Coastal vulnerability to storms at different time scales: application to the Catalan coast

Storm-induced impacts are known to cause important economic and environmental damages to coastal systems worldwide. Consequently, the relevance of including hazards and vulnerability assessments in coastal policies has been highlighted during the last years, so that coastal managers can make informed decision to apply mitigation and/or adaptation plans. The main purpose of this thesis is to develop a methodology to quantitatively assess coastal vulnerability to storms at different time scales, considering the two main storm-induced hazards separately (inundation and erosion). In this work, vulnerability is defined as the potential of a coastal system to be harmed by the impact of a storm. Thus, it has been quantified by comparing the magnitude of the hazards with the adaptation ability of the coast. The proposed methodology is based on a probabilistic approach where hazard time series are fitted to an extreme value distribution. Consequently, hazard magnitudes and vulnerability are related to a probability of occurrence instead of to a determined storm event. The coastal manager has to decide the probability of occurrence to be accepted in the analysis, which will determine the return period (Tr) to be considered. Vulnerability indicators that compare the magnitude of each hazard to the response capability of the beach are built for erosion and inundation independently. Final vulnerability is formulated in terms of these two intermediate variables by means of a linear function that ranges from a minimum value of 0 (optimum state) to a maximum of 1 (failure state), defining 5 qualitative categories. In this particular case, these thresholds have been defined for each hazard in terms of the protection function provided by the beach. In order to evaluate changes in vulnerability at different time scales, variations in the adaptation ability of the coast due to the effects of other medium and long-term processes have also been considered. Taking into account the characteristics of the study area, erosion due to longshore sediment transport (LST) gradients and erosion and inundation caused by relative sea-level rise (RSLR) have been selected as the main medium and long-term coastal processes, respectively, to be analysed. In this sense, shoreline evolution rates have been used as representative of accretion/erosion due to LST, whereas different combinations of sea-level and subsidence scenarios have been used to determine erosion and inundation due to RSLR. The developed methodology has been applied to most of the sedimentary coastline (219 km) of Catalonia (NW Mediterranean). The results obtained for a Tr=50-yr show similar percentages of high and very high vulnerable coastline for erosion and inundation. However, the increase in vulnerability due to the contribution of LST and RSLR is slightly higher in the case of erosion. Results also indicate that changes in vulnerability due to RSLR are generally lower than those obtained when only LST is accounted. RSLR contribution is detected at longer time scales and is significantly higher in the southern part of the Catalan coast. This is mainly due to the presence of dissipative beaches with very mild slope together with the potentially significant subsidence of the Ebre delta. On the opposite, LST contribution does not seem to target any specific beach type. To conclude, the proposed method permits to identify the most vulnerable spots of a coastal area considering the dynamic response of the system at different time scales. This information is relevant for coastal managers when it comes to efficiently allocate the available resources. Moreover, the versatility of this method allows, not only to update the results according to the available information on hazards magnitude and beach geomorphology, but also to easily apply it to other coastal zones.Los temporales pueden causar daños importantes en la costa, tanto a nivel económico como ambiental. En consecuencia, durante los últimos años se ha destacado la importancia de incluir estimaciones de la magnitud de los procesos y de la vulnerabilidad en las políticas costeras, de forma que los gestores puedan tomar decisiones informadas para aplicar planes de mitigación y/o adaptación. El principal objetivo de esta tesis es desarrollar una metodología que permita evaluar, cuantitativamente, la vulnerabilidad de la costa al impacto de temporales para diferentes escalas de tiempo, considerando por separado los principales procesos implicados (inundación y erosión). En este trabajo, la vulnerabilidad se define como el potencial de un sistema costero a ser dañado, por lo que se ha cuantificado comparando la magnitud de los procesos con la capacidad de adaptación de la costa. La metodología propuesta se basa en una aproximación probabilística en la que las series temporales de intensidad de los procesos se ajustan a una distribución de valores extremos. En consecuencia, tanto la magnitud de los procesos como la vulnerabilidad se asocian a una probabilidad de ocurrencia en vez de a un evento determinado. El gestor debe decidir la probabilidad de ocurrencia a tener en cuenta en el análisis, la cual determinará el periodo de retorno (Tr). Una vez seleccionado el periodo de retorno, se crean indicadores de vulnerabilidad que comparan la magnitud del proceso con la capacidad de respuesta de la playa de forma independiente para erosión e inundación. La vulnerabilidad final se formula en términos de estas dos variables intermedias por medio de una función lineal que va desde un valor mínimo de 0 (estado óptimo) a un máximo de 1 (estado de fallida), definiendo 5 categorías cualitativas. En este caso, estos umbrales se han definido considerando la función de protección de la playa. Para evaluar las variaciones temporales de la vulnerabilidad, se han analizado los cambios en la capacidad de adaptación de la costa frente al impacto de temporales inducidos por los efectos de otros procesos costeros. Considerando las características de la zona de estudio, la erosión debida a los gradientes en el transporte longitudinal de sedimentos (LST) y la erosión y e inundación causadas por la subida relativa del nivel del mar (RSLR) han sido seleccionados como los principales procesos que actúan a medio y largo plazo respectivamente. La erosión/acreción debida al LST se ha determinado mediante tasas de evolución costera, mientras que para caracterizar la erosión e inundación debidas a la RSLR se ha utilizado una combinación de distintos escenarios de nivel del mar y subsidencia. La metodología se ha aplicado a la mayor parte de la costa sedimentaria (219 km) de Cataluña (Mediterráneo noroeste). Los resultados obtenidos para un Tr= 50 años muestran porcentajes similares de costa sujeta a alta o muy alta vulnerabilidad a los dos procesos. Sin embargo, el incremento de vulnerabilidad debido a la contribución del LST y la RSLR es ligeramente mayor en el caso de la erosión. En general, los cambios inducidos por la RSLR son menores que los obtenidos considerando solo el LST. La contribución de la RSLR se detecta a escalas de tiempo mayores y es mayor en la parte sur de la costa catalana. Esto se debe a la presencia de playas disipativas con pendientes muy suaves y a la potencialmente significativa subsidencia del delta del Ebro. La contribución del LST no parece afectar a ningún tipo concreto de playa. Finalmente, este método permite identificar los puntos más vulnerables de la costa considerando la respuesta dinámica del sistema a lo largo del tiempo. Esta información es relevante para los gestores en cuanto a la organización de los recursos disponibles. Además, su versatilidad permite tanto actualizar los resultados en función de la información disponible sobre los procesos y la geomorfología costera, como aplicarlo fácilmente a otras regiones

Impacts of sea-level rise-induced erosion on the Catalan coast

The final publication is available at Springer via http://dx.doi.org/10.1007/s10113-016-1052-xThe Catalan coast as most of the developed Mediterranean coastal zone is characterized by the coincidence of stresses and pressures on the natural system with a high exposure and low adaptive capacity. Due to this, climate change-induced effects will increase natural hazards and aggravate their associated impacts and, in consequence, it is necessary to assess their effects for proper long-term management. In this work, we assess the impact of sea-level rise (SLR)-induced shoreline retreat on the Catalan coast for three scenarios ranging from 0.53 to 1.75 m by the year 2100. Implications are analysed in terms of affectation of two main functions provided by beaches, i.e. recreation and protection. Obtained results show that CC will be a serious threat to analysed functions since the expected enhanced shoreline retreat will severely decrease the recreational carrying capacity and the capacity of protection in the near future under tested scenarios. The actual level of development along the coastal zone reduces the natural resilient capacity of beaches to SLR in such a way that the lack of accommodation space can be identified as a main factor for the estimated impacts.Peer ReviewedPostprint (author's final draft

Erosion consequences on beach functions along the Maresme coast (NW Mediterranean, Spain)

A methodology to analyse the influence of erosion on beach functions at a regional scale is presented. The method considers erosion hazards at different timescales and assesses consequences by evaluating impacts on recreation and protection functions. To provide useful information to decision makers for managing these functions, hazard and consequences are integrated at the municipal level within a risk matrix. This methodology is applied at the Maresme, a 45-km sandy coast situated northward of Barcelona, which supports a strong urban and infrastructure development as well as an intensive beach recreational use. Obtained results indicate differentiated erosion implications along the region, depending on the management target considered. Thus, southern municipalities are more prone to erosion affecting the protection function of the beach and leisure use by the local population, whereas erosion will have a greater effect on foreign tourism in the northern municipalities. These results highlight the necessity to employ an articulated erosion risk assessment focusing on specific targets depending on the site in question. This methodology can help coastal managers to adopt tailored measures to manage erosion impacts towards specific goals, in a more efficient and sustainable manner

Vulnerabilidad costera a múltiples agentes : aplicación al litoral catalán

El proyecto “Vulnerabilidad costera a múltiples agentes. Aplicación al litoral Catalán” tiene como objetivo general desarrollar y validar una metodología para evaluar cuantitativamente la vulnerabilidad de las costas sedimentarias a los principales procesos que rigen su comportamiento. Dentro de este contexto y durante un periodo de 6 meses se ha estado trabajando en el principal objetivo parcial del proyecto: el desarrollo de una serie de indicadores de vulnerabilidad costera a procesos físicos, más específicamente en la obtención de un índice de vulnerabilidad costera a temporales. Para ello se ha analizado la variabilidad espacial y temporal de la intensidad de los procesos costeros inducidos por temporales a lo largo de la costa Catalana, teniendo en cuenta únicamente la contribución de las características del oleaje. Se han integrado datos reales y simulados de oleaje de tres sitios distribuidos a lo largo del litoral Catalán para obtener las series temporales de intensidad de los tres procesos costeros derivados de la acción de temporales más relevantes (transporte de sedimentos, erosión e inundación). Los resultados muestran que no existen tendencias significativas en las series temporales de los procesos estudiados. Por otro lado, el análisis de las series de la media móvil de 5 años de las anomalías de dichos procesos refleja tendencias positivas significativas en el transporte de sedimentos y la erosión para las zonas norte y sur de la costa, y en la inundación para la zona sur. En relación a la variabilidad espacial, los resultados muestran que la zona sur es la más vulnerable a los procesos de erosión costera y transporte de sedimentos, mientras que la parte norte es la más vulnerable al proceso de inundación.The main objective of the project “Coastal vulnerability to multiple agents. Application to the Catalan coast” is to develop and validate a method to quantitatively assess the vulnerability of sedimentary coasts to the main processes that govern their behaviour. Within this context and during a period of 6 months, the work has been focussing on the main partial objective of the project: the development of a range of indicators of coastal vulnerability to physical processes, specifically on obtaining an index of coastal vulnerability to storms. To do this, the spatial and temporal variation of the main storm-induced coastal processes along the Catalan coast has been analyzed, taking into account only the contribution of the storm properties. Simulated and recorded data from three points deployed along the Catalan coast have been integrated to obtain the temporal series of the three main storm-induced coastal processes (sediment transport potential, beach erosion and inundation). The results show that there are no statistically significant trends in storm-induced processes. However, the 5-year running average time series of hazards anomalies show statistically significant increasing trends in beach erosion and sediment transport potential for the northern and southern parts of the coast, and also in beach inundation for the southern part. Related to the spatial variability, the results show that the southern part of the coast is the most vulnerable to beach erosion and sediment transport potential while the northern part is the most vulnerable to inundation

Storm-induced coastal hazard assessment at regional scale: application to Catalonia (NW Mediterranean)

A methodology for coastal hazard assessment at regional scale is presented and applied to the Catalan coast (NW Mediterranean). The method separately evaluates erosion and inundation hazards by using wave time series and beach characteristics (slope and sediment grain size). Obtained hazard time series are fitted to extreme probability distributions for different coastal sectors which are defined in function of local wave climate. This approach allows to compare the spatial variation of hazard intensities for a given probability of occurrence and, thus, to objectively identify the most hazardous areas along the coast in terms of erosion and inundation. Obtained results indicate that the coast north of Barcelona is more hazardous than the southern coast regarding inundation for any given probability. With respect to storm-induced erosion, the central coast of Catalonia is the less hazardous area, although spatial variations in erosion along the coast are smaller than the observed for inundation.Peer Reviewe

Probabilistic coastal vulnerability assessment to storms at regional scale : application to Catalan beaches (NW Mediterranean)

A methodology to assess storm-induced coastal vulnerability taking into account the different induced processes separately (inundation and erosion) is presented. It is based on a probabilistic approach where hazards time series are built from existing storm data and later used to fit an extreme probability function. This is done for different sectors along the coast defined in terms of the wave climate and for representative beach types of the area to be analyzed. Once probability distributions are available, coastal managers must decide the probability of occurrence to be accepted as well as the period of concern of the analysis in function of the importance of the hinterland. These two variables will determine the return period to be considered in the assessment. The comparison of hazards and vulnerabilities associated with the selected probability of occurrence permit to identify the most hazardous areas along the coast in a robust manner by including the spatial variability in forcing (storm climate) and receptor (beaches). The methodology has been applied to a 50 km long coastal stretch of the Catalonia (NW Mediterranean) where offshore wave conditions can be assumed to be homogeneous. In spite of this spatially constant wave field, obtained results indicate a large variability in hazards intensity and vulnerability along the coast.Peer Reviewe

Storm-induced damages along the Catalan coast (NW Mediterranean) during the period 1958–2008

11 pages, 12 figures, 4 tablesThe temporal and spatial patterns of storm-induced damage along the Catalan coast (NW Mediterranean) during the last 50 years have been analyzed to identify main climatic and non-climatic forcings. In the absence of systematic data, a storm-induced damage database compiled from press news has been built, which together with an intensity scale has allowed us to characterize the frequency and intensity of damage. Although no temporal trend has been detected in storm-induced hazards, coastal damage has increased at a rate of about 40% per decade during the last 50 years along the Catalan coast. The main non-climatic factors identified controlling this trend were the urban growth along the coastal fringe and the generalized erosive behavior of beaches. The first one increased values at risk and the second one increased their exposure to storm-induced hazards. In spite of the importance of non-climatic factors to modulate coastal damage, an exponential dependence of damages on storm-induced inundation and erosion was detected. In addition to this, storm-induced geomorphic changes along the Ebro delta coast have also been analyzed. During the period analyzed, “harmful” storms seem to be clustered, with most of the events being present in the late 1990s and especially from 2001 to 2004, resulting in frequent events of intense beach/barrier breaching, massive overwash and flooding. They are mainly expressed in sensitive areas which are subject to long-term erosional processes and comprise a low-lying profile and a narrow beach. This reflects the role of coastal morphology in controlling the intensity of storm-induced hazards along the deltaic coast. Shoreline evolution rates calculated during this period were significantly larger than the previously recorded ones, reflecting a pulsating erosion behavior where large pulses occur during stormy periods and are reduced during post-storm periods. Under the present scenario of maximum coastal development, storm-induced damage has been reported almost every year which could indicate that the present overall beach configuration status along the Catalan coast has reached its limit for protecting the hinterland against stormsThis work has been done in the framework of the VuCoMA research project funded by the Spanish Ministry of Science and Innovation (CTM2008-05597/MAR). We thank the Department of Territorial Policy and Public Works of the Autonomous Government of Catalonia and to Puertos del Estado (Spanish Ministry of Public Works) for supplying wave data used in this study. This work could not been done without the effort and generosity of La Vanguardia in digitizing and making available their archives to the public. The second and third authors were supported by PhD grants from the CSIC and the Spanish Ministry of Education respectivelyPeer reviewe

Storm-induced damages along the Catalan coast (NW Mediterranean) during the period 1958-2008

11 pages, 12 figures, 4 tablesThe temporal and spatial patterns of storm-induced damage along the Catalan coast (NW Mediterranean) during the last 50 years have been analyzed to identify main climatic and non-climatic forcings. In the absence of systematic data, a storm-induced damage database compiled from press news has been built, which together with an intensity scale has allowed us to characterize the frequency and intensity of damage. Although no temporal trend has been detected in storm-induced hazards, coastal damage has increased at a rate of about 40% per decade during the last 50 years along the Catalan coast. The main non-climatic factors identified controlling this trend were the urban growth along the coastal fringe and the generalized erosive behavior of beaches. The first one increased values at risk and the second one increased their exposure to storm-induced hazards. In spite of the importance of non-climatic factors to modulate coastal damage, an exponential dependence of damages on storm-induced inundation and erosion was detected. In addition to this, storm-induced geomorphic changes along the Ebro delta coast have also been analyzed. During the period analyzed, “harmful” storms seem to be clustered, with most of the events being present in the late 1990s and especially from 2001 to 2004, resulting in frequent events of intense beach/barrier breaching, massive overwash and flooding. They are mainly expressed in sensitive areas which are subject to long-term erosional processes and comprise a low-lying profile and a narrow beach. This reflects the role of coastal morphology in controlling the intensity of storm-induced hazards along the deltaic coast. Shoreline evolution rates calculated during this period were significantly larger than the previously recorded ones, reflecting a pulsating erosion behavior where large pulses occur during stormy periods and are reduced during post-storm periods. Under the present scenario of maximum coastal development, storm-induced damage has been reported almost every year which could indicate that the present overall beach configuration status along the Catalan coast has reached its limit for protecting the hinterland against stormsThis work has been done in the framework of the VuCoMA research project funded by the Spanish Ministry of Science and Innovation (CTM2008-05597/MAR). We thank the Department of Territorial Policy and Public Works of the Autonomous Government of Catalonia and to Puertos del Estado (Spanish Ministry of Public Works) for supplying wave data used in this study. This work could not been done without the effort and generosity of La Vanguardia in digitizing and making available their archives to the public. The second and third authors were supported by PhD grants from the CSIC and the Spanish Ministry of Education respectivelyPeer reviewe

Erosion consequences on beach functions along the Maresme coast (NW Mediterranean, Spain)

A methodology to analyse the influence of erosion on beach functions at a regional scale is presented. The method considers erosion hazards at different timescales and assesses consequences by evaluating impacts on recreation and protection functions. To provide useful information to decision makers for managing these functions, hazard and consequences are integrated at the municipal level within a risk matrix. This methodology is applied at the Maresme, a 45-km sandy coast situated northward of Barcelona, which supports a strong urban and infrastructure development as well as an intensive beach recreational use. Obtained results indicate differentiated erosion implications along the region, depending on the management target considered. Thus, southern municipalities are more prone to erosion affecting the protection function of the beach and leisure use by the local population, whereas erosion will have a greater effect on foreign tourism in the northern municipalities. These results highlight the necessity to employ an articulated erosion risk assessment focusing on specific targets depending on the site in question. This methodology can help coastal managers to adopt tailored measures to manage erosion impacts towards specific goals, in a more efficient and sustainable manner.Peer Reviewe

Impacts of sea-level rise-induced erosion on the Catalan coast

The Catalan coast as most of the developed Mediterranean coastal zone is characterized by the coincidence of stresses and pressures on the natural system with a high exposure and low adaptive capacity. Due to this, Climate Change-induced effects will increase natural hazards and aggravate their associated impacts and, in consequence, it is necessary to assess their effects for proper long-term management. In this work, we assess the impact of sea-level rise (SLR) induced shoreline retreat on the Catalan coast for three scenarios ranging from 0.53 m to 1.75 m by the year 2100. Implications are analyzed in terms of affectation of two main functions provided by beaches, i.e. recreation and protection. Obtained results show that CC will be a serious threat to analyzed functions since the expected enhanced shoreline retreat will severely decrease the recreational carrying capacity and, the capacity of protection in the near future under tested scenarios. The actual level of development along the coastal zone reduces the natural resilient capacity of beaches to SLR in such a way that, the lack of accommodation space can be identified as a main factor for the estimated impact