Maritime transport and regional climate change impacts in large EU islands and archipelagos

Maritime transport is a vital sector for global trade and the world economy. Particularly for islands, there is also an important social dimension of this sector, since island communities strongly rely on it for a connection with the mainland and the transportation of goods and passengers. Furthermore, islands are exceptionally vulnerable to climate change, as the rising sea level and extreme events are expected to induce severe impacts. Such hazards are anticipated to also affect the operations of the maritime transport sector by affecting either the port infrastructure or ships en route. The present study is an effort to better comprehend and assess the future risk of maritime transport disruption in six European islands and archipelagos, and it aims at supporting regional to local policy and decision-making. We employ state-of-the-art regional climate datasets and the widely used impact chain approach to identify the different components that might drive such risks. Larger islands (e.g., Corsica, Cyprus and Crete) are found to be more resilient to the impacts of climate change on maritime operations. Our findings also highlight the importance of adopting a low-emission pathway, since this will keep the risk of maritime transport disruption similar to present levels or even slightly decreased for some islands because of an enhanced adaptation capacity and advantageous demographic changes.Open Access funding enabled and organized by Projekt DEAL.This work has received funding from the European Union’s H2020 Research and Innovation Programme under grant agreement no. 776661 (SOCLIMPACT project). It was also supported by the EMME-CARE project, which has received funding from the European Union’s Horizon 2020 Research and Innovation Programme under grant agreement no. 856612, as well as matching co-funding by the Government of the Republic of Cyprus.Peer reviewe

Le cycle de l'eau continental : moteurs climatiques et non-climatiques des débits de rivières et évolution de la ressources en eau

Predict and manage the evolution of water resources is a key challenge in a context of climate change and highly managed rivers. We propose an innovative method to detect and quantify the changes in river discharge due to climate processes or to non-climatic factors. A land surface model (LSM) is used to estimate the "natural" response of the continental surface to climate fluctuations. Then the Budyko framework is used to decompose the streamflow response into a direct response to climate fluctuations and an indirect response to changes in evaporation efficiency of the watershed. Comparing the application of the framework to the LSM outputs and to observations allows to highlight the areas where the "natural" response of watersheds to climate variability is insufficient to explain the recorded changes in river discharge.Results over Europe show that, over the past century, changes in discharge due to climate processes are dominated by trends in annual mean precipitation (P). Secondary climatic factors are potential evapotranspiration (PET) over most of Europe and the intra-annual distribution of P for the Mediterranean area. However, the changes due to factors not accounted for in the "natural" system dominate over the century. Our method allows to quantify the overall effect of these non-climatic factors and correlate them to changes in potential specific drivers such as dams water storage but this is not trully an attribution.Future developments in LSMs will allow to better include human drivers of the hydrological cycle. Then they will be able to decompose and attribute the non-climatic changes detected. Yet, most human activities impacting the water cycle are at the regional scale. Since LSMs are limited to the resolution of the atmospheric forcing used, the first step is to construct a higher resolution atmospheric forcing, to later on test the performance of LSMs at the scales at which human activities modify the hydrological cycle. With that in mind, we use kilometric-scale outputs of atmospheric models to disaggregate an observation-based dataset. We reconstitute spatially and altitudinaly coherent atmospheric fields, with daily averages matching observations.Prévoir l'évolution des ressources en eau est un défi majeur dans un contexte de changement climatique et de rivières hautement anthropisées. Nous proposons une méthode innovante pour détecter et quantifier les changements dans le débit des rivières, climatiques et non climatiques. Un modèle de surface (LSM) est utilisé pour estimer la réponse "naturelle" de la surface continentale aux fluctuations climatiques. Le cadre conceptuel de Budyko est ensuite utilisé, pour décomposer l’évolution du débit en une réponse directe aux fluctuations climatiques, et une réponse indirecte, due aux changements de l'efficacité évaporative du bassin versant. Comparer l’application de ce cadre aux sorties du LSM et à des débits observés permet de mettre en évidence les zones où la réponse "naturelle" des bassins versants à la variabilité climatique est insuffisante pour expliquer les changements enregistrés.Les résultats obtenus en Europe montrent que la part de l’évolution des débits due au climat est dominée par la tendance sur les précipitations moyennes (P), avec en facteurs secondaires l'évapotranspiration potentielle (PET) dans la majeure partie de l'Europe et la répartition intra-annuelle de P en Méditerranée. Cependant, l’évolution générale des débits est dominée à l’échelle du siècle par des facteurs non pris en compte dans le système "naturel".Notre méthode permet d’identifier et de quantifier l’effet général de ces facteurs et de les corréler à certains vecteurs potentiels comme l’installation de barrages mais seul les futurs développements des LSM pour mieux intégrer les facteurs anthropiques permettrons d’attribuer les tendances non climatiques détectées. Or, la plupart des activités humaines qui influent sur le cycle de l'eau prennent place à petite échelle, celle des réservoirs ou des périmètres d'irrigation, et les forçages atmosphériques limitent la résolution d’exécution des LSM. La première étape consiste donc à construire un forçage atmosphérique à plus haute résolution. Pour aborder ce défi, nous combinons un jeu de données issu d’observations avec les résultats de modèles atmosphériques à l’échelle kilométrique. Ces derniers permettent de désagréger les observations selon des champs atmosphériques cohérent spatialement et en altitude

Identifying and quantifying the impact of climatic and non-climatic effects on river discharge

International audienceIn a context of global change, the stakes surrounding water availability and use are getting higher. River discharge has significantly changed over the past century. Human activities, such as irrigation and land cover changes, and climate change have had impact on the water cycle. This raises the question of how to separate the impact of climate change from the impact of anthropogenic activities to better understand their role in the historical records.We propose a methodology to semi-empirically separate the effect of climate from the impact of the changing catchment characteristics on river discharge. It is based on the Budyko framework and long land surface simulation. The Budyko parameter is estimated for each basin and represents its hydrological characteristics. Precipitations and potential evapotranspiration are derived from the forcing dataset GSWP3 (Global Soil Wetness Project Phase 3) – from 1901 to 2010 –. The ORCHIDEE Land Surface Model is used to estimate the terrestrial water and energy balance for the past climate but assuming humans do not modify land surface processes. This is a first guess of evaporation and its evolution due to climatic factors. Not having reliable observations of the evolution of the actual evaporation, river discharge and atmospheric observations are used to reconstruct it. This provides estimates of the evolution of the catchment characteristic and the evaporation efficiency which can then be compared to the modelled natural system. The aim is to separate anthropogenic changes from the effect of climatic forcing. To better understand the sensitivity of our methodology we applyied modifications to the atmospheric forcing to see how specific climate variations impact the sensitivity of the Budyko detection.Our results show that for most basins tested over Spain, there is an increasing trend in the Budyko parameter representing increasing evaporation efficiency of the watershed over the past century which can not be explained by the climate forcing. This trend is consistent with changes in irrigation equipment and development of dams over the studied period. However when looking at decadal trends, climatic fluctuations take precedence over non-climatic trends. In a context of climate changes, the balance between these trends could change in the future. The methodology was extended to other areas in Europe. The clear non-climatic trends were especially significant in semi-arid climate

Budyko Framework Based Analysis of the Effect of ClimateChange on Watershed Evaporation Efficiency and Its Impacton Discharge Over Europe

manuscript submitted to Water Resources ResearchInternational audienceIn a context of climate change, the stakes surrounding water availability are getting higher. Decomposing and quantifying the effects of climate on discharge allows to better understand their impact on water resources. We propose a methodology to separate the effect of change in annual mean of climate variables from the effect of intra-annual distribution of precipitations. It combines the Budyko framework with outputs from a Land Surface Model (LSM). The LSM is used to reproduces the behavior of 2134 reconstructed watersheds over Europe between 1902 and 2010, with climate inputs as the only source of change. We fit to the LSM outputs a one parameter approximation to the Budyko framework. It accounts for the evolution of annual mean in precipitation (P) and potential evapotranspiration (PET). We introduce a time-varying parameter in the equation which represents the effect of long-term variations in the intra-annual distribution of P and PET. To better assess the effects of changes in annual means or in intra-annual distribution of P, we construct synthetic forcings fixing one or the other. The results over Europe show that the changes in discharge due to climate are dominated by the trends in the annual averages of P. The second main climate driver is PET, except over the Mediterranean area where changes in intra-annual variations of P have a higher impact on discharge than trends in PET. Therefore the effects of changes in intra-annual distribution of climate variables are not to be neglected when looking at changes in annual discharge

Method to identify and quantify the effect of climatic and non-climatic drivers on river discharge in Europe

International audienceTo predict and manage the evolution of water resources is a high stake for society in the context of climate change and largely managed rivers. A first step in this endeavour is to be able to determine in the past records which of both processes has dominated changes.We propose an innovative way to detect and quantify the changes in river discharge due to climate processes or to non climatic factors over the past century for European catchments. The Land surface model (LSM) ORCHIDEE forced with a century long climate data set is used to simulate the complex hydrological response of natural catchments to change in climatic variables. The Budyko framework is applied with a time-moving window to decompose the direct discharge response to changes in precipitation P and potential evapotranspiration PET and the indirect response due to climate induced changes in the evaporation efficiency of the watersheds. We then apply the same methodology to discharge observations from gauging stations over Europe. It enables to highlight the areas where the model misrepresents (or omits) important catchment processes and where non-natural changing factors impacting the watershed’s apparent evaporation efficiency significantly contribute to trends in the observed discharge over the century. Results over Europe show that long-term changes and variability in discharge due to climate processes are dominated by changes in P. The second main climatic driver is PET except over the Mediterranean area where water is more limiting and where intra-annual changes in the distribution of P outweigh the effect of PET trends on discharge changes. Over most catchments however and mostly in southern Spain, the changes due to factors not accounted for in the "natural" system dominate over the  century. When the focus is on decadal periods, the effect of non-climatic factors is still significant but small compare to the high effect of climate variability. Attempts to attribute non-climatic changes in the catchments evaporation efficiencies are presented. For instance, good correlations are found  between changes in the evaporation efficiency of Spain catchment with the evolution of water stored in dams showing that it is a reliable indicator of the effect of human activities on the hydrological changes of watersheds in that area. Adding the effect of land-use and land-cover changes in the current implementation of the LSM has no significant effects on the hydrological behaviour of the watersheds at the studied scale of this study. Many processes especially related to human factors impact the watershed’s apparent evaporation efficiency, often with complex and inter-correlated feedback effects and further studies are needed to better attribute the non-climatic trends detected. Further developments in LSM would allow to better include these factors