La afección del cambio climático a las costas españolas

La costa española está sometida a una altísima presión de origen antrópico, que se verá fuertemente agravada por el cambio climático. Este artículo pretende dar una visión general sobre cuál es el estado del conocimiento y de algunas de las acciones que se han emprendido en España para hacer frente al cambio climático en la costa. Además de mostrar los instrumentos de gobernanza más importantes, se presenta una visión general sobre las proyecciones de la dinámica costera y sus efectos sobre algunos sectores críticos, haciendo especial énfasis sobre el papel de la ingeniería civil para afrontar este reto

Neglecting the effect of long- and short-term erosion can lead to spurious coastal flood risk projections and maladaptation

ABSTRACT: Flooding and erosion are among the most relevant hazards for coastal regions and although they are linked, their inherent complexity has typically led them to be addressed separately, potentially leading to highly uncertain estimates. This paper has three aims: (a) to present a methodology for coupling coastal flood projections with shoreline changes; (b) to quantify the effects of neglecting the coupling of flooding and erosion on future projections at a case study location; and (c) to analyse the relative importance of the climate-related uncertainty sources. We use a suite of statistical, process-based, and physics-based models to generate and downscale storms, compute water levels affected by storm morphodynamics and long-term profile changes and propagate flooding over topo-bathymetries that are in turn modified to incorporate the impact of sea-level rise, longshore sediment transport and storm-driven erosion. We sample climate uncertainty by considering storm variability (synthetic generation) and ensembles of radiative forcing scenarios, regional climate models, and sea-level rise trajectories. For illustration purposes, we consider a 40-km coastal stretch in the Spanish Mediterranean. We find that if the effect of erosion is neglected, the mean values of the total water level and flooded area can be either over- or underestimated by up to 18% and 22%, and up to 7% and 85%, respectively, with respect to our coupled results. The factors that most influence total water levels are storm erosion and profile geometry, highlighting the relevance of using real profiles in shoreface translation. In the flooded area, longshore transport can play a fundamental enhancing role. We also find that the coupling approach used can contribute more to the projection of flooded areas than the choice of climate models and sea-level rise trajectories even by 2100 (up to 76% versus 8% and 16%, respectively). We conclude that neglecting erosion effects on coastal flooding can have management implications, especially for urban beaches, leading to poor adaptation planning and maladaptation.This study was partially funded by the Spanish Government through the grant COASTALfutures (PID2021-126506OB-100); the Government of Cantabria through the FENIX Project; and the European Union’s Horizon 2020 CoCliCo Project (grant agreement No 101003598). AT and MA-C are also funded by the Spanish Ministry of Science and Innovation through the Ramon y Cajal Programme (RYC2021-030873-I) and the FPI studentship (PRE-2018-085009), respectively

Which data assimilation method to use and when: unlocking the potential of observations in shoreline modelling

Shoreline predictions are essential for coastal management. In this era of increasing amounts of data from different sources, it is imperative to use observations to ensure the reliability of shoreline forecasts. Data assimilation has emerged as a powerful tool to bridge the gap between episodic and imprecise spatiotemporal observations and the incomplete mathematical equations describing the physics of coastal dynamics. This research seeks to maximize this potential by assessing the effectiveness of different data assimilation algorithms considering different observational data characteristics and initial system knowledge to guide shoreline models towards delivering results as close as possible to the real world. Two statistical algorithms (stochastic ensemble and extended Kalman filters) and one variational algorithm (4D-Var) are incorporated into an equilibrium cross-shore model and a one-line longshore model. A twin experimental procedure is conducted to determine the observation requirements for these assimilation algorithms in terms of accuracy, length of the data collection campaign and sampling frequency. Similarly, the initial system knowledge needed and the ability of the assimilation methods to track the system nonstationarity are evaluated under synthetic scenarios. The results indicate that with noisy observations, the Kalman filter variants outperform 4D-Var. However, 4D-Var is less restrictive in terms of initial system knowledge and tracks nonstationary parametrizations more accurately for cross-shore processes. The findings are demonstrated at two real beaches governed by different processes with different data sources used for calibration. In this contribution, the coastal processes assimilated thus far in shoreline modelling are extended, the 4D-Var algorithm is applied for the first time in the field of shoreline modelling, and guidelines on which assimilation method can be most beneficial in terms of the available observational data and system knowledge are provided.

Future behavior of wind wave extremes due to climate change

ABSTRACT: Extreme waves will undergo changes in the future when exposed to different climate change scenarios. These changes are evaluated through the analysis of significant wave height (Hs) return values and are also compared with annual mean Hs projections. Hourly time series are analyzed through a seven-member ensemble of wave climate simulations and changes are estimated in Hs for return periods from 5 to 100 years by the end of the century under RCP4.5 and RCP8.5 scenarios. Despite the underlying uncertainty that characterizes extremes, we obtain robust changes in extreme Hs over more than approximately 25% of the ocean surface. The results obtained conclude that increases cover wider areas and are larger in magnitude than decreases for higher return periods. The Southern Ocean is the region where the most robust increase in extreme Hs is projected, showing local increases of over 2 m regardless the analyzed return period under RCP8.5 scenario. On the contrary, the tropical north Pacific shows the most robust decrease in extreme Hs, with local decreases of over 1.5 m. Relevant divergences are found in several ocean regions between the projected behavior of mean and extreme wave conditions. For example, an increase in Hs return values and a decrease in annual mean Hs is found in the SE Indian, NW Atlantic and NE Pacific. Therefore, an extrapolation of the expected change in mean wave conditions to extremes in regions presenting such divergences should be adopted with caution, since it may lead to misinterpretation when used for the design of marine structures or in the evaluation of coastal flooding and erosion

Tsunami wave interaction with mangrove forests: A 3-D numerical approach

ABSTRACT: A three dimensional numerical approach based on IHFOAM to study the interaction of tsunami waves with mangrove forest is presented. As a first approximation, the problem is modelled by means of solitary waves impinging on emergent rigid cylinders. Two different conceptual approaches are implemented into IHFOAM. Solving the URANS equations provides a direct simulation of the flow field considering the actual geometry of the array of cylinders. A modified version of the volume-average URANS equations by introducing a drag force to model the momentum damping created by the cylinders is used in the second approach. Both the direct and macroscopic simulations are validated against laboratory experiments for wave damping with very high agreement. A large set of numerical experiments to analyse flow parameters and uniform and random cylinder array distributions are analysed and use to compare pros and cons of the different approaches. Large differences are found in the forces exerted on the vegetation for uniform and random distributions. Generalizations obtained from uniform arrangements could lead to underestimation of wave-exerted forces, especially for low dense configurations. Wave forces calculated with the macroscopic approach by means of the drag coefficient yields clear underestimations.M. Maza is indebted to the MEC (Ministerio de Educación, Cultura y Deporte, Spain) for the funding provided in the FPU (Formación del Profesorado Universitario) studentship (BOE-A-2012-6238). This work has been partially funded under the RETOS program of the Spanish Ministry of Economy and Competitiveness (BIA2014-59718)

Flow Interaction with Natural Structures: a Case Study of a Model

This work has been funded under the RETOS INVESTIGACION 2014 (grant BIA2014-59718-R) program of the Spanish Ministry of Economy and Competitiveness. M. Maza is indebted to the Spanish Ministry of Science, Innovation and Universities for the funding provided in the grant Juan de la Cierva Incorporación (BOE de 27/10/2017)

Using quantitative dynamic adaptive policy pathways to manage climate change-induced coastal erosion

ABSTRACT: Adaptation requires planning strategies that consider the combined effect of climatic and non-climatic drivers, which are deeply uncertain. This uncertainty arises from many sources, cascades and accumulates in risk estimates. A prominent trend to incorporate this uncertainty in adaptation planning is through adaptive approaches such as the dynamic adaptive policy pathways (DAPP). We present a quantitative DAPP application for coastal erosion management to increase its utilisation in this field. We adopt an approach in which adaptation objectives and actions have continuous quantitative metrics that evolve over time as conditions change. The approach hinges on an adaptation information system that comprises hazard and impact modelling and systematic monitoring to assess changing risks and adaptation signals in the light of adaptation pathway choices. Using an elaborated case study, we force a shoreline evolution model with waves and storm surges generated by means of stochastic modelling from 2010 to 2100, considering uncertainty in extreme weather events, climate variability and mean sea-level rise. We produce a new type of adaptation pathways map showing a set of 90-year probabilistic trajectories that link changing objectives (e.g., no adaptation, limit risk increase, avoid risk increase) and nourishment placement over time. This DAPP approach could be applied to other domains of climate change adaptation bringing a new perspective in adaptive planning under deep uncertainty.Alexandra Toimil acknowledges the financial support from the FENIX Project funded by the Government of Cantabria. This research was also funded by the Spanish Government through the grant RISKCOADAPT (BIA2017-89401-R)

Numerical modeling of tsunami waves interaction with porous and impermeable vertical barriers

ABSTRACT: Tsunami wave interaction with coastal regions is responsible for very important human and economic losses. In order to properly design coastal defenses against these natural catastrophes, new numerical models need to be developed that complement existing laboratory measurements and field data. The use of numerical models based on the Navier-Stokes equations appears as a reasonable approach due to their ability to evaluate complex flow patterns around coastal structures without the inherent limitations of the classical depth-averaged models. In the present study, a Navier-Stokes-based model, IH-3VOF, is applied to study the interaction of tsunami waves with porous and impermeable structures. IH-3VOF is able to simulate wave flow within the porous structures by means of the volume-averaged Reynolds-averaged Navier-Stokes (VARANS) equations. The equations solved by the model and their numerical implementation are presented here. A numerical analysis of the interaction of a tsunami wave with both an impermeable and porous vertical breakwater is carried out. The wave-induced three-dimensional wave pattern is analysed from the simulations. The role paid by the porous media is also investigated. Finally, flow around the breakwater is analyzed identifying different flow behaviors in the vicinity of the breakwater and in the far field of the structure

Visualising the Uncertainty Cascade in Multi-Ensemble Probabilistic Coastal Erosion Projections

ABSTRACT:Future projections of coastal erosion, which are one of the most demanded climate services in coastal areas, are mainly developed using top-down approaches. These approaches consist of undertaking a sequence of steps that include selecting emission or concentration scenarios and climate models, correcting models bias, applying downscaling methods, and implementing coastal erosion models. The information involved in this modelling chain cascades across steps, and so does related uncertainty, which accumulates in the results. Here, we develop long-term multi-ensemble probabilistic coastal erosion projections following the steps of the top-down approach, factorise, decompose and visualise the uncertainty cascade using real data and analyse the contribution of the uncertainty sources (knowledge-based and intrinsic) to the total uncertainty. We find a multi-modal response in long-term erosion estimates and demonstrate that not sampling internal climate variability?s uncertainty sufficiently could lead to a truncated outcomes range, affecting decision-making. Additionally, the noise arising from internal variability (rare outcomes) appears to be an important part of the full range of results, as it turns out that the most extreme shoreline retreat events occur for the simulated chronologies of climate forcing conditions. We conclude that, to capture the full uncertainty, all sources need to be properly sampled considering the climate-related forcing variables involved, the degree of anthropogenic impact and time horizon targeted.AT acknowledges the financial support from the FENIX Project by the Government of Cantabria. This research was also funded by the Spanish Government via the grant RISKCOADAPT (BIA2017-89401-R)

Projecting compound wave and sea-level events at a coastal structure site under climate change

In this paper, an innovative framework is introduced for assessing the impact of climate change on coastal structures, with a primary emphasis on modeling future climate conditions. The framework encompasses several key components: the development of a new climate emulator to facilitate multivariate extreme value analysis; a hybrid statistical?numerical wave propagation strategy; and the integration of a novel compound modeling approach specific to coastal structure sites. These advancements are designed to effectively manage multiple climate scenarios and models within the context of high uncertainty. The methodology is applied and validated for a coastal structure located on the Mediterranean coast in Spain. Focusing on compound wave and sea-level events, the projections indicate an increase in the frequency and severity of extreme conditions, exacerbating coastal impacts such as wave overtopping. For instance, the present-day 500-year coastal flooding level would be associated with a return period of 50 years by mid-century under a stabilization scenario and would be further reduced to 25 years under a high-emission global warming scenario, resulting in important consequences for structure performance if no adaptation is implemented.D. Lucio is indebted to the Spanish Ministry of Science, Innovation and Universities for the funding provided in the FPI, Spain studentship (PRE2018-086142). This work has been also partially funded under the RETOS program, Spain (BIA2017-87213-R) and the State R&D Program Oriented to the Challenges of the Society, Spain (PID2020-118285RB-I00) of the Spanish Ministry of Science, Innovation and Universities