No abstract

Testing hydrological models under changing conditions is essential to evaluate their ability to cope with changing catchments and their suitability for impact studies. With this perspective in mind, a workshop dedicated to this issue was held at the 2013 General Assembly of the International Association of Hydrological Sciences (IAHS) in Göteborg, Sweden, in July 2013, during which the results of a common testing experiment were presented. Prior to the workshop, the participants had been invited to test their own models on a common set of basins showing varying conditions specifically set up for the workshop. All these basins experienced changes, either in physical characteristics (e.g. changes in land cover) or climate conditions (e.g. gradual temperature increase). This article presents the motivations and organization of this experiment-that is-the testing (calibration and evaluation) protocol and the common framework of statistical procedures and graphical tools used to assess the model performances. The basins datasets are also briefly introduced (a detailed description is provided in the associated Supplementary material).

Much has been written on the subject of objective functions to calibrate rainfall-runoff models. Many studies focus on the best choice for low-flow simulations or different multiobjective purposes. Only a few studies, however, investigate objective functions to optimise the simulations of low-flow indices that are important for water management. Here, we test different objective functions, from single objective functions with different discharge transformations or using low-flow indices to combinations of single objective functions and we evaluate their robustness and sensitivity to the rainfall-runoff model. We found that the Kling and Gupta efficiency (KGE) applied to a transformation of discharge was inadequate to fulfil all assessment criteria, whereas the mean of the KGE applied to the discharge and the KGE applied to the inverse of the discharge was sufficient. The robustness was dependent on the climate variability rather than the objective function and the results were not sensitive to the model.

Intermittent rivers and ephemeral streams (IRES) are now recognized to support specific freshwater biodiversity and ecosystem services and represent approximately half of the global river network, a fraction that is likely to increase in the context of global changes. Despite large research efforts on IRES during the past few decades, there is a need for developing a systemic approach to IRES that considers their hydrological, hydrogeological, hydraulic, ecological, and biogeochemical properties and processes, as well as their interactions with human societies. Thus, we assert that the interdisciplinary approach to ecosystem research promoted by critical zone sciences and socio‐ecology is relevant. These approaches rely on infrastructure—Critical Zone Observatories (CZO) and Long‐Term Socio‐Ecological Research (LTSER) platforms—that are representative of the diversity of IRES (e.g., among climates or types of geology. We illustrate this within the French CZO and LTSER, including their diversity as socio‐ecosystems, and detail human interactions with IRES. These networks are also specialized in the long‐term observations required to detect and measure ecosystem responses of IRES to climate and human forcings despite the delay and buffering effects within ecosystems. The CZO and LTSER platforms also support development of innovative techniques and data analysis methods that can improve characterization of IRES, in particular for monitoring flow regimes, groundwater‐surface water flow, or water biogeochemistry during rewetting. We provide scientific and methodological perspectives for which this interdisciplinary approach and its associated infrastructure would provide relevant and original insights that would help fill knowledge gaps about IRES. This article is categorized under: Water and Life > Stresses and Pressures on Ecosystems Science of Water > Hydrological Processes Water and Life > Conservation, Management, and Awareness

This study deals with the Rimbaud catchment, a sub-catchment within the Réal Collobrier hydrological observatory in southeastern France, managed by Irstea since 1966. This observatory suffered a wildfire in 1990. Because of the dense network of streamgauges and raingauges available, this site provides a unique opportunity to test and compare two types of analysis, one based on paired catchments and the other a rainfall-runoff model, used to assess the hydrological impact of forest fire. In the present case, more than 20 years of pre-fire and post-fire data are available. We compare the ability of the two approaches to detect gradual changes at a daily time step. This case study illustrates how natural climatic variability (here a long drought which preceded the wildfire) can make the identification of hydrological changes extremely difficult. Key words paired catchments; rainfall-runoff modelling; hydrological impact of wildfire; change detection Mise en perspective de la méthode des bassins appariés et de la modélisation pluie-débit sur l'impact hydrologique d'un incendie de forêt Résumé Cet article traite du bassin versant du Rimbaud situé dans le Sud de la France. Il fait partie de l'observatoire hydrologique du Réal Collobrier suivi depuis 1966 par Irstea. Cet observatoire a subi un incendie de forêt en 1990. Grace à son réseau dense de stations hydrométriques et pluviométriques, ce site fournit une occasion unique de comparer la méthode des bassins appariés et la modélisation pluie-débit pour évaluer l'impact hydrologique de l'incendie de forêt. Dans notre cas, plus de 20 années de données avant et après incendie sont disponibles. Nous pouvons donc comparer la capacité des deux méthodes à détecter des changements graduels au pas de temps journalier. L'étude illustre comment la variabilité climatique naturelle (ici une longue sécheresse précédent l'incendie) rend extrêmement difficile toute interprétation de modification du comportement hydrologique. Mots clefs bassins versants appariés ;modélisation pluie-débit ; impact hydrologique d'un incendie de forêt ; détection de changement 1 INTRODUCTION This study proposes a detailed analysis of a French catchment that was used as one of the case studies for the workshop: Testing simulation and forecasting models in nonstationary conditions, organized within the IAHS/IAPSO/IASPEI Joint Assembly in Gothenburg, Sweden in July 2013. More information on the workshop is available in