High-Tide Floods and Storm Surges During Atmospheric Rivers on the US West Coast

Area of Science:

• Climatology
• Oceanography
• Coastal Hazards

Background:

• Atmospheric rivers (ARs) are known for inland flooding but their coastal impacts are understudied.
• Coastal hazards like high-tide floods (HTFs) and storm surges during ARs require further investigation.

Purpose of the Study:

• To investigate the co-occurrence and drivers of high-tide floods (HTFs) and storm surges during atmospheric rivers (ARs) on the US West Coast.
• To clarify the relationship between ARs, tides, sea level, and coastal flooding.
• To identify the primary forcings of storm surges during AR events.

Main Methods:

• Analysis of historical data from 1980-2016 for ARs, HTFs, and storm surges on the US West Coast.
• Statistical analysis to determine the co-occurrence frequency of ARs and HTFs.
• Investigation of meteorological and oceanographic drivers of storm surge during ARs.

Main Results:

• HTFs and ARs co-occur more often than by chance, with 10-63% of HTFs coinciding with ARs depending on location.
• Interannual-to-decadal variations in HTFs are primarily influenced by tides and mean sea level, not storminess.
• Only 2-15% of ARs coincide with HTFs, indicating a need for co-occurrence with high tides or sea levels.
• Storm surges during ARs are primarily driven by local wind and barometric pressure, with precipitation as a secondary factor.

Conclusions:

• ARs are relevant to coastal impacts, specifically HTFs, though often require tidal or sea-level amplification.
• Understanding the interplay of ARs, tides, and sea level is crucial for coastal flood risk assessment.
• Meridional wind and barometric pressure are key drivers of AR-associated storm surges, with precipitation contributing secondarily.