Water in lochs and reservoirs warming due to climate change, report finds

Water in Scotland’s lochs and reservoirs has undergone “rapid and extensive climate change driven warming” in recent years, according to new research.

The report by Scotland’s Centre of Expertise for Waters (Crew) found that between 2015 and 2019, 97% of Scottish lochs and reservoirs increased in temperature.

Most warmed by between 0.25C and 1C per year, however, 9% of them increased by 1C to 1.3C per year.

Researchers warn that these changes increase the risk of harmful algal blooms developing, which could restrict their use for recreation and water supply, and as a safe habitat for wildlife.

Waters in the south and east of Scotland are expected to warm the most at first, but the report warns that this climate-related impact will reach all parts of Scotland by 2040.

Environment Minister, Mairi McAllan, said: “This important research provides yet more worrying evidence of the risks of harm from climate change on Scotland’s water environment.

“It is vital that we do more to mitigate those impacts; to seek to reduce the pace of warming but also to adapt to it.

“We have committed £243 million since 2015 through the Agri-Environment Climate Scheme to support land management practices which protect and enhance Scotland’s natural heritage, improve water quality, manage flood risk and mitigate and adapt to climate change.”

The report states that short periods of extremely high water temperatures known as “lake heatwaves” are likely to increase in occurrence, exacerbating the adverse effects of long-term warming.

It warns that lake heatwaves are “likely to push aquatic ecosystems beyond the limits of their resilience, posing a threat to their biodiversity and related benefits they provide to society.”

The study says that average April to September air temperatures are projected to rise by about 2.5C between 2020 and 2080.

Researchers said that because loch and reservoir temperatures appear to be increasing by 1.2 times the rate of increase in air temperature, “this equates to a corresponding increase of about 3C in Scottish standing waters by 2080.”

Freshwater ecologist, Dr Linda May, of the UK Centre for Ecology & Hydrology (UKCEH), lead author of the report, said: “This research has shown, for the first time, that climate change is already warming our lochs and reservoirs in Scotland, and that this trend is likely to continue.

“It provides early warning of the potential impacts of climate change on biodiversity, water supply and recreational use, and highlights the need for mitigation measures to be put in place as quickly as possible.”

The report makes a number of recommendations to address the impacts of warming in the immediate term.

These include reducing the amount of phosphorus and nitrogen entering lochs and reservoirs from their catchments, because these are the main driver of algal blooms.

Sources of these plant nutrients, present in synthetic fertilisers as well as human and animal waste, include farm runoff and waste water discharges.

Actions such as the creation of buffer strips and constructed wetlands, are already under way in many catchments across Scotland aimed at reducing nutrient inputs.

NatureScot Freshwater and Wetlands Advice Manager, Iain Sime, said: “Scotland, like the rest of the world, is facing an unprecedented climate emergency. The findings of this comprehensive review are stark, demonstrating the impact that climate change is already having on our freshwater lochs and reservoirs, and their biodiversity.

“The need for urgent action is clear, and at NatureScot we are using the £65 million Nature Restoration Fund to prioritise efforts that support the conservation of our lochs and ponds.”

Funded by the Scottish Government, Crew is a partnership between the James Hutton Institute and Scottish higher education and research institutes.