River temperature is of great importance to the growth and survival of a range of iconic fish species such as Atlantic salmon and Brown trout. However, there are concerns that climate change could increase water temperatures, altering the thermal suitability of UK rivers to native species. As a result, better understanding of the impacts of a warming climate on UK rivers is urgently required.

Research by the University of Birmingham, in collaboration with Marine Scotland Science (MSS), is demonstrating how cutting-edge technology can be used to inform river management and policy in order to respond to this threat. The work, combining drones and river temperature modelling (part of the EU Horizon 2020-funded Marie Curie project HoTRiverS), aims to better understand stream temperature patterns, controls and response to climate change.

One of the ways in which river managers currently regulate stream temperature is by planting trees to shade rivers. However, there is considerable uncertainty regarding how and where trees should be planted in order to produce ‘optimum’ temperature reductions. This is because detailed information on tree cover is difficult to obtain, especially in remote locations. There is, therefore, a pressing need to develop methods capable of accurately and cost-effectively characterising bankside tree cover and the impacts of shading.

To address this research problem, my colleagues (Professor David Hannah from the University of Birmingham and Dr Iain Malcom from Marine Scotland Science) and I have developed a novel methodology to simulate the impacts of tree cover on stream temperature. We used a drone to obtain high-resolution aerial photography of Girnock Burn, a tributary of the Aberdeenshire River Dee where MSS has monitored salmon populations for over 50 years. Using a technique called ‘structure-from-motion photogrammetry’, which enables the extraction of 3D data from 2D photos (in much the same way as stereo vision allows humans to perceive depth), we were able to generate a highly accurate 3D map of tree heights in the lower Girnock Burn. By inputting this tree height data into a computer model that simulates the impacts of shade on stream temperature, we were subsequently able to highlight the extent to which tree shading reduces stream temperature in Girnock Burn.

This new low-cost, high-accuracy methodology has the potential to improve our understanding about how and where tree shading produces optimal stream temperature reductions. It is hoped that the research will help furnish river scientists and managers with the information necessary to target planting in locations where it will have the greatest benefits in reducing the effects of climate change.

The HoTRiverS project is also highlighting other ways in which drone technology can help scientists to better understand stream temperature patterns. Previous research has shown how airborne thermal infrared (TIR) river surveys can be used to identify important cool-water habitats used by salmon and trout during summer high temperature. However, TIR survey flights using conventional aircraft are costly, meaning that the location of these critical habitats often remains unknown. In order to try and resolve this issue, we used a drone equipped with a miniaturised thermal infrared imaging camera to map surface water temperature patterns in Baddoch Burn, another salmon monitoring tributary in the Aberdeenshire Dee catchment.

Although the analysis of these data is ongoing, early indications are that the drone-based thermal imaging data will be useful for detecting cool-water habitats that are of key importance to fish and other species. This cutting-edge research project demonstrates how advances in geospatial technology and computer modelling are helping to better understand and protect the UK’s freshwater environments.

Through these results, it is hoped that we will arrive at a better understanding of the interactions between the landscape, rivers and climate change, with a view to preserving the UK’s valuable rivers for future generations.