Predictions of hotter weather with reduced precipitation and streamflow under climate change make it highly likely that Pacific salmon populations will be increasingly exposed to future water temperature extremes. Given the importance of temperature to regulate vital physiological processes in Pacific salmon, the availability of discrete cold-water patches in rivers and streams to act as thermal refugia may become increasingly critical for the survival of Pacific salmon. Such refugia can be provided by the input of a cooler tributary, an influx of cold groundwater, or hyporheic flow (a place in the streambed where groundwater and surface water mix). Developing reliable monitoring and mapping methods to efficiently identify accessible cold-water refuge areas within basin river networks will become increasingly important tools for salmon conservation and management in a warming world.

Through funding provided by a Mitacs Accelerate Program, the Salmon Watersheds Program is working with the BC Institute of Technology (BCIT) and Simon Fraser University (SFU) in the North Alouette River watershed to evaluate the use of a remotely piloted aircraft system (RPA or drone) for thermal infrared mapping of streams to identify seasonal cold-water patches that could benefit salmon. Information from RPA flights for this project will directly feed into a larger Pacific Institute for Climate Solutions (PCIS) funded study (Drought and Deluge: Informed Water Allocation Decision Making in a World of Intensifying Hydrologic Extremes) being undertaken by SFU researchers in the North Alouette River watershed. Among other elements, the broader SFU study aims to characterize the various thermal buffers available within the watershed (e.g., cool headwaters, groundwater discharge, riparian vegetation) and to compare the results of different water temperature assessment techniques (i.e., remote sensing of thermal conditions through thermal infrared data acquired by RPAs and by satellite vs. direct monitoring of water temperature via boat-mounted thermal cameras and instream stationary temperature monitoring stations).

Outcomes

• Thermal mapping of a section of the North Alouette River from RPA (drone) imagery
• Evaluating changes in seasonal stream temperatures within the section using interpreted RPA collected data
• Evaluating how well (and at what scales) thermal refugia for salmon can be detected in streams using thermal imagery from RPAs.

Information from this project will feed into the larger SFU-led comparative study and will help to inform monitoring of salmon habitats throughout BC through a refined understanding of the ability of different water temperature assessment and monitoring techniques (remote sensed and direct) to accurately reflect the potentially variable temperature conditions both in time and space that salmon populations will face within their freshwater life stage.