A potentially exceptional El Niño is developing across the tropical Pacific. Earth observation is helping scientists see it evolve, anticipate its wider effects and measure the floods, droughts, heat and ecosystem disruption that may follow.

Whilst El Niño may be starting in a remote stretch of the tropical Pacific its influence will extend around the planet. By changing the exchange of heat and moisture between the ocean and atmosphere, it alters atmospheric circulation, shifts rainfall patterns and changes the probability of weather extremes thousands of kilometres away.

The latest observations show that El Niño is now firmly established. The World Meteorological Organization expects it to strengthen further with an exceptionally high likelihood that it will persist through the Northern Hemisphere autumn and winter. NOAA support this prediction by noting that the event is intensifying and has a greater than 90% chance of becoming very strong during autumn and winter 2026–27.

What is El Niño?

El Niño is the warm phase of the El Niño–Southern Oscillation, or ENSO: an irregular cycle involving both the tropical Pacific Ocean and the atmosphere above it.

Under normal conditions, easterly trade winds push warm surface water towards the western Pacific. Cooler, nutrient-rich water rises near the west coast of South America to replace it. During El Niño, those trade winds weaken and warm water spreads eastwards across the central and eastern equatorial Pacific.

That movement of warm water shifts tropical rainfall and convection, reorganising large-scale atmospheric circulation. These changes can influence storm tracks, monsoons and seasonal temperature and rainfall patterns around the world.

El Niño does not ’cause’ every subsequent flood, drought or heatwave but, it does change their likelihood. Local outcomes also depend on other influences, including the Indian Ocean Dipole, the North Atlantic Oscillation, soil and ocean conditions and the long-term warming of the climate.

Seeing El Niño develop in real time

The 2026 event is already visible from space. In June, satellite measurements showed a rapid increase in sea-surface temperatures across the tropical Pacific. Copernicus Sentinel-6 and Sentinel-3 altimeters also recorded changes in sea-surface height as warm water expanded and moved eastwards. These measurements provided some of the earliest basin-wide evidence that El Niño was developing.

ESA’s SMOS satellite is contributing another part of the picture. Its measurements show how the Pacific’s freshwater pool and hence the sea-surface salinity, is moving as rainfall, evaporation and ocean circulation change. Scientists are comparing the developing 2026 pattern with observations from the 2023 El Niño to investigate whether salinity can provide earlier warning of future events.

These satellite observations are combined with measurements from the TAO/TRITON buoy network and Argo profiling floats. Whereas satellites provide repeated coverage of the entire Pacific surface, Argo floats measure temperature and salinity in-situ and at depth. Bringing the two together helps forecasters determine whether surface warming is supported by a deep reservoir of warm water which is an important indication that El Niño may continue strengthening.

Turning a climate signal into evidence of drought

El Niño commonly increases the risk of below-normal rainfall in parts of Australia, Indonesia (a country that is currently being ravaged by forest fires), southern Africa, India and South America. EO allows agencies to determine whether that climate risk is translating into actual water and agricultural stress.

An operational example comes from Tamil Nadu, India. During the state’s severe 2016–17 drought, Sentinel-1 radar observations were used to identify paddy fields that had not been planted or had failed. Because the assessment did not depend upon thousands of individual field inspections, the evidence could be used to accelerate crop-insurance claims. More than 200,000 farmers received payments through the resulting programme.

In Argentina, Sentinel-1 data were used to compare agricultural water conditions during a normal year and the 2020 drought. A radar-derived index acted as a proxy for water in vegetation and exposed soil across Santa Fe, Córdoba and Santiago del Estero. Some intensively cultivated districts showed differences of more than 50% between the two years, giving agricultural organisations a district-level measure of where winter crops and livestock forage were under the greatest pressure.

During the coming El Niño, similar combinations of radar, optical imagery, land-surface temperature and satellite soil-moisture data can show where forecast rainfall deficits have become real crop losses.

Mapping floods while they are happening

Other regions face the opposite hazard. El Niño can increase the probability of intense rainfall in western South America, parts of East Africa and the southern United States.

Synthetic-aperture radar is particularly useful during these events because it can map the surface through cloud and at night. The operational value was demonstrated during the May 2023 floods in Emilia-Romagna, Italy. Around 350 million cubic metres of rain fell in 36 hours, 23 rivers overflowed and more than 400 landslides were triggered.

Sentinel-1 radar and Sentinel-2 optical imagery were combined with commercial satellite data to map the affected area. The results were compared with flood products generated by the Copernicus Emergency Management Service, supporting emergency assessment and subsequent analysis of damage across one of Italy’s most important agricultural regions.

Latvia provides a further example of EO affecting financial decisions. After extreme rainfall flooded fields immediately before the 2017 harvest, persistent cloud and inaccessible roads made field inspections difficult. Sentinel-1 and Sentinel-2 data were used to map flooded farmland and support compensation for farmers. Radar proved especially useful because observations could continue while rain and cloud remained over the area.

If El Niño produces comparable rainfall extremes during the next six months, these established methods can be used to map flooded areas, identify damaged crops and infrastructure and show where water remains after the initial emergency has passed.

Watching the effects below the ocean surface

El Niño also affects marine ecosystems. As warm surface water spreads eastwards, it can weaken the upwelling of cold, nutrient-rich water. Ocean-colour observations can reveal the resulting changes in phytoplankton whilst measurements of sea-surface temperature identify areas exposed to potentially damaging heat.

The 2015–16 El Niño demonstrated the consequences. Around Jarvis Island in the central Pacific, satellite observations showed sea temperatures remaining above the coral-bleaching threshold for almost a year. Subsequent NOAA surveys found that approximately 98% of coral cover had died. Satellite monitoring helped establish the duration and geographical extent of the heat stress and field surveys confirmed its biological impact.

NOAA’s Coral Reef Watch now converts satellite-derived temperatures into daily global heat-stress products and bleaching alerts. Reef managers use these warnings to determine where field surveys, protective measures and limited conservation resources should be directed.

Those observations have economic relevance. Changes in temperature, upwelling and ocean productivity can alter the location and availability of fish stocks. Satellite-informed fisheries services already combine sea temperature, ocean colour and other environmental measurements to support stock assessment, habitat monitoring and decisions at sea.

What the next six months could look like

The latest WMO outlook gives a ~100% probability that El Niño will persist through both September–November 2026 and December 2026–February 2027. The event is expected to become very strong before peaking towards the end of 2026.

In the Pacific, El Niño is creating conditions favourable for increased hurricane activity. Hurricanes including Fausto, Genevieve, Lowell, Karina and Lala have already formed during 2026 and NOAA forecasts 9–14 eastern Pacific hurricanes over the full season, including 5–9 major hurricanes. El Niño is expected to suppress activity in the Atlantic, although a quieter season does not eliminate the risk of a damaging landfall. EO will track storm development and help map subsequent flooding, coastal erosion, crop losses and infrastructure damage.

The EO community will also have a host of other regions to keep an eye on:

• In southern Africa and north-eastern Australia, falling soil moisture, declining vegetation condition and changes in reservoir extent could provide early evidence of emerging drought.
• In western South America and other regions facing increased rainfall risk, radar imagery can identify flooded settlements, farmland and transport routes through persistent storm cloud.
• Across the tropical Pacific, sea-surface temperature, salinity, sea level and ocean colour will show how El Niño develops and affects marine productivity.
• Around vulnerable reefs, satellite heat-stress products can identify where prolonged warming makes coral bleaching more likely.

The UK Met Office expects El Niño to increase the chances of wetter and stormier conditions across north-west Europe during autumn and early winter. A colder, calmer period may become more likely later in winter, although the UK outcome will depend on other influences such as the North Atlantic Oscillation and the polar stratosphere.

It is worthwhile to remember that these are predictions. The role of earth observation will be to show where these anticipated effects are actually appearing, how severe they are and who or what is exposed. Remote sensing will bridge the gap between a global climate forecast and the evidence required to act.