---
title: "When El Niño and Ocean Warming Converge: Assessing the Risk of a Heat Wave in the Summer of 2026"
locale: en
category: report
category_name: "Report"
translation_status: reviewed
license: cc_by
source_url: https://injoys.com/en/articles/el-nino-ocean-heat-2026-summer-heat-risk
published_at: 2026-07-07T14:52:14+09:00
---

# When El Niño and Ocean Warming Converge: Assessing the Risk of a Heat Wave in the Summer of 2026

> In early July 2026, the WMO announced that El Niño conditions had developed in the tropical Pacific and could intensify between July and September. The already elevated global background temperatures and warm ocean waters are exacerbating the risks of heat waves, droughts, marine heatwaves, and increased electricity demand caused by El Niño.

## Key Points

- El Niño alters sea surface temperatures and atmospheric circulation in the tropical Pacific, increasing the likelihood of heat waves, droughts, heavy rains, and marine heatwaves in some regions.
- The background temperature, which has risen due to climate change, causes even El Niño events to result in higher maximum temperatures and more dangerous nighttime heat.
- When assessing the risk of heat waves in the summer of 2026, it is important to consider not only daytime high temperatures but also nighttime low temperatures, humidity, the urban heat island effect, sea surface temperatures, soil moisture, and electricity demand.
- In the fields of agriculture, the power grid, insurance, workplace safety, and the management of sports and cultural events, it is necessary to establish early warning systems and adopt more conservative operational standards when El Niño and warm ocean temperatures coincide.
- Since seasonal forecasts are probabilistic in nature, they should be continuously updated and interpreted using observational data and short-term forecasts, rather than being used to make definitive predictions about conditions in a specific region.

## Summary

On July 3, 2026, the World Meteorological Organization (WMO) announced that El Niño conditions had developed in the tropical Pacific and could intensify between July and September 2026. With reports of extreme heatwaves in Europe during the same period and record-high ocean temperatures in June 2026, the key risk of the summer of 2026 should be viewed not as simply “hot weather,” but as a complex climate risk resulting from the combination of El Niño, long-term warming, and accumulated ocean heat.

This article summarizes why El Niño alters the likelihood of heatwaves, droughts, torrential rains, and marine heatwaves; how the background temperature, elevated by climate change, amplifies these effects; and which indicators individuals, cities, businesses, and data analysts should monitor.

## 1. Signs for the Summer of 2026: The Simultaneous Occurrence of El Niño and Oceanic Warming

According to a WMO announcement, El Niño conditions developed in the tropical Pacific in early July 2026, with the possibility of them intensifying between July and September. While El Niño is a natural climate variability phenomenon, it now operates against the backdrop of global average temperatures that have risen since the Industrial Revolution. Consequently, even an El Niño of the same intensity as in the past could pose a greater perceived risk today.

At the same time, warm ocean temperatures are a critical underlying factor. The ocean stores vast amounts of heat from the Earth’s climate system. When the ocean is already warm, the supply of water vapor to the atmosphere increases, marine heatwaves persist longer, and nighttime cooling in coastal areas may weaken. This makes heatwaves more humid, longer-lasting, and harder to recover from.

## 2. Basic Terms and Observational Indicators

| Term | Meaning | Relationship to Heat Wave Risk |
|---|---|---|
| El Niño | The warm phase of ENSO, characterized by above-normal sea surface temperatures in the central and eastern tropical Pacific and associated changes in atmospheric circulation | Alters global atmospheric circulation, affecting the likelihood of heat waves, droughts, and heavy rainfall in various regions. |
| La Niña | The cold phase of ENSO, characterized by sea surface temperatures in the central and eastern tropical Pacific that are lower than normal | While many regions experience effects opposite to those of El Niño, there are significant regional variations. |
| ENSO | El Niño–Southern Oscillation, a tropical Pacific-atmosphere coupled oscillation that includes El Niño and La Niña | It is one of the most important natural variability signals in seasonal forecasts. |
| Marine Heatwave | A phenomenon in which sea surface temperatures in a specific region remain significantly above the normal range for an extended period | It is linked to coral bleaching, shifts in fishing grounds, hot and humid coastal conditions, and changes in the environment for tropical cyclones. |
| Background Warming | A state of long-term rise in global average temperatures due to increased greenhouse gases | It increases the likelihood that even natural variations will break records for extreme heat. |
| Nighttime Heat | A condition where nighttime minimum temperatures are high, making sufficient cooling and recovery difficult | Directly linked to heat-related illnesses, sleep disturbances, cardiovascular strain, and increased electricity demand. |
| Urban Heat Island | A phenomenon where city centers are hotter than surrounding areas due to paved surfaces, buildings, and artificial heat | This exacerbates nighttime heat and health risks for vulnerable populations. |

## 3. The Mechanism by Which El Niño Exacerbates Heat Waves and Extreme Weather

El Niño is not simply a phenomenon of rising Pacific Ocean temperatures. As the ocean and atmosphere interact, it alters the location and intensity of global atmospheric circulation.

### 3.1 Changes in the Location of Tropical Convection and the Jet Stream

Warm seawater in the tropical Pacific alters convection—the process by which warm, moist air rises to form clouds and precipitation. When the center of convection shifts, it affects atmospheric waves and the jet stream, potentially altering the stagnation of high-pressure systems, the paths of low-pressure systems, and the location of rain bands in mid-latitude regions.

As a result, some regions experience longer periods of dry, clear weather, increasing the risk of heat waves and droughts, while in other regions, precipitation bands intensify, raising the risk of heavy rainfall. The effects of El Niño do not manifest uniformly across the globe; they vary depending on the region, season, and ocean conditions.

### 3.2 Feedback Between High-Pressure Stagnation and Soil Drying

Heat waves typically intensify when strong sunlight, light winds, subsiding air, and dry ground surfaces occur simultaneously. When El Niño strengthens high-pressure circulation in a specific region, cloud cover decreases and the ground heats up more. As the soil dries out, solar energy is used more for heating the surface than for evaporation, causing temperatures to rise further.

This process can be described as a “dry-heat feedback.” A lack of rain causes the soil to dry out; dry soil heats up more quickly; and a hotter ground surface intensifies the heatwave.

### 3.3 Oceanic Heat and Humid Heatwaves

High sea surface temperatures can increase the amount of water vapor in the atmosphere. When humidity is high, even at the same temperature, the human body has a harder time dissipating heat through sweat evaporation. For this reason, humid heat waves can pose a much greater perceived risk than dry heat waves.

In coastal cities, warm seas prevent the air from cooling even at night, contributing to persistent tropical nights and hot, humid conditions.

## 4. Why Does Climate Change Amplify the Impact of El Niño?

El Niño is a natural fluctuation, but these natural fluctuations no longer occur against the backdrop of past average climate conditions. Climate change shifts the entire temperature distribution toward higher values. Even a slight rise in the average can lead to a significant increase in the frequency of extreme values.

For example, high temperatures around 40 degrees—which were rare in the past—may occur more frequently following background warming. Furthermore, if nighttime lows do not drop sufficiently, people, buildings, and power grids have less time to recover in preparation for the next day’s heatwave. This is why the risks of the summer of 2026 are difficult to explain based solely on “daily maximum temperatures.”

## 5. Heat Wave Indicators Affecting Daily Life: Factors to Consider Beyond Daily High Temperatures

When assessing heat wave risks, it is essential to consider not only the Korea Meteorological Administration’s warning criteria but also indicators related to health, electricity, and the urban environment.

| Indicator | Why It’s Important | How to Interpret |
|---|---|---|
| Daytime High Temperature | Indicates the risk of acute heat-related illnesses and outdoor activities. | Consider it alongside the number of consecutive hot days. It matters whether it’s just one hot day or whether the heat has been accumulating over several days. |
| Nighttime Low Temperature | Affects human recovery, sleep, and building cooling. | The higher the nighttime low, the greater the risk to the elderly and those with chronic illnesses. |
| Humidity and Heat Index | Reflects how difficult it is for sweat to evaporate. | Even at the same temperature of 33 degrees, the perceived risk increases significantly when humidity is high. |
| Sea Surface Temperature | Related to marine heatwaves, coastal humidity, and conditions for tropical cyclones. | Check both the deviation from the normal average and the duration. |
| Soil Moisture | A factor that amplifies heat waves and agricultural droughts. | As the soil dries out, surface heating and crop stress increase. |
| Electricity Load | Indicates cooling demand and the risk of power outages. | Examine both peak load times and the reserve margin. |
| Fine Dust and Ozone | These increase health burdens during heat waves. | Strong sunlight and stagnant air can lead to increased ground-level ozone. |
| Emergency Room and Mortality Data | These are lagging indicators of actual health impacts. | They are used to improve short-term warnings and identify vulnerable areas. |

## 6. Vulnerable Populations and Urban Risks

Heat waves do not pose the same risk to everyone. Risk is determined by a combination of temperature, exposure, health status, living conditions, and social support.

### 6.1 Groups at Particular Risk

- Seniors aged 65 and older
- Infants, toddlers, and pregnant women
- People with cardiovascular, respiratory, or kidney diseases
- Outdoor workers and those employed in delivery, construction, and agriculture
- Households with limited access to air conditioning
- Single-person households and socially isolated individuals
- Participants at events with large crowds, such as stadiums, festivals, and outdoor performances

### 6.2 How the Urban Heat Island Effect Exacerbates Nighttime Risks

Cities contain many concrete, asphalt, glass, and metal surfaces that store heat during the day. Even at night, this stored heat is slowly released, compounded by artificial heat from air conditioner outdoor units and traffic. As a result, nighttime low temperatures in city centers can remain higher than in outlying areas.

High nighttime temperatures are not merely a source of discomfort but a health risk. Insufficient sleep increases the burden on the cardiovascular system and reduces the body’s ability to adapt to heat waves the following day.

## 7. Data Points Expanding into Economic and Cultural Spheres

The impacts of El Niño combined with warm ocean temperatures extend beyond meteorology to encompass the economy and everyday life.

| Sector | Potential Impacts | Data to Monitor |
|---|---|---|
| Agriculture | Heat stress, increased irrigation demand, yield fluctuations, spread of pests and diseases | Soil moisture, temperatures by growth stage, precipitation anomalies, reservoir levels |
| Electricity | Surge in cooling demand, peak load, equipment overheating, risk of power outages | Hourly electricity demand, reserve margin, minimum temperature, humidity |
| Insurance | Losses related to crop damage, wildfires, storms and flooding, and health impacts | Disaster claim data, risk maps, exposed assets, distribution of vulnerable populations |
| Occupational Safety | Heatstroke and reduced productivity during outdoor work | Heat index, work intensity, rest periods, access to drinking water |
| Sports and Events | Game postponements, heat-related illnesses among spectators, and reduced athlete performance | Heat index at venues, shade and water stations, and emergency response times |
| Tourism | Heatwave-avoidance travel, and changes in demand at beaches and mountain areas | Accommodation reservations, sea surface temperature, wildfire risk, and traffic volume |
| Fisheries and Marine | Fish migration, aquaculture mortality, coral bleaching | Sea surface temperature variability, dissolved oxygen, duration of marine heatwaves |

## 8. Practical Checklist for Assessing Summer 2026 Risks

### 8.1 Individuals and Households

- Check not only the daytime high but also the nighttime low and humidity levels.
- If a heatwave lasts for 2–3 days or more, the risk of fatigue and dehydration is considered to accumulate.
- Households with elderly members, people with chronic illnesses, or infants and toddlers should designate an alternative location in case of power outages or air conditioning failures.
- Avoid outdoor exercise not only during the hottest hours of the day but also when humidity is high.
- Be aware of the risk of dehydration after consuming caffeine or alcohol.

### 8.2 Local Governments and City Operators

- Manage areas with high concentrations of vulnerable populations, semi-basement and rooftop units, aging housing, and areas lacking green spaces using heat risk maps.
- Inspect the actual accessibility of heat shelters, their nighttime operating status, and their cooling performance.
- Include heat index, emergency medical access routes, shade, and water supply plans in the criteria for permitting downtown events.
- Prepare for complex disaster scenarios where heat waves occur simultaneously with ozone, wildfire smoke, and power outage risks.

### 8.3 Businesses and Event Organizers

- Establish rules for suspending work or taking breaks during outdoor work based not only on temperature but also on the heat index.
- Facilities with high cooling loads should develop power usage plans for peak hours.
- For sporting events and performances, confirm in advance adjustments to start times, water supply, shade, and the deployment of emergency medical personnel.
- Supply chains should comprehensively review fluctuations in agricultural products, refrigerated logistics, and energy costs.

### 8.4 Variables That Data Analysts and AI Systems Should Monitor Together

- ENSO index and tropical Pacific sea surface temperature anomalies
- Global and regional sea surface temperature anomalies
- Maximum, minimum, and average surface air temperatures
- Human heat stress indicators such as humidity, heat index, and wet-bulb temperature
- Soil moisture, precipitation anomalies, and evapotranspiration
- Urban land cover, green space ratio, and impervious surface ratio
- Electricity demand and power outage history
- Health impact indicators, such as emergency room visits, mortality rates, and workplace injuries

## 9. Important Note: El Niño Does Not Mean “The Whole World Gets Equally Hot”

While an El Niño event increases the likelihood of a rise in global average temperatures, it does not mean that heatwaves will occur in the same way across all regions. Some regions may experience more severe heat and drought, while others may see more rainfall than usual. Furthermore, seasonal forecasts are probabilistic in nature. They do not guarantee the weather on a specific date in a specific city.

Therefore, it is appropriate to conduct the risk assessment for the summer of 2026 in the following order:

1. Identify large-scale background signals such as ENSO and ocean heat.
2. Review regional seasonal forecasts and monthly forecasts.
3. Update the likelihood of actual heatwaves using 1–2-week short-range forecasts.
4. Adjust guidelines for health, power, agriculture, and event operations to account for regional vulnerabilities.

## 10. Conclusion

The risk of heatwaves in the summer of 2026 cannot be explained by El Niño alone. El Niño is a powerful natural variability signal that alters atmospheric circulation and ocean conditions, and the elevated background temperature caused by climate change increases the probability that this signal will lead to extreme heat. When combined with high ocean temperatures, this can result in humid heat waves, nighttime heat, marine heatwaves, increased electricity demand, and damage to agriculture and fisheries.

Therefore, the key principle for responding to the summer of 2026 is: “Do not focus solely on maximum temperatures; consider nighttime temperatures, humidity, the ocean, urban areas, and vulnerable populations as well.” Heat waves are not only meteorological phenomena but also issues affecting public health, energy, food security, labor, and the operation of cultural events.

## FAQ

### Does El Niño cause temperatures to rise everywhere?
No. While El Niño can increase the likelihood of a rise in global average temperatures, its effects vary by region. In some areas, heat waves and droughts may intensify, while in others, there may be an increase in precipitation or a higher risk of heavy rainfall.

### Why is the risk of a heat wave in the summer of 2026 drawing particular attention?
This is because the WMO stated that El Niño conditions developed in the tropical Pacific in early July 2026 and could intensify from July through September. If this coincides with high background temperatures and warm ocean waters, it could lead to extreme heat, high nighttime temperatures, marine heatwaves, and increased electricity demand.

### How are El Niño and climate change different?
El Niño is a natural fluctuation that occurs in the tropical Pacific Ocean and atmospheric circulation. Climate change is a phenomenon in which the Earth’s average temperature rises over the long term due to an increase in greenhouse gases. El Niño is a temporary fluctuation, while climate change raises the background temperature against which these fluctuations occur.

### How are high ocean temperatures related to heat waves on land?
High sea surface temperatures can increase the supply of water vapor to the atmosphere and weaken nighttime cooling in coastal areas. This can increase the risk of humid heat waves, tropical nights, marine heat waves, and damage to aquaculture facilities.

### When assessing the risk of a heat wave, is it enough to just check the high temperature?
That is not enough. To more accurately assess the actual health and social risks, we must consider nighttime low temperatures, humidity, heat indices, the number of consecutive days of extreme heat, the urban heat island effect, electricity demand, and the distribution of vulnerable populations together.

### Why are high nighttime temperatures dangerous?
If nighttime temperatures do not drop sufficiently, the human body and buildings have less time to cool down. This can lead to sleep deprivation, increased strain on the cardiovascular system, dehydration, and an increased risk of heat-related illnesses the following day.

### How does the urban heat island effect exacerbate the damage caused by heat waves?
Asphalt and concrete release the heat they have stored during the day at night, and when combined with artificial heat generated by traffic and air conditioning, this causes nighttime temperatures in urban areas to rise. The impact may be even greater in areas with little green space and a high concentration of vulnerable populations.

### Can droughts and heavy rains both increase at the same time during an El Niño event?
This is possible on a global scale. Because El Niño alters atmospheric circulation and the location of precipitation belts, some regions may experience more severe droughts, while others may face an increased risk of rainfall and heavy downpours.

### What risks are associated with the power grid?
When heat waves and high nighttime temperatures persist, demand for air conditioning surges and peak loads increase. Since power generation and transmission facilities are also exposed to high temperatures, it is important to monitor the reserve margin, power outage history, and demand management during peak hours.

### What criteria should be used to adjust the schedule for sports games or outdoor events?
We must consider not only the temperature but also the heat index, humidity, shade, water supply, access to emergency medical care, crowd density, and waiting times for transportation. If necessary, we should delay the start time or increase the number of rest and cooling areas.

## Sources

- [World Meteorological Organization: El Niño is forecast to intensify, increasing the likelihood of extreme weather](https://wmo.int/media/news/el-nino-forecast-intensify-increasing-likelihood-of-extreme-weather)
- [World Meteorological Organization: El Niño/La Niña Update, May 2026](https://public.wmo.int/resources/publication-series/el-ninola-nina-updates/el-ninola-nina-update-may-2026)
- [World Meteorological Organization: Records Are Being Broken as Extreme Heat Grips Europe](https://wmo.int/media/news/records-fall-extreme-heat-grips-europe)
- [Mercator Ocean International: Ocean Temperature Bulletin, June 2026](https://www.mercator-ocean.eu/bulletin/ocean-temperature-bulletin-june-2026/)

## Images

![Illustration of drought, overheated ocean, city skyline, and power grid under a blazing sun](https://injoys.com/rails/active_storage/blobs/redirect/eyJfcmFpbHMiOnsiZGF0YSI6Njg1LCJwdXIiOiJibG9iX2lkIn19--2bac265ae4332b720388bb1a61c3d4b70aeb094c/ai-350fe20a.webp)
![Globe with hot ocean currents, heat warnings, a coastal city, and drought-stressed crops](https://injoys.com/rails/active_storage/blobs/redirect/eyJfcmFpbHMiOnsiZGF0YSI6NjkxLCJwdXIiOiJibG9iX2lkIn19--6ba1999fcabe388e7701134f838535f51fece39b/ai-9dad15ad.webp)