Sandra Marta Nobre Plecha
@fc.ul.pt
DEGGE/FCUL
IDL/FCUL
Scopus Publications
Scholar Citations
Scholar h-index
Scholar i10-index
Scopus Publications
Gerard D. McCarthy, Sandra Plecha, Guillaume Charria, Amélie Simon, Coline Poppeschi, and Ana Russo
Wiley
Amélie Simon, Coline Poppeschi, Sandra Plecha, Guillaume Charria, and Ana Russo
Copernicus GmbH
Abstract. The latest Intergovernmental Panel on Climate Change (IPCC) report describes an increase in the number and intensity of marine heatwaves (MHWs) and a decrease in marine cold spells (MCSs) in the global ocean. However, these reported changes are not uniform on a regional to local basis, and it remains unknown if coastal areas follow the open-ocean trends. Surface ocean temperature measurements collected by satellites (from 1982–2022) and 13 coastal buoys (from 1990–2022) are analyzed in the northeastern Atlantic and three subregions: the English Channel, Bay of Brest and Bay of Biscay. The activity metric, combining the number of events, intensity, duration and spatial extent, is used to evaluate the magnitude of these extreme events. The results from in situ and satellite datasets for each of the studied regions are quite in agreement, although the satellite dataset underestimates the amplitude of activity for both MHWs and MCSs. This supports the applicability of the method to both in situ and satellite data, albeit with caution on the amplitude of these events. Also, this localized study in European coastal northeastern Atlantic water highlights that similar changes are being seen in coastal and open oceans regarding extreme events of temperature, with MHWs being more frequent and longer and extending over larger areas, while the opposite is seen for MCSs. These trends can be explained by changes in both the mean of and variance in sea-surface temperature. In addition, the pace of evolution and dynamics of marine extreme events differ among the subregions. Among the three studied subregions, the English Channel is the region experiencing the strongest increase in summer MHW activity over the last 4 decades. Summer MHWs were very active in the English Channel in 2022 due to long events, in the Bay of Biscay in 2018 due to intense events and in the Bay of Brest in 2017 due to a high occurrence of events. Winter MCSs were the largest in 1987 and 1986 due to long and intense events in the English Channel. Finally, our findings suggest that at an interannual timescale, the positive North Atlantic Oscillation favors the generation of strong summer MHWs in the northeastern Atlantic, while low-pressure conditions over northern Europe and a high off the Iberian Peninsula in winter dominate for MCSs. A preliminary analysis of air–sea heat fluxes suggests that, in this region, reduced cloud coverage is a key parameter for the generation of summer MHWs, while strong winds and increased cloud coverage are important for the generation of winter MCSs.
Amelie Simon, Sandra M. Plecha, Ana Russo, Ana Teles-Machado, Markus G. Donat, Pierre-Amael Auger, and Ricardo M. Trigo
Frontiers Media SA
Marine temperature extremes are anomalous ocean temperature events, often persisting over several weeks or longer, with potential impacts on physical and ecological processes that often encompass socio-economic implications. In recent years, a considerable effort has been directed at the development of metrics allowing an objective characterization of both marine heatwaves (MHWs) and marine cold spells (MCSs). However, the majority of these metrics do not consider explicitly the spatial extent of the events. Here, we rank and evaluate the relative importance of marine temperature extreme events thanks to a metric, called activity, that combines the number of events, duration, intensity and spatial extent. According to this definition, in the Mediterranean basin between 1982 and 2021, summer 2018 experienced slightly more MHW activity than summer 2003, documented as an exceptional extreme event. Besides, MHW activities were higher in the last two decades while winter MCS activities were higher in the 1980s-1990s. The highest MHW activities occurred preferentially in the western Mediterranean while the strongest MCS activities took place preferentially in the eastern Mediterranean. Moreover, the duration, mean intensity, and activity of the three strongest MHWs are twice as high as those of the three strongest MCSs. The long-term tendency of extreme events activity shows an accelerated increase for summer MHWs (about +150°C.days.10⁶km²) and a linear decrease for winter MCSs in the Mediterranean (about -60°C.days.10⁶km²) over the last four decades.
Andrea Casaucao, Enrique González-Ortegón, María P. Jiménez, Ana Teles-Machado, Sandra Plecha, Alvaro J. Peliz, and Irene Laiz
Elsevier BV
Abstract Modelling the environmental factors influencing the spatial variation of fish early life stages density and their drift history can identify the key biological and physical processes for the recruitment variability. Distance-based linear multivariate techniques were used to characterize the spawning areas of the European anchovy Engraulis encrasicolus in the Gulf of Cadiz (GoC). Chlorophyll is the environmental variable that best characterized its spawning areas with a time-lag of three days. The use of Lagrangian models to simulate the dispersal of small pelagic species more dependent on advection such as the European anchovy early life stages (early larvae and eggs) in the GoC could provide the degree of connectivity between spawning and nursery areas and identify the physical drivers of the recruitment variability. The larval final destination is critical for the survival of a marine species which is coastal-dependent during its early life stages. Simulations with a Lagrangian transport model in the Southwest Iberian Peninsula were performed during the most intense spawning peak of 2016, when a strong and persistent countercurrent event developed. Most of the simulated early life stages were transported to the western Portuguese coast and, to a lesser extent, to the Atlantic oligotrophic waters, suggesting an increase in the connectivity between the subdivision 9a South and West components. Although different environmental processes occurring during ontogenetic stages, as well as overfishing, among others, can explain part of the variability observed in recruitment, events such as the development of coastal countercurrents during the spawning season could partly account for an increase of anchovy on the western Portuguese coast and a decrease in the Gulf of Cadiz one year later.
Pedro Mateus, Virgílio B. Mendes, and Sandra M. Plecha
MDPI AG
The neutral atmospheric delay is one of the major error sources in Space Geodesy techniques such as Global Navigation Satellite Systems (GNSS), and its modeling for high accuracy applications can be challenging. Improving the modeling of the atmospheric delays (hydrostatic and non-hydrostatic) also leads to a more accurate and precise precipitable water vapor estimation (PWV), mostly in real-time applications, where models play an important role, since numerical weather prediction models cannot be used for real-time processing or forecasting. This study developed an improved version of the Hourly Global Pressure and Temperature (HGPT) model, the HGPT2. It is based on 20 years of ERA5 reanalysis data at full spatial (0.25° × 0.25°) and temporal resolution (1-h). Apart from surface air temperature, surface pressure, zenith hydrostatic delay, and weighted mean temperature, the updated model also provides information regarding the relative humidity, zenith non-hydrostatic delay, and precipitable water vapor. The HGPT2 is based on the time-segmentation concept and uses the annual, semi-annual, and quarterly periodicities to calculate the relative humidity anywhere on the Earth’s surface. Data from 282 moisture sensors located close to GNSS stations during 1 year (2020) were used to assess the model coefficients. The HGPT2 meteorological parameters were used to process 35 GNSS sites belonging to the International GNSS Service (IGS) using the GAMIT/GLOBK software package. Results show a decreased root-mean-square error (RMSE) and bias values relative to the most used zenith delay models, with a significant impact on the height component. The HGPT2 was developed to be applied in the most diverse areas that can significantly benefit from an ERA5 full-resolution model.
Sandra M. Plecha, Pedro M. M. Soares, Susana M. Silva-Fernandes, and William Cabos
Springer Science and Business Media LLC
Marine Heatwave (MHW) events have been increasing all around the world, causing severe impacts on marine ecosystems and on the economy of the aquaculture, fishing and tourism industries. In this study, the occurrence and characteristics of MHW events in the North Atlantic are analyzed for a recent period (1971–2000) and the two future periods (2041–2070 and 2071–2100). The analysis is based on Sea Surface Temperature (SST) data obtained from observations and from Global Climate Models (GCM) in the CMIP5 archieve. The results show that the GCMs present significant shortcomings in reproducing the SST and MHWs. The model results regarding the recent trends in MHW are in agreement with the ones observed, although they underestimate the values of MHW intensity and overestimate the values of both frequency and duration of events. The MHWs observed occur at a mean frequency of 1.90 events per year and are characterized by ~ 13 days of mean duration and 0.37 ºC of mean intensity, while the multi-model ensemble mean characterizes the events with 12 additional days and 0.15 ºC less intensity. Under climate change scenarios, when considering a stationary threshold, the models project noticeable increases in MHW event intensity that could reach 2 ºC above the 90th percentile and a quasi-permanent state of MHW by the end of the century. When a non-stationary threshold is considered, the characteristics of the events are similar to those obtained during the historical period. The GCMs significant biases in simulating the SST and leading to extremes like MHWs highlight the importance of improving GCM performance.
I. Laiz, S. Plecha, A. Teles-Machado, E. González-Ortegón, D. Sánchez-Quiles, A. Cobelo-García, D. Roque, A. Peliz, R.F. Sánchez-Leal, and A. Tovar-Sánchez
Elsevier BV
The GoC shelf waters present much higher concentrations of dissolved Cu, Cd, and Zn than other coastal areas, constituting an important source of these elements onto its neighbouring basins, i.e., the Atlantic Ocean and the Mediterranean Sea. In this study we assessed the role of the GoC surface currents in the trace metals transport. For this purpose, ten dissolved (<0.22 µm) trace metals were sampled (Ag, Cd, Co, Cu, Fe, Mo, Ni, Pb, Zn, V) along the GoC continental shelf, and their spatial and temporal distribution was interpreted according to the surface circulation. Results show that the complex surface circulation over the shelf confines the metals concentration mainly along the inner shelf and determines their transport patterns: under southeastward currents, Cd, Co, Cu, Ni, and Pb are transported toward the Mediterranean Sea; under northwestward countercurrents, Cd, Co, Cu, Fe, Ni, and Zn are transported toward the southern and, occasionally, the western Portuguese shelf; under variable currents, Ag, Cd, Co, Cu, Fe, Pb, and Zn tend to accumulate near their source. Considering that some of these metals have not been analysed before in this region (Ag, Mo, V), or that the spatial distribution of certain metals (Ag, Fe, Mo, Pb, V) has not been interpreted in terms of the ocean circulation, this work could be considered as a baseline study for future comparisons.
Silja Frankenbach, João Ezequiel, Sandra Plecha, Johannes W. Goessling, Leandro Vaz, Michael Kühl, João Miguel Dias, Nuno Vaz, and João Serôdio
Frontiers Media SA
Tidal estuaries are regarded as highly important ecosystems, mostly due to their high primary productivity and associated role as carbon sinks. In these ecosystems, primary productivity is mainly due to the photosynthetic carbon fixation by phytoplankton and microphytobenthos. The productivity of the two communities has been mostly studied separately, and directly comparable estimates of their carbon fixation rates in the same estuary are relatively scarce. The present study aimed to characterize the spatio-temporal variability of the productivity of phytoplankton and microphytobenthos in a tidal estuary, the Ria de Aveiro (Portugal). The productivity of the two communities was determined using a common methodological approach, based on measurements of in vivo chlorophyll fluorescence, allowing the estimation of the annual ecosystem-level budget for carbon fixation by the two groups. Productivity rates were determined based on synoptic in situ measurements of absolute rates of electron transport rate of photosystem II, using Pulse Amplitude Modulation fluorometry. Chlorophyll fluorescence indices were accompanied by measurements of salinity, temperature, water turbidity, solar irradiance, and planktonic and benthic microalgal biomass. Measurements were carried out hourly, along four spring-neap tidal cycles distributed along 1 year, on three sites of the estuary. The most pronounced trends in the spatio-temporal variability of the photophysiology and productivity of the two communities were the following: (i) maximum biomass and productivity were reached later for microphytobenthos (summer-autumn) than for phytoplankton (spring-summer); (ii) the absorption cross-section of PSII was generally higher for phytoplankton; (iii) the two groups showed a similar photoacclimation state, but microphytobenthos appeared as high light-acclimated when compared to phytoplankton. Biomass-specific productivity was on average higher for phytoplankton than for microphytobenthos, averaging 68.0 and 19.1 mg C mg Chl a–1 d–1, respectively. However, areal depth-integrated production rates were generally higher for the microphytobenthos than for the phytoplankton, averaging 264.5 and 140.0 mg C m–2 d–1, respectively. On an annual basis, phytoplankton productivity averaged 49.9 g C m–2 yr–1 while the productivity of microphytobenthos averaged 105.2 g C m–2 yr–1. When upscaling to the whole estuary, annual primary production rates of phytoplankton and microphytobenthos reached 4894.3 and 7534.0 t C yr–1, respectively, representing 39.4 and 60.6% of the combined total of 12428.3 t C yr–1 determined for the two communities in the Ria de Aveiro.
Sandra M Plecha and Pedro M M Soares
IOP Publishing
Abstract In recent years, research related to the occurrence of marine heatwave (MHW) events worldwide has been increasing, reporting severe impacts on marine ecosystems which led to losses of marine biodiversity or changes in world fisheries. Many of these studies, based on regional and global coupled models, show relevant biases in the MHW properties when compared with observations. In this study, the MHW frequency of occurrence, the duration and mean intensity over the global oceans are characterized, taking advantage of the new global climate model (GCM) dataset, from the Coupled Model Project Intercomparison Phase 6 (CMIP6). The MHWs result for the historical period are compared with observations, and the future projected changes are characterized under three socioeconomic pathways (SSPs) (SSP1, SSP2 and SSP5), for the middle and end of century (2041–2070 and 2071–2100). The results show a reasonable agreement between the modeled and observed MHW property trends, indicating increases in the frequency, duration and intensity of MHWs along the historical period. For the period 1982–2014, both the ∼2 mean observed events per year and the mean intensity of 0.35 °C above the threshold are underestimated by the multi-model ensemble (MME) mean by 21% and 31%, respectively, while the observed duration of ∼12 d are overestimated by 100%. The future MHWs are expected to increase in duration and intensity, where a near permanent MHW occurs with reference to the historical climate conditions, mainly by the end of the 21st century. The future MHWs intensity, projected by the MME mean, increases in the range of 0.2 °C to 1.5 °C, from the least to the most severe pathways. The GCMs biases obtained with CMIP6 revealed to be in line with the CMIP5 biases, reinforcing the need to use high spatial resolution models to characterize MHW.
N. Vaz, M. Mateus, S. Plecha, M.C. Sousa, P.C. Leitão, R. Neves, and J.M. Dias
Elsevier BV
Abstract This work studies the influence of the Tagus estuary, Portugal, on the near coastal system using a model application to describe the main physical and biogeochemical processes in the Region of Freshwater Influence (ROFI). It was used as nested modeling approach, downscaling the solution for the general circulation from a larger domain model (the Portuguese coast), to the local Tagus estuary domain. The model is evaluated during a very dynamic and biologic productive period of the year, corresponding to the winter and early summer (January–May 2007). Also during this period, there is a strong freshwater inflow into the Tagus estuary, which in turn modulates the estuarine outflow to the Tagus ROFI. The results focus on water temperature and chlorophyll and a skill assessment was made, given the lack of data required to perform a thorough validation. Simulation results reveal an adequate reproduction of the vertical thermal structure and chlorophyll concentrations. While a fairly reasonable agreement is seen for water temperature, showing no significant thermal stratification at the study area (average surface-to-bottom difference ranging from 1.3 °C to 1.6 °C), chlorophyll vertical profiles show some differences between the model results and the measurements. Maximum model bias for surface temperature is 1.4 °C and ranges from 1 to 2 mg m− 3 for chlorophyll, revealing an underestimation of the predicted chlorophyll and surface temperature for the area in the vicinity of the Tagus mouth. The general trends of surface chlorophyll and surface water temperature are satisfactorily reproduced by the model.
Sandra Plecha, Ana Picado, Pedro Chambel-Leitão, João M. Dias, and Nuno Vaz
Coastal Education and Research Foundation
ABSTRACT Plecha, S., Picado, A., Chambel-Leitão, P., Dias, J.M., Vaz, N., 2014. Study of suspended sediment dynamics in a temperate coastal lagoon: Ria de Aveiro (Portugal). In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 604–609, ISSN 0749-0208. Suspended sediment concentrations are simulated at Ria de Aveiro, a lagoon located in a temperate climate area in the northwest of Portugal. The fine-grained suspended sediment concentration is analyzed using the numerical model MOHID (www.mohid.com) and spatial maps of instantaneous and maximum concentration and also temporal variability at specified locations are analyzed in order to characterize the influence of the tide and sea level conditions in the suspended sediment concentrations within the lagoon. The highest suspended sediment concentrations were found in upstream areas during ebb conditions due to the river's proximity, while the minimum concentrations were observed near the inlet due to the presence of marine water poor in suspended sediments. When a 0.42 m sea-level rise (an estimate of conditions in 2100) is modelled, a decrease in suspended sediment concentration is observed for the overall study area, as result of an increase in the tidal prism.
Sandra Plecha, Paulo A. Silva, Anabela Oliveira, and João M. Dias
Springer Science and Business Media LLC
The morphologic changes in estuaries and coastal lagoons are very complex and constitute a challenging task in coastal research. The bathymetric changes result from the combined action of tides, waves, rivers discharge and wind stress in the area of interest. Additionally, an accurate knowledge of the sediment transport is essential to achieve a good morphological characterization. This work establishes the influence of the wave climate on the morphodynamics of the Ria de Aveiro lagoon inlet by analysing the numerical results of the morphodynamic modelling system MORSYS2D. The numerical simulations considered a realistic coupled forcing of tidal currents and waves. The computed sediment fluxes and bathymetric changes are analysed and compared with the erosion and accretion trends obtained from the numerical simulations forced only by tidal currents, in order to establish the wave climate influence. The final bathymetry and the corresponding changes are compared with bathymetric data collected through surveys. It is concluded that: (a) the morphodynamics of the study area is dominated by the wave regime in the lagoon inlet and nearshore areas, while in the inner areas is tidally dominated; and (b) the inclusion of the wave regime forcing constitutes an improvement in order to accurately reproduce the local morphodynamics.
Sandra Plecha, Carina L. Lopes, Nicolas Bruneau, Nuno A. Ribeiro, Paulo A. Silva, André B. Fortunato, and João M. Dias
Coastal Engineering Research Council
The wave regime has a strong influence on the sediment transport in coastal systems. Modifications in wave regime induced by climate changes can influence the sediment dynamics of those coastal systems. To access wave regime changes it is crucial to analyse the future modifications in the wave height, period and direction. This work aims to analyse the influence of a future wave regime in the sediment budget of a coastal lagoon inlet and at the nearshore adjacent coast. To achieve this goal a morphodynamic modelling system was used, forced by present and future waves, corresponding to a typical year of present and future wave climates. A methodology to determine a typical year of each climate was developed based on the determination of correlation coefficients between each climate and corresponding year data. The comparison between present and future wave climates evidences that wave period and height are in general similar for both climates, and confirms the anticlockwise rotation of waves in the future. The morphodynamic simulations revealed analogous results for both wave climates, resulting in similar patterns for the residual sediment fluxes, but slightly more intense in the present. The consequent bathymetric changes show that the deposition trend presently observed offshore the inlet tends to increase for future waves climate. The transport budgets were also analysed for both wave regimes, evidencing that the alongshore transport slightly decreases (~1%) for future waves.
Carina L. Lopes, Paulo A. Silva, João M. Dias, Alfredo Rocha, Ana Picado, Sandra Plecha, and André B. Fortunato
Elsevier BV
Abstract Sea level change is an important consequence of climate change due to its impact on society and ecosystems. Analyses of tide-gauge data have indicated that the global sea level has risen during the 20th century and several studies predict that the mean sea level will continue to rise during the 21st century, intensifying coastal hazards worldwide. In Portugal, the Ria de Aveiro is expected to be one of the regions most affected by sea level change. The main aim of this study is to evaluate the potential impacts of the mean sea level change on the hydrodynamics and morphodynamics of the Ria de Aveiro. With this purpose, local mean sea level change was projected for the period 2091–2100 relative to 1980–1999, for different Special Report on Emission Scenarios (SRES) scenarios developed by the Intergovernmental Panel on Climate Change (IPCC). These projections revealed an increase in the mean sea level between 0.28 m under scenario B1 and 0.42 m under scenario A2. The results obtained for sea level rise scenario A2 projection were used to force the morphodynamic model MORSYS2D, previously implemented for the Ria de Aveiro. The modelling results were compared with model forecasts for the present sea level. The residual sediment transport and its balance at the lagoon inlet were computed and analysed for both situations. While the residual sediment transport is generally seaward, sediments tend to deposit inside the inlet due to the weak sediment transport at its mouth. The direction of the residual flux will not change with the sea level rise, but sediment fluxes will intensify, and accretion inside the inlet will increase. The rise in mean sea level will also affect the lagoon hydrodynamics. The tidal prism at the lagoon mouth will increase by about 28% in spring tide. In the lower lagoon only a slight increase of the tidal asymmetry is predicted.
Sandra Plecha, Paulo A. Silva, Nuno Vaz, Xavier Bertin, Anabela Oliveira, André B. Fortunato, and João M. Dias
Springer Science and Business Media LLC
This work investigates the recent morphological changes at the inlet of a complex coastal system (Ria de Aveiro lagoon, Portugal). This study was carried out using bathymetric data analysis and numerical simulations obtained with the 2DH morphodynamic modelling system MORSYS2D. The present simulations considered only tidal forcing, and a sensitivity analysis was performed by tuning the formula used to compute the sediment transports. A non-uniform sediment grain size distribution for the Ria de Aveiro inlet is considered in the numerical simulations, based on surveys performed in this area. The model results are analysed to assess if they resemble the observed trends of erosion and deposition, as calculated from bathymetric data. A quantitative analysis of the differences between the bathymetric changes obtained through surveys and the numerical results over a period of 3 years considering different sediment transport formulations shows that the formulations of Ackers and White (1973) and Engelund and Hansen (1967) are the ones that best describe the morphodynamic changes driven by tides in the Ria de Aveiro inlet.