Vazken Andréassian - Academia.edu (original) (raw)

Papers by Vazken Andréassian

Hydrology and Earth System Sciences, 2014

Precipitation is the key factor controlling the highfrequency hydrological response in catchments... more Precipitation is the key factor controlling the highfrequency hydrological response in catchments, and streamflow simulation is thus dependent on the way rainfall is represented in a hydrological model. A characteristic that distinguishes distributed from lumped models is the ability to explicitly represent the spatial variability of precipitation. Although the literature on this topic is abundant, the results are contrasting and sometimes contradictory. This paper investigates the impact of spatial rainfall on runoff generation to better understand the conditions where higher-resolution rainfall information improves streamflow simulations. In this study, we used the rainfall reanalysis developed by Météo-France over the whole country of France at 1 km and 1 h resolution over a 10 yr period. A hydrological model was applied in the lumped mode (a single spatial unit) and in the semidistributed mode using three unit sizes of subcatchments. The model was evaluated against observed streamflow data using split-sample tests on a large set of French catchments (181) representing a variety of sizes and climate conditions. The results were analyzed by catchment classes and types of rainfall events based on the spatial variability of precipitation. The evaluation clearly showed different behaviors. The lumped model performed as well as the semidistributed model in western France, where catchments are under oceanic climate conditions with quite spatially uniform precipitation fields. By contrast, higher resolution in precipitation inputs significantly improved the simulated streamflow dynamics and accuracy in southern France (Cévennes and Mediterranean regions) for catchments in which precipitation fields were identified to be highly variable in space. In all regions, natural variability allows for contradictory examples to be found, showing that analyzing a large number of events over varied catchments is warranted.

We enjoyed very much reading the paper by Savenije (2008), with which we agree (almost) entirely.... more We enjoyed very much reading the paper by Savenije (2008), with which we agree (almost) entirely. We particularly like the call for more creativity, more imagination in hydrology, for a continuous interaction between the elements of the ’hydrologic trinity’: science, technology and art. When reading the literature, we get sometimes the feeling 1Invited contribution by H. H. G. Savenije, the EGU Henry Darcy Medallist 2008 for outstanding contributions

Lumped hydrological models are useful and convenient tools for research, engineering and educatio... more Lumped hydrological models are useful and convenient tools for research, engineering and educational purposes. They propose catchment-scale representations of the precipitation-discharge relationship. Thanks to their limited data requirements, they can be easily implemented and run. With such models, it is possible to simulate a number of hydrological key processes over the catchment with limited structural and parametric complexity, typically evapotranspiration, runoff, underground losses, etc. The Hydrology Group at Irstea (Antony) has been developing a suite of rainfall-runoff models over the past 30 years with the main objectives of designing models as efficient as possible in terms of streamflow simulation, applicable to a wide range of catchments and having low data requirements. This resulted in a suite of models running at different time steps (from hourly to annual) applicable for various issues including water balance estimation, forecasting, simulation of impacts and scen...

Lumped hydrological models are useful and convenient tools for research, engineering and educatio... more Lumped hydrological models are useful and convenient tools for research, engineering and educational purposes. They propose catchment-scale representations of the precipitation-discharge relationship. Thanks to their limited data requirements, they can be easily implemented and run. With such models, it is possible to simulate a number of hydrological key processes over the catchment with limited structural and parametric complexity, typically evapotranspiration, runoff, underground losses, etc. The Hydrology Group at Irstea (Antony) has been developing a suite of rainfall-runoff models over the past 30 years. This resulted in a suite of models running at different time steps (from hourly to annual) applicable for various issues including water balance estimation, forecasting, simulation of impacts and scenario testing. Recently, Irstea has developed an easy-to-use R-package (R Core Team, 2016), called airGR (Coron et al., 2016, 2017), to make these models widely available. Although...

This paper with the issue of catchment memory, it asks a novel question and is well in the scope ... more This paper with the issue of catchment memory, it asks a novel question and is well in the scope of the journal. I have some issues that worry me, and should be clarified.

Prior to their use under future changing climate conditions, all hydrological models should be th... more Prior to their use under future changing climate conditions, all hydrological models should be thoroughly evaluated regarding their temporal transferability (application in different time periods) and extrapolation capacity (application beyond the range of known past conditions). This note presents a straightforward evaluation framework aimed at detecting potential undesirable climate dependencies in hydrological models: the robustness assessment test (RAT). Although it is conceptually inspired by the classic differential split-sample test of Klemeš (1986), the RAT presents the advantage of being applicable to all types of models, be they calibrated or not (i.e. regionalized or physically based). In this note, we present the RAT, illustrate its application on a set of 21 catchments, verify its applicability hypotheses and compare it to previously published tests. Results show that the RAT is an efficient evaluation approach, passing it successfully can be considered a prerequisite for any hydrological model to be used for climate change impact studies.

The ability of hydrological models to perform in climatic conditions different from those encount... more The ability of hydrological models to perform in climatic conditions different from those encountered in calibration is crucial to ensure a reliable assessment of the impact of climate change on river regimes and water availability. However, most evaluation studies based on the differential split-sample test (DSST) endorsed the consensus that rainfall-runoff models lack climatic robustness. Models applied under climatologically different conditions typically exhibit substantial errors in streamflow volumes. In this technical note, we propose a new performance metric to evaluate model robustness without applying the DSST, and it can be performed with a single hydrological model calibration. The proxy for model robustness (PMR) is based on the systematic computation of model error on sliding sub-periods of the whole streamflow time series. We demonstrate that the PMR metric shows patterns similar to those obtained with the DSST for a conceptual model on a set of 377 French catchments. An analysis of the sensitivity to the length of the sub-periods shows that this length influences the values of the PMR and its equivalency with DSST biases. We recommend a range of a few years for the choice of sub-period lengths, although this should be context dependent. Our work makes it possible to evaluate the temporal transferability of any hydrological model, including uncalibrated models, at a very low computational cost.

Year 2019 was very dry in several regions of northern France and year 2020 is following the same ... more Year 2019 was very dry in several regions of northern France and year 2020 is following the same trend. Hydrological forecasting tools are crucial to design adaptative policies for many economic sectors and surface water users. More than oods, droughts are generally following long-term dynamics over several hydrological years; piezometric data, broadly available over French territory, are likely to be good indicators of these dynamics, which represent the memory of a catchment. How can an assessment of the hydrological memory help build a better low-ow forecasting model?

This technical note deals with the mathematical representation of concentration-discharge relatio... more This technical note deals with the mathematical representation of concentration-discharge relationships. We propose a two-sided affine power scaling relationship (2S-APS) as an alternative to the classic one-sided power scaling relationship (commonly known as "power law"). We also discuss the identification of the parameters of the proposed relationship, using an appropriate numerical criterion. The application of 2S-APS to the high-frequency chemical time series of the Orgeval-ORACLE observatory is presented here (in calibration and validation mode): it yields better results for several solutes and for electrical conductivity in comparison with the power law relationship.

This paper presents a new method for hydrograph separation. It is well-known that all hydrologica... more This paper presents a new method for hydrograph separation. It is well-known that all hydrological methods aiming at separating streamflow into baseflow and quickflow present large imperfections, and we do not claim to provide here a perfect solution. However, the method described here is at least (i) impartial in the determination of its two parameters (a quadratic reservoir capacity and a response time), (ii) coherent in time (as assessed by a split-sample test) and (iii) geologically coherent (an exhaustive validation on 1,664 French catchments shows a good match with what we know of France's hydrogeology). Last, an R package is provided to ensure reproducibility of the results presented. 1 Introduction Hydrograph separation and the identification of the baseflow contribution to streamflow is definitely not a new subject in hydrology. This age-old topic (Boussinesq (1904); Horton (1933); Maillet (1905)) is almost as universally decried as it is universally used. Indeed, two adjectives appear repeatedly in hydrology textbooks: artificial and arbitrary (see. e.g., Linsley et al. (1975); Réméniéras (1965); Roche (1963); Chow (1964)). Hewlett and Hibbert (1967)-the famous forest hydrology precursorseven added desperate, where Klemes (1986) compared the hydrograph separation procedures with the astronomical epicycles (i.e., the absurd trajectories that had been invented to maintain the geocentric theory before the time of Copernicus and Galilei). To assess baseflow, direct measurement is generally impossible, because aquifer-river exchanges are usually continuous processes that take place all along the stream network. Proxy approaches involving chemical tracer-based procedures are efficient but need chemical data and involve their load of assumptions. Most approaches rely on solving an inverse problem, i.e, reckoning the quantitative causes (here baseflow and quickflow) of an observed physical phenomenon-total runoff. This procedure is very common in hydrology and it is reasonably feasible when the variable can be measured and a calibration procedure can be implemented; but here again, the non-measurable character of baseflow renders the question difficult. It is perhaps impossible to propose a physically based baseflow separation procedure (just because of the multiplicity of flow paths that make the procedure fundamentally equifinal), and we will not argue on this point. But we believe that even the imperfect conceptual-mathematical-empirical methods in use could receive an unarbitrary, impartial, repeatable parameterization that could be used as a general-purpose study tool over large catchment sets.

Australasian Journal of Water Resources, 2007

Review(s) of: Large Sample Basin Experiments for Hydrological Model Parameterization: Results of ... more Review(s) of: Large Sample Basin Experiments for Hydrological Model Parameterization: Results of the Model Parameter Experiment - MOPEX, edited by Vazken Andreassian, Alan Hall, Nanee Chahinian and John Schaake, IAHS Publication 307 (2006) 348 + iv pp, plus a DVD with data.

La Houille Blanche, 2019

Cet article présente une cartographie de l'écoulement des cours d'eau de Corse, constitué... more Cet article présente une cartographie de l'écoulement des cours d'eau de Corse, constituée de deux débits caractéristiques : le débit moyen annuel (module), qui caractérise les écoulements moyens d'une rivière, et le débit mensuel minimal de fréquence quinquennale sèche (QMNA5), qui caractérise les basses eaux d'une rivière. Ces débits ont été calculés en tout point du réseau hydrographique corse grâce à deux modèles de prédétermination construits à l'échelle nationale et transposés en Corse. Ces modèles s'appuient sur une base de données hydro-climatiques récentes et critiquées regroupant 20 bassins versants jaugés. Les cartographies finales de ces débits seront diffusées par l'Agence Française pour la Biodiversité sur le portail Eaufrance (urihttp://www.eaufrance.fr/http://www.eaufrance.fr/). Ce travail permet également de quantifier de manière synthétique les écoulements des rivières de Corse, territoire très productif en eau superficielle relativement...

Hydrology and Earth System Sciences Discussions, 2019

This Technical Note documents and analyzes the confounding similarity of two widely used water ba... more This Technical Note documents and analyzes the confounding similarity of two widely used water balance formulas: Turc-Mezentsev and Tixeront-Fu. It details their history, their hydrological and mathematical properties, and discusses the mathematical reasoning behind their slight differences. Apart from the difference identified in their partial differential expressions, both formulas share the same hydrological properties and it seems impossible to recommend one over the other as more "hydrologically founded": hydrologists should feel free to choose the one they feel more comfortable with.

Proceedings of the International Association of Hydrological Sciences, 2016

Ideally, semi-distributed hydrologic models should provide better streamflow simulations than lum... more Ideally, semi-distributed hydrologic models should provide better streamflow simulations than lumped models, along with spatially-relevant water resources management solutions. However, the spatial distribution of model parameters raises issues related to the calibration strategy and to the identifiability of the parameters. To analyse these issues, we propose to base the evaluation of a semi-distributed model not only on its performance at streamflow gauging stations, but also on the spatial and temporal pattern of the optimised value of its parameters. We implemented calibration over 21 rolling periods and 64 catchments, and we analysed how well each parameter is identified in time and space. Performance and parameter identifiability are analysed comparatively to the calibration of the lumped version of the same model. We show that the semi-distributed model faces more difficulties to identify stable optimal parameter sets. The main difficulty lies in the identification of the parameters responsible for the closure of the water balance (i.e. for the particular model investigated, the intercatchment groundwater flow parameter).

Prediction on ungauged basins is a big issue for operational hydrology and a challenge for scient... more Prediction on ungauged basins is a big issue for operational hydrology and a challenge for scientists. For regionalization objectives, the first step of the development of a priori parameter estimation is to look for correlations between calibrated parameters and physical catchment descriptors. This article investigates the relationships between the parameters of the GR4J rainfallrunoff model and catchment vegetation characteristics over a large sample of 221 French catchments. First, the possible links between the calibrated parameters of the GR4J model and catchment vegetation types are investigated by linear regression. Then, we try to improve these relationships by introducing a more detailed description of the evapotranspiration process, explicitly taking into account vegetation types, following a downward approach. Results show that the GR4J model parameters cannot be determined directly from vegetation characteristics, and that the situation is not improved by a more detailed approach to evapotranspiration modelling.

IAHS publication, 2006

Today, due to the increasing availability of spatial representations of our environment, there se... more Today, due to the increasing availability of spatial representations of our environment, there seems to be a growing feeling that hydrological modelling can eventually produce efficient distributed physically-based rainfall-runoff (RR) models. However, the improvement brought by such models is still to be demonstrated. Several authors have already sounded the alarm bell on the development and application of these models, apparently to no avail. In this paper, we argue that hydrological modelling has not gone far beyond an empirical view of the way basins transform rainfall into streamflow at their outlet. We address simple questions relative to: (a) the unit physical object that should be represented by RR models; (b) the actual limits of lumped RR models; (c) the impact of the time step on the structure of RR models; (d) the necessity of a priori conceptualization in the design of RR model structures; and last (e) what defines a "good" model. We are convinced that, up to now, the empirical modelling approach has not been studied with the rigour that would help to discriminate between the numerous mathematical tools at the hydrologist's disposal to build model structures. Thus, the purpose of this paper is to recall that before considering complex models, a lot remains to be done in the area of simple lumped models.

Water Resources Research, 2012

ABSTRACT The calibration of rainfall-runoff models is commonly carried out on a single gauging st... more ABSTRACT The calibration of rainfall-runoff models is commonly carried out on a single gauging station to reproduce streamflows only at this catchment outlet. Unfortunately, the use of a single site is usually not sufficient to derive robust parameter sets for distributed or semi-distributed models, which leads to large uncertainties in the parameter values and therefore limits model performance. This uncertainty may be reduced by using other gauging stations upstream on the catchment as complementary calibration targets. To test this assumption, a semi-distributed model was applied to 195 catchments in France where streamflow is measured at the main catchment outlet and at one upstream station. This dataset is quite varied in terms of catchment characteristics and, hydrometeorological conditions and ratios between the upstream and downstream catchments areas. Three different calibration strategies were compared: 1. In the benchmark strategy, the parameters are optimized to reproduce the streamflow at the main outlet only, without using internal streamflow measurements. 2. In a second approach, the model is calibrated sequentially: first, on the internal subcatchment against the internal streamflows, then on the remaining area against the streamflow at the outlet. 3. The last approach is a multiobjective optimization using simultaneously the streamflows at the two locations with the Multiobjective Shuffled Complex Evolution Metropolis algorithm (MOSCEM). Surprisingly, the results show that, on average, the use of internal streamflow measurements for model calibration did not provide substantial performance improvement compared to the benchmark strategy at the main outlet.

Water Resources Research, 2003

This paper presents a distribution-free statistical test aimed at detecting gradual changes in th... more This paper presents a distribution-free statistical test aimed at detecting gradual changes in the hydrological behavior of watersheds. The proposed test uses a rainfall-runoff model to identify watershed behavior over successive time periods and a resampling approach to quantify the significance of trends. The method can be applied with any model deemed suitable for the studied watershed. To assess test efficiency, we used three different case studies: An afforested agricultural watershed, a burnt-over forested watershed, and a watershed covered by old-growth forest. All three watersheds had a long period of rainfall and runoff records (60, 35, and 40 years, respectively), on which stationarity could be tested. The test was shown to adequately detect gradual changes, and it can therefore be useful to identify hydrological trends, wherever rainfall and streamflow time series are available.

Hydrology and Earth System Sciences, 2014

Precipitation is the key factor controlling the highfrequency hydrological response in catchments... more Precipitation is the key factor controlling the highfrequency hydrological response in catchments, and streamflow simulation is thus dependent on the way rainfall is represented in a hydrological model. A characteristic that distinguishes distributed from lumped models is the ability to explicitly represent the spatial variability of precipitation. Although the literature on this topic is abundant, the results are contrasting and sometimes contradictory. This paper investigates the impact of spatial rainfall on runoff generation to better understand the conditions where higher-resolution rainfall information improves streamflow simulations. In this study, we used the rainfall reanalysis developed by Météo-France over the whole country of France at 1 km and 1 h resolution over a 10 yr period. A hydrological model was applied in the lumped mode (a single spatial unit) and in the semidistributed mode using three unit sizes of subcatchments. The model was evaluated against observed streamflow data using split-sample tests on a large set of French catchments (181) representing a variety of sizes and climate conditions. The results were analyzed by catchment classes and types of rainfall events based on the spatial variability of precipitation. The evaluation clearly showed different behaviors. The lumped model performed as well as the semidistributed model in western France, where catchments are under oceanic climate conditions with quite spatially uniform precipitation fields. By contrast, higher resolution in precipitation inputs significantly improved the simulated streamflow dynamics and accuracy in southern France (Cévennes and Mediterranean regions) for catchments in which precipitation fields were identified to be highly variable in space. In all regions, natural variability allows for contradictory examples to be found, showing that analyzing a large number of events over varied catchments is warranted.

We enjoyed very much reading the paper by Savenije (2008), with which we agree (almost) entirely.... more We enjoyed very much reading the paper by Savenije (2008), with which we agree (almost) entirely. We particularly like the call for more creativity, more imagination in hydrology, for a continuous interaction between the elements of the ’hydrologic trinity’: science, technology and art. When reading the literature, we get sometimes the feeling 1Invited contribution by H. H. G. Savenije, the EGU Henry Darcy Medallist 2008 for outstanding contributions

Lumped hydrological models are useful and convenient tools for research, engineering and educatio... more Lumped hydrological models are useful and convenient tools for research, engineering and educational purposes. They propose catchment-scale representations of the precipitation-discharge relationship. Thanks to their limited data requirements, they can be easily implemented and run. With such models, it is possible to simulate a number of hydrological key processes over the catchment with limited structural and parametric complexity, typically evapotranspiration, runoff, underground losses, etc. The Hydrology Group at Irstea (Antony) has been developing a suite of rainfall-runoff models over the past 30 years with the main objectives of designing models as efficient as possible in terms of streamflow simulation, applicable to a wide range of catchments and having low data requirements. This resulted in a suite of models running at different time steps (from hourly to annual) applicable for various issues including water balance estimation, forecasting, simulation of impacts and scen...

Lumped hydrological models are useful and convenient tools for research, engineering and educatio... more Lumped hydrological models are useful and convenient tools for research, engineering and educational purposes. They propose catchment-scale representations of the precipitation-discharge relationship. Thanks to their limited data requirements, they can be easily implemented and run. With such models, it is possible to simulate a number of hydrological key processes over the catchment with limited structural and parametric complexity, typically evapotranspiration, runoff, underground losses, etc. The Hydrology Group at Irstea (Antony) has been developing a suite of rainfall-runoff models over the past 30 years. This resulted in a suite of models running at different time steps (from hourly to annual) applicable for various issues including water balance estimation, forecasting, simulation of impacts and scenario testing. Recently, Irstea has developed an easy-to-use R-package (R Core Team, 2016), called airGR (Coron et al., 2016, 2017), to make these models widely available. Although...

This paper with the issue of catchment memory, it asks a novel question and is well in the scope ... more This paper with the issue of catchment memory, it asks a novel question and is well in the scope of the journal. I have some issues that worry me, and should be clarified.

Prior to their use under future changing climate conditions, all hydrological models should be th... more Prior to their use under future changing climate conditions, all hydrological models should be thoroughly evaluated regarding their temporal transferability (application in different time periods) and extrapolation capacity (application beyond the range of known past conditions). This note presents a straightforward evaluation framework aimed at detecting potential undesirable climate dependencies in hydrological models: the robustness assessment test (RAT). Although it is conceptually inspired by the classic differential split-sample test of Klemeš (1986), the RAT presents the advantage of being applicable to all types of models, be they calibrated or not (i.e. regionalized or physically based). In this note, we present the RAT, illustrate its application on a set of 21 catchments, verify its applicability hypotheses and compare it to previously published tests. Results show that the RAT is an efficient evaluation approach, passing it successfully can be considered a prerequisite for any hydrological model to be used for climate change impact studies.

The ability of hydrological models to perform in climatic conditions different from those encount... more The ability of hydrological models to perform in climatic conditions different from those encountered in calibration is crucial to ensure a reliable assessment of the impact of climate change on river regimes and water availability. However, most evaluation studies based on the differential split-sample test (DSST) endorsed the consensus that rainfall-runoff models lack climatic robustness. Models applied under climatologically different conditions typically exhibit substantial errors in streamflow volumes. In this technical note, we propose a new performance metric to evaluate model robustness without applying the DSST, and it can be performed with a single hydrological model calibration. The proxy for model robustness (PMR) is based on the systematic computation of model error on sliding sub-periods of the whole streamflow time series. We demonstrate that the PMR metric shows patterns similar to those obtained with the DSST for a conceptual model on a set of 377 French catchments. An analysis of the sensitivity to the length of the sub-periods shows that this length influences the values of the PMR and its equivalency with DSST biases. We recommend a range of a few years for the choice of sub-period lengths, although this should be context dependent. Our work makes it possible to evaluate the temporal transferability of any hydrological model, including uncalibrated models, at a very low computational cost.

Year 2019 was very dry in several regions of northern France and year 2020 is following the same ... more Year 2019 was very dry in several regions of northern France and year 2020 is following the same trend. Hydrological forecasting tools are crucial to design adaptative policies for many economic sectors and surface water users. More than oods, droughts are generally following long-term dynamics over several hydrological years; piezometric data, broadly available over French territory, are likely to be good indicators of these dynamics, which represent the memory of a catchment. How can an assessment of the hydrological memory help build a better low-ow forecasting model?

This technical note deals with the mathematical representation of concentration-discharge relatio... more This technical note deals with the mathematical representation of concentration-discharge relationships. We propose a two-sided affine power scaling relationship (2S-APS) as an alternative to the classic one-sided power scaling relationship (commonly known as "power law"). We also discuss the identification of the parameters of the proposed relationship, using an appropriate numerical criterion. The application of 2S-APS to the high-frequency chemical time series of the Orgeval-ORACLE observatory is presented here (in calibration and validation mode): it yields better results for several solutes and for electrical conductivity in comparison with the power law relationship.

This paper presents a new method for hydrograph separation. It is well-known that all hydrologica... more This paper presents a new method for hydrograph separation. It is well-known that all hydrological methods aiming at separating streamflow into baseflow and quickflow present large imperfections, and we do not claim to provide here a perfect solution. However, the method described here is at least (i) impartial in the determination of its two parameters (a quadratic reservoir capacity and a response time), (ii) coherent in time (as assessed by a split-sample test) and (iii) geologically coherent (an exhaustive validation on 1,664 French catchments shows a good match with what we know of France's hydrogeology). Last, an R package is provided to ensure reproducibility of the results presented. 1 Introduction Hydrograph separation and the identification of the baseflow contribution to streamflow is definitely not a new subject in hydrology. This age-old topic (Boussinesq (1904); Horton (1933); Maillet (1905)) is almost as universally decried as it is universally used. Indeed, two adjectives appear repeatedly in hydrology textbooks: artificial and arbitrary (see. e.g., Linsley et al. (1975); Réméniéras (1965); Roche (1963); Chow (1964)). Hewlett and Hibbert (1967)-the famous forest hydrology precursorseven added desperate, where Klemes (1986) compared the hydrograph separation procedures with the astronomical epicycles (i.e., the absurd trajectories that had been invented to maintain the geocentric theory before the time of Copernicus and Galilei). To assess baseflow, direct measurement is generally impossible, because aquifer-river exchanges are usually continuous processes that take place all along the stream network. Proxy approaches involving chemical tracer-based procedures are efficient but need chemical data and involve their load of assumptions. Most approaches rely on solving an inverse problem, i.e, reckoning the quantitative causes (here baseflow and quickflow) of an observed physical phenomenon-total runoff. This procedure is very common in hydrology and it is reasonably feasible when the variable can be measured and a calibration procedure can be implemented; but here again, the non-measurable character of baseflow renders the question difficult. It is perhaps impossible to propose a physically based baseflow separation procedure (just because of the multiplicity of flow paths that make the procedure fundamentally equifinal), and we will not argue on this point. But we believe that even the imperfect conceptual-mathematical-empirical methods in use could receive an unarbitrary, impartial, repeatable parameterization that could be used as a general-purpose study tool over large catchment sets.

Australasian Journal of Water Resources, 2007

Review(s) of: Large Sample Basin Experiments for Hydrological Model Parameterization: Results of ... more Review(s) of: Large Sample Basin Experiments for Hydrological Model Parameterization: Results of the Model Parameter Experiment - MOPEX, edited by Vazken Andreassian, Alan Hall, Nanee Chahinian and John Schaake, IAHS Publication 307 (2006) 348 + iv pp, plus a DVD with data.

La Houille Blanche, 2019

Cet article présente une cartographie de l'écoulement des cours d'eau de Corse, constitué... more Cet article présente une cartographie de l'écoulement des cours d'eau de Corse, constituée de deux débits caractéristiques : le débit moyen annuel (module), qui caractérise les écoulements moyens d'une rivière, et le débit mensuel minimal de fréquence quinquennale sèche (QMNA5), qui caractérise les basses eaux d'une rivière. Ces débits ont été calculés en tout point du réseau hydrographique corse grâce à deux modèles de prédétermination construits à l'échelle nationale et transposés en Corse. Ces modèles s'appuient sur une base de données hydro-climatiques récentes et critiquées regroupant 20 bassins versants jaugés. Les cartographies finales de ces débits seront diffusées par l'Agence Française pour la Biodiversité sur le portail Eaufrance (urihttp://www.eaufrance.fr/http://www.eaufrance.fr/). Ce travail permet également de quantifier de manière synthétique les écoulements des rivières de Corse, territoire très productif en eau superficielle relativement...

Hydrology and Earth System Sciences Discussions, 2019

This Technical Note documents and analyzes the confounding similarity of two widely used water ba... more This Technical Note documents and analyzes the confounding similarity of two widely used water balance formulas: Turc-Mezentsev and Tixeront-Fu. It details their history, their hydrological and mathematical properties, and discusses the mathematical reasoning behind their slight differences. Apart from the difference identified in their partial differential expressions, both formulas share the same hydrological properties and it seems impossible to recommend one over the other as more "hydrologically founded": hydrologists should feel free to choose the one they feel more comfortable with.

Proceedings of the International Association of Hydrological Sciences, 2016

Ideally, semi-distributed hydrologic models should provide better streamflow simulations than lum... more Ideally, semi-distributed hydrologic models should provide better streamflow simulations than lumped models, along with spatially-relevant water resources management solutions. However, the spatial distribution of model parameters raises issues related to the calibration strategy and to the identifiability of the parameters. To analyse these issues, we propose to base the evaluation of a semi-distributed model not only on its performance at streamflow gauging stations, but also on the spatial and temporal pattern of the optimised value of its parameters. We implemented calibration over 21 rolling periods and 64 catchments, and we analysed how well each parameter is identified in time and space. Performance and parameter identifiability are analysed comparatively to the calibration of the lumped version of the same model. We show that the semi-distributed model faces more difficulties to identify stable optimal parameter sets. The main difficulty lies in the identification of the parameters responsible for the closure of the water balance (i.e. for the particular model investigated, the intercatchment groundwater flow parameter).

Prediction on ungauged basins is a big issue for operational hydrology and a challenge for scient... more Prediction on ungauged basins is a big issue for operational hydrology and a challenge for scientists. For regionalization objectives, the first step of the development of a priori parameter estimation is to look for correlations between calibrated parameters and physical catchment descriptors. This article investigates the relationships between the parameters of the GR4J rainfallrunoff model and catchment vegetation characteristics over a large sample of 221 French catchments. First, the possible links between the calibrated parameters of the GR4J model and catchment vegetation types are investigated by linear regression. Then, we try to improve these relationships by introducing a more detailed description of the evapotranspiration process, explicitly taking into account vegetation types, following a downward approach. Results show that the GR4J model parameters cannot be determined directly from vegetation characteristics, and that the situation is not improved by a more detailed approach to evapotranspiration modelling.

IAHS publication, 2006

Today, due to the increasing availability of spatial representations of our environment, there se... more Today, due to the increasing availability of spatial representations of our environment, there seems to be a growing feeling that hydrological modelling can eventually produce efficient distributed physically-based rainfall-runoff (RR) models. However, the improvement brought by such models is still to be demonstrated. Several authors have already sounded the alarm bell on the development and application of these models, apparently to no avail. In this paper, we argue that hydrological modelling has not gone far beyond an empirical view of the way basins transform rainfall into streamflow at their outlet. We address simple questions relative to: (a) the unit physical object that should be represented by RR models; (b) the actual limits of lumped RR models; (c) the impact of the time step on the structure of RR models; (d) the necessity of a priori conceptualization in the design of RR model structures; and last (e) what defines a "good" model. We are convinced that, up to now, the empirical modelling approach has not been studied with the rigour that would help to discriminate between the numerous mathematical tools at the hydrologist's disposal to build model structures. Thus, the purpose of this paper is to recall that before considering complex models, a lot remains to be done in the area of simple lumped models.

Water Resources Research, 2012

ABSTRACT The calibration of rainfall-runoff models is commonly carried out on a single gauging st... more ABSTRACT The calibration of rainfall-runoff models is commonly carried out on a single gauging station to reproduce streamflows only at this catchment outlet. Unfortunately, the use of a single site is usually not sufficient to derive robust parameter sets for distributed or semi-distributed models, which leads to large uncertainties in the parameter values and therefore limits model performance. This uncertainty may be reduced by using other gauging stations upstream on the catchment as complementary calibration targets. To test this assumption, a semi-distributed model was applied to 195 catchments in France where streamflow is measured at the main catchment outlet and at one upstream station. This dataset is quite varied in terms of catchment characteristics and, hydrometeorological conditions and ratios between the upstream and downstream catchments areas. Three different calibration strategies were compared: 1. In the benchmark strategy, the parameters are optimized to reproduce the streamflow at the main outlet only, without using internal streamflow measurements. 2. In a second approach, the model is calibrated sequentially: first, on the internal subcatchment against the internal streamflows, then on the remaining area against the streamflow at the outlet. 3. The last approach is a multiobjective optimization using simultaneously the streamflows at the two locations with the Multiobjective Shuffled Complex Evolution Metropolis algorithm (MOSCEM). Surprisingly, the results show that, on average, the use of internal streamflow measurements for model calibration did not provide substantial performance improvement compared to the benchmark strategy at the main outlet.

Water Resources Research, 2003

This paper presents a distribution-free statistical test aimed at detecting gradual changes in th... more This paper presents a distribution-free statistical test aimed at detecting gradual changes in the hydrological behavior of watersheds. The proposed test uses a rainfall-runoff model to identify watershed behavior over successive time periods and a resampling approach to quantify the significance of trends. The method can be applied with any model deemed suitable for the studied watershed. To assess test efficiency, we used three different case studies: An afforested agricultural watershed, a burnt-over forested watershed, and a watershed covered by old-growth forest. All three watersheds had a long period of rainfall and runoff records (60, 35, and 40 years, respectively), on which stationarity could be tested. The test was shown to adequately detect gradual changes, and it can therefore be useful to identify hydrological trends, wherever rainfall and streamflow time series are available.