Impacts of climate change on marginal nights for road salting

Spreading salt on roads costs UK highways authorities millions of pounds each year. As temperatures rise under climate change, the number of nights with freezing temperatures are projected to fall, potentially reducing salting costs. However, this may also mean more nights drop close to freezing, rather than falling comfortably below zero. These ‘marginal nights’ often require a judgement call as to whether salting is required. The analysis presented here considers how climate change is projected to affect the number of marginal nights at nine locations in England in the near-term (2020s). Synthetic temperature timeseries from the UK Climate Projections 2009 weather generator are used to calculate frequencies of marginal nights in the current and potential future climate. The results show a reduction in the average number of marginal nights for all locations under the median estimate of the medium emissions scenario. The full range of results shows that, despite the reduction, marginal nights will still occur, and in some years the frequency will exceed the baseline. This serves as a reminder that, even under a warmer climate, there will be cold periods that require roads to be salted.