Assessing the role of weirs and riparian cover on river longitudinal temperature profile using airborne TIR in a lowland agricultural catchment

International audienc

Diversité thermique spatiale et aménagement des rivières

International audienc

Diversité thermique spatiale et aménagement des rivières

International audienc

Assessing the role of weirs and riparian cover on river longitudinal temperature profile using airborne TIR in a lowland agricultural catchment

International audienc

Assessing the role of weirs and riparian cover on river longitudinal temperature profile using airborne TIR in a lowland agricultural catchment

International audienc

Riparian shading mitigates warming but cannot revert thermal alteration by impoundments in lowland rivers

International audienc

Assessing the role of weirs and riparian cover on river longitudinal temperature profile using airborne TIR in a lowland agricultural catchment

International audienc

Diversité thermique spatiale et aménagement des rivières

International audienc

Riverscape-scale airborne TIR assessment of weirs and riparian cover effects on lowland river temperature

International audienceThe development of Airborne Infrared Thermal sensing (TIR) is an example of how technological advancement and the field that they focus on have fostered one another. The pace at which global change is occurring has fed the demand for better understanding of the thermal behaviour of rivers. In turn, the improvement of remote sensing and data processing techniques has provided researchers and managers with new tools to apprehend such aspects at ever larger scales. Still, recent studies have mostly focussed on rivers showing little human alteration, with a particular interest on groundwater-surface water interactions. Lowland streams are scarcely considered when it comes to the study of temperature despite their widespread occurrence, their relatively high degree of disturbance and the risks that they face in the light of temperature rising following climate change. Some of these streams already display critically high maximum summer temperatures and their state is likely to worsen in the future, putting all compartments of biota at risk.The aims of this project were twofold. We first tested the applicability of airborne TIR to study lowland, slow-flowing stream reaches draining agricultural catchments, some of which being particularly narrow and sinuous. We then sought to understand the role of different environmental factors, observed in such context, on driving river temperature during the warmest days of the year. A number of anthropogenic actions such as clear-cutting of riparian trees, stream rectification and the construction of weirs are likely to influence the longitudinal temperature profile of such streams. By choosing rivers with no or limited groundwater inputs, we were able to quantify the relative role of each of the three tested factors and identify stream sections showing critically high maximum temperature over the summer. A final step was proposed to upscale these results in order to identify sections of streams showing high risks of reaching critically high summer temperature at a regional network scale. To do so, we used a combination of high resolution land-cover data, digital elevation models and other existing databases (e.g. national inventory of weirs). Identification of the risks in relation with the relative contribution of the different factors is key to process-based river management. This type of output is valuable to river basin managers and decision makers as it can be used to implement targeted restoration initiatives or remediation actions in areas where these have higher chances of being effective

Combining expert‐based and computational approaches to design protected river networks under climate change

International audienceAim: Estimate the current and future distribution of brown trout and identify priority areas for conservation of the species.Location: Rhône River basin and Mediterranean streams.Methods: We first developed a spatially explicit species distribution model to es- timate the current and future distribution of brown trout for three time horizons (2030, 2055 and 2080) and two climate change scenarios (RCP 4.5 and RCP 8.5). We then performed a prioritization analysis to identify priority areas for brown trout conservation, accounting for: (a) spatial dependencies along the riverine system, (b) several sources of uncertainty arising from climate-related forecasts and (c) different protected area scenarios by comparing hypothetical, optimal protected networks to an actual protected network designed by regional fish experts.Results: Future projections of brown trout densities exhibited a general trend to- wards a gradual range contraction, with a significant risk of extirpation across moun- tainous regions of low to mid-elevation. Overall, the projected current and future distributions were well-covered by the existing protected network. In addition, up to 70% of the river reaches included in this expert-based protection network were also priorities in the optimal priority set (e.g. the best set of areas to maximize biodiversity protection). Finally, a large proportion of these reaches were invariably identified re- gardless of climate change scenarios and uncertainties or spatial dependencies. Main conclusions: Our analytical approach highlighted priority areas for brown trout conservation which were robust to a set of climate and connectivity assumptions. This core priority network could be further refined by taking into account key fine- scale processes like thermal refugia. Therefore, we advocate for combining computa- tional and expert-based approaches in conservation planning of riverine ecosystems to achieve a relevant consensus between regional-scale management and fine-grain ecological knowledge