Francesca Dominici: Heat-Related Mortality and Adaptation to Heat in the United States. In: Environ Health Perspect , Volume 122, Issue 8, August 2014, doi : 10.1289 / ehp.1307392 .
  22. ↑ See for example Climate change> Indicators- European Commission: ec.europa.eu> Public health: Over mortality due to European heat wave in 2007/2006/2003 (accessed on July 21, 2015).
  23. ↑ Health risks from ozone. Federal Environment Agency, December 7, 2018, accessed on July 25, 2019 .
  24. ↑ Steffen Merte: Estimating heatwave-related mortality in Europe using singular spectrum analysis . In: Climatic Change . 2017, doi : 10.1007 / s10584-017-1937-9 .
  25. ^ Jeff Masters: Unprecedented June Heat on Four Continents; Wimbledon Roasts in Record Heat. Section Death Tolls From the 10 Deadliest Heat Waves in World History . wunderground.com, July 1, 2015, accessed July 6, 2015.