Compound Cold Events, Impacts and Weather Patterns: A Case Study of the Scottish Rail Network

Abstract

Winter weather events disrupt critical national infrastructure, with rail networks particularly vulnerable to blocked tracks, mechanical faults, and frozen infrastructure leading to service delays and cancellations. The impacts of these cold weather events can be amplified by the compounding effect of another meteorological variable, particularly whether heavy precipitation is present or absent, with subsequent impacts dependent on the nature of the cold event. For example, a ‘compounding’ cold-wet event could incur heavy snowfall, whereas a cold-dry event could result in extreme low temperatures and icy conditions. Despite their prevalence, such compound cold extremes remain understudied compared to compound heat extremes. In this study, we analyse 10,500 Scottish rail incidents (2006–2023, October to March) using Network Rail impact data, the set of Met Office 30 weather patterns (MO30), and HadUK-Grid observations to link incidents with compound cold events. We identify high-impact days based on two classifications: (1) days exceeding the 99th percentile of aggregated daily incidents; (2) days exceeding the 99th percentile of daily customer minutes lost. The majority of high-impact days were snow-related, occurring under cold-dry or cold-wet conditions with the definition depending on whether snow was falling or lying. These findings highlight the importance of considering co-occurring cold hazards, as real-world impacts may diverge from traditional hazard-based detection. This provides useful insight for compound cold early warning systems.