Mixed populations and annual flood frequency estimates in the western United States: The role of atmospheric rivers

This study investigates the extent to which the diagnosed contribution of atmospheric rivers (ARs) to the seasonal cumulative snowfall (CS) is related to the AR detection approach utilized. Using both satellite integrated water vapor (IWV)‐based and reanalysis integrated vapor transport (IVT)‐based methodologies, the corresponding AR‐derived CS distributions were characterized over the Sierra Nevada (USA) from 1998 to 2015. AR detection methods indicated that ARs yield greater orographic enhancement of the seasonal CS than non‐AR storms above ~2,100–2,300 m for the IWV‐based approach and over all elevations for the IVT‐based detection approach across the western (i.e., windward) Sierra Nevada. Due to differences in the methodologies, the IWV‐based approach diagnosed 2.1 times fewer ARs than the IVT‐based approach. As a result, the ARs diagnosed using the IWV‐based detection method yielded an average 33% of the total range‐wide CS annually as opposed to 56% from the IVT‐based detection method.

Section: Resultsmentioning

confidence: 96%

Implications of Detection Methods on Characterizing Atmospheric River Contribution to Seasonal Snowfall Across Sierra Nevada, USA

Huning

Margulis

Guan

et al. 2017

“…This pattern reflects the spatial distribution of frequency of ARs and the increasing intensity of precipitation over high‐elevation terrain (Dettinger, ; McCabe et al, ; Neiman et al, ; Ralph & Dettinger, ; Rutz et al, ). While lowland streams on the Pacific Coast have lower rates of maximum runoff (e.g., Puget Trough, Willamette, and Sacramento River valley), annual maximum streamflow (peaks and mean daily) in these streams is still largely a response to ARs (Barth et al, ; Figure S1 in the supporting information).…”

Section: Discussion Of Conditional Flood Responses To Atmospheric Rivmentioning

confidence: 99%

“…Atmospheric rivers (ARs) are long (>2,000 km) corridors in the lower troposphere where water vapor is transported poleward at high rates that have been identified as the primary cause of flooding in the western United States (U.S.) (Barth et al, 2017;Dettinger & Ingram, 2013;Dettinger et al, 2011;Florsheim & Dettinger, 2015;Neiman et al, 2011Neiman et al, , 2013Ralph et al, 2006). Geographic variation in the frequency of ARrelated flooding across the western U.S. reflects the strong west-to-east gradient in AR-forced precipitation (Barth et al, 2017;Ralph & Dettinger, 2012;Rutz et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

Flood Runoff in Relation to Water Vapor Transport by Atmospheric Rivers Over the Western United States, 1949–2015

Konrad

Dettinger

2017

Atmospheric rivers (ARs) have a significant role in generating floods across the western United States. We analyze daily streamflow for water years 1949 to 2015 from 5,477 gages in relation to water vapor transport by ARs using a 6 h chronology resolved to 2.5° latitude and longitude. The probability that an AR will generate 50 mm/d of runoff in a river on the Pacific Coast increases from 12% when daily mean water vapor transport, DVT, is greater than 300 kg m−1 s−1 to 54% when DVT > 600 kg m−1 s−1. Extreme runoff, represented by the 99th quantile of daily values, doubles from 80 mm/d at DVT = 300 kg m−1 s−1 to 160 mm/d at DVT = 500 kg m−1 s−1. Forecasts and predictions of water vapor transport by atmospheric rivers can support flood risk assessment and estimates of future flood frequencies and magnitude in the western United States.

“…They are known as a major cause of extreme precipitation and flooding events in the western United States, especially along the west coast (Leung & Qian, ; Neiman et al, , ; Ralph et al, ; Ralph & Dettinger, ). Previous studies have established the relationship between ARs and the likelihood of hydrological extremes (Barth et al, ; Guan et al, ; Lamjiri et al, ; Ralph et al, ). For example, Ralph et al () found that all seven floods in the Russian River of coastal northern California between 1997 and 2006 were associated with landfalling ARs.…”

Section: Introductionmentioning

confidence: 99%

Predictability of Extreme Precipitation in Western U.S. Watersheds Based on Atmospheric River Occurrence, Intensity, and Duration

Chen

Leung

Gao

et al. 2018

We quantified the relationship between atmospheric rivers (ARs) and occurrence and magnitude of extreme precipitation in western U.S. watersheds, using ARs identified by the Atmospheric River Tracking Method Intercomparison Project and precipitation from a high‐resolution regional climate simulation. Our analysis shows the potential of ARs in predicting extreme precipitation events at a daily scale, with Gilbert Skill Scores of ~0.2. Monthly extreme precipitation amount in west coast watersheds is closely related to AR intensity, with correlation coefficients of up to 0.6. The relationship between ARs and precipitation is most significant in the Pacific Northwest and California. Using a K‐means clustering algorithm, ARs can be classified into three categories: weak ARs, flash ARs, and prolonged ARs. Flash ARs and prolonged ARs, though accounting for less than 50% of total AR events, are more important in controlling extreme precipitation patterns and should be prioritized for future studies of hydrological extreme events.