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The ENSO phenomenon

Global impact of ENSO

 

introduction

The warm (El Niño) as well as the cold (La Niña) phases of the ENSO cycle stimulate global atmospheric circulation patterns that cause climate anomalies on a multi-year scale around the globe. Because of its climatic effects (temperatures, precipitation, cloud cover), and also because of its relatively large predictive potential, the ENSO phenomenon is one of the central areas of current climate research.

The climate in the area of ​​the equatorial Pacific acts as a coupled system, since the state of the ocean and atmosphere are interdependent. When the conditions in the ocean change, the atmosphere reacts and vice versa.

In its oceanic sphere of activity, ENSO influences sea surface temperatures, the vertical thermal structure of the ocean (especially in coastal regions), the speed and strength of ocean currents, as well as upwelling processes.

As a result, ENSO, with its significant variations in weather phenomena and its influence on the physical quality of large parts of the sea, has profound effects on mankind due to droughts, floods, heat waves and other anomalies, which in turn have consequences for agriculture and forestry, fisheries, the environment, Energy demand and supply, financial markets, tourism, transportation, health, water supply, air quality or fire risks. It should be noted that the effects are not only disadvantageous, but can also bring benefits to people and ecosystems, e.g. through increased rainfall in arid regions or the reduced number of Atlantic hurricanes during El Niño.

Factors affecting ENSO and the impact on society

The ENSO properties are influenced by many factors, including coupled feedback processes, atmospheric and oceanic noise and climate forcing from other ocean basins, and the basic mean state that develops over long time scales. All of these components interact with each other and are influenced by external influences (e.g. greenhouse gases, aerosols, solar variability), which in turn influences the predictability and effects of ENSO.

Source: Santoso et al. 2019

Each El Niño and also each La Niña have their own characteristics, e.g. with regard to timing and intensity, and their respective effects differ accordingly. In addition, the atmospheric effects that result from changes in sea surface temperatures are only partly responsible for the regionally observed weather events. Chaotic fluctuations in the atmosphere and sea surface temperatures in other areas of the world also influence the atmospheric events that we experience. For this reason, ENSO effects predicted in seasonal forecasts are probabilistic (DWD) and not absolute in character.

This chapter primarily presents impacts that are associated with El Niño events; to a lesser extent, La Niña-related impacts are also dealt with. The sections are overwritten accordingly.
This 'disadvantage' of the second extreme phase type of ENSO, which can also be found in the relevant literature, may be due to the fact that La Niña is not viewed by all experts as an independent element of ENSO, rather as an intensified variant of the neutral state of the ocean / atmosphere system in the tropical Pacific. It may also be because the Pacific equatorial area does not cool as much during La Niña as it warms up during El Niño, or because significant impacts from La Niña events are less common.

It should also be noted in this chapter that the sectoral effects (economy, health, transport, plant growth, etc.) are currently only shown separately for the areas of water resources, economy, raw material markets, agriculture, health sector and ecosystems, otherwise they are included in the regional considerations.

The effects on countries such as Peru, Ecuador or Colombia, which are more likely to be classified as "regional", are included in this chapter because of the difficult spatial delimitation of the effects. Please refer to the Peru-related chapter "Effects of El Niño on the fish world".

Possible chains of effects at El Niño events

 

Source: Caviedes, C.N. (2005):
El Niño. Climate makes history. Darmstadt

The events described here cannot be described with unassailable certainty as the effects of ENSO extreme events. Many weather events are made more likely or less likely by El Niño or La Niña. But their only cause is ENSO in the rarest of cases.
Statistics and graphics illustrate how one can assume that there is an influence on the part of ENSO. But even these data can at best be viewed as an indication, not as evidence. This is precisely what makes this chapter interesting. Some of the effects described are the subject of heated discussions. A useful El Niño / La Niña forecast could also predict damaging events and avoid high levels of damage and human loss.

However, it turns out again and again that many effects do not occur in the same way with every El Niño or La Niña event. It is even possible that an El Niño, for example, leads to a drought in a certain area, even though another caused a flood disaster there a few years earlier. Or is the explanation simply that the weather events had nothing to do with El Niño? As long as this has not been clarified with a high degree of reliability, caution is advisable when it comes to making simple connections between cause and consequence.

There are no ENSO impacts where there is 100% correspondence between individual variants of the impacts and those of ENSO. This is because ENSO is variable as a climate phenomenon and because climate in general is not the only influence on the occurrence of a particular impact. Therefore, it is important to find out how strong the relationship is. Statistical methods such as correlation relationships are one way of finding out. For example, if the outbreak of a certain disease often corresponds to El Niño events, one can ask: Has the outbreak occurred with every El Niño event? Does the strength of the eruption have any equivalent to the strength of the El Niño? Was there such an outbreak during the El Niño-free years?

Problems and uncertainties in determining the impact of ENSO


The figure on the left illustrates problems associated with assigning certain impacts to ENSO. In this case, there are several steps between assigning a more intense jet stream to El Niño and CO poisoning in residents of poorly ventilated houses who have used gas heaters after an ice storm. Each step has some degree of uncertainty in the attribution.

Another potentially very relevant question to be considered is how ENSO influences the behavior of higher-frequency patterns - such effects of modulation would not correlate linearly with ENSO, but would still be connected to it.

Source: IRI / MetEd / UCAR (access via free registration)

Even if more space is given to the effects of the warm phase (El Niño), it should not be overlooked that the cold phase (La Niña) can also be accompanied by extreme weather events across almost the entire globe. Some scientists assume that in some regions La Niña-related extreme events have an opposite expression than El Niño-related ones. For example, drought in southern Africa accompanies El Niño, while exceptionally high rainfall is associated with La Niña. "Researchers are just beginning to realize that they should focus more attention on the cold part of the cycle to enhance their overall forecast possibilities."
(M. Glantz in "Encyclopedia of World Climatology", 2005)

In general, scientific statements about the remote effects or "teleconnections" of El Niño become more uncertain the further one gets away from the Pacific "weather kitchen".
(Topics, Munich Re, Natural Disasters 1997)

John Houghton from the Royal Commission on Environmental Pollution assume that all anomalies in circulation and precipitation in all tropical areas, and to a lesser extent in the mid-latitudes, are due to El Niño.
(J. Houghton, "Global Warming: Facts, Dangers, and Solutions", 1997)

"Also, it is often the adverse impacts of ENSO variations that receive the most publicity, whereas the benefits, at least for some regions of the globe, are much less understood and appreciated. It is estimated, for example, that the 1997-1998 El Niño resulted in a net benefit of $ 20 billion to the US economy because of the reduced number of land-falling hurricanes and the unusually warm winter in the Midwest. "

McPhaden, M. J., Zebiak, S. E., Glantz, M. H. (2006): ENSO as an Integrating Concept in Earth Science

What is striking is the significantly higher number of scientific and journalistic works on the negative effects of ENSO events compared to the positive effects. One can speculate about the causes of this imbalance. Creating a reliable global balance sheet for individual ENSO events is likely to be an almost impossible task.

The present compilation of effects does not claim to be complete.

 

 

SECTORAL IMPACT

Note: In three of the mentioned fields, the chapter is based heavily on the presentation by Zebiak, Stephen E. et al. (2015). Its focus is on three important climate-sensitive sectors, which can be traced back to a range of impacts, as well as related societal responses: water, agriculture and the health sector. There is a large amount of published research on each of these sectors that focuses on understanding the impacts of ENSOs and using ENSO information to predict impacts and improve the management of the information. The sectors differ in terms of their complexity and their connection to the climate, the simplest for water and the most complex for health. A second difference relates to the decision-making environment. In the water and health sectors, the use-oriented research results are aimed at institutional decision-makers. Agriculture has a more complex decision-making environment, mostly decentralized and appealing to a larger number of individual actors (farmers who make climate-sensitive decisions on site, often at remote locations with severe restrictions on resources and infrastructure). The third difference is the extent to which decisions are geared towards the entirety of climate variability (e.g. water management and most management decisions at farm level) or only on the reaction to extreme events (e.g. reaction to floods or climate-dependent epidemics).

For the three sectors mentioned, Zebiak, S. (p. 26 f) offers three case studies from Queensland, Australia (agriculture), Washington State, U.S. (Water) and the Horn of Africa (health) region.

 

Meteorological processes

As mentioned above, the effects of a strong El Niño can be almost global, because the rise in surface temperatures near the equator in the central and eastern Pacific "heats up" the weather in much larger regions.

But how "knows" the atmosphere of El Niño? To do this, one has to imagine a chain of atmospheric processes in which each link transfers information from the direct environment in which El Niño-related SST anomalies occur into the global climate system. The first link is the tropical reaction by means of rain-bringing cumulonimbus clouds. They are crucial because deep convection is the main actor in bringing heat from the surface of the earth to the free atmosphere, conveying the presence of El Niño to it. During El Niño, precipitation increases for several thousand kilometers along the equator from the central to the eastern Pacific in response to the increased SST. The reverse effect usually occurs during La Niña events, although the strength of the W-E precipitation anomaly over the equatorial Pacific is less than that of warm events.

The second link in the chain relates to the sensitivity of the atmospheric circulation to displacements of extensive cumulonimbus convection. Atmospheric wave movements are triggered, which are necessary to adapt the currents in the atmosphere to the new tropical energy sources. The main convection anomalies remain limited to the equatorial region. But at the same time there is an atmospheric air mass and energy transport that extends thousands of kilometers into the subtropics. The distracting force of the earth's rotation acts on this polar outflow and gives it a wave pattern. In the further course the current experiences a W-E direction along the jet streams in the higher latitudes. It is also characterized by stationary waves with alternating low and high air pressure. The current often takes an unusual course during El Niño. The result is a strengthening of the Pacific jet stream and an eastward shift of the steady wave pattern over the Pacific-North American area. These changes in the upper troposphere shift the trajectories of storms, which control the daily changes in weather at higher latitudes. The statistically recognizable changes in the storm characteristics (frequency, strength, origin, trajectory) are responsible for a large part of the ENSO signal, which is reflected in precipitation and temperature at higher latitudes. Such storm track feedback is a third and important link in the chain that began in the Pacific SST anomalies.

El Niño strengthens the Hadley circulation


El Niño affects global atmospheric circulation by intensifying the Hadley circulation, in which heat is transported from the earth's surface to the upper atmosphere through convection and latent heating.

When an El Niño causes additional warming in the upper atmosphere of the tropical Pacific, the air flow towards the poles becomes stronger. Changing the strength of Hadley's circulation leads to changes in global circulation patterns, including e.g. B. the position of the jet stream that flows from west to east across the North Pacific during the winter months. El Niño tends to result in an elongated jet stream that can extend into North America and bring an above-average number of storms over the southern part of the United States.

Source: NOAA ENSO blog

 

temperature

In general, the heat released as a result of deep tropical convection in the troposphere is one of the most important driving forces for planetary circulation. The increased sea surface temperature in the tropical Pacific increases evaporation and convection and ultimately also the meridional Hadley circulation. The condensation that takes place when the air masses rise releases heat in the middle and upper troposphere. This energy is transported towards the pole with the Hadley circulation, so that the extra-tropical wind flow patterns of El Niño are also influenced.

Changes in the location of these tropical heat sources during El Niño therefore lead to far-reaching changes in wind and weather patterns outside the tropical Pacific.

For example, the westerly winds of mid-latitudes are intensified, especially in winter. In various parts of the world droughts, floods, unusual storm events, heat waves and other weather extremes with serious social, economic and health effects can also be the result of the changed flow patterns, as well as positive effects, e.g. mild winters in North America.

Furthermore, during an El Niño phase in the winter months there is a tendency towards above-average warm conditions in South and Southeast Asia, in South Africa and in Northeast North America, while in South North America too cool weather is expected.

El Niño years often help to raise the global annual mean temperature, most recently in 2015 with the El Niño of 2015/16.However, its contribution is only estimated at 8-10%. The expected new annual record for 2016 is based on an El Niño contribution of 25% (Earth Institute 2016).

Changes in global temperature, as well as the likelihood of ENSO events, are also closely related to the state of the Pacific Decade Oscillation (PDO), a pattern of ocean temperatures that reverses every 20-30 years. If the PDO shows negative values, there will be more La Niñas, if the PDO values ​​more El Niños.

 

Global warming

As part of global warming, the Eastern Pacific is expected to warm by around 3 ° C by the year 2100, much more than the Western Pacific, whose temperature will only rise by around 1 ° C. Some climatologists use model-based studies to come to the conclusion that El Niño-like situations will occur much more frequently in the future if global emissions of greenhouse gases, especially CO2, is not drastically reduced. In particular, one assumes an accumulation of extreme El Niños (W. Cai et al. 2014). The hypothesis is controversial, especially when the precise observation series are only a few decades old and one has to be aware of the natural variability of ENSO over longer periods of time.

However, there seems to be a consensus that global warming provides the climatic background and El Niño determines the development of regional weather patterns. When both act in the same direction, they have the greatest impact and weather records are broken. (Trenberth 2016)

El Niño and Climate Change

"We have to think climate change will influence El Niño in some way and will impact its impacts." But how El Niño events themselves change because of global warming? It's hard to say, and harder to observe because there is so much variation in El Niño by itself from decade to decade. It's a tough question to answer. "

"Extreme El Niño and La Niña events are projected to likely increase in frequency in the 21st century and to likely intensify existing hazards, with drier or wetter responses in several regions across the globe."

Sources: Lisa Goddard IRI (2016) and IPCC, 2019: Special Report on the Ocean and Cryosphere in a Changing Climate

At the beginning of this century, climate skeptics - especially with reference to the period from 1998 to 2013 - claimed a break in the global warming trend (warming hiatus), which met with strong opposition from many scientists. In particular, the fifth status report by the IPCC indicates that the global average surface temperatures show a “pronounced decadal and annual variability”. Due to natural fluctuations, analyzes based on short data series are “highly dependent on the selected start and end date” and would therefore not reflect the long-term trend. (IPCC 2013)

The natural property of the global climate to show a fluctuating temperature profile is caused, among other things, by the Atlantic Multi-Decade Oscillation (AMO), the Pacific Decade Oscillation (PDO) and the El Niño-Southern Oscillation (ENSO). For example, the occurrence of El Niño or La Niña events can increase or decrease the global average temperature from one year to the next by 0.2 K and, for a few years, cover but also intensify the annual warming trend of around 0.02 K. During La Niña events, heat is transported into deeper ocean layers (> 300 m), as has been confirmed with measurements and with the help of climate simulations. (Wikipedia 8/27/2016)

In fact, La Niña patterns predominated over the tropical Pacific during the period mentioned above, so that one sees a partial cause of the supposed warming pause in this framework.

A look at climate history shows that warming and droughts in the northern hemisphere from 950 to 1250 were accompanied by an El Niño pattern in the Pacific, which swung into a La Niña-like pattern from 1350 to 1900.

 

Precipitation

The following maps from the Met Office provide an initial global overview of the most important effects on seasonal precipitation and surface air temperatures during El Niño and La Niña events. It should be noted that every ENSO event is different and occurs together with other climate events. Not all of the recorded impacts occur in all events, and the real impacts need not be confined to the recorded regions. In this respect, such maps should not be viewed as a forecast for a current event, but rather as an indication of areas in which historical experience shows that effects are likely.

Effects of El Niño on temperature

Effects of El Niño on precipitation

The Met Office's analyzes for the temperature impact maps used the monthly mean near-surface land temperature data from the National Centers for Environmental Prediction's atmospheric reanalysis (1948-2011) and the CRUTEM4 grid analysis (1850-2010).

For the precipitation impact maps, the Met Office used the University of East Anglia Climatic Research Unit's monthly precipitation dataset 1900-1998 and the Global Precipitation Climatology Project 1979-2010 monthly gridded precipitation dataset in its analyzes.

Source: Met Office

Please note the following information about the cards:

  • The maps are only schematic and are not geographically precise.
  • Recent research suggests two subtypes of El Niño. Terminology is inconsistent, but the terms Central Pacific (CP) and East Pacific (EP) associated with these subtypes of El Niño indicate regional variations in sea surface temperature anomalies. The cards combine the effects of both types.
  • For example, some regions have an El Niño effect but none at La Niña: for example, the El Niño and La Niña maps may have many areas affected in common, usually with opposite effects, but there are also some different areas that are affected.
  • Some regions may experience different effects during an ENSO event at different times of the year, which is expressed by overlapping colored areas.
  • Some regions have an impact that depends on the severity of the event. For example, the El Niño map for Northern Europe has a cooling effect, but very strong El Niño events (e.g. 1982/83, 1997/98) have the opposite, warming effect.
  • Observation data are not available in the same quality across the board. There may be regions with a relatively weak impact that are not captured by the analyzes.
  • These summary maps do not reflect the extent of the effects. The probability of occurrence and the strength vary considerably from region to region.
  • The areas with impacts shown depend on the selection criteria, i.e. maps that use different criteria arrive at a different result. E.g. the present presentation also includes weak ENO events. A restriction to moderate or strong events changes the picture. Unfortunately, such information is often not included in comparable presentations.

Effects of La Niña on temperature

Impact of La Niña on precipitation

The Met Office's analyzes for the temperature impact maps used the monthly mean near-surface land temperature data from the National Centers for Environmental Prediction's atmospheric reanalysis (1948-2011) and the CRUTEM4 grid analysis (1850-2010).

For the precipitation impact maps, the Met Office used the University of East Anglia Climatic Research Unit's monthly precipitation dataset 1900-1998 and the Global Precipitation Climatology Project 1979-2010 monthly gridded precipitation dataset in its analyzes.

Source: Met Office

In the case of El Niño events, the normal patterns of tropical precipitation and atmospheric circulation under neutral conditions are disrupted. This is the result of the increased warming of the tropical atmosphere over the central and eastern Pacific

El Niño usually has its strongest expression during the northern hemisphere autumn and winter. At this time, it typically provides more abundant rainfall in the southern parts of North and South America, on the Peruvian Pacific coast, on the Galapagos Islands, in eastern Africa and in south-east China. At the same time, it rains less than usual in southern Africa, north-east South America to the Caribbean, in Australia, India, Indonesia and the Philippines.

If an El Niño occurs already or still in spring or summer, the Indian summer monsoon is drier than usual. An El Niño in the northern hemisphere summer does not have any significant influence on precipitation in California and in southern Africa, as this is a comparatively low rainfall period there. Due to the lower rainfall in southern Africa and Australia, for example, there is less water available to store for the subsequent dry season. Regions with abnormally heavy rainfall can suffer from flooding and landslides. (Ziese et al. 2015)

Total precipitation from February 2015 and 2016 over the sea

In the winter of 2014/15, most of the near-equatorial precipitation fell over the Pacific to the west of 180 °, whereas the main area of ​​precipitation in February 2016 was further east due to the El Niño-related warmer water.

The data comes from NASA's Integrated Multi-Satellite Retrievals for GPM (IMERG), which brings together the data from several orbits of the GPM satellite and from approx. 10 partner satellites every 30 minutes to form a common product.

Source: NASA / JPL

Even during La Niña events, the normal patterns of tropical precipitation and atmospheric circulation under neutral conditions are disrupted. The abnormally cool water masses in the equatorial central Pacific act to suppress convection, cloud cover and precipitation in this region, especially during the northern hemisphere winter and spring. At the same time, rainfall has increased over Indonesia, Malaysia and northern Australia. The Walker circulation with its easterly winds close to the ground is also significantly intensified at these times of the year, as the pressure gradient between the anomalously cool East Pacific and the West Pacific is increased.

Higher precipitation is also observed at La Niña in southeastern Africa and in NE Brazil during the northern winter. The rainfall of the Indian summer monsoon tends to be higher, especially in NW India. Drier conditions than usual are observed during cold events along the west coast of tropical South America, as well as in the subtropical latitudes of North America (Gulf Coast) and from South America (southern Brazil to central Argentina) during their respective winter months.

If one stays in the area of ​​the Pacific and the Indies, it can be stated that the eastward shift of the precipitation areas along the equator occurs during an El Niño in India, Australia, Indonesia and neighboring countries droughts. On the other hand, the island states of the central Pacific and the west coast of South America are hit by heavy rainfall.

In the short term, the precipitation caused by El Niño can turn deserts green or lakes with abundant fish in arid areas (e.g. Peru).

Deviations in precipitation during the last strong El Niño from the average (1980-2004)

in mm / month (months December 1997, January 1998, February 1998)

The basis for this combined data product are measurements from weather stations with regard to land areas and satellite observations with regard to sea areas.


For a corresponding representation of the La Niña event 1999/2000 click here!

Source: Deutscher Wetterdienst / GPCC, personal. Message

The Global Precipitation Climatology Center, which is part of the German Weather Service, has created an impressive graph showing the correlation between the Southern Oscillation Index and the precipitation values ​​for various tropical regions (see figure below).

Time series of the values ​​of the Southern Oscillation Index compared to the amounts of precipitation in various tropical regions

 

 

Source: GPCC (personal communication)

The WZN also carried out precipitation analyzes using the example of the El Niño event in 1997/98 for the DWD climate status report in 1998.

Certain basic patterns can be identified in the spatial distribution of various long-range effects (droughts, heavy precipitation, storms, etc.), but in individual areas or sub-areas, contradicting phenomena can sometimes occur in different El Niños.

In the field of oceanographic research, a close correlation between the anomalous warming in the Eastern Pacific and that in the southwest Indian Ocean has been demonstrated for El Niño episodes.

additional Information

 

convection

The connection between Southern Oscillation and precipitation is shown, among other things, in the amount of long-wave radiation that leaves the atmosphere. When the sky is clear, a large part of the long-wave radiation released from the earth's surface into the atmosphere can escape into space. When the sky is cloudy, some of this radiation is prevented from escaping. Satellites are able to measure the amount of long-wave radiation emitted, and from these observations the relative amount of convection can be estimated.

 

Carbon dioxide

CO2 can have significant effects on various ecosystems. A terrestrial ecosystem can be transformed from a CO2-Sink to a CO2-The source will be what American scientists discovered between 1980 and 1994 using a biogeotechnical model and measurements in the forests and savannas of the Amazon basin (Nature, vol. 396, p. 619, 1998). Up to 200 million t of the greenhouse gas CO. Can be released from the Amazon basin in one El Niño year2 be emitted. The reason lies in the lower rainfall.

On the other hand, a strong El Niño leads to a considerable decrease in CO2Emissions from the equatorial Pacific. In contrast to most parts of the sea, the equatorial Pacific is usually a CO2-Source. The causes are the CO2-rich deep waters that come to the surface here and the low biological activity. Researchers estimate that over the course of a year during the El Niño event of 1997/98, 700 million tons of CO2 fewer were emitted than in the previous year. This corresponds to half of the total US CO2-Emissions from burning fossil fuels.

Another aspect in the discussion about CO2-Balance concerns the logging-related forest fires in Indonesia. The destruction of forests often serves to create palm oil plantations. The palm oil produced there is added to fuels in Europe, among other things, in order to increase the share of renewable energies. This means that the "bio-fueling" in Europe was purely arithmetically the CO2-Emissions reduced, but at best shifted in the global balance and the absorption of CO2 additionally reduced, as the lack of forests due to clearing as CO2-Sink fall away. (Ziese et al. 2015)

Using satellite data and ground measuring stations, an international group of scientists has determined that in 2015/2016, 8.8 billion tons of CO2 were also released into the atmosphere. This amount corresponds to about a quarter of all annual anthropogenic carbon dioxide emissions. The researchers see the drought triggered by El Niño in parts of the southern hemisphere as the cause, which weakens the vegetation and reduces CO2 than usual. So far, the additional increase in carbon dioxide caused by drought-related more frequent peat, bush and forest fires has mainly been investigated. However, earlier satellite data did not agree with the new figures: Based on the heat radiation of the fires and the carbon dioxide and carbon monoxide content of the smoke plumes, the scientists have calculated "only" about 0.75 to 1.2 billion tons of additional CO2Emissions during an El Niño year. In addition to complex computer models, the researchers use data from the American NASA satellite OCO-2 and the Japanese JAXA satellite GOSAT, both of which measure the carbon dioxide content in the earth's atmosphere. (Patra 2017)

Additional Information:

 

Tropical cyclones

The formation of tropical cyclones (often summarily hurricanes) is also influenced by El Niño and its counterpart La Niña.These influences are like a swing between the Atlantic and the Pacific, each strengthening activity in one region and at the same time weakening it in the other. Causes for the influence are abnormal water temperatures (warm is favorable for the formation, cool is a hindrance) and above all changes in the vertical wind shear, a process which becomes noticeable through the change in wind speed and direction between approx. 5,000 and 35,000 ft above ground. Strong vertical wind shear can tear apart a nascent hurricane or even prevent it from forming.

La Niña suppresses cyclone activity via the processes mentioned in the central and eastern Pacific and intensifies it in the Atlantic.

El Niño events are associated with fewer hurricanes over the Atlantic, but an increased number over the Pacific. Tropical cyclones usually develop stronger when moving over warm water, and they dissolve over cool water. During El Niño, the upwelling that is otherwise common in the equatorial East Pacific is suppressed. This causes an increase in the water surface temperatures in the Pacific and thus supports the formation of tropical storms. The 2015 hurricane season was particularly lively in the North Pacific, partly due to the strong El Niño. (NASA 2015)

Typical influence of El Niño on seasonal hurricane activity in the Pacific and Atlantic

Typical influence of La Niña on seasonal hurricane activity in the Pacific and Atlantic

Source: NOAA ENSO Blog 2014

Additional Information:

 

ozone

El Niño also affects atmospheric ozone, a substance that plays an important role within the Earth system and for human health. Near the ground, the ozone affects the air quality. Within the troposphere, ozone acts as a greenhouse gas. When an El Niño occurs there is a significant change in the tropical E-W circulation resulting in a significant redistribution of gases like ozone. These changes take place vertically within the troposphere and at El Niño lead to higher ozone concentrations over Indonesia and lower concentrations over large parts of the central and eastern Pacific. Scientists use NASA's Aura satellite to measure the ozone concentration in the troposphere. With the now more than ten-year data series, the researchers are able to separate the reaction of ozone concentrations to an El Niño from the reaction to human activities, such as man-made fires. Most of the ozone is found in the stratosphere, where it acts as a shield against harmful UV radiation. Although El Niño has a stronger influence on ozone in the troposphere, the researchers are increasingly recognizing how it also changes the concentration in the stratosphere, whereby these changes can occasionally be around 15% in the tropics. (NASA 2015)

additional Information

 

Water resources

The effects of ENSO on various sectors such as the health sector and agriculture are often noticeable through the effects of ENSO on the water cycle. For example, an increased likelihood of drought is a hydrological phenomenon that affects agricultural yields. Correspondingly, a higher probability of above-average rainfall can affect agriculture, with farmers having to keep an eye on the possibility of flooding. It is therefore crucial to understand the effects of ENSO on the water cycle in different regions and how these influences propagate as effects on water resources.

Before narrowing down the areas with ENSO influence on precipitation, it should be noted that only 20-30% of the land surface experience a change in probability of higher or lower precipitation due to ENSO, and that the majority of these areas are in the tropics (Lall, U. 2013). Is considered globally El Niño associated with below-average precipitation, La Niña however, with above-average rainfall. However, there are considerable geographical differences. For example, an El Nino event in the months of December to February leads to high rainfall over southern Brazil, but in central Indonesia, the southern Philippines, and also over large parts of South America and South Africa, below-average rainfall. On the other hand, there is above-average rainfall in parts of North America in the period from June to August, but below-average rainfall in India and Pakistan.

For a La Niña-Event applies in the months of March to May increased rainfall in Australia and northwestern South America. Above-average precipitation falls in northeast Brazil from December to February. During the period June through August, the central United States experiences below average rainfall.

In India, an eastward shift in Walker circulation over the tropical Pacific during ENSO warm events typically results in reduced summer monsoons in India and southern China, both areas where monsoons are critical to food production.

Effects of El Niño on precipitation and temperature from December to February

Particularly dramatic for the drinking water supply are the areas shown in the figure, which are labeled “dry and warm”, because there both the temperature and the precipitation show anomalies that massively promote the occurrence of droughts. South Africa in particular should be mentioned here, where the ENSO is responsible for around 50% of the variability in precipitation. In the event of an El Niño warning for the coming summer in the south, the responsible countries in this region are particularly requested to take appropriate precautions in good time for the drinking water supply through appropriate adaptation measures.

Source: NWS / NCEP / CPC - There are also three more graphics on other monthly constellations and on La Niña episodes

In addition to influencing the average variables, ENSO can also have an impact on the severity of hydrological extremes, both in terms of heavy precipitation and flooding, as well as droughts. For example lead El Niño-Years in the Southwest of the United States have more frequent heavy precipitation events, but less frequent heavy rain and less runoff over the northwest. The ENSO signal is also statistically noticeable in the frequency of heavy precipitation in parts of South America (e.g. Peru) and in the area of ​​the Yangtze River.

ENSO is also associated with changes in tropical cyclone occurrences and their preferred trajectories, affecting the likelihood of extreme precipitation and, at the same time, storm damage in regions such as the Caribbean, North America and Southeast Asia.

The spatial extent of tropical droughts is closely related to the strength of a El Niño-Event. Floods also have a spatial signature associated with ENSO: Tropical basin landscapes have a positive correlation with ENSO insofar as La Niña causes the probability of a higher maximum annual runoff. In the extra-tropics the picture is more complicated with negative correlations in the southern US and parts of Eurasia and positive correlations in Australia and the Pacific Northwest of the US and Canada.

Since ENSO influences precipitation and temperatures in different areas of the world, there are related significant consequences for the runoff volumes of bodies of water and thus the water resources in these regions. Strong teleconnections exist between ENSO and discharge volumes in Australia, New Zealand, South and Central America, whereas the dependencies in North America and Africa are weaker. The Blue Nile is more likely to have large amounts of water at La Niña and smaller amounts at El Niño. El Niño-related low water levels also occur in the rivers Senegal, Orange, Indus, Narmada, Murray-Darling Amazonas and others.

The teleconnection pattern between ENSO and precipitation is reflected globally in the water storage on land, in some regions associated with a time delay. The strongest correlations are found in tropical regions, especially in large river systems.

In addition to its effects on the water cycle, ENSO is also associated with snow depths in the Tibetan Plateau, and with water quality and the water table in the southeastern United States during the winter months. There are hardly any systematic surveys on the effects on water quality and groundwater supplies outside the USA and Canada, although the effect of ENSO is particularly significant in the tropics.

The connection of ENSO and runoff behavior of water bodies enables seasonal forecasts of runoff quantities with the aim of making decisions on water management (water distribution, reservoir control, flood planning). Similarly, the link between ENSO and seasonal rainfall in the monsoon areas is used to make overall forecasts for monsoons. For example, in India a number of seasonal monsoon forecasts are available for all of India, and the most important variables in the climate models used are ENSO indicators. ENSO information is also used to predict Ganges runoff with lead times of up to a year. This information can then be used to make growing decisions (suitable crops) depending on the forecasted irrigation needs.

At first glance, water management appears to be the obvious addressee for seasonal climate forecasts and their use, provided that water managers are used to dealing with quantitative information and short-term weather forecasts (approx. 3 days lead time). Often, however, this is not the case, especially if they are hesitant to make decisions due to institutional, legal and infrastructural restrictions, which accordingly reduces the usefulness of the forecasts. Well-established practices are reluctant to abandon, imprecise working methods can be added as further barriers to the effective use of seasonal forecasts. In addition, there may also be a scale incompatibility between the forecast information (large-scale scale) and the work area of ​​the water manager (small-scale, local scale).

In the water sector there is still a lot of potential to use ENSO-related climate information in those regions of the world where ENSO has a strong connection with precipitation. Obstacles that stand in the way are named.

The precipitation data of the ENSO-sensitive regions are e.g. also made available by the World Center for Precipitation Climatology (WZN), which the German Weather Service (DWD) operates on behalf of the World Meteorological Organization (WMO). The WZN, with its more than 110 years of analysis, enables the precise determination of the ENSO-sensitive precipitation regions. On the basis of this knowledge, e.g. for a El Niño-Prediction timely preparations are made in the affected regions.


Global distribution of the correlation of the El Niño occurrence with the
winter land surface precipitation (DJF) since January 1901
(Fig. 16, Becker, Andreas et al., 2013)

Global distribution of the correlation of the El Niño occurrence with the
winter precipitation (DJF)
in the period 1988-2008 (adapted from Anderson, Axel et al., 2010)

Source: Fröhlich, Kristina et al. (2014): El Niño probably in winter 2014/15. DWD background report July 21, 2014. Offenbach

For example, the WZN determined the ENSO-sensitive regions for global land surface precipitation on the basis of its analysis of the global distribution of precipitation for the months from December to February (DJF). For this purpose, the correlation of the total precipitation with the El Niño-sensitive index SOI (Southern Oscillation Index) is calculated for each 0.5 degree grid cell (approx. 50 km) and the result fields for the months of December, January and February (DJF) are arithmetically averaged (see figure above left).

By combining the WZN analyzes with the satellite-based analyzes of the Satellite Application Facility on Climate Monitoring (CM-SAF) operated by the DWD on behalf of EUMETSAT, this investigation can also be extended to the oceans (Fig. Above right). There, for the winter months (DJF) in the period 1988 - 2008, there is an enormous positive anomaly in the pacific regions with strong cloud lift (area of ​​the intertropical convergence zone), and the ENSO sensitivity patterns are essentially repeated over land, as are the has left figure. This cannot be taken for granted in view of the different reference periods of the two analyzes (1901-2011 vs. 1988-2008). Differences in different regions across the country therefore also arise due to a lack of statistical significance.

The extensive congruence confirms that a natural climate variability such as the ENSO phenomenon is rather indifferent to the reference period. It also shows that the climatological evaluation of the satellite-based data set is already valid in many land regions of the world, despite the relatively short reference period, and of course provides exclusive information about the ocean.

Additional Information:

economy

Some significant El Niño events over the past 40 years (1972-1973, 1982-1983, 1997-1998) have been linked to global macroeconomic crises. Even if there is not necessarily a tightly coupled relationship between El Niño and the global economy, the effects in connection with El Niño teleconnections are potentially destabilizing given the given geopolitical and economic conditions.

From an economic point of view, the different effects of ENSO can act both as a cause of recession and as an economic stimulus.

In the global context, there are two macroeconomic threats:

  • simultaneous crop failures or other ENSO-related emergencies in impoverished countries and
  • Tipping points in some countries with medium wealth that are already on the brink of crises.

ENSO can act as a shock or a crisis intensifier in countries that are already under political or financial stress. For example, ENSO-related tremors can lead to local conflicts if they encounter poor countries with weather-dependent agriculture and with little buffer against these impairments. The potentially wider economic effects affect countries with medium wealth, where El Niño is an additional force that affects instability.

When looking at the 2015-16 El Niño event, there are regions with sufficient instability to allow the El Niño long-range effects to create new tipping elements or positive feedbacks with globally destabilizing effects. These areas include the Middle East, North Africa, Southeast Asia (ASEAN countries), the Horn of Africa, and South America. In these regions, the effects of El Niño have the potential to mix up the effects of ecological vulnerabilities, geopolitical tensions and financial instabilities (Sachs 2016).

Additional Information:

Commodity markets

Every few years the extreme phases of ENSO, El Niño and La Nina occur with particular strength and threaten or favor the production of raw materials worldwide in different regions and with different meteorological, hydrological and ecological effects. Primarily raw materials and food from the agricultural and fishing sectors are affected, but the energy sector and industrial metals are also feeling the impact of the climatic change. Precise knowledge of meteorological developments is of the utmost importance for all those involved with raw materials, from producers to traders, investors, stock exchanges, insurers and consumers.

If one looks at the economic effects of El Niño at the level of individual states, one will find that they mainly depend on the share of the primary economic sector (agriculture, fishing, mining) in the overall economic performance of the state concerned. As a result, this can affect inflation and monetary policy. Most soft commodities show price reactions to past El Niño events. This is perhaps most likely to be the case for palm oil, as its main geographical area is in the Pacific. This statement is somewhat relativized by the possible substitution of palm oil with soybean oil.The global production of other agricultural products reduces the impact on world market prices and this may reduce the impact of El Niño on corporate profits within the food production value chain. The impact on utilities depends on their location, with hydropower plants being the most vulnerable, which in some countries can lead to increased demand for electricity from thermal power plants. It can also have implications for the insurance and retail sectors.

A 2015 study by the International Monetary Fund concluded that the impact of El Niño on a country's gross domestic product (GDP) is smaller when

  • the geographic area of ​​the country is large,
  • the share of the primary economic sector (agriculture and forestry, fishing, mining) in GDP is small,
  • the economy is rather diversified.

Before the current El Niño 2015/16, the balance sheet of which is not yet available, the last strong El Niño occurred in 1997/1998 and taught the raw material markets fear. Droughts and floods severely affected agricultural raw materials and the mines for mining copper also had to interrupt their production due to heavy rainfall and the resulting landslides. How dramatic the effects of El Niño can be was highlighted in a study published by the World Meteorological Organization (WMO). According to this, the worldwide damage at that time amounted to 34.3 billion US dollars and 24,120 people lost their lives due to storms, floods, storm surges or droughts.

Agricultural commodities are by far the hardest hit by the effects of an El Niño. However, estimates of the global impact of previous El Niño episodes on the production of agricultural commodities vary widely, but in general it can be said that the yields of agricultural products tend to decline and prices tend to rise, even if only marginally. For example, during an El Niño episode, corn, rice, and wheat yields can decrease by as much as 4%, and global soybean yields can increase between 2.1% and 5.4% (Iizumi et al. 2014). Since the weather conditions are very different from the usual prevailing conditions due to the anomaly, the crop yields decrease sharply in many cases. Dry weather and prolonged droughts can affect supply and prices just as much as significantly increasing rainfall, extreme temperature fluctuations or environmental disasters.

El Niño 1997/98, defined “the climate event of the century” did not have major impacts on the agricultural areas of the world. The reasons are not completely clear. El Niño 1997/98 started at the same time as El Niño 1991/92 in April / May / June with a similar duration (only two months shorter) at almost twice the intensity, but had very little influence on agriculture: El Niño 1991 / 92 caused drought in approximately 350 million hectares while El Niño 1997/98 affected 80 million hectares (77 percent less). Additional information is necessary (beyond the ENSO indices ONI and SOI) to capture the complexity of the interaction between agricultural production, climate and oceanic temperatures and currents.
Any characterization of El Niño and connection with its impacts on agriculture is difficult to ascertain because many variables also have a sway in each event, including the gestation period, which may start from a neutral, positive (La Niña) or negative (El Niño) phase and in the onset time, intensity and duration of an El Niño occurrence. All these variables, in turn, interact with other dynamic variables of vegetation development. The real numbers of variables are unknown, making the situation more complex, while atmosphere, ocean and crop dynamics interact at different moments of time. The whole situation is similar to trying to solve Rubik’s Cube.

Source: El Niño and the effects on horticulture in North America - Literature review, CHC January 2016

El Niño is likely to have a greater impact on more isolated local or national food markets that are not connected to international markets. This is often the case in local third world food markets.

Considering the impact of ENSO on the agricultural markets, it should not be forgotten that the effects of natural disasters on partially or completely subsistent farms in less developed regions are significantly more serious, as these do not have the compensatory possibilities that a global market offers its actors . This differentiation is often neglected in presentations in the business press.

In the case of raw materials traded on the world market, a distinction must also be made between the effects of ENSO on the world market price and those that affect the individual producers' areas of production, disadvantageous or favorable.

It appears that the impact of the ENSO phenomenon on international agricultural markets has increased over the past ten to 15 years. During this period, the interdependence of the agricultural markets via agricultural trade and the international futures markets has grown considerably, and with it the reaction of the markets to real or even expected changes in production and world trade.

In a 2015 online article by the CME Group, NOAA's 30-year records of the fluctuations in the ENSO phenomenon were compared to the price reactions of agricultural goods. The raw materials examined included corn, wheat, soybeans, soybean oil, soybean meal, live cattle, beef cattle, lean pigs, paddy rice and dairy products. There have been 11 El Niño and 8 La Niña episodes since 1959, during which sea surface temperatures deviated from their average by more than one degree Celsius.

Under El Niño conditions, the real (adjusted for inflation) value of these goods tends to increase without exception. With the exception of paddy rice, these goods tend to decline under La Niña conditions. Under both conditions there are clear differences from one similar event to the next.

Correlations between ENSO and spot prices for a range of raw materials

 

Source: CME Group (2015)

The result of this paper is not generally shared. The analyst Olaf Zinke (agrarmanager November 13, 2015) states in an article that the strength of the meteorological characteristics of the El Niño phenomenon does not directly correlate with the effect on agricultural prices. On the one hand, this is due to the possible positive effects of El Niño / La Niña on some important production regions. For example, extensive rainfall before sowing or during important growth phases in South and North America has correspondingly positive effects on production.

On the other hand, other globally effective effects can superimpose, compensate for or even reverse the effects of El Niño. Such factors recently included, for example, the effects of the global financial crisis in 2008/09, significantly changed demand behavior in China and trade restrictions such as export bans.

Within the supply situation for the raw materials mentioned above, which is characterized by weather uncertainties, special weather phenomena play the role of an amplifier. The 2010/2011 season has shown, not least, that this can exacerbate crises or turn a tense situation into a crisis. However, the relationship between El Niño and crop yields is not clear. Depending on the region and time period, increased rainfall can have positive effects on yields, while in other regions and a few weeks earlier or later it has a negative effect on the growth of the plants. In addition, the stocks of most agricultural commodities are well filled due to the very good harvests in recent years and therefore form a buffer in the event of a strong El Niño.

The Coconut oil market is a much-cited example of El Niño's influence on agricultural commodities. Since the droughts in SE Asia, the most important coconut cultivation area, lead to crop failures during El Niño events, the price rises.

Coconut oil price from 1962 to 2005 (blue)
and
Multivariate ENSO index (red)

The self-made graphic is based on a data series on coconut oil prices that were kindly made available to us by the former specialty chemicals company Cognis, as well as on the time series for the MEI.Graphic: N. Marshal

wheat is one of the raw materials that is hardest hit by El Niño. Since a distinction can be made between summer and winter wheat, not only the harvest and cultivation conditions in summer have to be observed, but also those of the winter months. In Australia, where most of the winter wheat is grown, the impact is significant. In winter and spring in particular, precipitation is significantly reduced, especially in the east of the country, and thus dramatically reduces the harvest yield, whereby the time at which the weather phenomenon occurs is decisive for the result of the harvest. Usually, the development of an El Niño at the beginning of spring reduces the yields dramatically and a development in November or December can be beneficial for them. According to the University of Queensland and the model developed there to determine crop yields in Australia, this year's weather could have a strong negative impact on the (winter) wheat season. In the last eight El Niño years, the Australian wheat harvest has declined by an average of 29 percent (chart below). In the following harvest year, the yields normalized again. In general, a wheat crop yield decline of almost 50 percent is possible.

On the other hand, it should not be overlooked that the wheat yield is generally highly dependent on the weather, also independent of ENSO influences. But at least El Niño events coincided with the sharpest declines in wheat growth in the past 30 years. Globalized wheat production mitigates the impact of lower wheat yields on global supplies.

Australian wheat harvest and El Niño

The Australian wheat harvest usually shows sharp declines during El Niño events.

 

Source: ideas (2016)

Corn: In the case of corn, El Niño has more positive effects, e.g. on US crop yields, as long as the anomaly does not reverse to La Niña, as it did in mid-1988. During this so-called menopause, the corn harvest was significantly weaker. This is by far the worst scenario for both yields and corn. In addition to the change between El Niño and La Niña, a rainy spring in the global growing areas has a negative effect on yields. Due to the heavy rain, the sowing is delayed and the very hot, dry summer months affect the plants that were sown too late. However, it should be noted that a continuous El Niño phenomenon, which develops in the second half of the year, usually has positive effects on the maize harvests, as the rainfall begins after the sowing and thus promotes plant growth. In eight out of eleven El Niño years, yields were better.

US corn harvest and El Niño

The US corn harvest will benefit from El Niño as long as no La Nina event follows.

 

Source: ideas (2016)

Soybeans: On average, soybean yields increase by 3.5% during El Niño events. For El Niño 2015/16, only a moderate increase is expected, as inventories are still large after record harvests in the two previous years. The increased demand for soy products as a result of the El Niño-induced higher palm oil prices does nothing to change this.

The global impact of El Niño on soybean production is shown in the graph below. It shows that the yields are falling in China and India, whereas the additional rainfall in North and South America increases the yields. In Brazil, for example, the weak El Niño in 2006/07 increased soy production by 6% and in 2009/10 by 20%; in Argentina, yields can increase by 15% in El Niño years.

Impact of El Niño on Soybean Crop Yield Anomalies

The 5 year average method was used to calculate normal yield. The significance level of the difference in the mean yield anomaly between El Niño years and neutral years was set at 10% (using the bootstrap with an iteration of 10,000 times; the sample size is 7 for El Niño and 8 for neutral years). The pie charts show the percentage of the harvested area in the areas mentioned above. All data in the pie charts are standardized to the global harvested area in 2000.

Source: Toshichika Iizumi (2014)

In an extensive older study, American researchers (Letson / McCullough