Guest blog by Alex Priestley, PhD student in snow science at the University of Edinburgh School of Geosciences as part of the NERC-funded E3 Doctoral Training Partnership.

Our uplands are home to species which are affected by snow cover in many ways, such as mountain hares’ or ptarmigans’ white colours in winter, and rare alpine plants living on ground that is snow-covered for months at a time. But Scottish snow cover is decreasing as our climate warms, and how this will affect some of our most iconic species is difficult to predict. During my placement with RSPB, I’ve been using my experience as a snow scientist, meteorologist and all-round fan of nature in the Scottish mountains to help understand the future prospects of montane species in Scotland.

As part of my PhD research, I have been running a high resolution snow model to understand how liquid water (either from melting snow, or rain falling onto the snow) moves through the snow layers. This liquid water movement is a big factor in the risk of avalanches, and whether the snow acts as a reservoir for water supplies or contributes to flood risk. Where I have been working in the French Alps, these issues will become even more important as our climate warms. But how will changes to snow cover affect us closer to home?

Long lying snow high on the Cairngorm plateau in July 2021. This snow may have fallen as long ago as October 2020, and will have been over 5m deep at the end of the winter! © Steven Ewing

Snow in the Scottish Highlands

Snow cover is not as significant in Scotland when compared to higher latitude or altitude parts of the world, but it is nonetheless an important factor in the climate and biodiversity of the Scottish uplands. Widespread snow cover can persist at modest altitudes for several months even in average winters, and some long lying snow in the highest remote corries has only been recorded completely melting on a handful of occasions in the past century.

Despite this, long term records of snow cover extent in the Scottish highlands are few and far between. Observations do exist from low lying sites, but due to the variable nature of snow cover (just think about how deep drifts can form adjacent to almost snow-free areas when it’s windy!) it is difficult to extrapolate these records to remote montane habitats. Satellite information does exist, but it’s severely limited by cloud cover and records only start in the 1980s.

This lack of data means that if we want to look at montane snow cover in detail, we need to use models.

Surveying the vast expanse of the Cairn Lochan plateau at 1200m in the Cairngorms National Park. No dotterels to be seen but lots of breeding snow buntings and ring ouzels © Steven Ewing

How do we model snow

Snow models take weather inputs such as temperature, rain or snowfall, solar radiation and relative humidity, and predict the resultant snow using equations. We can get the required weather data to run snow models from long term datasets recently developed by the European Centre for Medium Range Weather Forecasting which gives us data back to 1950.

This data isn’t at quite the resolution required to pick out the summits and glens of the Highlands, so we need to ‘downscale’ it to our specific sites using some higher resolution rainfall data produced by the Centre for Ecology and Hydrology, and adjust the weather data for altitude effects too. We can then run a model that can produce predictions of snow cover from 1950 until the present day at any point in the Highlands!

Looking for breeding dotterels

As part of my placement, we spent a few days surveying montane birds at the sites in the Scottish Highlands with the longest existing records, with a particular focus on dotterels. Naturally, after weeks of fair weather, cloud and rain pushed in over the Highlands while we were there, but careful consideration of the weather forecasts and a large amount of luck meant we avoided most of the downpours!

A male dotterel on a nest at around 850m in the Drumochter hills. He was only spotted after a helpful mountain hare we were watching nearly stood on him! © Steven Ewing

As someone who normally heads straight to the summit of mountains, spending time surveying the lesser-visited corries and ridges was fantastic. We did find breeding dotterels, along with snow buntings, ring ouzels, golden plovers, dunlin and a pair of golden eagles. After such a cold spring, we found some dotterels to be breeding later than average, with a possible downwards shift in altitude, although we would need to survey more sites to really be sure of this. For the sites we did survey, we have added an extra year in the long records already available with which we will be comparing the snow cover model results.

I’m now approaching the end of my placement with RSPB. It’s been fantastic to apply my skills in modelling and snow science in a subject I’m passionate about, along with the opportunity to learn from RSPB’s scientists about ecological science and surveying technique. Spending a week in the field was the icing on the cake, even if the weather didn’t always behave!

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