The study, published in the journal Weather and Climate Dynamics by Aleksa Stanković, Rodrigo Caballero and Gabriele Messori, tackles a long-standing puzzle in atmospheric science. By most bulk measures, such as zonally averaged eddy kinetic energy or median annual surface winds, the Southern Ocean is the stormier hemisphere. Its vast, unbroken expanse of water, largely free of continental barriers, allows storms to circle the planet with little interference. Yet when it comes to the extremes, the picture flips: the strongest surface winds consistently occur over the Northern Hemisphere oceans, and above all over the North Atlantic. Understanding why the hemisphere with the calmer average winds produces the fiercest storms is essential for improving projections of how wind extremes will change as the climate warms.

To answer the question, the team turned to ERA5, the most advanced atmospheric reanalysis produced by the European Centre for Medium-Range Weather Forecasts, which blends observations with a numerical weather model to create a physically consistent record of the atmosphere. The researchers focused on the winter months, December through February in the Northern Hemisphere and June through August in the Southern Hemisphere, when cyclones in both hemispheres reach their peak intensity. They restricted their analysis to the satellite era beginning in 1979, because satellite observations are crucial for reliably capturing the sparsely monitored Southern Ocean, and extended the record through 2020.

Identifying the top 100 extremes in each basin required a careful, two-step procedure. First, the team defined storm tracks as regions where the annual 98th percentile of daily maximum surface wind speed exceeds 18 metres per second, a criterion that isolates three comparable basins: the North Atlantic, the North Pacific and the Southern Ocean. Areas within 300 kilometres of the coasts of Greenland and Antarctica were excluded, since the ferocious winds there arise mainly from small-scale katabatic and barrier processes rather than the large-scale cyclone dynamics of interest. Then, for every winter day, the researchers computed a wind severity index over contiguous footprints of extreme winds. The index, widely used in insurance loss modelling, scales with the cube of the wind speed relative to the local climatological threshold, a choice with physical grounding because the cube of wind speed represents the flux of kinetic energy. The 100 days with the highest severity in each basin defined the top 100 extremes, and each event was linked to the nearest objectively tracked cyclone centre.

The heart of the analysis is a time-lagged composite technique. Rather than examining storms one by one, the researchers averaged the atmospheric fields of all 100 extreme events in each basin, aligning them by the location of the cyclone centre and the time of maximum surface winds. Because lines of latitude converge toward the poles, the fields were regridded onto radial grids centred on each storm. Statistical significance was assessed by generating 100 random composites for each basin, in which the real cyclone locations were paired with randomly chosen winter dates, yielding 10,000 random samples, with anomalies accepted as significant only after correction for false discovery.

The composites revealed a strikingly consistent large-scale recipe. A few days before the peak winds, a pre-existing cyclone is already present downstream, situated poleward and eastward of the developing extreme storm. The young cyclone begins as a weak, spatially limited pressure anomaly that grows in size and intensity as it approaches its older neighbour. By the time of maximum winds, the two systems merge into a broad area of low sea-level pressure. In fact, roughly half of the top 100 extremes in each basin, 49 in the North Atlantic, 53 in the North Pacific and 56 in the Southern Ocean, were formally classified as multi-centre cyclones by the tracking algorithm around the time of peak winds. The pre-existing storm is not a passive bystander: it advects high potential vorticity air equatorward, sharpening the upper-level potential vorticity gradients and strengthening the jet streak, the narrow band of ferocious winds near the tropopause, within which the new storm develops and crosses the jet.

Where the hemispheres diverge is in the numbers, not the narrative. Northern Hemisphere extremes develop under stronger upper-level potential vorticity gradients, more powerful jet streaks and broader regions of high mid-tropospheric Eady growth rate, a classical measure of how rapidly baroclinic instabilities amplify in a sheared, stratified atmosphere. Higher Eady growth rates signal a greater potential for rapid intensification, and the observations bear this out dramatically. The rate at which eddy kinetic energy rises in the two days before peak winds is far greater in the Northern Hemisphere, and explosively deepening storms, those whose central pressure falls by more than 24 hectopascals in 24 hours, account for 69 percent of North Atlantic and 75 percent of North Pacific extremes but only 38 percent of Southern Ocean ones. Since vertical wind shear below the jet is the main driver of the hemispheric difference in growth rates, the stronger jets of the Northern Hemisphere, reinforced by the pre-existing downstream cyclones, emerge as the key to the hemisphere’s more violent wind extremes.

To test whether these dynamical differences trace back to the underlying geography of each basin, the team ran sensitivity experiments with ISCA, an open-source intermediate-complexity climate model developed at the University of Oxford and collaborators. Encouragingly, even at the coarse T42 resolution used, ISCA reproduced both the hemispheric asymmetry in extreme winds and the correct ranking of basins, with the North Atlantic strongest, followed by the North Pacific and the Southern Ocean. This suggests the asymmetry is driven primarily by large- and planetary-scale processes rather than by fine-scale features the model cannot resolve. The researchers then systematically altered the model’s boundary conditions across 11 experiments, comparing a realistic control configuration with setups in which sea-surface temperatures were smeared into zonal bands, made hemispherically symmetric, and combined with a planet stripped of mountains.

The results were remarkably clean. When sea-surface temperatures were zonalized across the tropics and extratropics, the difference in extreme winds between the North Atlantic and North Pacific nearly vanished, shrinking by 82 percent, as warming spread over the Pacific storm track and cooling weakened the Atlantic jet. Removing the interhemispheric contrast in sea-surface temperatures and flattening the orography reduced the Atlantic–Southern Ocean asymmetry by 83 percent, through a combination of weaker Atlantic extremes and stronger Southern Ocean ones. Across all experiments and basins, the winter 98th percentile of mid-tropospheric Eady growth rate correlated with the 98th percentile of surface wind speed with a Pearson coefficient of 0.97, significant at the 1 percent level. In other words, one number, the potential for storms to grow quickly, largely determines how extreme the winds can become, regardless of which ocean they form over.

The study comes with honest caveats. The focus on large scales leaves out mesoscale and boundary-layer processes that can contribute to surface wind extremes, and the analysis deliberately set aside the detailed mechanics of cyclone merging and storm–storm interaction. ISCA, lacking a realistic representation of clouds, could not reproduce the pre-existing downstream cyclone in the evolution of its own most extreme individual storms, even though it captured the climatological relationship between growth rates and winds. Still, the broader message stands: the recipe for the planet’s most extreme oceanic windstorms is written once and applied everywhere, with a helper storm downstream, a strong jet overhead and a fast-deepening cyclone at the centre. The only thing that varies between hemispheres is how generously the ocean basins supply the ingredients, a conclusion that should help sharpen both weather forecasting and the climate models on which future windstorm projections depend.

Subject of Research: Large-scale dynamics of extreme surface winds in extratropical cyclones across the Northern and Southern Hemisphere storm tracks

Article Title: Interhemispheric perspective on the most extreme surface winds in the storm tracks

Article References: Stanković, A., Caballero, R., & Messori, G. (2026). Interhemispheric perspective on the most extreme surface winds in the storm tracks. Weather and Climate Dynamics, 7(3), 1507-1523. https://doi.org/10.5194/wcd-7-1507-2026

Image Credits: AI Generated

DOI: 10.5194/wcd-7-1507-2026

Keywords: extratropical cyclones, storm tracks, extreme winds, Eady growth rate, ERA5 reanalysis, jet stream, potential vorticity, Southern Ocean, North Atlantic, North Pacific, ISCA climate model, explosive cyclogenesis

The team assembled its benchmark sample from an unusual and valuable archive: special warnings issued by the Peruvian Navy between 2008 and 2025. These operational records classify swell episodes by their expected coastal impact, with a very strong swell defined as waves exceeding three times their normal height and a strong swell between two and three times normal. From this record, the researchers identified five very strong events, all arriving during the austral winter months of May through September with pronounced south-westerly directions from the South Pacific, and six strong events originating in the North Pacific, mostly during boreal winter. Because the Navy archive is the only homogeneous operational classification available for the Peruvian coast, the authors treat these eleven cases as a benchmark sample rather than an exhaustive climatology.

A central challenge in studying remote swells is timing. The waves that batter a Peruvian beach were generated days earlier, sometimes on the far side of an entire ocean basin, so the atmospheric conditions that matter occurred long before the coastal impact. The researchers solved this by applying deep-water wave theory, calculating the group velocity of a swell packet from its wave period and the great-circle distance between the storm’s wind region and the coast. Using representative swell periods of 16 to 20 seconds, consistent with long-period swells previously reported for Peru, they estimated travel times of roughly three to four days for Southern Hemisphere events and eight to eleven days for Northern Hemisphere events. These windows then defined the periods over which they examined atmospheric fields from the ERA5 reanalysis.

The composite analysis of the Southern Hemisphere events revealed a strikingly organized pattern. Days before the swell peak, sea-level pressure anomalies form a tripolar structure over the southeast Pacific: a deep extratropical cyclone south of 40 degrees south, flanked by broad anticyclonic anomalies to its southwest and southeast. This arrangement dramatically tightens the meridional pressure gradient along the storm’s equatorward flank, driving a wide corridor of intensified westerly and south-westerly winds between roughly 35 and 55 degrees south. Crucially, the disturbance is barotropic, meaning the pressure anomalies at the surface, at 500 hectopascals, and at 250 hectopascals are nearly vertically aligned, allowing the storm to persist and sustain its winds over the same stretch of ocean. The result is a swath of enhanced significant wave height exceeding one meter across the high-latitude source region, with wave energy radiating directly toward Peru and Chile.

The jet stream diagnostics added a decisive layer to the picture. Applying a multiparametric method that measures not just jet intensity but also sharpness, tilt, and meridional coherence, the team found that Southern Hemisphere events coincide with a polar-front jet that is significantly stronger and sharper than the austral-winter climatology, with its core confined to a narrow latitude band and a modest southwest-to-northeast tilt. This compact, energized jet reinforces the storm-jet coupling that keeps the surface wind corridor locked in place over the swell-generation region. In the Northern Hemisphere, the configuration is different but equally coherent: the subtropical jet intensifies, sharpens, and extends longitudinally across the North Pacific, while the polar-front jet weakens and becomes less continuous. This redistribution of upper-level momentum supports deep, slow-moving cyclones over the central and western North Pacific, whose westerly to north-westerly winds can still fling wave energy across the Equator toward northern Peru.

The hemispheric contrast also explains why Southern Hemisphere events hit harder. Swell from the South Pacific travels a shorter path, arriving in three to four days with limited dispersion, and the tripolar pressure pattern sustains winds over an exceptionally long fetch. Northern Hemisphere swells must cross the entire Pacific and the Equator, a journey of eight to eleven days during which the wave energy spreads and attenuates. That is why, in the Navy’s classification, Southern Hemisphere events reached the very strong category while their Northern counterparts topped out at strong. Recent episodes illustrate the stakes: a May 2023 anomalous southwest swell caused coastal flooding and closed dozens of Peruvian ports, while a late-December 2024 swell from a North Pacific winter storm surprised tourist beaches and small ports on Peru’s northern coast under otherwise fair local weather.

Perhaps the most consequential finding concerns climate change. Because extreme swell records span only a few years, the team turned to a flow-analogue framework, searching the ERA5 record from 1950 to 2025 for days with atmospheric circulations dynamically similar to each event and comparing the surface winds associated with those analogues in past and present climate periods. Because circulation is held fixed across analogues, any difference in wind speed cannot be attributed to changes in the circulation pattern itself. For the Southern Hemisphere events, the result was unambiguous: analogous circulation patterns are now associated with significantly stronger surface winds than in the past, and the corresponding significant wave heights have increased as well. The one exception was event E3, which showed no significant influence of the dominant climate mode but may instead respond to the regional forcing of the Amundsen Sea Low.

The likely culprit behind this Southern Hemisphere intensification is the Southern Annular Mode, the leading mode of extratropical Southern Hemisphere variability. Analogue days in the recent period occurred predominantly under positive SAM phases, which strengthen and shift the westerly wind belt poleward, boosting windiness over the high-latitude South Pacific exactly where the swell-generating storms live. The trend toward more positive SAM conditions has been linked in the scientific literature to stratospheric ozone depletion and rising greenhouse gas concentrations, providing a plausible physical pathway from anthropogenic forcing to stronger swell-producing winds. The authors are careful to note that differences between past and present analogues may also reflect internal climate variability or other external factors, but the coherence of the signal across nearly all Southern Hemisphere events, supported by statistically significant wave-height increases, makes it physically compelling.

The Northern Hemisphere story is far messier. Analogue reconstructions revealed no consistent climate-change signal: the three most recent events showed stronger present-day winds, while the three earlier ones showed weaker winds, and no single mode of Pacific variability, whether the Pacific Decadal Oscillation, ENSO, the Pacific-North American pattern, the Arctic Oscillation, the Western Pacific pattern, or the Interdecadal Pacific Oscillation, could account for the split. The two groups of events appear governed by opposing configurations of large-scale climate modes, and regression analysis found these modes explain only a modest fraction of the wind variability, implying that local synoptic processes and factors such as aerosol changes, Arctic sea-ice variations, and subtropical tropospheric warming may also be at play. The high interannual and decadal variability of the North Pacific, the authors note, is precisely why the IPCC expresses low confidence in attributing observed changes in extratropical cyclones there to human influence.

The practical payoff of this work lies in early warning. Because the precursor patterns, a deep barotropic cyclone aligned with an energized jet, emerge days before coastal impact, monitoring these large-scale configurations could give Peruvian authorities substantially longer lead times than current approaches, allowing ports to close, fishing fleets to stay ashore, and coastal communities to prepare before the waves arrive. The authors caution that their sample is concentrated after 2010 and that extending the analysis further back will require reconstructing pre-2008 events. They also propose applying the flow-analogue framework to large ensembles of climate model simulations under historical and future forcing scenarios, which would allow a formal attribution of the circulation changes and a more robust assessment of how anthropogenic climate change will shape the swell hazards of Peru’s coastline in the decades ahead.

Subject of Research: Meteorological and jet-stream drivers of extreme remote swell events affecting the Peruvian coast

Article Title: Meteorological drivers of extreme swells on the Peruvian coast

Article References: Meteorological drivers of extreme swells on the Peruvian coast. (n.d.). https://doi.org/10.5194/wcd-7-1779-2026

Image Credits: AI Generated

DOI: 10.5194/wcd-7-1779-2026

Keywords: extreme swells, Peru, jet stream, extratropical cyclones, ERA5 reanalysis, Southern Annular Mode, Pacific Decadal Oscillation, coastal flooding, wave climate, flow analogues, climate change attribution, early warning systems

Storm tracks, the preferred highways along which extratropical cyclones and their attendant wind, rain and temperature swings travel, are among the most consequential features of the climate system. They regulate weather variability and extremes throughout the midlatitudes of both hemispheres, yet climate models still struggle with stubborn biases in their strength and location, and emerging discrepancies have appeared between simulated and observed storm track trends in some regions. That makes a return to first principles, asking which parts of Earth’s uneven surface actually build the storm tracks we observe, both timely and practical.

The team attacked the problem using MiMA, the Model of an idealized Moist Atmosphere, an intermediate-complexity general circulation model that bridges the gap between stripped-down aquaplanet experiments and fully comprehensive climate models. Crucially, MiMA carries full radiative transfer through the Rapid Radiative Transfer Model, a physically consistent treatment of moisture transport and latent heat release, and a slab ocean with prescribed ocean heat fluxes. That combination allowed the researchers to switch Earth-like land–sea contrast, topography and ocean heat transport on and off in any combination, an experiment that no single comprehensive model could perform cleanly, since in the real world it is difficult to imagine mountains without land or ocean circulation without continents.

The authors ran a suite of eight core configurations, each lasting 38 years after spin-up, beginning with a perfectly zonally symmetric aquaplanet and building up to a realistic ALL3 configuration containing all three surface inhomogeneities. By comparing each partial configuration with the full one, they could isolate both the isolated nonlinear response of a single ingredient, added first onto an aquaplanet, and its full nonlinear response, added last to a world that already had the other two. In parallel, they updated the model’s prescribed albedo profile to match satellite observations from CERES and revised the implied ocean heat transport so that the net flow of heat from the Southern Hemisphere to the Northern Hemisphere reached 0.54 petawatts, in line with observationally derived estimates, up from just 0.24 petawatts in the earlier configuration.

The realism check was encouraging. When all three ingredients were switched on, the model reproduced the observed pattern of storm tracks, with peaks over the North Pacific, the North Atlantic and the Indian-Ocean sector of the Southern Ocean, although the North Pacific came out somewhat too strong, the North Atlantic somewhat too weak, and the finer zonal structure of the Southern Hemisphere storm track was only fully captured at the higher T85 resolution. With the earlier albedo and ocean-flux settings, storm tracks had been 17 percent too weak at T85 and 29 percent too weak at T42; the updated configuration brought that bias down to 7 percent at T42 and essentially eliminated it at T85.

The central result concerns additivity. If the climate system were linear, the storm tracks in the full realistic configuration would equal the sum of the responses to land, mountains and ocean heat transport imposed individually. They do not. The team found substantial non-additivity both in the regional structure of the storm tracks and in the hemispheric asymmetry. Adding all three inhomogeneities reduces transient kinetic energy everywhere, partly because more energy is handed off to stationary waves forced by the uneven surface, and partly because realistic ocean heat transport carries some of the poleward energy load that transient eddies would otherwise shoulder. But the size of that effect depends dramatically on the order of assembly. In most sectors, the impact of the surface inhomogeneities is magnified when they are imposed on an aquaplanet compared with when they are removed from the full configuration, and the regional signature of ocean heat transport flips qualitatively between the two, weakening storm tracks most strongly over Eurasia when added first but over the North Pacific and North Atlantic when added last.

The same story holds for the headline asymmetry: in the full configuration the model’s Southern Hemisphere storm tracks are roughly 48 percent stronger than the north’s when measured with 2-to-8-day filtered transient kinetic energy, and about 25 percent stronger with a sub-monthly filter, broadly consistent with the observed excess of about 23 to 24 percent in the moist static energy framework applied to ERA5 reanalysis. Yet the sum of the isolated responses of the three ingredients accounts for only half of that asymmetry, while the sum of the full nonlinear responses overshoots it by 30 percent. Among the individual ingredients, land–sea contrast emerges as the most important driver of the hemispheric asymmetry, followed by ocean heat transport, with topography a distant third, a ranking that challenges earlier conclusions from comprehensive models in which topography and ocean circulation dominated.

To explain the mechanisms, the authors turn to the atmospheric moist static energy budget, decomposing poleward heat transport into contributions from the ocean, the mean meridional circulation, stationary eddies and transient eddies. In the realistic configuration, the surface energy input term, reflecting the ocean’s preferential delivery of heat to the Northern Hemisphere extratropics, contributes about 15.6 percentage points to the hemispheric asymmetry, while the stationary eddy term contributes 22.4 points, partially offset by a top-of-atmosphere term of minus 5.2 points. A striking simplification emerges when the researchers examined outgoing longwave radiation: across all 21 simulations, the correlation between the hemispheric asymmetry in longwave emission and the asymmetry in surface temperature was 0.99, meaning surface temperature essentially dictates how much energy the planet radiates to space in each hemisphere. Ocean heat transport and topography both preferentially cool the Southern Hemisphere, warming the north and increasing its longwave loss, which partially cancels their own intensifying effect on the asymmetry; land–sea contrast, by contrast, preferentially cools the north, deepening the asymmetry.

Two sensitivity experiments underline how delicate these balances are. Boosting the implied Southern-Ocean-to-North-Atlantic heat transport from 0.54 to 0.74 petawatts, a shift well within observational uncertainty, produced dramatic cancellations: transient eddy heat transport in the north actually increased by 0.34 petawatts rather than decreasing, because the stationary eddy term weakened by nearly the same amount, even as the North Atlantic storm track intensified locally. Likewise, tweaking midlatitude albedo over Northern Hemisphere land and ocean produced compensating changes in absorbed shortwave and emitted longwave radiation, leaving the hemispheric asymmetry nearly untouched despite pronounced regional shifts. The authors caution that MiMA lacks radiatively active clouds, whose treatment differs widely across climate models, and that its overly strong stationary eddy asymmetry may inflate the apparent importance of land–sea contrast. Even so, the message is clear: storm tracks cannot be understood ingredient by ingredient. Each piece of Earth’s patchwork surface sets the background state on which the others act, and that entanglement may be precisely why climate models, with their differing ocean heat transports and cloud biases, still disagree about where and how strongly the planet’s storms will rage in a warming world.

Subject of Research: How land–sea contrast, ocean heat transport and topography shape the localization and hemispheric asymmetry of midlatitude storm tracks

Article Title: Building blocks of localized storm tracks: revisiting asymmetries between the NH and SH in storm track strength

Article References: Building blocks of localized storm tracks: revisiting asymmetries between the NH and SH in storm track strength. (n.d.). https://doi.org/10.5194/wcd-7-1951-2026

Image Credits: AI Generated

DOI: 10.5194/wcd-7-1951-2026

Keywords: storm tracks, midlatitude cyclones, land-sea contrast, ocean heat transport, topography, stationary waves, transient eddies, moist static energy budget, general circulation model, hemispheric asymmetry, albedo, climate modeling

Overwash occurs when the combined elevation of storm surge, wave runup and astronomical tide exceeds the crest of a barrier’s frontal dunes, sending pulses of water and sand surging over the top. The sand carried by these flows is deposited on the landward side as lobate features called washover fans, which can merge into terraces or spread out as sheetwash where dunes are absent. Geologists regard this landward transfer of sediment as the engine of barrier ‘rollover’, the process by which a retreating barrier climbs across its own back-barrier environment instead of simply eroding away. It is one of nature’s strangest survival strategies: the barrier keeps its shape only by abandoning its old footprint and rolling inland.

The research team, led by Edvan Casagrande dos Santos of the Federal University of Rio Grande do Sul, took advantage of the PlanetScope constellation of small imaging satellites to watch this process unfold almost in real time. Over eighty-four months, the team visually inspected 1,240 true-color images at spatial resolutions of three to five metres, tracking the appearance of fresh washover deposits by their shape and by the telltale tonal contrast between wet and dry sand. They subdivided the sand spit barrier into five sectors based on dune heights and the recurrence of overwash, then cross-checked each candidate event against tide gauge measurements from Balneário Rincón, synoptic weather charts from the Brazilian Navy, and hourly ocean and atmosphere data from the ERA5 reanalysis.

The screening protocol was deliberately conservative. Any observed tide of 1.2 metres or more above local mean sea level flagged a potential event, yielding 129 candidates. Each one was then validated against the storm impact scale developed by Sallenger and later refined by Stockdon and colleagues, which compares the maximum water level to the elevation of the dune base and crest. Only when the hydrodynamic threshold, the modeled overwash regime and a visually confirmed washover fan all converged within a window of a few days was the event counted. The result: ninety-three confirmed overwashes, concentrated overwhelmingly between April and July, the southern hemisphere’s autumn and winter.

The meteorological fingerprint of these events is remarkably consistent. Virtually every overwash coincided with the passage of low-pressure systems, typically extratropical cyclones spawned near Patagonia, the Río de la Plata or the coasts of Uruguay and Rio Grande do Sul, often trailing cold fronts across southern Brazil. Winds swung from the northeast ahead of the front to the south and southwest behind it, piling coastal water against the shore through wind shear and Ekman transport. Storm surge emerged as the dominant driver of extreme water levels, contributing an average of forty-one percent of the observed tide during events, and in the record April 2020 storm a staggering seventy-seven percent of the elevation above mean sea level. On that day, a surge of 1.314 metres combined with six-metre significant waves and maximum individual waves of 11.2 metres to drown the barrier entirely.

Not every stretch of the spit suffered equally, and the differences map directly onto dune geometry. Sector 2, protected by foredunes averaging more than four metres high and reaching six to seven metres at their peaks, remained essentially untouched throughout the study, with washover fans appearing only once, in 2023, and even then only after human activity had disturbed adjacent Sector 1. Sector 3, where segmented dunes average just 2.2 metres, responded to nearly every moderate storm, hosting continuous washover fans, terraces and narrow overwash channels since 2017. Sectors 4 and 5, near the migrating river mouth, experienced repeated complete overtopping and inundation. The message is blunt: dune height and continuity are the barrier’s first line of defense, and even modest waves can breach it where the dunes are low or fragmented.

Human engineering turns out to be a co-conspirator in the barrier’s retreat. Since the late nineteenth century, the Araranguá River mouth has been artificially opened at least five times, and machinery was dispatched again in May 2022 and October 2023 to cut drainage channels through the spit during river floods. Each artificial breach lowers and segments the foredune field, creating depressions that invite subsequent overwash. The study draws parallels with the Ria Formosa barrier system in Portugal, where human interventions accounted for roughly twelve percent of washover occurrences, and with Masonboro Island in North Carolina, where hurricane-eroded dunes left the barrier prone to years of follow-on overwash. In Araranguá, the engineered inlets transformed Sector 1 into a persistent vulnerability that later amplified the ocean’s reach into the river channel.

Perhaps the most consequential finding lies in the eighty-three-year historical record. By orthorectifying aerial photographs from 1938, 1957 and 1978 using Structure-from-Motion photogrammetry, and combining them with later orthophotos and satellite scenes, the team computed four morphometric indicators along transects spaced every hundred metres: shoreline position, the outer and inner margins of the river channel, and channel width. Three evolutionary phases emerged. From 1938 to 1978 the system prograded seaward by an average of 207 metres, a textbook regressive barrier fed by ample sediment supply. From 1978 to 2005 a milder transgression set in, with the shoreline retreating an average of 24 metres between key transects. Then, after 2005, the retreat accelerated sharply, averaging 65 metres in just sixteen years, with erosion extending deep into the barrier interior, including a 94-metre landward migration of the inner channel margin.

The synchrony is hard to ignore: the sectors retreating fastest on the decadal scale are precisely those where washover fans recur most often on the monthly scale. The authors conclude that the Araranguá barrier has entered a rollover regime driven by the sheer frequency of overwash, reversing the regressive behavior that dominated the Holocene evolution of the broader coastal system. They also note a hydrodynamic compensation mechanism: no single parameter triggers overwash on its own, but when a surge nears a threshold, even modest increases in wave height or period push the total water level over the dune crest. This explains why overwash can occur with significant wave heights as low as two metres in the low sectors, while tall dunes shrug off far larger storms elsewhere along the spit.

The implications stretch well beyond one Brazilian estuary. Coastal barriers line up to fifteen percent of the world’s shorelines and ten percent of open-ocean coasts, sheltering lagoons, wetlands and communities from the sea. As sea level rises and storm climates intensify, the balance between sediment supply and overwash frequency will determine which barriers roll landward and survive, and which narrow into breaching and collapse. Washover deposits in Araranguá proved ephemeral, buried by wind-blown sand within days and reworked by the river, a caution for anyone hunting these features in the geological record. But the real-time satellite record offers something the rock archive cannot: a front-row seat to a barrier deciding, one storm at a time, to move inland.

Subject of Research: Overwash processes and the interdecadal evolution of the Araranguá sand spit barrier in southern Santa Catarina, Brazil

Article Title: Overwash processes: spatio-temporal scales and dynamics of the coastal system in southern Santa Catarina, Brazil

Article References: dos Santos, E. C., Medina, V. V., da Costa Cristiano, S., & da Camara Rosa, M. L. C. (2026). Overwash processes: spatio-temporal scales and dynamics of the coastal system in southern Santa Catarina, Brazil. Natural Hazards, 122(19), Article 630. https://doi.org/10.1007/s11069-026-08399-w

Image Credits: AI Generated

DOI: 10.1007/s11069-026-08399-w

Keywords: overwash, washover fans, coastal barrier, sand spit, storm surge, extratropical cyclones, shoreline retreat, barrier rollover, remote sensing, Santa Catarina, Brazil, coastal geomorphology