Gil Lemos

PORWAVES is a new high-resolution, long-term wave hindcast developed for the Portuguese mainland coastal areas. The dataset was produced with SWAN forced by ERA5 wave fields over the 1940-2024 period, being structured in two tiers: a regional grid (G001PT), at ~1 km resolution, and nine nested sub-domains (G0001PT), at ~100 m resolution. G001PT was evaluated against in-situ observations and altimetry measurements from the ESA Sea State CCI initiative, while G0001PT boundary conditions were bias corrected using a directional quantile-mapping approach. Against in-situ observations, G001PT achieved a mean significant wave height (Hs) bias, RMSE and correlation coefficient of 0.15 m (absolute), 0.42 m, and 0.90, respectively, while substantially improving the depiction of local wave climate heterogeneities. The correction further reduced the location-wide mean (99th percentile) Hs absolute biases from 0.15 m to 0.06 m (0.62 to 0.04 m), and the corresponding mean wave period (Tm02) ones from 0.68 s to 0.19 s (0.88 s to 0.23 s). Long-term Hs trends are predominantly positive, within 1–3 cm/decade along the western Portuguese coastlines. The ~100 m simulations reveal pronounced spatial and seasonal contrasts in Hs and wave energy flux, and associated return values, demonstrating the relevance of bathymetry, coastal orientation and sheltering in controlling local exposure. PORWAVES bridges the gap between global reanalysis products and nearshore wave information required for Portuguese coastal management and adaptation planning, considering the ever-greater impacts of climate change.

As climate change intensifies heat extremes, the Urban Heat Island (UHI) effect amplifies local thermal stress. Assessing the UHI using robust observational data, whether ground- and/or satellite-based, is essential for climate risk assessment and evidence-based urban adaptation. Therefore, this study aims to provide a comprehensive climatological assessment of air temperature patterns and UHI intensity across the Lisbon Metropolitan Area (LMA) over a 26-year period (2000–2025). The methodology employs a dense, high-quality integrated network of in-situ weather stations from the Portuguese Institute for Sea and Atmosphere (IPMA) and the National Water Resources Information System (SNIRH). To bridge critical gaps in traditional climate assessments, this research implements a dual-perspective approach that combines the high temporal resolution of MSG-SEVIRI and the spatial precision of MODIS Land Surface Temperature (LST). This framework accurately captures the lag effects between surface heating and atmospheric response. Validation results demonstrate that satellite-derived LST is a robust proxy for monitoring the nocturnal UHI, with differences generally below 1 °C compared with near-surface air temperature observations (T2m). However, daytime LST significantly overestimates atmospheric temperatures, with deviations of 2–8 °C due to solar radiation and urban geometry. The selection of rural reference stations constitutes a critical methodological factor, as a baseline shift can alter perceived UHI intensities by more than 3 °C. Despite these sensitivities, the results unequivocally confirm a persistent and spatially heterogeneous UHI effect in Lisbon, which intensifies during extreme heat events by up to an additional 4 °C. Analysis of the 2003 and 2018 heatwaves reveals surface LST anomalies exceeding 10 °C and urban–rural thermal differentials reaching up to 7 °C under conditions of suppressed maritime breezes. These nocturnal anomalies are particularly pronounced in densely built-up areas, limiting thermal dissipation and preventing physiological recovery. Integrating multi-sensor satellite data with in-situ validation provides a new benchmark for climate risk assessments, delivering the reliable, reproducible data required to strengthen long-term urban resilience under increasingly frequent extreme heat events.

Swells generated in the Southern Ocean regularly impact the Pacific coasts of the Americas, with the most energetic events causing severe infrastructure damage, coastal flooding, and loss of life. This study presents a detailed, comprehensive analysis of these high-energy swells along this coastline, characterizing their primary characteristics and examining their variability across multiple timescales. These swells occur most frequently during austral winter, with a considerable proportion also occurring in austral spring and autumn. The Southern Annular Mode exerts a strong influence, with its positive phase (SAM + ) being associated with more energetic swells. Significant positive trends in wave height, power, and occurrence rate along much of the studied coastline in recent decades highlight the increasing risk posed by these swell events. Our findings offer valuable insights for enhancing coastal resilience and informing effective risk management strategies in response to this coastal hazard.

In the beginning of 2014, exceptionally energetic swells associated with the Hercules storm (also known as “Christina”) produced one of the most devastating coastal events ever recorded in Portugal. Between January 6th and 7th, coastal flooding affected more than 30 municipalities along the Portuguese coastline, with offshore buoys registering maximum individual wave heights and periods of 14.91 m and 28.10 s, respectively. The storm resulted in more than 16 million euros in direct damages due to overtopping and coastal flooding, while indirect losses (considering affected businesses and populations) are estimated to have reached hundreds of millions of euros. In this study, two physical climate storylines are developed to assess the impacts of a “Hercules”-like storm, at five key-locations along the Portuguese coastline, occurring by the end of the 21st century, under the combined influence of sea-level rise (SLR), projected changes in wave climate, and altered coastal morphology, while retaining the same statistical representativeness observed in 2014. The storyline approach enables a clear linkage to the original event and facilitates the assessment of future extreme events such as Hercules within the context of a changing climate, supporting decision-making by working backwards from specific vulnerabilities or decision points. Results indicate that the impacts of a future Hercules-like storm are projected to intensify, considering SLR and increases in high-percentile wave energy. Extreme coastal flooding is expected to affect 1.9 to 2.4 times more area than in 2014, resulting in 3.2 to 6.5 times more physically impacted buildings, particularly in densely urbanized coastal sectors. As coastal erosion is expected to reduce the natural protection of Portuguese sandy coastlines, the currently employed protection mechanisms will require robust adaptation measures, strategically defined to withstand long-return-period extreme events. This work is supported by FCT, I.P./MCTES through national funds (PIDDAC): LA/P/0068/2020 - https://doi.org/10.54499/LA/P/0068/2020, UID/50019/2025, https://doi.org /10.54499/UID/PRR/50019/2025, UID/PRR2/50019/2025. The authors would like also to acknowledge the project “Elaboração do Plano Municipal de Ação Climática de Barcelos (PMACB).

Some of the most disruptive effects of climate change are projected to be felt along the coastlines. The combined effects of future changes in water levels and wave climate along the coastal areas constitute one of the most serious threats to their sustainable evolution, compromising critical infrastructures, resources, ecosystems, and communities. Understanding long-term changes in coastal areas remains challenging, however, due to their multivariate and multi-time-and-space-scale nature. In this study, we propose an innovative methodology for a complete vulnerability assessment of sandy low-lying coastal areas, based on dynamic, ensemble-based projections from the Coupled Model Intercomparison Project phase 5 (CMIP5). The effects of sea level rise (SLR) and nearshore wave climate changes on future shoreline evolution are firstly assessed at five key-locations along the Portuguese coastline. Longshore sediment transport (LST) projections are computed, and sedimentary imbalances are quantified. Robust shoreline retreat of up to 300 m is projected, especially along the Portuguese northern and central coastal areas, with continued erosion driven mainly by sediment imbalance and SLR. The projected decrease in future nearshore wave energy is responsible for a slight alleviation in erosion trends, up to 6.33%, whereas the increase of northerly incoming waves is expected to lead to northward beach rotations along western Mainland Portugal. The resulting shoreline evolution is responsible for the loss of up to 0.786 km2 of dry land by 2100 along the 14 kilometers of analyzed coastline. Based on the shoreline projections, new digital terrain models are built for the five key-locations, and future extreme total water levels are obtained through a probabilistic approach, defining wave events considering high wave energy thresholds in a changing climate. The results reveal that extreme coastal flooding is projected across several urbanized sections along the Portuguese coastline, especially in areas without artificial protection infrastructures. As dune erosion is expected along the sandy stretches, the natural protection against extreme coastal events is projected to be reduced by up to 13.3%, promoting widespread overtopping, leaving populations more exposed. Future projections reveal the episodic flooding of up to 1.47 km2 of land across the five key-locations (and up to 604 km2 at a national scale), threatening households and commercial hubs, besides services and communication routes. Overall, as physical and human losses may increase substantially in the future, our results call for the implementation of adequate coastal management and adaptation plans, strategically defined to withstand changes until 2100 and beyond.This work is supported by the Portuguese Fundação para a Ciência e Tecnologia, FCT, I.P./MCTES through national funds (PIDDAC): UID/50019/2025 and LA/P/0068/2020 https://doi.org/10.54499/LA/P/0068/2020).

Wave storms present a significant hazard to the coastal environment, particularly affecting the 10% of the population residing in low-lying coastal areas, as well as coastal zone infrastructure and developments. This study utilizes a ~40-year wave hindcast to conduct an analysis of wind-wave storminess along the worldwide coast (Lobeto et al., 2024). The main characteristics of wave storms, such as the associated wave height and direction, as well as the occurrence rate, duration and intensity, are analyzed. Additional climatic wave features including the relative importance of wind seas versus swells during wave storms are also explored. The combination of key storm features has led to a categorization of coastal regions based on their degree of wave storminess.Results indicate Northwestern Europe and Southwestern South America to be the coastal regions experiencing the most severe storms, while the Yellow Sea, along with the South African and Namibian coastlines, are noted for their high frequency of storms. A global holistic analysis of the wave storminess reveals that, for example, the exposed shores of northwestern Europe experience over 10 storms annually, with mean significant wave heights exceeding 6 meters. A general latitudinal pattern in degree of wave storminess is observed, with the main exception of those coasts affected by wave storms generated by tropical cyclones. Accordingly, regions such as Iceland, Ireland, Scotland, Chile, and Australia exhibit the highest storminess levels, contrasting with lower levels observed in Indonesia, Papua-New Guinea, Malaysia, Cambodia, and Myanmar. Lobeto, H, Semedo, A., Lemos, G., Dastgheib, A., Menendez, M., Ranasinghe, R., Bidlot, R. (2024). Global coastal wave storminess. Scientific Reports (in press).

Climate change poses a formidable strain on societies worldwide, demanding viable and timely adaptation measures to ensure future prosperity while avoiding the impact of more frequent and intense extreme events, like wildfires, that affect all continents and biomes, leaving authorities grappling to respond effectively. Here, we focus on mainland Portugal that is inserted in the Mediterranean climate change hotspot and investigate the impact of different adaptation strategies on wildfire risk. Relying on an ensemble of regional climate models from the EURO-CORDEX initiative, we project fire weather index and fire radiative power for various representative concentration pathways (RCPs). Our findings reveal that very energetic fires, with energy release exceeding 1000 MW, may increase up to more than three-fold, depending on the RCP. Even under strong mitigation scenarios, the likelihood of having megafires increases by 1.5-fold. This underscores the need for proactive adaptation regardless of mitigation efforts. We present three different ignition avoidance strategies under different climate change scenarios. For all cases results indicate that a reduction between 20 and 60% is achievable for intense wildfires (above 1000 MW).