As we’ve previously reported on here, many parts of the North and West Highlands of Scotland can be spared major flooding impacts even when significant rainfall (100 to 200 mm) can fall.
In October 2018, although the town of Oban was impacted by localised flooding, many areas were spared more property flooding. Likewise in March 2015, a hydrologically significant event across much of the Highlands again only led to minor property flooding. However, it’s often the road and rail infrastructure that is most significantly impacted by these types of events as we recently observed.
A frontal wave affecting parts of western Scotland overnight on the 12 and 13 September brought with it strong winds and orographically enhanced rainfall across the mountains. Quite widely 50 to 60 mm of rain was recorded with peaks of 80 to 120 mm recorded across Skye and Lochaber. The forecast (see below) was for widespread minor flooding to occur, but the guidance also suggesting a very low likelihood of more significant impacts.
During the Sunday morning reports started to materialise of major disruption across the transport network. Impacts included flooding and disruption on the Crainlarich to Fort William rail line at Bridge of Orchy and flooding of main trunk roads including the A890 and A82 in Skye and Lochaber and the A8 in Renfrewshire.
Attempting to link our forecasting capabilities with the transport receptors is the focus of a new area of work for us. In partnership with Transport Scotland, we’re now exploring ways of developing an impact-based forecasting approach for the Trunk Road network in Scotland.
The research will look at how best to predict the impacts of flooding across the vulnerable parts of the transport network and explore whether empirical links are sufficient or whether these links need to be developed through pre-simulated scenarios as set out in the recent research on towards improved surface water flood forecasts in Scotland.