The core insight of the study is deceptively simple. Tides are not random. They are governed by the gravitational interplay between the Earth, the Moon and the Sun, producing regular cycles of rising and falling water that can be calculated years in advance. In many coastal locations, the tide determines whether a given storm surge is sufficient to push water levels above established flood thresholds. When a moderate surge coincides with a high tide, flooding follows; when the same surge arrives at low tide, water levels may remain safely below the threshold. As Haigh explains, even storm-driven flooding often inherits the timing of the tides, because the tide acts as the gatekeeper that decides whether the surge crosses the critical line.

What makes the new work distinctive is its focus on the hour of the day rather than the season or the year. Previous research on flooding has concentrated heavily on seasonal patterns, examining, for example, why river floods cluster in certain months or why coastal floods are more frequent during particular times of the year. Haigh notes that surprisingly little attention has been paid to what hour of the day flooding actually occurs. Part of the reason, he argues, lies in how flooding is measured. Flood impacts are commonly summarized as the number of flood days per year, and once an event is compressed into a single day, the information about whether the flooding happened at 3 a.m., 8 a.m. or 3 p.m. simply disappears. By returning to the underlying records and preserving the temporal detail, the research team was able to recover patterns that conventional flood statistics had erased.

The regional results are striking in their specificity. In Boston, floods occur predominantly around noon and midnight, mirroring the timing of that harbor’s high tides. In Southern California, flooding is more common in the morning, again tracking the local tidal cycle. In Florida, the picture is more varied, because tidal behavior differs substantially from one stretch of coastline to another. Along the Atlantic Coast and down toward the Florida Keys, coastal flooding is moderately predictable in its timing, while along the Gulf Coast, where tidal ranges are smaller and more complex, flooding is less predictable. These differences matter, because they show that the daily fingerprint of flooding is not a universal pattern but a local one, shaped by the specific tidal regime of each coastline.

The study also establishes that the phenomenon is not confined to places with semidiurnal tides, the familiar pattern of two high tides and two low tides each day that characterizes much of the U.S. East Coast and the U.K. The researchers found that predictable daily timing also emerges in locations with diurnal tidal systems, which experience only one high tide and one low tide per day. The reason lies in the way different tidal signals interact. Tides are generated by multiple astronomical constituents, each with its own period, and their superposition produces the observed water-level cycle. Whether a coastline experiences two highs a day or one, the resulting pattern remains regular enough that flood events, which require water levels to cross a threshold, cluster around the recurring peaks of that cycle.

The technical implication is that flood risk is not evenly distributed across the hours of a day, even when the weather is. A storm system that lingers offshore for twelve hours does not pose a uniform threat throughout its passage. Its most dangerous moments are those that coincide with high tide, and in many locations those moments can be identified in advance with the same precision used to publish tide tables. This reframing has consequences for how flood forecasting is constructed. Traditional forecasts emphasize the magnitude of expected water levels, but the timing of when those levels are most likely to be exceeded is equally important for operational decisions, from closing roads to repositioning emergency assets.

Haigh argues that this matters because timing influences impacts. The same flood can have very different consequences depending on whether it occurs during the morning commute, during business hours or in the middle of the night. A flood that peaks at rush hour can strand commuters, snarl traffic and endanger drivers who attempt to cross inundated roadways. A flood of identical height at 3 a.m. may cause comparable physical damage but far fewer casualties and disruptions, simply because fewer people are exposed. Understanding these temporal patterns, the study suggests, could improve flood forecasting, emergency planning, infrastructure operations and long-term coastal adaptation. Utilities, hospitals, schools and transit agencies could all incorporate the known tidal windows into their contingency planning, aligning preparedness measures with the hours when flooding is statistically most likely.

The research arrives at a moment when the baseline for coastal flooding is shifting. As sea levels continue to rise, coastal flooding is increasingly occurring without storms to spur it on, a phenomenon often described as nuisance or sunny-day flooding, in which exceptionally high tides alone are enough to inundate low-lying streets. Haigh points out that higher mean sea levels mean it takes only a relatively small weather contribution, or sometimes simply a very high astronomical tide, to cross a flood threshold. In such conditions, the timing of the tides becomes even more decisive, and understanding exactly when those critical tidal windows occur could become an increasingly important component of coastal flood forecasting and preparedness.

The practical payoff of the work could be substantial. Haigh says the findings could make existing flood forecasts more predictable, providing more warning before disasters occur. That added lead time can help residents, businesses and emergency managers anticipate disruption and plan accordingly, whether that means scheduling deliveries around high-tide windows, warning drivers before morning inundations or pre-positioning pumps and barriers. Because the tidal component of flood timing is deterministic, it can be computed far in advance, offering a layer of foresight that weather-driven forecasting alone cannot match. The uncertainty in a flood forecast then narrows to the meteorological contribution, while the tidal contribution is already known.

The study, titled Coastal flooding at predictable hours and published in Nature Communications on 28 July 2026, represents a collaboration among international researchers and reflects Haigh’s long career in sea level and coastal impacts. A professor who joined the University of Central Florida in 2025 as director of the Center for Integrated Coastal Research, Haigh previously held the chair in sea level and coastal impacts at the University of Southampton and directed the Center for Doctoral Training for Resilient Flood Futures. His team’s work suggests a quiet but consequential shift in coastal science: the hazard that communities have treated as random now reveals a schedule, and learning to read that schedule may prove one of the most practical tools available as rising seas make the ocean’s high-water moments an ever more frequent visitor to the world’s coastlines.

Subject of Research: Predictable daily timing of coastal flooding driven by tidal cycles

Article Title: Study shows coastal flooding occurs at predictable times

Article References: Study shows coastal flooding occurs at predictable times. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: coastal flooding, tides, sea level rise, flood forecasting, storm surge, tidal cycles, Nature Communications, University of Central Florida, emergency planning, nuisance flooding, tide gauges, coastal adaptation

High tide flooding occurs when ocean water reaches unusually high levels during astronomical high tides and spills onto normally dry land. The water may enter through coastal barriers, stormwater systems, groundwater pathways or low points in roads and neighborhoods. Unlike storm surge, which is driven primarily by winds and atmospheric pressure during storms, high tide flooding can happen under calm weather conditions. Its apparent unpredictability often makes it difficult for communities to plan. The study’s central message is that the timing and speed of this flooding are influenced not only by the slow, persistent rise of the ocean, but also by natural climate patterns that reorganize winds, currents and atmospheric pressure across entire ocean basins.

Climate oscillations are recurring shifts in the ocean-atmosphere system that can last from months to decades. They alter the movement of heat and water, redistribute atmospheric mass and change the direction and strength of winds over the ocean. Along the East Coast, these changes can temporarily raise or lower sea level by modifying ocean circulation and by pushing seawater toward or away from the coastline. When an oscillation produces conditions that elevate coastal water levels, its effect can combine with an already higher baseline sea level. A tide that once remained safely below a road or seawall may then cross the threshold into flooding. The result is not simply a gradual increase in flood frequency, but periods in which the increase appears to accelerate.

This distinction matters because coastal risk is often estimated using long-term averages. A community may calculate how frequently high tide flooding is expected to occur by extending a historical trend into the future. But if large-scale climate variability periodically amplifies coastal water levels, the historical average can conceal bursts of rapid change. Two locations with similar rates of sea-level rise may therefore experience very different flooding trajectories over a given decade. One may see a relatively steady increase, while another may undergo a sudden run of frequent flooding when ocean circulation and atmospheric conditions align. The researchers’ analysis highlights why coastal forecasts must account for both the background trend and the shorter-term climate signals superimposed on it.

The physical mechanism is closely linked to the fact that sea level is not uniform, even across a single coastline. Ocean water can pile up against a shore when winds drive surface waters landward, while changes in currents can alter the slope of the ocean surface over hundreds or thousands of kilometers. Atmospheric pressure also matters: lower pressure allows the sea surface to rise slightly, while higher pressure tends to suppress it. In addition, changes in the Gulf Stream and other components of Atlantic circulation can affect coastal sea level along the eastern United States. These processes operate alongside the gravitational pull of the Moon and Sun, which generates the tides. When climate-driven ocean and atmospheric anomalies coincide with an exceptionally high tide, flooding becomes much more likely.

The consequences extend far beyond temporary pools of water on streets. Repeated high tide flooding can corrode vehicles and infrastructure, contaminate soils with salt, damage electrical equipment and overwhelm drainage networks designed to move rainwater away from cities. Saltwater intrusion can also affect wetlands, groundwater and urban vegetation. Because these floods may arrive without dramatic weather, they can be underestimated by residents, insurers and policymakers even when their cumulative effects are severe. A series of shallow floods can disrupt commuting, close roads, accelerate pavement deterioration and impose repeated costs on households and local governments. Over time, what was once called a nuisance can become a chronic infrastructure problem.

The study also carries an important warning about the meaning of “adaptation windows.” Coastal planners often use thresholds—such as the number of flood days a road, wastewater plant or neighborhood can tolerate—to decide when expensive protective measures should be built. If natural climate oscillations accelerate flooding for several years, a threshold may be reached sooner than expected. Conversely, a period of temporarily lower coastal water levels could create a false sense of security, even though the long-term trend remains unchanged. Planning based on a single projected curve may therefore be less reliable than planning with a range of possible pathways that include variability in climate patterns.

The findings reinforce a broader scientific understanding: natural variability does not cancel human-caused sea-level rise; it modulates its impacts. Global warming is expanding seawater and melting land-based ice, raising the baseline on which tides and climate oscillations operate. As that baseline climbs, relatively modest fluctuations become capable of producing major consequences. A climate oscillation that caused little or no flooding in the past can become highly disruptive when the coast has moved closer to its physical thresholds. This interaction helps explain why communities may experience a sudden surge in high tide flooding even when the underlying rise in average sea level appears gradual.

For coastal communities, the practical message is to treat high tide flooding as a measurable climate risk rather than an occasional annoyance. Monitoring stations, tide gauges, satellite observations and ocean models can help distinguish long-term sea-level rise from temporary climate-driven fluctuations. Improved early-warning systems could give residents and emergency managers advance notice of days when astronomical tides are likely to combine with unfavorable ocean and atmospheric conditions. Engineers may also need to design roads, drainage systems, transit networks and coastal defenses for changing flood frequencies rather than relying on historical extremes alone. The new research makes the case that the future of East Coast flooding will be shaped by both the slow movement of the climate baseline and the rhythmic, sometimes abrupt behavior of the planet’s largest ocean-atmosphere systems.

Subject of Research: The influence of large-scale climate oscillations on accelerated high tide flooding along the U.S. East Coast.

Article Title: Large-scale climate oscillations induce accelerated high tide flooding along the U.S. East Coast.

Article References: Zhu, Y., Han, W., Garuba, O. et al. “Large-scale climate oscillations induce accelerated high tide flooding along the U.S. East Coast.” Communications Earth & Environment (2026). https://doi.org/10.1038/s43247-026-03932-y

Image Credits: AI Generated

DOI: 10.1038/s43247-026-03932-y

Keywords: high tide flooding, U.S. East Coast, climate oscillations, sea-level rise, coastal flooding, ocean circulation, climate variability, coastal risk, tidal flooding, climate change