Électricité de France (France)

Abstract. This study evaluates the impact of freshwater fluxes on the Atlantic Ocean. The river discharge has been estimated at the outlet of 18 major rivers flowing into the Atlantic by solving the water mass balance equation at the river basin scale. In this approach, water storage changes are evaluated with satellite gravimetry measurements. In contrast, atmospheric fluxes (i.e., precipitation, evapotranspiration) are assessed with atmospheric reanalyses, in situ measurements from a global network of rain gauges, or a global hydrological model. The river discharge estimated with the water mass balance is consistent with independent river gauge measurements across all South American rivers, in particular the Amazon, where the annual and monthly climatology can be estimated with an error of less than 5 % when compared with in situ measurements. Larger discrepancies are observed for other basins, likely due to uncertainties in the precipitation and evapotranspiration fluxes. When climatological estimates of the river discharge are replaced by the water mass balance approach in ocean model simulations, a decrease in the sea surface salinity bias is observed at the outlet of the Amazon and across the whole Atlantic. The water mass balance approach can bring new observational constraints on freshwater fluxes flowing from the continent to the ocean, but is not universally reliable due to potential biases in atmospheric flux estimates. When combined with in situ measurements or hydrological model predictions, the water mass balance approach can enhance freshwater flux quantification, leading to improved ocean model simulations near major river outlets. In particular, the enhanced river runoff dataset significantly reduces salinity biases, with associated changes in reduced vertical stratification, enhanced upper ocean circulation, and meridional transports.

Rivers provide many ecosystem services. However, in densely populated urban areas, they are polluted by multiple sources including combined sewer overflows (CSOs). By studying the behavior of the combined sewer system, whose capacity can be saturated during heavy rainfall episodes, it is possible to anticipate these contamination periods. In addition, by using an inverse method (quantifying causes from effects), it would be possible to determine the quantity of contaminants released by the CSO. In this paper, we present the design of the method on the study site of the Seine River, in Paris. The spatial extension of the combined sewer network is described by a directed graph. Temporal consistency is achieved through event definition. The use of these data for CSO assessment would make it possible to anticipate contamination and guide decisions to contain it.

Droughts are a growing concern for water managers, as climate change is expected to intensify both their severity and frequency. Accurately forecasting these events is crucial to mitigate their impacts. Semi-distributed hydrological modelling, by dividing the catchment into interconnected hydrological units, provides flow estimation at gauged and ungauged locations and explicitly accounts for some physical and climatic spatial variability across the catchment.In this study, four semi-distributed models (GRSD, MORDOR-TS, PRESAGES, RAMEAU) are implemented in the Meuse River catchment at Chooz, an area characterized by contrasting geological, topographic, and meteorological conditions. The models differ in their structural assumptions, notably regarding groundwater exchanges beyond topographic boundaries and the potential use of piezometric data during calibration.Following a joint calibration exercise, the four models provide consistent results on streamflow across the entire catchment and comparable performance at the outlet at Chooz in comparison to their lumped-model counterparts. Similar biases are observed among the models, which may reflect common limitations in their assumptions or uncertainties in flow measurements and meteorological data. The case study of the 2022 low-flow event highlights variability in simulated low flows, linked in particular to the choice of model and to the climate data used for calibration. Gauging measurements taken during low-flow periods would help strengthen these results. Future work should focus on improving the understanding and the representation of groundwater flows in semi-distributed hydrological models.

The Alps, often referred to as Europe's water tower, are undergoing profound changes as a result of climate change. Declining snow cover, accelerated glacier retreat, and increasingly severe periods of low flow raise urgent questions for water resource management, biodiversity, and energy security. Hydropower, one of the pillars of the European renewable energy strategy, is particularly exposed to these changes. To understand and anticipate these impacts, it is necessary to have detailed modeling of Alpine hydrological systems, combined with reliable climate projections.To meet these challenges, the spatially distributed hydrological model MORDOR-TS (Garavaglia et al., 2017; Rouhier et al., 2017) now includes an explicit glacier component to simulate glacier dynamics in warming scenarios (Rouzies et al., 2024). Applied to the Isère basin in the French Alps, this model supports strategic decisions relating to hydroelectric exploitation by simulating hydrological responses at the basin scale under different future climate scenarios (Le Lay et al., 2022). However, glaciers remain relatively poorly instrumented today, and their ice volumes are often poorly known, making such modeling inevitably imprecise. In this context, local observations and modeling produced by glaciologists are valuable for better quantifying the relative contribution of glaciers to river flows and improving the robustness of hydrological projections.This study focuses on the modeling of a representative alpine glacier in the Vanoise massif, which feeds the Doron des Allues River. On this glacier, combining historical glaciological monitoring with radar-based surveys of current geometry and ice volume has enabled a detailed modelling of the glacier geometry, its evolution and meltwater discharge throughout the 21st century. These data are used to refine glacier representation in the MORDOR-TS hydrological model —surface area, volume, and meltwater flows—improving the reliability of basin-scale hydrological simulations, distinguishing between precipitation-driven and glacier-driven contributions. Results confirm strong consistency between the local glaciological model and the regional hydrological model and highlight pathways for further parameterization improvements.The glacier is projected to almost completely disappear by 2100, with cascading impacts on discharge regimes. Beyond reduced mean flows, significant shifts in seasonal patterns and diminished summer flows are expected—posing challenges for hydropower production, ecosystem resilience, and water allocation. These results highlight the importance of coupling regional hydrological models with high-resolution glaciological data to improve the robustness of climate impact assessments in mountain regions.These findings underscore the urgency of adaptation strategies for mountain water resources in a warming climate. They also illustrate the value of coupling large-scale hydrological models with high-resolution glaciological data to support energy planning and climate resilience across Europe’s alpine regions.

In order to model concrete cracking, a phase-field model is retained which converges toward cohesive fracture when its regularisation length goes to zero. The damage threshold in stress-space is adapted from experimental failure surface. In addition, damage in compression is introduced to bound the stress response. The model is deliberately kept as simple as possible to preserve its robustness. Two test-cases are computed in order to assess its capabilities. The first one consists of a shear-mode pull-out test. It is focused on robustness in the presence of other sources of nonlinearity (finite strain plasticity, contact boundary conditions). The second one consists of a reinforced concrete beam submitted to four-point bending. It is characterised by multi-cracking and enables a comparison with experimental results.

Wind and solar energy curtailment is seen as one of the most important power system issues in multiple countries, and it will grow in importance for electricity systems that are targeting high shares of renewable energy. International cooperation, under the scheme of the International Energy Agency's (IEA) TCP (Technical Cooperation Programme) Wind Task 25 (Design and operation of energy systems with large amounts of variable generation) and its continuation task, Task 63 (Twenty Fifty Integration of Variable Energy), as well as Tasks 14 (Solar PV in the 100% RES Power System) and 19 (Photovoltaic Integration in Electricity Networks and Markets) of the Photovoltaic Power Systems (PVPS) Programme, have been investigating the global situation of wind and solar curtailment for more than a decade. This joint paper includes four topics: (1) proposing unified curtailment statistics, (2) rethinking and redefining curtailment, (3) updating statistics in various areas / countries, and (4) surveying and summarising future curtailment estimates in various country/areas. Specifically, the paper reviews previous publications and discussions on curtailment and rethinks the definition of curtailment. The paper also makes recommendations to governments, regulators and system operators around the world for uniform statistics on curtailment.

A mixed integer maximization problem involving several additional constraints defined with both a lower and an upper bound is considered. It is assumed that one of such constraints is more restrictive than the others. As it can be seen as a resource window constraint, it defines the so-called window-constrained problem. From a bi-objective perspective, a 2-phase algorithm, called BORWin, is devised. It stands for Bi-Objective Relaxation for Window-constrained problems. The first phase is generic for any window-constrained problem and provides a family of upper bounds based on a bi-objective relaxation of the additional constraints. It is shown that the latter bounds strongly relate to the Lagrangian dual bounds. The second phase is derived for a variant involving a graph structure, namely the window-constrained longest-path problem on an acyclic graph. The aim is to take advantage of the upper bounds to devise an efficient label extension algorithm. It is shown that complementary upper bounds could be derived to further improve performance in some special cases. A typical example is when the additional constraints have special knapsack structures. This is the case for the Hydro-Unit Commitment problem with a single plant (1-HUC). From numerical experiments for the 1-HUC, BOR-Win appears to be very efficient compared to state-of-the-art approaches.

Coupling between creep and damage is studied in order to properly describe tertiary creep of concrete. Evolution of damage is governed by a strain tensor through an energy norm, obtained by weighting total and elastic strain tensor by means of a constant parameter. In fact, previous analyses show that, if coupling between creep and damage rely upon total strains, tertiary creep occurs too early. In this study, damage model with bilinear constitutive law and Benboudjema’s creep model are employed. Numerical simulations provide the structural response after the introduction of the coefficient.