Towards multi-scale integrated hydrological models using the LIQUID® framework. Overview of the concepts and first application examples

Distributed hydrological models are valuable tools that can be used to support water management in catchments. However, the complexity of management issues, the variety of modelling objectives, and the variable availability of data require a flexible way to customize models and adapt them to each individual problem. Environmental modelling frameworks offer such flexibility; they are designed to build and run integrated models on the basis of reusable and exchangeable components. This paper presents the LIQUID® framework, developed by Hydrowide since 2005. The purpose of developing LIQUID® was to provide both easier integration of hydrological processes and preservation of their characteristic temporal and spatial scales. It suits a wide range of applications, both in terms of spatial scales and of process conceptualisations. LIQUID® is able to synchronize different time steps, to handle irregular geometries, and to simulate complex connections between components, in particular involving feedback. The paper presents the concepts of LIQUID® and the technical choices made to meet the above requirements, with focuses on the simulation run system and on the spatial discretization of process components. The use of the framework is illustrated by five application cases associated with contrasted spatial and temporal scales

An Improved Framework for Watershed Discretization and Model Calibration: Application to the Great Lakes Basin

Large-scale (~103–106 km2) physically-based distributed hydrological models have been used increasingly, due to advances in computational capabilities and data availability, in a variety of water and environmental resources management, such as assessing human impacts on regional water budget. These models inevitably contain a large number of parameters used in simulation of various physical processes. Many of these parameters are not measurable or nearly impossible to measure. These parameters are typically estimated using model calibration, defined as adjusting the parameters so that model simulations can reproduce the observed data as close as possible. Due to the large number of model parameters, it is essential to use a formal automated calibration approach in distributed hydrological modelling. The St. Lawrence River Basin in North America contains the largest body of surface fresh water, the Great Lakes, and is of paramount importance for United States and Canada. The Lakes’ water levels have huge impact on the society, ecosystem, and economy of North America. A proper hydrological modelling and basin-wide water budget for the Great Lakes Basin is essential for addressing some of the challenges associated with this valuable water resource, such as a persistent extreme low water levels in the lakes. Environment Canada applied its Modélisation Environnementale-Surface et Hydrologie (MESH) modelling system to the Great Lakes watershed in 2007. MESH is a coupled semi-distributed land surface-hydrological model intended for various water management purposes including improved operational streamflow forecasts. In that application, model parameters were only slightly adjusted during a brief manual calibration process. Therefore, MESH streamflow simulations were not satisfactory and there was a considerable need to improve its performance for proper evaluation of the MESH modelling system. Collaborative studies between the United States and Canada also highlighted the need for inclusion of the prediction uncertainty in modelling results, for more effective management of the Great Lakes system. One of the primary goals of this study is to build an enhanced well-calibrated MESH model over the Great Lakes Basin, particularly in the context of streamflow predictions in ungauged basins. This major contribution is achieved in two steps. First, the MESH performance in predicting streamflows is benchmarked through a rather extensive formal calibration, for the first time, in the Great Lakes Basin. It is observed that a global calibration strategy using multiple sub-basins substantially improved MESH streamflow predictions, confirming the essential role of a formal model calibration. At the next step, benchmark results are enhanced by further refining the calibration approach and adding uncertainty assessment to the MESH streamflow predictions. This enhancement was mainly achieved by modifying the calibration parameters and increasing the number of sub-basins used in calibration. A rigorous multi-criteria comparison between the two experiments confirmed that the MESH model performance is indeed improved using the revised calibration approach. The prediction uncertainty bands for the MESH streamflow predictions were also estimated in the new experiment. The most influential parameters in MESH were also identified to be soil and channel roughness parameters based on a local sensitivity test. One of the main challenges in hydrological distributed modelling is how to represent the existing spatial heterogeneity in nature. This task is normally performed via watershed discretization, defined as the process of subdividing the basin into manageable “hydrologically similar” computational units. The model performance, and how well it can be calibrated using a limited budget, largely depends on how a basin is discretized. Discretization decisions in hydrologic modelling studies are, however, often insufficiently assessed prior to model simulation and parameter. Few studies explicitly present an organized and objective methodology for assessing discretization schemes, particularly with respect to the streamflow predictions in ungauged basins. Another major goal of this research is to quantitatively assess watershed discretization schemes for distributed hydrological models, with various level of spatial data aggregation, in terms of their skill to predict flows in ungauged basins. The methodology was demonstrated using the MESH model as applied to the Nottawasaga river basin in Ontario, Canada. The schemes differed from a simple lumped scheme to more complex ones by adding spatial land cover and then spatial soil information. Results reveal that calibration budget is an important factor in model performance. In other words, when constrained by calibration budget, using a more complex scheme did not necessarily lead to improved performance in validation. The proposed methodology was also implemented using a shorter sub-period for calibration, aiming at substantial computational saving. This strategy is shown to be promising in producing consistent results and has the potential to increase computational efficiency of this comparison framework. The outcome of this very computationally intensive research, i.e., the well-calibrated MESH model for the Great Lakes and all the final parameter sets found, are now available to be used by other research groups trying to study various aspects of the Great Lakes System. In fact, the benchmark results are already used in the Great Lakes Runoff Intercomparison Project (GRIP). The proposed comparison framework can also be applied to any distributed hydrological model to evaluate alternative discretization schemes, and identify one that is preferred for a certain case

Apport de la modélisation hydrologique régionale à la compréhension des processus de crue en zone méditerranéenne

The hydrological risk associated with flash-floods in the mediteranean area is temporally and spatially variable. Recent works showed the vulnerability of mobile people during floods occurring on small catchments (area 1000 km²). The model used in this thesis is built within the LIQUID hydrological modeling platform, which allows a modular coupling of the chosen hydrological processes. The model is used without calibration, with the purpose to test different hypotheses on the hydrological functioning of catchments. The studied area is the Cevennes-Vivarais region (south-east of France). The first simulations show a high sensitivity of the model results to soil properties (hydraulic conductivity, thickness), and to the bottom flux boundary condition (deep percolation). A different behavior is observed between catchments located on sedimentary rocks and catchments located in the mountain area, on metamorphic schists. A version of the model which accounts for lateral surface and sub-surface flows is developed, and tested on the Cartaou (0.5 km²) experimental catchment. Preliminary results highlight the importance of lateral flow processes in flood generation at small spatial scales. A streamflow recession analysis is performed to estimate hydraulic and thickness properties of weathered rock horizons, which are not described by regional soil databases. The results show a hierarchy in the estimated parameters, in relation with geology. The weathered rock horizons are implemented in the hydrological model, which is used at the regional scale. Simulations performed over the 2008 year bring out the better results obtained when using the weathered rock layer, for flood events simulations as well as for long-term simulations. The results also show differences between the hydrological behavior of north catchments (Ardèche, Tarn) and south catchments (Cèze, Gardon, Vidourle), which can be linked to the geology.Le risque hydrologique associé aux crues rapides survenant en région méditerranéenne est variable dans l'espace et le temps. Des travaux ont montré une vulnérabilité forte des personnes mobiles face aux crues touchant les bassins versants de petite taille ( 1000 km²). Le modèle utilisé dans cette thèse est construit avec la plate-forme de modélisation LIQUID, qui permet un couplage « à la carte » de modules représentant les processus que l'on souhaite intégrer au modèle. C'est un modèle utilisé sans calibration, dans une démarche de test d'hypothèses de fonctionnement hydrologique des bassins. La zone d'étude est la région Cévennes-Vivarais. Les premières simulations effectuées montrent une sensibilité forte des résultats du modèle aux propriétés des sols (conductivité hydraulique, épaisseurs), ainsi qu'au type de condition limite employée (percolation profonde ou non). Une distinction apparaît entre les comportements en crue des bassins situés sur roche sédimentaire et des bassins schisteux situés sur les reliefs cévenols. Une version du modèle intégrant la représentation des écoulements latéraux de surface et de subsurface est également développée, et déployée sur le bassin expérimental du Cartaou (0.5 km²). Les premiers résultats soulignent l'important rôle joué par ces écoulements à petite échelle. Une méthodologie d'analyse des récessions de débit est mise en place pour l'estimation des propriétés hydrauliques et des épaisseurs des horizons de roche altérée, non-décrits par les bases de données des sols de la région. Les résultats de l'analyse suggèrent une hiérarchie dans les valeurs des paramètres, contrôlée par le type de géologie. Les horizons de roche altérée sont ensuite intégrés dans la version finale du modèle, qui est déployée à l'échelle de la région entière. Les simulations effectuées sur l'année 2008 montrent l'intérêt de la prise en compte de ces épaisseurs de roche altérée, tant pour la simulation des débits en crue que lors des périodes inter-événementielles. Les simulations mettent également en évidence des différences de comportement entre les bassins du nord de la région (Ardèche, Tarn) et ceux du sud (Cèze, Gardon, Vidourle) que l'on peut relier à la géologie