<p>To 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.<br />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. </p>

<p>In a context of <span>global</span> 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. <span>This raises the question of</span> how to separate the impact of climate change from the impact of anthropogenic activities to better understand their role in the historical records.</p><p>We <span>propose</span> a methodology to semi-empirically separate the effect of climate from the impact of the changing catchment characteristics on river discharge. <span>It is based on</span> the Budyko framework and long land surface simulation. The Budyko parameter is estimated for each basin and <span>represents</span> its hydrological characteristics. Precipitations and potential evapotranspiration are derived from the forcing dataset GSWP3 (Global Soil Wetness Project Phase 3) – from 1901 to 2010 –. <span>T</span><span>he ORCHIDEE Land Surface Model</span> <span>is used to</span> <span>estimate</span><span> the</span><span> terrestrial water and energy balance </span><span>for the past</span><span> climate but assuming humans do not modify land surface processes</span><span>. </span><span>This is a first </span><span>guess of</span><span> evaporation and its evolution due to climatic factors.</span> <span>Not having reliable observations of the evolution of </span><span>the actual </span><span>evaporation, river discharge and atmospheric observations are used to reconstruct </span><span>it</span><span>. This provides estimates of the evolution of the catchment characteristic and the evaporation efficiency </span><span>which can then be compared to the modelled natural system.</span> <span>The aim is to</span> 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.</p><p>Our results show that for most basins tested over Spain, there is an increasing trend in the <span>Budyko parameter representing increasing evaporation efficiency</span> of the watershed over the past century which <span>can not be</span> 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.</p>

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.