Inland-penetrating Atmospheric Rivers and Hydrometeorological Impacts in Colorado

Atmospheric rivers (ARs) play a leading role in high-impact weather and long-term hydroclimate across the Western U.S. However, relatively little work has been done to understand AR characteristics inland from the U.S. West Coast and this is especially true for Colorado, where high and complex topography, as well as distance from the coast, hinder attempts to track moisture from ARs and their impacts. While anecdotal evidence suggests that ARs play a fundamental role in extreme precipitation and longer-term hydroclimate across Colorado, this relationship is yet to be systematically analyzed and quantified.

This work uses novel methods to explore the role of inland penetration of water vapor along ARs, their landfalling intensity, and their interannual variability on hydrometeorological extremes across the state. In particular, this study focuses on the relative contribution of water vapor along inland-penetrating ARs to heavy precipitation events and seasonal snowfall (accumulated snow water equivalent) in subbasins across Colorado. We show that while the overhead AR frequency across Colorado is very low, moisture sourced from ARs affects this area much more frequently, penetrating inland along relatively low-elevation corridors through the Interior West. Consequently, AR contributions to precipitation across Colorado are higher than previous studies suggest, and exhibit substantial geographic and interannual variability.