Marta Marcos

Sea level extremes in southern Europe

Knowledge of sea level extremes is important for coastal planning purposes. Temporal changes in the extremes may indicate changes in the forcing parameters, most probably the storm surges. Sea level extremes and their spatial and temporal variability in southern Europe are explored on the basis of 73 tide gauge records from 1940. This study uses all data available to infer risks at the coast caused by extreme sea levels. Extreme values of 250 cm are observed at the Atlantic coasts with smaller values in the Mediterranean where, with the exception of the Strait of Gibraltar and the Adriatic Sea, the extreme values are less than 60 cm. At the Adriatic Sea values of up to 200 cm are found. When the tidal contribution is removed the differences between the various areas reduce. The spatial distribution of the extremes of the tidal residuals is well represented by the hindcast of a two-dimensional hydrodynamic model forced by the atmospheric pressure and the wind, although the model underestimates the extremes. Higher return levels (200–300 cm for the 50-year return level) are observed in the Atlantic stations due to the larger tides. In the Mediterranean, higher values are found in the northern Adriatic (between 150 and 200 cm) while in the rest of the domain they vary between 20 and 60 cm. The nonlinear interaction between tides and surges is negligible in the Mediterranean, thus the joint tides-surges distribution can be applied. The interannual and decadal variability in time of extremes is caused by mean sea level changes.

Health-related quality of life of patients with HIV: impact of sociodemographic, clinical and psychosocial factors.

Objectives: This study aims to analyse how a wide group of clinical, social, demographic and psychological factors are related to both physical and mental quality of life in HIV+ patients. Design: A cross-sectional study was carried out of 320 HIV+ patients in antiretroviral treatment who attended infectious diseases units in four hospitals in the region of Andalusia (Spain). Methods: Health-Related Quality of Life was measured by the MOS-HIV. Included as independent variables were: sociodemographic variables, variables related to antiretroviral therapy, psychosocial variables like social support (Duke-UNC-11) and psychological morbidity (GHQ-28), variables related to main risk behaviours and clinical variables. Results: In the multiple linear regression analysis, a better PHS quality of life was found to be associated with the absence of mental illness, social support, not being an intravenous drug user and using more than one type of non-injectable drug. A better quality of life, in mental terms, was found to be associated with fewer years as a non-intravenous drug user, having social support, absence of mental illness, not being an intravenous drug user taking only one additional pill, not having any difficulty in taking the medication, and being female. Conclusions: The study of other non-biological factors that may be related to quality of life has been limited practically to social support and the emotional state. This study highlights the importance of these factors independently from the clinical state, as well as the existence of other psychological and behavioural factors that are also related.

Coastal sea level rise in southern Europe and the nonclimate contribution of vertical land motion

[1] In this study, we extend the advanced approach of combining tide gauge and satellite altimetry data with supplemental equations from adjacent tide gauge records of at least 30 years of common data to investigate the relative importance of the nonclimate contribution of vertical land movement to the observed rates of sea level change along the coasts of southern Europe. The sensitivity tests proved that the advanced approach is robust and accurate at the submillimeter per year level of around 0.4 mm yr � 1 in estimating rates of vertical land movements. It enabled identifying stations displaying large rates of vertical land movements that must be taken into account when predicting future sea level rise and appraising the exposure to its impacts on populations and assets. The average rate of coastal climate-related sea level rise in the Mediterranean Sea was consequently revisited to be of 1.7 mm yr � 1 over the past century, whereas the Atlantic northern Iberian coast revealed a significant high rate of sea level rise in excess of 3.4 mm yr � 1 for the past 70 years. Future work should consider applying this powerful approach to other geographic contexts as a useful source of supplementary data for geodynamic studies.

Vertical land motion as a key to understanding sea level change and variability

Vertical land motions are a key element in understanding how sea levels have changed over the past century and how future sea levels may impact coastal areas. Ideally, to be useful in long-term sea level studies, vertical land motion should be determined with standard errors that are 1 order of magnitude lower than the contemporary climate signals of 1 to 3 mm/yr observed on average in sea level records, either using tide gauges or satellites. This metrological requirement constitutes a challenge in geodesy. Here we review the most successful instrumental methods that have been used to determine vertical displacements at the Earth’s surface, so that the objectives of understanding and anticipating sea levels can be addressed adequately in terms of accuracy. In this respect, the required level of uncertainty is examined in two case studies (global and local). A special focus is given to the use of the Global Positioning System (GPS) and to the combination of satellite radar altimetry with tide gauge data. We update previous data analyses and assess the quality of global satellite altimetry products available to the users for coastal applications. Despite recent advances, a near-plateau level of accuracy has been reached. The major limitation is the realization of the terrestrial reference frame, whose physical parameters, the origin and the scale factor, are beyond the scope of a unique technique such as the GPS. Additional practical but nonetheless important issues are associated with the installation of GPS antennas, such as ensuring that there is no unknown differential vertical motion with the tide gauge.

Comparing the sea level response to pressure and wind forcing of two barotropic models: Validation with tide gauge and altimetry data

The sea level output from two barotropic models, Hindcast of Dynamic Processes of the Ocean and Coastal Areas of Europe (HIPOCAS) and Dynamic Atmospheric Correction (DAC), are compared and evaluated on the basis of coastal tide gauges (TG) and TOPEX/POSEIDON measurements in the Mediterranean Sea and the NE Atlantic Ocean for the period 1993–2001. Both models reduce the observed sea level variance more than the classical inverted barometer correction. However, differences between the models arise for different regions and frequency bands. In coastal areas, Hindcast of Dynamic Processes of the Ocean and Coastal Areas of Europe (HIPOCAS) reproduces observed (TG recorded) sea level better than DAC (residual variance of 70.81 ± 0.69 cm2 versus 74.05 ± 0.68 cm2). This is particularly true in the Atlantic Iberian coasts (49.58 ± 1.09 cm2 versus 68.53 ± 1.12 cm2), where HIPOCAS is able to reproduce a wind-generated signal probably linked with seasonal upwelling. The exception is the northern Adriatic, where HIPOCAS gives higher residual variance than DAC (118.80 ± 0.60 cm2 versus 107.15 ± 0.60 cm2). At low frequencies (T > 20 days) the atmospherically induced coastal sea level is better reproduced by HIPOCAS in the entire domain (23.43 ± 0.34 cm2 versus 32.35 ± 0.33 cm2). At high frequencies (T < 20 days), DAC and HIPOCAS perform on average similarly (37 ± 0.5 cm2). In the open ocean, both corrections provide equivalent results (60 ± 5 cm2 residual altimeter variance). Our general recommendation would be to use either DAC or HIPOCAS for the correction of altimetry, and to use HIPOCAS for coastal studies aiming at separating the atmospheric contribution to sea level variability from the steric and mass contributions.

Reassessment of 20th century global mean sea level rise

Significance Estimates of global mean sea level (GMSL) before the advent of satellite altimetry vary widely, mainly because of the uneven coverage and limited temporal sampling of tide gauge records, which track local sea level rather than the global mean. Here we introduce an approach that combines recent advances in solid Earth and geoid corrections for individual tide gauges with improved knowledge about their geographical representation of ocean internal variability. Our assessment yields smaller trends before 1990 than previously reported, leading to a larger overall acceleration; identifies three major explanations for differences with previous estimates; and reconciles observational GMSL estimates with the sum of individually modeled contributions from the Coupled Model Intercomparison Project 5 database for the entire 20th century. The rate at which global mean sea level (GMSL) rose during the 20th century is uncertain, with little consensus between various reconstructions that indicate rates of rise ranging from 1.3 to 2 mm⋅y−1. Here we present a 20th-century GMSL reconstruction computed using an area-weighting technique for averaging tide gauge records that both incorporates up-to-date observations of vertical land motion (VLM) and corrections for local geoid changes resulting from ice melting and terrestrial freshwater storage and allows for the identification of possible differences compared with earlier attempts. Our reconstructed GMSL trend of 1.1 ± 0.3 mm⋅y−1 (1σ) before 1990 falls below previous estimates, whereas our estimate of 3.1 ± 1.4 mm⋅y−1 from 1993 to 2012 is consistent with independent estimates from satellite altimetry, leading to overall acceleration larger than previously suggested. This feature is geographically dominated by the Indian Ocean–Southern Pacific region, marking a transition from lower-than-average rates before 1990 toward unprecedented high rates in recent decades. We demonstrate that VLM corrections, area weighting, and our use of a common reference datum for tide gauges may explain the lower rates compared with earlier GMSL estimates in approximately equal proportion. The trends and multidecadal variability of our GMSL curve also compare well to the sum of individual contributions obtained from historical outputs of the Coupled Model Intercomparison Project Phase 5. This, in turn, increases our confidence in process-based projections presented in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change.

Detecting anthropogenic footprints in sea level rise

While there is scientific consensus that global and local mean sea level (GMSL and LMSL) has risen since the late nineteenth century, the relative contribution of natural and anthropogenic forcing remains unclear. Here we provide a probabilistic upper range of long-term persistent natural GMSL/LMSL variability (P=0.99), which in turn, determines the minimum/maximum anthropogenic contribution since 1900. To account for different spectral characteristics of various contributing processes, we separate LMSL into two components: a slowly varying volumetric component and a more rapidly changing atmospheric component. We find that the persistence of slow natural volumetric changes is underestimated in records where transient atmospheric processes dominate the spectrum. This leads to a local underestimation of possible natural trends of up to ∼1 mm per year erroneously enhancing the significance of anthropogenic footprints. The GMSL, however, remains unaffected by such biases. On the basis of a model assessment of the separate components, we conclude that it is virtually certain (P=0.99) that at least 45% of the observed increase in GMSL is of anthropogenic origin.

Long‐term variations in global sea level extremes

Decadal to multidecadal variations in sea level extremes unrelated to mean sea level changes have been investigated using long tide gauge records distributed worldwide. A state space approach has been applied that provides robust solutions and uncertainties of the time evolving characteristics of extremes, allowing for data gaps and uneven sampling, both common features of historical sea level time series. Two different models have been formulated for the intensity and for the occurrence of extreme sea level events and have been applied independently to each tide gauge record. Our results reveal two key findings: first, the intensity and the frequency of occurrence of extreme sea levels unrelated to mean sea level vary coherently on decadal scales in most of the sites examined (63 out of 77) and, second, extreme sea level changes are regionally consistent, thus pointing toward a common large-scale forcing. This variability of extremes associated with climate drivers should be considered in the framework of climate change studies.

Evidence for a differential sea level rise between hemispheres over the twentieth century

Tide gauge records are the primary source of sea level information over multidecadal to century timescales. A critical issue in using this type of data to determine global climate-related contributions to sea level change concerns the vertical motion of the land upon which the gauges are grounded. Here we use observations from the Global Positioning System for the correction of this vertical land motion. As a result, the spatial coherence in the rates of sea level change during the twentieth century is highlighted at the local and the regional scales, ultimately revealing a clearly distinct behavior between the Northern and the Southern Hemispheres with values of 2.0 mm/yr and 1.1 mm/yr, respectively. Our findings challenge the widely accepted value of global sea level rise for the twentieth century.

Annual Sea Level Changes on the North American Northeast Coast: Influence of Local Winds and Barotropic Motions

AbstractUnderstanding the relationship between coastal sea level and the variable ocean circulation is crucial for interpreting tide gauge records and projecting sea level rise. In this study, annual sea level records (adjusted for the inverted barometer effect) from tide gauges along the North American northeast coast over 1980–2010 are compared to a set of data-assimilating ocean reanalysis products as well as a global barotropic model solution forced with wind stress and barometric pressure. Correspondence between models and data depends strongly on model and location. At sites north of Cape Hatteras, the barotropic model shows as much (if not more) skill than ocean reanalyses, explaining about 50% of the variance in the adjusted annual tide gauge sea level records. Additional numerical experiments show that annual sea level changes along this coast from the barotropic model are driven by local wind stress over the continental shelf and slope. This result is interpreted in the light of a simple dynamic...