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Mitigating the impacts of global warming on wildlife entails four practical steps. First, we need to study how processes of interest vary with temperature. Second, we need to build good temperature scenarios. Third, processes can be forecast accordingly. Only then can we perform the fourth step, testing mitigating measures. While having good temperature data is essential, this is not straightforward for stream ecologists and managers. Water temperature (WT) data are often short and incomplete and future projections are currently not routinely available. There is a need for generic models which address this data gap with good resolution and current models are partly lacking. Here, we expand a previously published hierarchical Bayesian model that was driven by air temperature (AT) and flow (Q) as a second covariate. The new model can hindcast and forecast WT time series at a daily time step. It also allows a better appraisal of real uncertainties in the warming of water temperatures in rivers compared to the previous version, stemming from its hybrid structure between time series decomposition and regression. This model decomposes all-time series using seasonal sinusoidal periodic signals and time varying means and amplitudes. It then links the contrasted frequency signals of WT (daily and six month) through regressions to that of AT and optionally Q for better resolution. We apply this model to two contrasting case study rivers. For one case study, AT only is available as a covariate. This expanded model further improves the already good fitting and predictive capabilities of its earlier version while additionally highlighting warming uncertainties. The code is available online and can easily be run for other temperate rivers.

Providing generic and cost effective modelling approaches to reconstruct and forecast freshwater temperature using predictors as air temperature and water discharge is a prerequisite to understanding ecological processes underlying the impact of water temperature and of global warming on continental aquatic ecosystems. Using air temperature as a simple linear predictor of water temperature can lead to significant bias in forecasts as it does not disentangle seasonality and long term trends in the signal. Here, we develop an alternative approach based on hierarchical Bayesian statistical time series modelling of water temperature, air temperature and water discharge using seasonal sinusoidal periodic signals and time varying means and amplitudes. Fitting and forecasting performances of this approach are compared with that of simple linear regression between water and air temperatures using i) an emotive simulated example, ii) application to three French coastal streams with contrasting bio-geographical conditions and sizes. The time series modelling approach better fit data and does not exhibit forecasting bias in long term trends contrary to the linear regression. This new model also allows for more accurate forecasts of water temperature than linear regression together with a fair assessment of the uncertainty around forecasting. Warming of water temperature forecast by our hierarchical Bayesian model was slower and more uncertain than that expected with the classical regression approach. These new forecasts are in a form that is readily usable in further ecological analyses and will allow weighting of outcomes from different scenarios to manage climate change impacts on freshwater wildlife.

Résumé: En 1997, Joseph PARÉ publiait son ouvrage Écritures et Discours dans le roman africain francophone. Dans son livre, l’auteur se proposait d’observer spécifiquement le discours romanesque, dans la littérature africaine francophone. L’objet observé selon l’auteur est spécifique en ce sens qu’il est ontologiquement hybride, c’est-à-dire qu’il est un dérivé de deux imaginaires différents, clairement identifiables. Il s’agit d’une part de la culture occidentale acquise grâce ou à cause de la colonisation et qui se manifeste par l’utilisation de la langue (le français) ; et d’autre part la culture africaine, à travers la littérature orale et certaines pratiques langagières. La spécificité de l’objet à examiner nécessitait la construction d’une démarche méthodologique en vue de le prendre en charge. Cette démarche s’appelle, l’herméneutique de l’hybridité. La présente réflexion est une proposition qui vise un double objectif : repenser la démarche critique (l’herméneutique de l’hybridité) et envisager son prolongement. Le corpus de base dans cette étude est constitué entre autres de « Les Soleils des indépendances » (A. Kourouma) ; « Ça tire sous le Sahel » ( T. Pacéré) ; « Les Dieux délinquants » ( A. S. Coulibaly), etc. Mots-clés : sémiotique ; hybridité ; Hybridation ; littérature africaine francophone