In France, groundwater is an important resource for industry, irrigation, and drinking water. As the dry periods become more frequent and longer due to the changing climate, it is crucial to forecast water table level evolution for the forthcoming months. Regional groundwater flow models can be useful to reach this objective (e.g., Mackay et al., 2015). Downscaled atmospheric seasonal forecasts are generally used to feed hydrological surface models, which provide surface conditions (drainage, runoff) to groundwater flow models. Our application aims at using the Aqui-FR hydro-geological modelling platform for assessing the groundwater level for the forthcoming months. Aqui-FR was developed in order to gather in a single numerical tool several regional hydrogeological models covering much of the French metropolitan area (Vergnes et al., 2019). It allows to simulate the evolution of groundwater resources on short to long term periods. Since the beginning of 2020, a real time prototype has been set up. Every month, it provides a status of the water table and a monthly forecast for the next six months (see figure) using the atmospheric seasonal forecast produced at Météo-France (Voldoire et al., 2019). These results are posted on an experimental website accessible to a group of beta-users. Some of them rely on this tool to help them in their decision making in a drought alert situation. For the first time in 2021, a hydro-geological seasonal forecast bulletin has been produced and provided to the national committee for drought monitoring and anticipation.

Le contenu en eau du sol près de la surface, variable essentielle de notre environnement, reste assez méconnu en raison des difficultés pour l'observer. La chaîne de modélisation hydrométéorologique SIM2 permet de le simuler à partir des conditions météorologiques. La comparaison des résultats du modèle avec les observations d'une vingtaine de stations du sud de la France montre une bonne adéquation des deux jeux de données, la dynamique temporelle du contenu en eau du sol étant bien représentée (amplitude et saisonnalité). Les performances de SIM2 se détériorent un peu en été lors de la survenue d'orages intenses très locaux. The water content of the soil near the surface, an essential variable of our environment, remains rather unknown because of the observation difficulties. The hydro-meteorological modeling chain SIM2 allows to simulate it from meteorological conditions. Comparison of the model results with observations from about 20 stations in southern France shows a good match between the two data sets. The temporal dynamics of soil water content is well represented (amplitude and seasonality). The SIM2 performance slightly deteriorates in summer when very local intense thunderstorms occur.

Low-flow forecasting can help to improve water management at places where a number of uses can be affected by diminishing water supply from rivers. Several French institutes (INRAE, BRGM, EDF, Lorraine University and Météo-France) have been collaborating to set up an operational platform, called PREMHYCE, for low-flow forecasting at the national scale, in cooperation with operational services. PREMHYCE includes five hydrological models and low-flow forecasts can be issued up to 90 days ahead for more than 800 basins. Several input scenarios are considered: ECMWF 14-days ensemble forecasts, ensemble streamflow prediction (ESP) using historical climatic data, and a no precipitation scenario. Outputs from the different hydrological models are combined into a multi-model approach to improve robustness of the forecasts. The tool provides text files and graphical representation of forecasted low-flows, as well as key low-flow indicators, such as the probabilities of being under low-flow thresholds provided by operational services. The presentation will show the main characteristics of this operational forecast platform, its latest developments and the results on the recent low-flow periods.

In the framework of the MEDSCOPE project, Météo-France has initiated the development of new prototypes for seasonal water resource management in the Mediterranean region, addressing different scientific and technical challenges essential for a future operationalization of the services . In order to have a replicable result on the Mediterranean area, we decided first to consider the three large watersheds onof the Rhone river in France, the Ebro river in Spain and the Po river in Italy. Our first challenge was to use a new hydrologic model SURFEX-CTRIP, covering the whole Mediterranean area. Another point was to perfect and evaluate a new downscaling tool named ADAMONT permitting to debiase all seasonal forecast input variables needed for hydrology applications and not only (temperature and, precipitation and 5 other surface meteorological parameters). We decided also to assess the new UERRA hydrological analyse available on these three countries. Lthe last challenge was to identify local end users facing with decision making process at seasonal scale for water resources management and develop decision help products adapted to their needs. The evaluation of these prototypes, carried out over the period 2019-2020 using the MF Syst 6 and then Syst 7 seasonal forecasting model, has highlighted a significant potential in a future operational application but also difficulties to be overcome. The communication will present the main results of this work and discuss the lessons to be learnet from this experience

In many countries, rivers are the primary supply of water. A number of uses are concerned (drinking water, irrigation, hydropower, etc.) and they can be strongly affected by water shortages. Therefore, there is a need for the early anticipation of low-flow periods to improve water management. This is strengthened by the perspective of having more severe summer low flows in the context of climate change. Several French institutions (Inrae, BRGM, Météo-France, EDF and Lorraine University) have been collaborating over the last years to develop an operational tool for low-flow forecasting, called PREMHYCE. It was tested in real time on 70 catchments in continental France in 2017, and on 48 additional catchments in 2018. PREMHYCE includes five hydrological models: one uncalibrated physically-based model and four storage-type models of various complexity, which are calibrated on gauged catchments. The models assimilate flow observations or implement post-processing techniques. Low-flow forecasts can be issued up to 90 d ahead, based on ensemble streamflow prediction (ESP) using historical climatic data as ensembles of future input scenarios. These climatic data (precipitation, potential evapotranspiration and temperature) are provided by Météo-France with the daily gridded SAFRAN reanalysis over the 1958–2017 period, which includes a wide range of conditions. The tool provides numerical and graphical outputs, including the forecasted ranges of low flows, and the probability to be under low-flow warning thresholds provided by the users. Outputs from the different hydrological models can be combined through a simple multi-model approach to improve the robustness of forecasts. Results are illustrated for the Ill River at Didenheim (northeastern France) where the 2017 low-flow period was particularly severe and for which PREMHYCE provided useful forecasts.

In the framework of the MEDSCOPE project, a forecasting chain is developed at Météo-France for hydrological long term predictions over the Euro-Mediterranean region, from one month up to seven months. This new prototype is based on the Météo-France System 6 global seasonal forecast system. Atmospheric forecasts are interpolated to 5.5 km and corrected by the statistical method ADAMONT using the UERRA regional atmospheric reanalysis as reference. These high resolution forecasts drive the physically-based model SURFEX coupled to CTRIP providing seasonal forecasts of surface variables : river discharges, soil wetness indices, snow water equivalent. A forecast using the climatology (ESP approach) has been produced on the period 1993-2016. It is use to explore the sources of predictability in the different watersheds (Ebro, Po, Rhône). Predictability is mostly coming from the snow pack built during the winter and the soil moisture evolution in spring and summer. A hindcast on the period 1993-2016 is produced to assess the added value of the seasonal forecast compared to the climatology for the end-users in agriculture and energy.

This paper describes the impact of the various changes made to the Safran–Isba–Modcou (SIM) hydrometeorological system and demonstrates that the new version of the model performs better than the previous one by making comparisons with observations of daily river flows and snow depths. SIM was developed and put into operational service at Météo-France in the early 2000s. The SIM application is dedicated to the monitoring of water resources and can therefore help in drought monitoring or flood risk forecasting on French territory. This complex system combines three models: SAFRAN, which analyses meteorological variables close to the surface, the ISBA land surface model, which aims to calculate surface fluxes at the interface with the atmosphere and ground variables, and finally MODCOU, a hydrogeological model which calculates river flows and changes in groundwater levels. The SIM model has been improved first by reducing the infrared radiation bias of SAFRAN and then by using the more advanced ISBA multi-layer surface diffusion scheme to have a more physical representation of surface and ground processes. In addition, more accurate and recent databases of vegetation, soil texture, and orography were used. Finally, in mountainous areas, a sub-grid orography representation using elevation bands was adopted, as was the possibility of adding a reservoir to represent the effect of aquifers in mountainous areas. The numerical simulations carried out with the SIM model covered the period from 1958 to 2018, thereby providing an extensive historical analysis of the water resources over France.

The new AquiFR hydrometeorological modelling platform was developed to provide short-to-long-term forecasts for groundwater resource management in France. This study aims to describe and assess this new tool over a long period of 60 years. This platform gathers in a single numerical tool several hydrogeological models covering much of the French metropolitan area. A total of 11 aquifer systems are simulated through spatially distributed models using either the MARTHE (Modélisation d'Aquifères avec un maillage Rectangulaire, Transport et HydrodynamiquE; Modelling Aquifers with Rectangular cells, Transport and Hydrodynamics) groundwater modelling software programme or the EauDyssée hydrogeological platform. A total of 23 karstic systems are simulated by a lumped reservoir approach using the EROS (Ensemble de Rivières Organisés en Sous-bassins; set of rivers organized in sub-basins) software programme. AquiFR computes the groundwater level, the groundwater–surface-water exchanges and the river flows. A simulation covering a 60-year period from 1958 to 2018 is achieved in order to evaluate the performance of this platform. The 8 km resolution SAFRAN (Système d'Analyse Fournissant des Renseignements Adaptés à la Nivologie) meteorological analysis provides the atmospheric variables needed by the SURFEX (SURFace EXternalisée) land surface model in order to compute surface runoff and groundwater recharge used by the hydrogeological models. The assessment is based on more than 600 piezometers and more than 300 gauging stations corresponding to simulated rivers and outlets of karstic systems. For the simulated piezometric heads, 42 % and 60 % of the absolute biases are lower than 2 and 4 m respectively. The standardized piezometric level index (SPLI) was computed to assess the ability of AquiFR to identify extreme events such as groundwater floods or droughts in the long-term simulation over a set of piezometers used for groundwater resource management. A total of 56 % of the Nash–Sutcliffe efficiency (NSE; Ef) coefficient calculations between the observed and simulated SPLI time series are greater than 0.5. The quality of the results makes it possible to consider using the platform for real-time monitoring and seasonal forecasts of groundwater resources as well as for climate change impact assessments.

Since 2003, Meteo-France operates in real-time a hydro-meteorological model chain used to monitor the hydrological situation. The SAFRAN atmospheric analysis drives the ISBA land surface model. The latter feeds a hydrological model called MODCOU. The original version of SIM (SAFRAN-ISBA-MODCOU) was updated in 2016 to improve the radiative forcing from SAFRAN, soil modelling, sub-grid processes representation. Besides the real-time application, a reanalysis has been performed to cover years from 1958 in order to characterize the water resources monitoring precipitation, soil wetness, snow water equivalent. In the meantime, forecast applications have been developed to document the expected evolution of the hydrological context. Hydrological initial states come from the real-time analysis and meteorological forecasts drive the hydrological ISBA-MODCOU component. Using 10-days meteorological forecasts from ECMWF (European Centre for Medium-Range Weather Forecasts) enables daily productions of rainfall, soil moisture and snow water equivalent forecasts. For longer lead-time (up to 6 months), two forecast applications are operated every month. The first one uses meteorological forcing from climatology as input, while the second one uses data from a seasonal atmospheric forecast modelling system (Meteo-France System). The use of both climatological and seasonal forecasts makes it possible to know the likely evolution of the hydrological situation and then to adapt water resource management.

De nombreux usages de l'eau peuvent être fortement impactés par les pénuries d'eau (eau potable, irrigation, hydroéléctricité...). Il est donc nécessaire d'anticiper les périodes d'étiage afin d'améliorer la gestion de l'eau. Ceci est renforcé par la perspective d'étiages futurs plus sévères dans le contexte du changement climatique. Cinq institutions françaises ont développé un outil opérationnel de prévision des bas débits, PREMHYCE. Il est testé en temps réel sur une centaine de bassins versants de France métropolitaine depuis 2017. PREMHYCE comprend cinq modèles hydrologiques qui peuvent être calés sur des bassins versants jaugés et assimilent les dernières observations de débit. Les prévisions de débits sont émises jusqu'à un horizon de 90 jours selon l'approche Ensemble Streamflow Prediction (ESP) (données météorologiques historiques utilisées comme ensemble de scénarios d'entrée). Ces données météorologiques (précipitations, évapotranspiration et température) sont issues de la réanalyse SAFRAN journalière de Météo-France, sur la période 1958–2018. Les performances de l'outil sont analysées sur les étiages 2017–2018 pour 38 bassins versants sur lesquels les prévisions sont disponibles pour tous les modèles. Ces derniers ont montré des capacités d'anticipation de l'ordre de 40 jours en moyenne. La plupart des modèles présentent une précision satisfaisante pour prévoir les bas débits à courte échéance (j + 7).

Météo-France opère en temps réel depuis 2003 la chaîne de modélisation hydro-météorologique SIM, composée du module d'analyse des conditions atmosphériques en surface (SAFRAN), d'une modélisation détaillée des interactions sol-biosphère-atmosphère (ISBA) et du modèle hydrogéologique MODCOU. Cette chaîne a connu une évolution majeure en 2016 afin d'améliorer certains de ses composants. Cette application temps-réel, complétée par une réanalyse depuis 1958 permet de caractériser la situation par rapport aux années antérieures pour plusieurs variables du cycle hydrologique (précipitations, humidité du sol, enneigement). Les épisodes de sécheresse, l'évolution du stock nival, etc. peuvent ainsi être suivis au jour le jour sur l'ensemble de la France métropolitaine. Des applications de prévisions ont également été mises en place pour anticiper l'évolution de la situation hydrologique. L'initialisation des conditions hydrologiques provient de la chaîne d'analyse temps-réel et des données météorologiques prévues sont utilisées en entrée d'ISBA-MODCOU. Ainsi une application pour les échéances allant jusqu'à 10 jours utilise comme forçage météorologique les prévisions d'ensemble du CEPMMT (Centre Européen de Prévision Météorologique à Moyen Terme). Chaque jour des prévisions sont produites sur différentes zones (départements, bassins versants, etc.), l'ensemble de prévision fournit des informations pour les différentes variables hydrologiques au pas de temps quotidien. De plus la visualisation de la dispersion des prévisions renseigne sur l'incertitude associée à chaque prévision. Pour des échéances plus lointaines (jusqu'à 6 mois), deux applications de prévisions sont opérées tous les mois. La première utilise en entrée des scénarios météorologiques issus de la climatologie, alors que la seconde utilise des données issues du modèle de prévisions saisonnières atmosphériques de Météo-France. Malgré l'incertitude des prévisions, l'exploitation complémentaire des prévisions climatologique et saisonnière est un outil pour la gestion des ressources en eau. Les débits moyens mensuels prévus pour chacune des applications comparés aux débits des années précédentes permettent en effet de caractériser la situation pour les mois à venir et l'incertitude associée.

For many years real-time climate monitoring for temperature over France has been performed using a national index built by averaging the daily mean temperatures of constant subset of 30 stations with long-term series. In order to derive climate indices at finer scales, a spatialization of extreme daily temperatures (called ANASTASIA) had been produced on a 1 km regular grid using a regression-kriging method. The production covers 1947 to present period. Cross-validation shows low biases after the 1960s. The temporal homogeneity of the product is satisfying at the national scale from the 1970s. However, a high impact of the network density has been found and the use of a too coarse observation network deteriorates the analysis creating temporal heterogeneities. Finally, the ANASTASIA analysis has been used for real-time monitoring over France and detection of heat and cold wave episodes. The new products based on ANASTASIA are consistent with the current operational ones at national scale while bringing added values at local scales.

The AquiFR project aims at taking benefits of existing groundwater modeling applications used by stakeholders to develop new products in order to provide useful information for water resources management. Indeed, it aims at providing forecasts of the groundwater resources at10 days ahead upto seasonal scale. In its present form, the AquiFR system includes 3 hydrogeological models covering 8 multilayers sedimentary aquifers and 10 karstic aquifers. These applications were assembled within a coupling system facilitating the parallel computation and coupled to a land surface model used in the French numerical weather model that provides the recharge. The whole system is expected to run operationally at Meteo France. To do so, a real time application will be run daily forced by an analysis of the observed atmospheric conditions. This real time simulation will then be able to provide initial conditions for the forecasts. Ensemble 10-day forecast will then be run daily, and seasonal forecasts will be run monthly. The monitoring and the forecasts could be compared to the long term reanalysis of the groundwater that is being built by using an atmospheric reanalysis.

In this article, we describe the design and the validation of the Mescan precipitation analysis system developed for climatological purposes under the EURO4M project. The system is based on an optimal interpolation algorithm using the 24-h aggregated gauge measurements from the surface network. The background fields are the total accumulated precipitation forecasts at different resolutions from the ALADIN or HIRLAM mesoscale models, downscaled to 5.5 km grid spacing, chosen to match the time period of the climatological gauge reports. The validation of the Mescan system is carried out over the French territory employing various metrics and by providing forcing to a hydrological model to produce river discharges. The investigations have shown that the precipitation analyses have almost the same quality as the well-validated SAFRAN analysis system. In addition, the analysis of the precipitation variance spectra computed on the same horizontal domain has indicated that at short wavelengths the downscaled fields have significantly lower variability than a field produced by time integrating a forecast model. The Mescan precipitation analysis system has successfully been used to produce 24-h total accumulated precipitation re-analyses on a 5.5 km grid over Europe for the period 2007–2010.