An Examination of an Inland-Penetrating Atmospheric River Flood Event under Potential Future Thermodynamic Conditions

Atmospheric rivers (ARs) are well-known producers of precipitation along the U.S. West Coast. Depending on their intensity, orientation, and location of landfall, some ARs penetrate inland and cause heavy rainfall and flooding hundreds of miles interior of the coastline. Climate change is projected to potentially alter a variety of AR characteristics and impacts, with most previous research in this area focusing on potential changes in AR intensity, frequency, and precipitation type (i.e., rain versus snow) upon AR landfall. Here we investigate possible changes in moisture transport and pathways under projected climate change conditions for an inland-penetrating AR flood event using a pseudo-global warming (PGW) modeling approach.

The PGW modeling method is applied to a flood event that occurred across coastal and inland regions of the U.S. Pacific Northwest in November 2006 when a sequence of storms generated record-breaking precipitation across the Pacific Northwest. An ensemble of PGW simulations based on this event is used to investigate in detail how changes in possible future thermodynamic conditions may lead to changes in (1) precipitation intensity and distribution both at AR landfall and inland locations; (2) specific components of moisture transport, (3) moisture transport pathways, and (4) the distribution of rain vs. snow and its possible implications for future flood risk.