Use of expert elicitation to assign weights to climate and hydrological models in climate impact studies

Various methods are available for assessing uncertainties in climate impact studies. Among such methods, model weighting by expert elicitation is a practical way to provide a weighted ensemble of models for specific real-world impacts. The aim is to decrease the influence of improbable models in the results and easing the decision-making process. In this study both climate and hydrological models are analysed, and the result of a research experiment is presented using model weighting with the participation of six climate model experts and six hydrological model experts. For the experiment, seven climate models are a priori selected from a larger EURO-CORDEX (Coordinated Regional Downscaling Experiment - European Domain) ensemble of climate models, and three different hydrological models are chosen for each of the three European river basins. The model weighting is based on qualitative evaluation by the experts for each of the selected models based on a training material that describes the overall model structure and literature about climate models and the performance of hydrological models for the present period. The expert elicitation process follows a three-stage approach, with two individual rounds of elicitation of probabilities and a final group consensus, where the experts are separated into two different community groups: a climate and a hydrological modeller group. The dialogue reveals that under the conditions of the study, most climate modellers prefer the equal weighting of ensemble members, whereas hydrological-impact modellers in general are more open for assigning weights to different models in a multi-model ensemble, based on model performance and model structure. Climate experts are more open to exclude models, if obviously flawed, than to put weights on selected models in a relatively small ensemble. The study shows that expert elicitation can be an efficient way to assign weights to different hydrological models and thereby reduce the uncertainty in climate impact. However, for the climate model ensemble, comprising seven models, the elicitation in the format of this study could only re-establish a uniform weight between climate models

Le partage de la ressource en eau sur la Durance en 2050 : vers une évolution du mode de gestion des grands ouvrages duranciens ?

Congrès SHF: Water Tensions in Europe and in the Mediterranean: water crisis by 2050?, Paris, FRA, 08-/10/2015 - 09/10/2015International audienceUne vision prospective de la gestion de l'eau du bassin de la Durance et des territoires alimentés par ses eaux à l'horizon 2050 a été élaborée, appuyée par une chaine de modèles incluant des représentations du climat, de la ressource naturelle, des demandes en eau et du fonctionnement des grands ouvrages hydrauliques (Serre-Ponçon, Castillon et Sainte-Croix), sous contraintes de respect des débits réservés, de cotes touristiques dans les retenues et de restitution d'eau stockée pour des usages en aval. Cet ensemble, validé en temps présent, a été alimenté par des projections climatiques et paramétré pour intégrer les évolutions du territoire décrites par des scénarios de développement socio-économique avec une hypothèse de conservation des règles de gestion actuelles. Les résultats suggèrent à l'horizon 2050 : une hausse de la température moyenne de l'air impactant l'hydrologie de montagne ; une évolution incertaine des précipitations ; une réduction des stocks de neige et une fonte avancée dans l'année qui induisent une réduction des débits au printemps ; une diminution de la ressource en eau en période estivale ; une diminution de la demande globale en eau à l'échelle du territoire, cette demande étant fortement conditionnée par les scénarios territoriaux élaborés ici ; la satisfaction des demandes en eau en aval des ouvrages considérées comme prioritaires, au détriment de la production d'énergie en hiver (flexibilité moindre en période de pointe) et du maintien de cotes touristiques en été ;une diminution de la production d'énergie due notamment à la réduction des apports en amont des ouvrages hydroélectriques

On the visual detection of non-natural records in streamflow time series: challenges and impacts

Large datasets of long-term streamflow measurements are widely used to infer and model hydrological processes. However, streamflow measurements may suffer from what users can consider anomalies, i.e. non-natural records that may be erroneous streamflow values or anthropogenic influences that can lead to misinterpretation of actual hydrological processes. Since identifying anomalies is time consuming for humans, no study has investigated their proportion, temporal distribution, and influence on hydrological indicators over large datasets. This study summarizes the results of a large visual inspection campaign of 674 streamflow time series in France made by 43 evaluators, who were asked to identify anomalies falling under five categories, namely, linear interpolation, drops, noise, point anomalies, and other. We examined the evaluators' individual behaviour in terms of severity and agreement with other evaluators, as well as the temporal distributions of the anomalies and their influence on commonly used hydrological indicators. We found that inter-evaluator agreement was surprisingly low, with an average of 12 % of overlapping periods reported as anomalies. These anomalies were mostly identified as linear interpolation and noise, and they were more frequently reported during the low-flow periods in summer. The impact of cleaning data from the identified anomaly values was higher on low-flow indicators than on high-flow indicators, with change rates lower than 5 % most of the time. We conclude that the identification of anomalies in streamflow time series is highly dependent on the aims and skills of each evaluator, which raises questions about the best practices to adopt for data cleaning.</p

Twenty-three unsolved problems in hydrology (UPH) – a community perspective

This paper is the outcome of a community initiative to identify major unsolved scientific problems in hydrology motivated by a need for stronger harmonisation of research efforts. The procedure involved a public consultation through on-line media, followed by two workshops through which a large number of potential science questions were collated, prioritised, and synthesised. In spite of the diversity of the participants (230 scientists in total), the process revealed much about community priorities and the state of our science: a preference for continuity in research questions rather than radical departures or redirections from past and current work. Questions remain focussed on process-based understanding of hydrological variability and causality at all space and time scales. Increased attention to environmental change drives a new emphasis on understanding how change propagates across interfaces within the hydrological system and across disciplinary boundaries. In particular, the expansion of the human footprint raises a new set of questions related to human interactions with nature and water cycle feedbacks in the context of complex water management problems. We hope that this reflection and synthesis of the 23 unsolved problems in hydrology will help guide research efforts for some years to come