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Published on January 23, 2026 in Nature Communications, study shows that the sea warmed by marine heatwaves intensifies winds, convergence, and vapor, pushing extreme rain to coastal regions, where events under oceanic influence can gain 20% to 30% precipitation and worsen floods.
The sea is no longer seen only as a victim of warming and has started to appear as an active player in the formation of extreme rains over the continent. A study published in Nature Communications on January 23, 2026, indicates that marine heatwaves can intensify storms in coastal areas.
The research indicates that, in global coastal regions, about 5% to 25% of extreme rains over land occur in the direction of the wind from nearby marine heatwaves. In strong events, the average precipitation can increase by 20% to 30%, or 4 to 8 mm per day, compared to situations without this oceanic influence.
Marine heatwaves are no longer just an ocean problem
Marine heatwaves are periods of several days when the surface temperature of the sea is exceptionally above normal for a given region. Until recently, their effects were mainly discussed regarding the impact on ocean ecosystems, such as coral bleaching, habitat alteration, and damage to fishing.
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The new study broadens this discussion. The accumulated heat in the ocean can also affect the atmosphere and increase extreme rain over land, especially in coastal areas exposed to wind coming from the sea.
The research used observational data from multiple platforms since 2000 to investigate how localized ocean surface warming interferes with precipitation formation. The conclusion is that the temperature gradient associated with marine heatwaves intensifies winds and favors upward movements of moist air.
In practice, this means that an area of abnormally warm sea can act as a trigger to increase nearby atmospheric instability. The effect is not confined to the ocean: it can be carried by the wind to coastal regions.
How the warm sea pushes rain to the continent
The mechanism described by the researchers involves vertical mixing in the atmosphere. When air passes over an area of very warm sea, turbulence in the lower layer of the atmosphere increases, raising the speed of winds over the heated water.
This more intense wind creates convergence in the direction it blows. In other words, moist air tends to gather and rise on the side where the wind carries the influence of the marine heatwave.
When moist air rises, the chance of rain formation increases. The study shows that precipitation tends to intensify in the region downwind relative to the core of the marine heatwave.
This effect can reach a scale of several hundred kilometers. The local rain induced by the marine heatwave peaks about one day after the oceanic event, while extreme rain over land can peak around two days after.
Up to 25% of extreme coastal rains appear near these waves
One of the strongest points of the research is the link between marine heatwaves and extreme rain in coastal regions. The study considers extreme rain as that above the 99th percentile of rainy days, a criterion used to analyze truly intense events.
Within global coastal regions, the researchers found that about 5% to 25% of extreme rain over land occurs under the influence of nearby marine heatwaves, in the wind direction.
This does not mean that all extreme coastal rain is caused by warm seas. But it shows that a significant portion of these events can be worsened when there is a marine heatwave nearby.
The result changes the way we look at storms on the coast. In addition to cold fronts, terrain, atmospheric circulation, and continental humidity, it is also necessary to observe the thermal state of the nearby ocean.
Storms can gain 20% to 30% strength
When the marine heatwave is strong, the impact on extreme rain becomes clearer. According to the study, the average precipitation in extreme events influenced by a marine heatwave can increase 20% to 30% compared to events without this influence.
In volume, this represents an increase of 4 to 8 mm per day. In coastal urban areas, this difference can be enough to worsen flooding, overload drainage systems, and increase damage associated with floods.
The number seems small in isolation, but it weighs when it falls on an already soaked city. In extreme storms, each additional millimeter can increase the risk on streets, slopes, channels, urban rivers, and tidal zones.
The research also found an increase of about 30% in flood fatalities in events located in the wind direction of marine heatwaves, although the authors themselves indicate that other factors may also influence this data.
Almost half of the population lives near the coast
The study notes that almost half of the world’s population lives within 200 kilometers of a coast. This makes the problem especially sensitive, as many of the potentially affected areas concentrate cities, ports, industries, dense neighborhoods, and critical infrastructure.
Additionally, a significant part of high-impact marine heatwaves occurs near coastal regions. The combination of a heated ocean, favorable wind, and human occupation near the coast creates a new layer of climate risk.
For coastal cities, the message is straightforward: monitoring the ocean can help better understand the formation of extreme storms. The prediction of intense rainfall may depend not only on what happens in the atmosphere but also on the heat accumulated in the sea.
This has implications for civil defense, urban planning, drainage, flood alerts, and climate adaptation. A coastal city may need to look at the ocean as part of its risk system.
The effect grows with global warming
Marine heatwaves have been occurring since the early 20th century, but research indicates that their duration, frequency, and intensity tend to increase with warming caused by greenhouse gases.
The authors also highlight that sea surface temperature gradients have been showing a global increasing trend since the 1990s. These gradients are important because they help explain the atmosphere’s response over warm water.
If marine heatwaves become stronger and more frequent, the risk of extreme coastal rainfall aggravated by them may also grow. This is especially concerning in subtropical and mid-latitude regions, where the precipitation response can be more intense.
The study does not claim that every future storm will be caused by marine heatwaves. But it indicates that this factor needs to be on the radar of meteorologists, public managers, and coastal communities.
Coastal floods gain a new climate ingredient
Coastal floods are usually explained by a combination of factors: heavy rain, insufficient drainage, urban impermeability, high tide, full rivers, and occupation of vulnerable areas. Now, the warmed sea enters as another relevant element.
When a marine heatwave is close to the coast, it can increase wind, humidity, convergence, and upward air movement. These ingredients favor more intense storms in the wind’s direction.
The ocean acts as temporary atmospheric fuel. It does not replace other meteorological factors but can reinforce events that already had the potential to cause problems.
This discovery helps connect oceanic and terrestrial extremes. Previously, marine heatwaves were mainly seen as a threat to marine ecosystems. Now, they also appear as a warning sign for extreme rainfall over coastal cities.
Warmed sea becomes an alert for coastal cities
The study published in Nature Communications shows that the warming of the sea can have effects far beyond marine life. Marine heatwaves near the coast can intensify extreme rainfall, increase precipitation by up to 30%, and exacerbate flood risks.
The discovery reinforces the need to integrate ocean monitoring and terrestrial weather forecasting. For coastal regions, looking only at clouds and atmospheric fronts may not be sufficient.
The future of coastal cities will increasingly depend on understanding what happens in the ocean before the rain arrives. If the sea is abnormally warm, the risk of intense storms can gain extra strength.
And you, do you think coastal cities are prepared to monitor the sea as part of extreme rain alerts, or do we still treat floods as if they were just an urban drainage problem? Share your opinion.
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