Improved Scaling and Impact Metrics for Euro-Atlantic Atmospheric Rivers

Atmospheric rivers (AR) are essential to the global water cycle, significantly impacting regional precipitation patterns and extreme weather events. Existing AR scales, while valuable, often lack regional specificity, particularly in capturing the nuances of ARs in subpolar regions. This study addresses these limitations by developing an improved AR scale and impact metrics tailored to the Euro-Atlantic region. Using high-resolution reanalysis data and the Bayesian AR Detector, we analyse AR characteristics and highlight contrasts between Pacific and Atlantic ARs. Recognising the limitations of the current AR scale developed by the Centre for Western Weather and Water Extremes, we introduce the new Uppsala University AR scale (NS), specifically designed for the Euro-Atlantic region. The NS incorporates a lower integrated water vapour threshold, equal weights for all categories, and a 72-hour persistence, reflecting regional AR behaviour more accurately. The study proposes alternative impact metrics - AR Severity Index (ARSI), ARSI-kinetic, and Risk Index - to comprehensively assess AR impacts. While ARSI focuses on physical strength, the Risk Index combines intensity with contextual factors for a broader view of overall risk. These refined metrics and the region-specific AR scale enhance understanding of AR impacts and hazards in the Euro-Atlantic region, contributing to improved forecasting, disaster preparedness, and water resource management.