The measurements establish a post-event rebound, but the study could not determine whether landslides were responsible or how long any disaster-related effect persisted. The case study focused on rainfall that began on the evening of February 18 and continued into February 19, when total precipitation reached 680 millimetres. The event was associated with a stationary cold front intensified by the orographic influence of the Serra do Mar mountain range.

Landslides blocked roads, disrupted water and food supplies, caused fatalities and displaced many residents. A separate mapping study cited by the researchers identified 983 landslide areas after the disaster. São Sebastião’s only automatic air-quality station was approximately 30 kilometres from the epicentre in Vila Sahy, limiting how directly its measurements could represent conditions in the most severely affected area.

To distinguish the event from ordinary seasonal and meteorological variation, the researchers converted hourly monitoring records into daily values and used k-means clustering to classify days according to meteorological conditions alone. Particulate matter was deliberately excluded from the classification, so the resulting groups were not selected according to pollution levels. The algorithm placed the February 18 and 19 event days in a smaller high-rainfall group alongside other days with similar conditions.

Of the 1,187 days in the full analysis period, 849 had complete records for all five meteorological variables and were retained for clustering; 337 days, or 28.41%, were excluded. A Silhouette analysis favored two clusters, while the Elbow method favored three, and the researchers selected the three-cluster solution to isolate the high-rainfall group. Hourly records revealed behavior that daily averages alone could obscure.

When rain began around 7 p.m. on February 18, PM10 initially ranged from 16 to 18 micrograms per cubic metre and PM2.5 from 6 to 10. During the most intense interval, from 9 p.m. on February 18 to 4 a.m. on February 19, hourly precipitation reached 34.31 millimetres at Juquehy and 101.59 millimetres at Barra do Una. Concentrations subsequently fell, with PM10 declining to between 6 and 16 micrograms per cubic metre and PM2.5 to between 0 and 7.

This sequence was consistent with wet scavenging, in which intense precipitation removes suspended particles from the atmosphere. After rainfall weakened or stopped at most stations late on February 19, PM concentrations began rising again as atmospheric washout declined and pollutant accumulation resumed. Theil–Sen analyses examined daily PM trends over one-, three- and seven-day post-event windows.

In all three scenarios, the estimated slopes were close to zero and their confidence intervals included the null value, meaning the short-term trends were not statistically significant. That result did not erase the pronounced day-to-day fluctuations: the measurements showed a rapid decline during heavy rain followed by a rebound as the rain subsided. The analysis therefore documents a temporal sequence rather than demonstrating a sustained increase in particulate matter.

It also shows why a trend statistic based on a short period can characterize differently from an hourly analysis of the same event. Wind conditions and topography offered only partial explanations for the rebound. During the event, elevated concentrations were associated mainly with low-speed easterly and east-southeasterly winds, consistent with weak ventilation and local accumulation before rainfall began.

In the northwestern part of the municipality, winds above 6 metres per second were linked to lower concentrations. After the event, elevated particle levels occurred under several wind directions rather than in a single transport corridor. Westerly winds accounted for approximately 30% of observations from February 20 to 22 and occurred predominantly at speeds of 1 to 3 metres per second; mean wind speed across the period was about 1.8 metres per second.

Weak winds would reduce dispersion, while the recurrent westerly and southwesterly flow was compatible with transport from western areas, including the landslide-affected region, but the monitoring data could not identify the origin of the measured particles. Changes in local human activity offered another possible influence. The disaster occurred during the 2023 Carnival holiday, when unusually heavy traffic was expected along the SP-055 coastal highway.

The study cited an estimate of 223,718 vehicles using the route during Carnival and reported that eastbound daily traffic on February 21 and 22 was approximately twice the typical level for the month, reaching about 6,395 vehicles per day. Rescue operations, excavators, trucks and other heavy machinery may also have disturbed soil and deposited material. Port operations, vessels and road traffic could have supplied additional particles, while newly exposed landslide soil could have been resuspended.

These mechanisms are compatible with the observed rebound, but the researchers did not measure emissions, soil composition or source contributions, so they could not quantify the role of any one process. Two other heavy-rain periods helped test whether the February pattern was unique. The researchers examined March 19–20, 2022, when no landslides were identified in the available records, and June 13, 2023, which meteorological clustering placed near the February event.

In both comparisons, PM10 and PM2.5 declined during intense rainfall, again consistent with wet scavenging. Their behavior after the rain differed: the March 2022 concentrations recovered gradually as rainfall diminished, while concentrations after the June 2023 event remained below their pre-rainfall levels during the period examined. Following the February event, both particle fractions increased rapidly and remained elevated over the following days.

The comparison shows that a post-rain increase is not unique to landslides, but neither rainfall cessation nor landslide occurrence alone fully explains the faster and more persistent February rebound. The findings fit São Sebastião’s broader seasonal pollution pattern. Across the monitoring record, the highest average particle concentrations occurred mainly from July through September, during the relatively cool and stable part of the year, rather than in the wet summer when the disaster occurred.

The Serra do Mar can restrict low-level circulation, while weaker winter winds favor pollutant accumulation. Air-quality data cited in the study indicated that all valid 24-hour PM2.5 measurements in 2025 were classified as good, while 97.3% of valid PM10 measurements were also classified as good. Concentrations during the February event week remained below the national daily standards applied in the analysis: 120 micrograms per cubic metre for PM10 and 60 micrograms per cubic metre for PM2.5.

The post-event increase was therefore an acute change in measured pollution rather than evidence of a prolonged regional standard violation. The study’s principal limitation is the mismatch between the disaster footprint and the monitoring network. Gaps in the daily record, the use of a single station and its distance from Vila Sahy may have obscured the strongest local peaks.

The researchers also could not separate resuspended landslide material from traffic, machinery, port activity, regional pollutant transport or ordinary post-rain recovery. Their comparison events reinforce that caution: the observed sequence of particle decline and rebound was real, but the available data do not establish a landslide-specific causal effect or its duration. Denser monitoring networks, stations closer to affected slopes, continuous measurements and targeted source analysis would be needed to determine whether and for how long post-disaster activity raises particulate concentrations in the most affected parts of São Sebastião.

Subject of Research: Observed particulate-matter changes during and after extreme rainfall and landslides in São Sebastião, Brazil

Article Title: Can extreme rainfall associated with landslides affect air quality? A case study in a coastal city (São Sebastião, São Paulo State, Brazil)

Article References: Magalhães, L. R., Pozza, S. A., & Nogarotto, D. C. (2026). Can extreme rainfall associated with landslides affect air quality? A case study in a coastal city (São Sebastião, São Paulo State, Brazil). Environmental Monitoring and Assessment, 198(11), Article 1241. https://doi.org/10.1007/s10661-026-16071-w

Image Credits: AI Generated

DOI: 10.1007/s10661-026-16071-w

Keywords: air quality, particulate matter, PM10, PM2.5, landslides, extreme rainfall, São Sebastião, wet scavenging, particle resuspension, Brazil, extreme, rainfall

The sea-level decline was spatially coherent across the analysed Baltic subregions, including the southern Baltic, Arkona Basin, Gotland Basin, Gulf of Gdańsk, Gulf of Finland and Gulf of Bothnia. Basin-mean sea surface height fell to approximately minus 60 centimetres at the February minimum, while some regions locally dropped below minus 70 centimetres. The common timing and broad pattern indicated a basin-scale barotropic response rather than a local anomaly around one coast or subbasin. After the minimum, sea level rose during late February and March, although it remained below early-winter levels for several weeks. The authors interpreted this sequence as a major reduction in the amount of water stored in the Baltic.

Atmospheric pressure supplied the clearest explanation for the sustained forcing. Mean sea-level pressure over the Baltic repeatedly exceeded 1,020 hectopascals from December 2025 into early February 2026, sometimes covering nearly the entire basin. A revised pressure-persistence index accumulated positive standardized values over a backward-looking 30-day window and reached its event maximum on 20 January. Sensitivity tests using 10-, 15-, 20- and 30-day windows confirmed the importance of sustained high pressure, although the exact date of the index maximum varied with the window length. This was therefore a multi-week anticyclonic episode, not simply the product of one exceptionally strong weather system.

Easterly winds added a coherent outflow-favourable influence. Over the southern Baltic, the strongest lagged association between wind forcing and sea surface height occurred when the wind led the sea-level response by six days, with a correlation of minus 0.78. For the North Sea, the corresponding lag was about one day, and the correlation remained at plus one day under one-, three- and five-day smoothing. The longer-term analysis linked Landsort and Landsort–Norra sea level to the pressure difference between the Baltic and North Sea, but the filtered relationship was moderate: a seven-day lag regression produced a slope of minus 1.33 centimetres per hectopascal, while the pressure gradient explained about 15% of the variance in the sea-level series. The pressure–sea-level relation therefore supported the proposed mechanism without representing a unique adjustment time or explaining the entire event.

Historical comparisons confirmed the event’s rarity. During the 30 days before the 7 February minimum, the easterly wind component over both the North Sea and southern Baltic ranked first among 87 winters. The North Sea component averaged 6.98 metres per second, above its historical 95th percentile of 5.12 metres per second, while the southern Baltic value averaged 5.58 metres per second, above its 95th percentile of 4.23 metres per second. A compound index combining these winds with pressure-gradient persistence ranked second among 78 winters with sufficient data and exceeded its historical 95th percentile. Alternative formulations placed the event consistently second or third. Its tidal sea-level minimum, measured at minus 75.9 centimetres relative to the early-winter reference, ranked fourth among 139 sufficiently complete winters, with the same ordinal result under alternative data-completeness thresholds.

Integrating sea-surface height across the Baltic produced a direct estimate of the associated water-volume loss. The area-integrated anomaly declined from about 12 cubic kilometres above the 1 November–15 December 2025 reference level to approximately minus 290 cubic kilometres on 7 February, a decrease of roughly 302 cubic kilometres. An independent calculation based on net transport across a Kattegat section broadly reproduced this evolution: the transport-derived and sea-level-derived series had a correlation of 0.892 and a root-mean-square difference of 45.3 cubic kilometres. By a spring maximum on 6 April, the sea-level-derived anomaly had improved to approximately minus 61 cubic kilometres, representing recovery of 229 cubic kilometres, or 76% of the preceding decrease. The estimates diverged more clearly after early April.

That recovery cannot be equated directly with an inflow of saline or dense water. The sea-level calculation describes total water-volume change, while the Kattegat calculation estimates exchange through one section; both are also affected by differences in their control domains, atmospheric corrections and unquantified freshwater terms such as river input and precipitation minus evaporation. By 6 April, the hydrographic observations nevertheless showed signs consistent with deep-water renewal in parts of the southern Baltic. April CTD sections revealed plume-like lower-layer water in the Słupsk Furrow with practical salinity locally near 14. In the Bornholm Basin and Słupsk Furrow, relatively saline and oxygenated deep water was observed, whereas the signal was weaker and more diluted in the Gdańsk Basin, where deep salinity was about 12 and oxygen-depleted water persisted.

Glider missions in the eastern Bornholm Basin supplied the clearest time sequence after the minimum. The 10 and 12 practical-salinity contours shoaled from roughly 55–60 metres in early March to about 45–50 metres by mid- to late April along the sampled trajectory. Water with salinity above 14–15 became more extensive below approximately 55–60 metres, and near-bottom salinity locally reached about 17 from mid-April onward. Deep oxygen concentrations were often below 2 milligrams per litre below approximately 60–65 metres during March and early April, but substantially higher values appeared from late April into May. These observations indicate marked, though spatially uneven, oxygenation of the sampled lower layer. Because successive missions sampled different positions, the shifts cannot be interpreted as a basin-wide change at one fixed location.

The findings place the event within the Baltic’s larger outflow–inflow cycle without establishing that the February depression directly caused a Major Baltic Inflow. The pronounced volume loss may have created favourable initial conditions for later exchange, but the subsequent 229-cubic-kilometre recovery combined strait transport and freshwater effects and did not by itself measure saline-water import. The hydrographic evidence was consistent with an inflow-related signal reaching the Bornholm Basin within several weeks, yet the absence of matched immediately pre-event CTD sections farther east prevents a unique reconstruction of the propagation route or attribution of every observed feature to this event. The evidence also showed incomplete deep-water ventilation: relatively oxygenated water appeared in the Bornholm Basin and Słupsk Furrow, while low-oxygen deep water remained in the Gdańsk Basin. The 2026 episode was therefore hydrographically detectable but still evolving, with its final salt import, oxygen impact and formal inflow classification left for further analysis.

Subject of Research: Atmospheric forcing and post-minimum water exchange during the winter 2025/2026 Baltic Sea-level depression

Article Title: Atmospheric forcing of an extreme Baltic Sea-level depression and post-minimum exchange in winter 2025/2026

Article References: Rak, D., Jakacki, J., Muzyka, M., Bulczak, A. I., Przyborska, A., Markowicz, K., Osiński, R., & Kitowska, M. (2026). Atmospheric forcing of an extreme Baltic Sea-level depression and post-minimum exchange in winter 2025/2026. Frontiers in Marine Science, 13, Article 1949814. https://doi.org/10.3389/fmars.2026.1949814

Image Credits: AI Generated

DOI: 10.3389/fmars.2026.1949814

Keywords: Baltic Sea, sea-level depression, atmospheric forcing, water exchange, Danish Straits, Bornholm Basin, deep-water ventilation, ocean circulation, glider observations, Atmospheric, forcing, extreme

The event was defined using station-specific 99th-percentile thresholds calculated for each season, rather than a single fixed rainfall amount. An event qualified when at least 20% of the 18 gauges simultaneously exceeded their local seasonal threshold. Across the full record, the mean extreme threshold was about 60 millimetres per day, but it ranged from 57 millimetres in winter to 97 millimetres in summer; some southern stations had summer thresholds exceeding 180 millimetres. Summer contained nine identified extremes, autumn seven, spring eight and winter four. This seasonal differentiation matters because the municipality’s warm-season baseline is far wetter than its winter baseline, making an annual threshold alone an incomplete description of local rainfall extremes.

Petrópolis displayed a pronounced rainfall gradient over an area of roughly 791 square kilometres, with an average elevation of 809 metres above sea level. Mean annual totals ranged from approximately 1,000 to more than 2,200 millimetres, with the wettest conditions consistently concentrated in the southern part of the municipality. Southern stations also carried the highest seasonal extreme thresholds: many exceeded 120 millimetres per day in summer, while some central and northern gauges had values around 60–70 millimetres. The difference between the southern Independência station and northern Itaipava station was approximately 125 millimetres in summer. The results indicate that steep slopes, valleys, elevation and exposure to moisture can produce major differences over short distances.

The seasonal cycle was even more pronounced. Summer supplied 48% of annual precipitation, while autumn and spring each contributed 23% and winter only 7%. January was especially wet, with a median near 225 millimetres in the northern sector and 260 millimetres in the south; July medians fell to approximately 18 and 45 millimetres, respectively. The monthly distributions also showed larger variability among southern gauges, with January upper whiskers reaching about 720 millimetres in that sector. The study linked the warm-season concentration to the mature phase of the South American Monsoon System, in which the South Atlantic Convergence Zone and frontal systems influence southeastern Brazil, while winter is comparatively dry.

Hourly records revealed a pronounced evening onset. Significant rainfall most frequently began between 17:00 and 21:00 UTC, with particularly high frequencies around 18:00–20:00 UTC, whereas initiation was least common from roughly 08:00 to 11:00 UTC. Mean event duration varied substantially among stations, from about 2.9 hours at Capim Roxo and 3.0 hours at Samambaia to 9.1 hours at Quitandinha and 8.8 hours at Independência. Because many events began late in the local day and lasted several hours, the researchers used an accumulation window running from 13:00 UTC to 12:00 UTC the following day. This window could keep a long-lived event intact instead of dividing its rainfall between two conventional calendar days and understating its apparent intensity.

The 17 March 2013 episode displayed both exceptional magnitude and broad spatial extent. Rain began around 18:00 UTC, or 15:00 local time, and intensified during the night, reaching its peak around 02:00 UTC on 18 March. Several gauges then recorded hourly totals above 50 millimetres per hour, with Quitandinha reaching 71.5 millimetres per hour and the LNCC station recording 64.25 millimetres per hour. Southern gauges including Quitandinha, Morin, LNCC and Coronel Veiga accumulated more than 400 millimetres over the event, while Posse, Cuiabá, Capim Roxo and Itaipava recorded less than 25 millimetres per day. The Independência station recorded no rain during the analyzed period despite lying in the most affected sector, a gap that raises questions about the representativeness of its record for this episode.

Global Forecast System analyses showed that the rainfall developed within a persistent synoptic environment rather than from one isolated atmospheric trigger. A low-pressure area and frontal system over the South Atlantic moved toward Brazil’s southeastern coast, while the low-pressure center remained nearly stationary around the rainfall peak. At 850 hPa, a south-southeasterly flow transported moist air from the Atlantic toward Rio de Janeiro. Specific humidity of 10–14 grams per kilogram was present before the event, rose above 12 grams per kilogram as intense rain began and remained high through the peak. Aloft, southeastern Brazil lay on the northern flank of a strong Atlantic jet, with core wind speeds exceeding 70 metres per second and locally approaching or surpassing 100 metres per second. Although no organized South Atlantic Convergence Zone episode was present, the offshore low, cold-front structure and persistent maritime moisture transport created favorable large-scale forcing.

Thermodynamic diagnostics indicated that moisture and vertical motion were as important to the event’s persistence as the changing instability. Over Petrópolis, convective available potential energy increased from 1,610 joules per kilogram at 12:00 UTC on 17 March to 2,465 joules per kilogram at 18:00, as the Lifted Index fell from −3.3 to −5.3 degrees Celsius. The K Index rose to 37 degrees Celsius and Total Totals to 44 degrees Celsius, both consistent in the analysis with a high thunderstorm potential. At the rainfall peak, CAPE had fallen to 1,090 joules per kilogram, but precipitable water reached 57.9 millimetres, its maximum value, while the K and Total Totals indices remained at 37 and 43 degrees Celsius. The decrease in CAPE therefore coincided with continued abundant moisture and active convection rather than an end to convective support.

Low-level saturation and ascending motion further organized the event. Relative humidity over Petrópolis reached approximately 100% when intense rainfall began and remained near saturation at the peak. The Galvez–Davison Index exceeded 50 across large parts of Rio de Janeiro, São Paulo and Minas Gerais during intensification, with local cores above 60. At the peak, omega values over the municipality were below −1 pascal per second at 850 hPa, while adjacent areas reached values below −3 pascal per second, indicating stronger ascent in the surrounding region. By 06:00 UTC on 18 March, CAPE had nearly vanished from the study area and vertical-motion maxima had become more scattered, corresponding with the weakening of the rain. The study interprets the episode as the interaction of persistent moisture, favorable upper-level circulation, low-level saturation, frontal forcing and local orographic modulation, rather than as the product of a single mechanism.

The study provides a quantitative local baseline for hydrometeorological monitoring, but its design also establishes important limits. It covers one municipality and 13 years, so it does not establish long-term changes in the frequency of extremes, and a percentile criterion identifies unusually wet days within the observed record rather than a fixed probability of future recurrence. MERGE was used to replace missing gauge hours rather than substitute for the station network; its mean Pearson correlation with gauge records was 0.6. Atmospheric mechanisms were diagnosed from GFS analyses at 0.5-degree resolution, and the derived soundings and fields cannot resolve Petrópolis’s steep terrain, boundary-layer processes or cloud microphysics at neighborhood scale. The authors therefore identify radar observations, satellite analysis and high-resolution numerical modeling as priorities for future work, while the 2013 case demonstrates how gauge-based event definitions and layered atmospheric diagnostics can reveal the distinctive hazards of extreme rainfall in complex tropical terrain.

Subject of Research: Observational and atmospheric-diagnostic analysis of extreme rainfall in Petrópolis, Brazil

Article Title: Extreme rainfall events in a tropical complex-terrain environment: Identification and dynamical–thermodynamic evaluation in Petropolis, Rio de Janeiro (Brazil)

Article References: Miranda, B. P., da Silva Bastos Guimarães, N., & Polifke, F. (2026). Extreme rainfall events in a tropical complex-terrain environment: Identification and dynamical–thermodynamic evaluation in Petropolis, Rio de Janeiro (Brazil). Theoretical and Applied Climatology, 157(11), Article 730. https://doi.org/10.1007/s00704-026-06660-7

Image Credits: AI Generated

DOI: 10.1007/s00704-026-06660-7

Keywords: extreme rainfall, Petrópolis, Brazil, rain gauges, topographic effects, atmospheric moisture, mesoscale convection, precipitation extremes, South Atlantic, weather dynamics, Extreme, rainfall

The study, led by researchers examining the 2013-2023 period across the Yellow River Basin, China’s second-largest grain-producing region, measured resilience across three dimensions: the ability of regions to resist temperature shocks, to recover from them, and to adapt over time. The findings show that each additional extreme temperature day significantly reduces all three capacities, with the effects persisting even after accounting for agricultural endowments, market conditions, production scale, consumption capacity, and urbanization.

What makes the research distinctive is its focus on resilience rather than yield alone. Previous studies have documented how heat stress cuts harvests, but the new work argues that such shocks destabilize the entire production system. When temperatures spike, farmers divert resources from long-term investments toward immediate survival, weakening the infrastructure, technology, and institutions that would otherwise support future harvests. The result is a spiral in which each shock leaves the system more vulnerable to the next.

The evidence is stark. Field experiments cited in the study show that heat stress during the flowering period of summer maize can reduce yields by more than 30 percent, with the damage concentrated in the grain-filling stage. But the broader consequences reach further: heat extremes disrupt planting schedules, increase water demand, and strain the irrigation and storage infrastructure that grain regions depend upon. In the Yellow River Basin, where water scarcity already constrains production, these pressures compound existing vulnerabilities.

Not all regions are equally exposed. The study finds that the negative effects of temperature extremes are concentrated in areas with weaker agricultural infrastructure and lower economic capacity. Regions with stronger irrigation systems, better storage facilities, and deeper digital penetration show significantly greater capacity to withstand shocks. In areas where digital infrastructure is well developed, the damage from temperature extremes is measurably reduced, suggesting that connectivity, early warning systems, and digital finance can buffer climate impacts.

The digital dimension is among the most intriguing findings. The researchers measured digital development across the basin using indicators of internet penetration, mobile coverage, and digital finance depth. Their analysis shows that each unit increase in digital development significantly reduces the negative effect of temperature extremes on grain resilience. The mechanism, they argue, operates through several channels: digital platforms deliver early warnings of incoming heat waves, allowing farmers to adjust planting and irrigation schedules; digital finance provides emergency credit when harvests fail; and online agricultural services connect farmers to technical advice and market information that would otherwise be unavailable.

The findings carry significant implications for climate adaptation policy. The researchers argue that building resilience requires more than expanding irrigation or improving crop varieties—it demands strengthening the digital, financial, and institutional infrastructure that allows grain regions to absorb shocks. In areas where digital infrastructure is weak, the study suggests, targeted investment in connectivity and digital services could deliver outsized adaptation benefits. The researchers also emphasize that adaptation strategies must account for regional differences in economic capacity, since the damage from temperature extremes is concentrated in areas least able to afford it.

The study’s evidence is robust across multiple specifications. The researchers tested their findings using lagged control variables to address potential simultaneity, matched specifications to address endogeneity, and alternative measures of temperature extremes to ensure the results were not driven by particular definitions. The negative relationship between temperature extremes and grain resilience persisted across all tests, with the coefficient remaining statistically significant at the 1 percent level. The researchers also found that the effects were stronger in areas with weaker agricultural infrastructure, confirming that the damage from climate shocks is concentrated where adaptive capacity is lowest.

What the research does not yet establish is the precise mechanism through which digital tools buffer climate impacts. The researchers acknowledge that their evidence shows correlation rather than causation, and that targeted experiments would be needed to isolate the specific channels through which connectivity, early warning, and digital finance operate. They also note that their measure of digital development captures breadth rather than depth, and that future research should examine how specific digital services—such as precision agriculture platforms or weather-indexed insurance—deliver adaptation benefits.

For the Yellow River Basin, the findings arrive at a critical moment. The region faces intensifying temperature extremes, deepening water scarcity, and growing pressure to maintain grain output for national food security. The study suggests that the path forward requires strengthening not just physical infrastructure but the digital and financial systems that allow grain regions to absorb shocks. In areas where connectivity is weak, targeted investment in digital services could deliver adaptation benefits that physical infrastructure alone cannot match. The researchers argue that building resilience demands a comprehensive approach—one that integrates irrigation, crop varieties, digital platforms, financial services, and institutional capacity into a single adaptation strategy.

Subject of Research: Agricultural Science

Article Title: Extreme temperature, digital rural development, and grain production resilience in the Yellow River Basin

Article References: Wang, W., Yu, Y., Yang, Y., & Zhang, Y. (2026). Extreme temperature, digital rural development, and grain production resilience in the Yellow River Basin. Frontiers in Sustainable Food Systems, 10, Article 1912640. https://doi.org/10.3389/fsufs.2026.1912640

Image Credits: AI Generated

DOI: 10.3389/fsufs.2026.1912640

Keywords: climate change, grain production, resilience, digital infrastructure, Yellow River Basin, extreme heat, agricultural adaptation, Extreme, temperature, digital, rural, development

The choice of cyclic olefin copolymer deserves particular attention. Unlike polyimide or silicone, this class of polymer combines optical clarity, very low water absorption, excellent moisture barrier properties, and a high glass transition temperature, all of which matter for a sealed device charged with water. Gas permeability is a chronic weakness of polymeric heat pipes because non-condensable gases that diffuse through the walls accumulate in the condenser and progressively degrade performance over the device lifetime. A wall material with low permeability extends operational life and preserves the vacuum or low-saturation-pressure internal environment on which the phase-change cycle depends. The material is also inherently an electrical insulator, eliminating the risk of short circuits that metallic spreaders pose when placed directly over dense circuitry in wearables or conformal electronics.

The asymmetric architecture referenced in the work refers to an intentional imbalance between the evaporator and condenser sides of the chamber. Asymmetric vapor chambers allow the evaporation area, vapor space depth, and condensation region to be tailored independently rather than mirrored, which is valuable in flexible electronics where heat sources and heat sinks rarely align symmetrically. Combined with the patterned wettability, this geometry helps maintain a stable liquid-vapor interface even when the entire device is curved, since the capillary-driven return path remains anchored within the superhydrophilic microchannels regardless of the external bend radius.

The systematic evaluation of filling ratios reflects a well-known sensitivity in miniaturized two-phase devices. At low charge, such as the 28 percent condition tested, insufficient liquid inventory leads to dry-out of the evaporator, a runaway condition in which the wick can no longer supply fluid fast enough and the local surface temperature climbs steeply. At excessive charge, such as 70 percent, liquid pools within or beneath the vapor space, throttling vapor transport and adding parasitic thermal mass that slows startup. The intermediate filling condition, 42 percent, represents the compromise where enough working fluid saturates the microchannels while leaving the vapor lane clear. This underfilling and overfilling sensitivity mirrors observations in ultra-thin copper foam-mesh hybrid devices reported in the literature, suggesting the phenomenon is generic to thin two-phase spreaders rather than an artifact of polymeric construction.

The bending experiments provide a window into a failure mode unique to flexible thermal devices. Bending to 45 degrees can locally compress the vapor space, pinch capillary channels on the inner radius of curvature, and stretch them on the outer radius, altering both the hydraulic resistance of the liquid return path and the effective evaporation area. The finding that thermal resistance remains low and stable between 0 and 20 degrees of bending for the plasma-treated devices indicates that within this range the wettability-enhanced microchannels preserve continuous liquid feeding. The reported 20 percent reduction in thermal resistance relative to untreated microchannels quantifies the direct benefit of surface functionalization, effectively demonstrating that wettability engineering can substitute for the metallic wick structures that flexible devices cannot accommodate.

It is worth contextualizing the thermal resistance values against prior art. Flexible polymer heat pipes fabricated from laminated films with sintered mesh wicks have historically shown resistances between roughly 1 and 3 kelvin per watt under bending, while hybrid copper-silicone devices have fared somewhat better at moderate bend angles. Achieving stable low resistance across a 0 to 20 degree deformation range in a device with no metallic components at all represents meaningful progress, since hybrid designs carry penalties in weight, stiffness, and electrical conductivity that undermine the rationale for a flexible spreader in the first place. The comparison to ultra-thin copper mesh devices with effective conductivities in the thousands of watts per meter-kelvin is less about raw performance and more about the performance-per-thickness and performance-per-flexibility trade space, where two-phase devices vastly outperform any solid conductor of equal thickness, polymeric or metallic.

The oxygen plasma treatment itself is a mature technique in polymer microfabrication. Plasma exposure breaks polymer chains and introduces oxygen-containing polar groups at the surface, raising the surface energy and driving the water contact angle toward zero. Over-treatment, however, can roughen or weaken the surface and generate low-molecular-weight oxidized material, so the nine-minute optimization reflects a practical balance between wettability enhancement and preservation of channel integrity. The subsequent polyethylene glycol coating serves to stabilize the hydrophilic state. Untreated plasma surfaces on many polymers gradually recover their hydrophobicity as polar groups reorient into the bulk, a process known as hydrophobic recovery, and a hydrophilic polymer overlay retards this aging, extending the functional lifetime of the wick.

From a manufacturing standpoint, the emphasis on a complete microfabrication process in cyclic olefin copolymer matters as much as the measured performance. Polymers are compatible with replication techniques such as hot embossing, injection molding, and roll-to-roll lamination, which scale to large areas at low unit cost in a way that sintered copper wicks cannot. A fully polymeric, 250-micrometer-thick cooler that survives repeated bending could plausibly be laminated directly onto flexible printed circuit boards, integrated into textile-based wearable systems, or wrapped around robotic joints in soft actuators where rigid copper spreaders would concentrate mechanical stress. The electrical insulation of the casing further simplifies design by removing the need for intermediate dielectric layers between the spreader and exposed conductors.

The work also fits into a broader biomimetic trend in thermal engineering. Recent designs inspired by leaf venation use hierarchical, asymmetric branching networks to balance capillary pressure against permeability, since narrow channels generate strong capillarity but high flow resistance while wide channels do the opposite. Graded microchannel networks approximate this optimum. The superhydrophilic channels described here can be viewed as one ingredient in such architectures, providing the wetting limit that natural transport systems exploit, while the channel geometry governs the hydraulic side of the capillary balance.

Finally, the framing of the approach as sustainable passive cooling is substantively accurate. Two-phase spreading requires no pumps, no fans, and no electrical input, moving heat by the latent heat of vaporization of water, which is the highest of any common working fluid. Eliminating metal reduces embodied energy and material cost and removes corrosion as a lifetime-limiting mechanism. For the growing class of flexible, wearable, and soft robotic systems where every gram and every millimeter of bending compliance counts, a thin polymeric vapor chamber with engineered wettability offers a credible route to heat spreading that neither solid polymers, with their thermal conductivities below one watt per meter-kelvin, nor rigid metallic spreaders can provide.

Subject of Research: Flexible polymeric asymmetric vapor chambers incorporating microchannels of extreme wettability for electronic device cooling

Article Title: Flexible polymeric asymmetric vapor chambers incorporating microchannels of extreme wettability for electronic device cooling

Article References: Tselepi, V., Nioras, D., Gogolides, E., & Ellinas, K. (2026). Flexible polymeric asymmetric vapor chambers incorporating microchannels of extreme wettability for electronic device cooling. Frontiers in Thermal Engineering, 6, Article 1850683. https://doi.org/10.3389/fther.2026.1850683

Image Credits: AI Generated

DOI: 10.3389/fther.2026.1850683

Keywords: Flexible, polymeric, asymmetric, vapor, chambers, incorporating, microchannels, extreme, wettability, electronic, device, cooling

The study employed two complementary data sources: ground-based measurements from weather stations across Bulgaria and the ERA5-Land reanalysis product, which provides gridded hourly data from 1950 to the present. The researchers found that the two datasets show good agreement in terms of the frequency of extreme precipitation events, but not in terms of their average values. Notably, the ERA5-Land reanalysis systematically underestimates heavy precipitation events, a finding consistent with previous evaluations of ERA5 precipitation over Spain and other regions.

To detect trends, the team applied a suite of statistical methods including Sen’s slope estimator, the Mann-Kendall test, and correlation analysis. Sen’s slope estimator provides a robust nonparametric measure of trend magnitude, while the Mann-Kendall test assesses the statistical significance of monotonic trends in time series data. These methods are particularly well-suited to precipitation data, which often violate the distributional assumptions of parametric tests.

The results show that the frequency of extreme precipitation events—the number of cases per year—increases in almost all studied stations and grid cells during the period 1979–2025, according to both instrumental observations and ERA5-Land reanalysis. However, when the analysis is extended to the longer period 1950–2025 using only the reanalysis data, no trend is detected in frequency. This discrepancy suggests that the intensification of extreme precipitation is a relatively recent phenomenon, likely linked to the accelerated warming of recent decades.

The average values of daily extreme precipitation also show predominantly positive trends for the period 1979–2025 according to both datasets, and weak positive or no trends for the longer 1950–2025 period. In some stations and grid cells, these trends are statistically significant. The most pronounced increases in extreme precipitation are observed in southern and, especially, southeastern Bulgaria, a region that appears to be experiencing a disproportionate intensification of heavy rainfall.

One of the most striking findings of the study is an increase in the 21st century in the duration of extreme precipitation periods that extend beyond a single day. Multi-day extreme precipitation episodes are particularly dangerous, as they can saturate soils and overwhelm drainage infrastructure, leading to severe flooding. This finding aligns with broader research across the Balkans, where studies in Serbia, Montenegro, Bosnia and Herzegovina, Romania, and Greece have documented similar trends toward more intense and persistent heavy rainfall under a warming climate.

The physical mechanisms underlying these trends are consistent with the expectations of climate science. As the atmosphere warms, the Clausius-Clapeyron relation dictates that its water-holding capacity increases by approximately 7% per degree Celsius of warming. This means that when precipitation systems develop, they have more moisture available to convert into rainfall, increasing the likelihood of extreme daily totals. Changes in atmospheric circulation patterns over the Mediterranean and the Balkans, which Nojarov has documented in previous work, may also contribute to the observed intensification.

The spatial heterogeneity of the trends is noteworthy. While positive trends dominate across most of the country, the concentration of the most significant increases in southern and southeastern Bulgaria suggests that regional factors—including proximity to the Aegean Sea, orographic effects, and the influence of Mediterranean cyclone tracks—play a crucial role in modulating how global warming translates into local extreme precipitation. This finding has important implications for water management, flood preparedness, and infrastructure planning in the region.

The methodological rigor of the study deserves emphasis. By comparing ground-based observations with reanalysis data over the same period, the researchers were able to validate the reliability of their trend detections and identify the limitations of the reanalysis product. The finding that ERA5-Land underestimates heavy precipitation events is particularly valuable for the research community, as it cautions against relying solely on reanalysis data for studies of precipitation extremes—a caution echoed by other evaluations of ERA5 and ERA5-Land precipitation in Europe.

As Bulgaria and its neighbors continue to experience the effects of a warming climate, the findings of this study provide crucial evidence for understanding how extreme precipitation is evolving in southeastern Europe. The predominance of positive trends in both the frequency and intensity of extreme precipitation events during recent decades, combined with the emergence of longer-duration extreme precipitation periods in the 21st century, suggests that the region faces increasing risks of flooding and water-related hazards. Continued monitoring, improved high-resolution modeling, and adaptive water management strategies will be essential for building resilience in the face of these changing precipitation patterns.

Subject of Research: Extreme precipitation trends in Bulgaria in conditions of a warming climate

Article Title: Extreme precipitation trends in Bulgaria in conditions of a warming climate

Article References: Nojarov, P., Svetozarevic, J., Parvanova, D., & Belev, G. (2026). Extreme precipitation trends in Bulgaria in conditions of a warming climate. Theoretical and Applied Climatology, 157(11), Article 727. https://doi.org/10.1007/s00704-026-06655-4

Image Credits: AI Generated

DOI: 10.1007/s00704-026-06655-4

Keywords: extreme precipitation, Bulgaria, climate change, ERA5-Land, Mann-Kendall test, Sen's slope estimator, Theoretical and Applied Climatology, Bulgarian Academy of Sciences, southeastern Europe, hydrology, Extreme, precipitation

The findings point to a direct relationship between the presence of sea ice and the intensity of ocean waves. When the Ross Sea was more extensively covered by ice, wave growth was strongly restricted. As the ice retreated, open water expanded, allowing winds to transfer energy across a much larger stretch of ocean. That additional distance, known as fetch, enabled waves to become higher, longer and more powerful before reaching the Antarctic coastline.

This process is familiar from modern storms, but its significance in Antarctica is particularly striking. Sea ice is not simply a frozen lid covering the ocean. It acts as a dynamic barrier that absorbs, scatters and disrupts wave energy. Even fragmented ice can reduce the distance over which waves develop. When the ice edge moves poleward or breaks apart, the ocean suddenly becomes more responsive to strong winds, creating conditions capable of generating extreme waves.

The Ross Sea is an ideal natural laboratory for studying this transformation. Located between the Antarctic Peninsula and the Ross Ice Shelf, it is one of the most climatically sensitive regions of the Southern Ocean. Its sea ice influences ocean circulation, the exchange of heat and gases between the ocean and atmosphere, and the stability of nearby ice shelves. Changes in wave activity therefore have consequences far beyond the immediate shoreline.

The study’s focus on the early-mid Holocene provides an important perspective on how the Antarctic system behaves during periods of natural warming. The Holocene began roughly 11,700 years ago, after the end of the last ice age. During its early and middle stages, changing sunlight patterns, declining ice sheets and evolving ocean circulation altered the balance between atmosphere, sea ice and the Southern Ocean. The new research suggests that these shifts were recorded not only in temperatures or ice extent, but also in the height of the largest waves.

Extreme waves are especially valuable climate indicators because they respond to several environmental factors at once. Their size depends on wind speed, wind direction, storm duration, water depth and the amount of open water available for wave development. In polar regions, sea ice adds another critical control. By linking past wave heights to changing ice conditions, researchers can investigate how the entire climate system worked together rather than treating sea ice as an isolated variable.

The researchers also identify the importance of ocean-atmosphere interactions. As the ocean loses its protective ice cover, more heat and moisture can move between the water and the air. Open water can intensify local exchanges of energy, influence atmospheric pressure patterns and modify storm behavior. At the same time, stronger waves can break up remaining ice, accelerate its dispersal and expose still more ocean. This creates a feedback loop in which retreating ice enables larger waves, and larger waves can help sustain further ice retreat.

That feedback matters today because the Ross Sea is already experiencing rapid environmental change. Although Antarctic sea-ice trends vary from year to year and from region to region, long-term shifts in ocean temperature, wind patterns and ice dynamics are reshaping the Southern Ocean. The historical record reconstructed in this study indicates that wave conditions may change sharply once the ice edge retreats beyond a critical point. A relatively modest reduction in ice cover could therefore produce a disproportionate increase in wave exposure.

The implications extend to Antarctic ice shelves, coastal ecosystems and future climate projections. Larger waves can deliver more mechanical energy to the edge of floating ice, potentially contributing to fracture, flexure and the breakup of vulnerable sections. Waves also affect the transport and mixing of heat in the upper ocean, processes that influence marine life and the formation of new sea ice. By showing that ancient wave extremes tracked sea-ice retreat and coupled ocean-atmosphere changes, the study adds a new dimension to efforts to understand Antarctica’s climate future.

The Ross Sea record ultimately delivers a vivid warning: in a warming world, the disappearance of sea ice can amplify more than sunlight reaching the ocean. It can transform the character of the sea itself. As open water expands, storms may gain a larger arena in which to build destructive waves, while those waves feed back into the fragile polar environment. The ancient signal described by Wang, Wang, Zhang and colleagues suggests that Antarctica’s wave climate is not a passive consequence of warming, but an active and potentially accelerating part of the system.

Subject of Research: Ross Sea extreme wave heights, sea-ice retreat, and ocean-atmosphere interactions during the early-mid Holocene

Article Title: Early-mid Holocene Ross Sea extreme wave heights reflect sea ice retreat and ocean-atmosphere interactions

Article References: Wang, S., Wang, N., Zhang, Y. et al. “Early-mid Holocene Ross Sea extreme wave heights reflect sea ice retreat and ocean-atmosphere interactions.” Nature Communications (2026). https://doi.org/10.1038/s41467-026-76311-y

Image Credits: AI Generated

DOI: 10.1038/s41467-026-76311-y

Keywords: Ross Sea, Antarctica, extreme waves, sea-ice retreat, Holocene climate, ocean-atmosphere interactions, Southern Ocean, Antarctic ice shelves