The detection of atmospheric rivers in atmospheric reanalyses and their links to British winter floods and the large‐scale climatic circulation

Abstract

[1] Atmospheric Rivers (ARs), narrow plumes of enhanced moisture transport in the lower troposphere, are a key synoptic feature behind winter flooding in midlatitude regions. This article develops an algorithm which uses the spatial and temporal extent of the vertically integrated horizontal water vapor transport for the detection of persistent ARs (lasting 18 h or longer) in five atmospheric reanalysis products. Applying the algorithm to the different reanalyses in the vicinity of Great Britain during the winter half-years of 1980-2010 (31 years) demonstrates generally good agreement of AR occurrence between the products. The relationship between persistent AR occurrences and winter floods is demonstrated using winter peaks-over-threshold (POT) floods (with on average one flood peak per winter). In the nine study basins, the number of winter POT-1 floods associated with persistent ARs ranged from approximately 40 to 80%. A Poisson regression model was used to describe the relationship between the number of ARs in the winter half-years and the large-scale climate variability. A significant negative dependence was found between AR totals and the Scandinavian Pattern (SCP), with a greater frequency of ARs associated with lower SCP values.

Atmospheric rivers: a mini-review

“…The estimated increase in ARs during the negative and positive phases (as opposed to their opposite phases) was 90% for the AO and 50% for the PNA. Studies of ARs impacting Britain found a significant negative relationship between winter ARs and the Scandinavian Pattern (SCP; Lavers et al, 2012). In subsequent work covering Western Europe, found that the North Atlantic Oscillation (NAO) affected AR activity in different parts of Europe; in southern Europe ARs are concurrent with negative NAO phases, whereas in northern Europe a more positive NAO-type pattern is associated with AR occurrence.…”

“…Waliser et al (2012) also found that the maximum number of ARs occurred in the northeastern Pacific. In regional studies over longer periods, about 15 landfalling ARs per year were counted in California (Neiman et al, 2008), and on average about 8-10 persistent winter ARs (of at least 18 h duration) affected Great Britain (Lavers et al, 2012). In terms of duration, Ralph et al (2013b) found that AR conditions lasted an average of 20 h, although the most persistent 10% lasted an average of 40 h with streamflows seven times higher than for the average events.…”

Development and Evaluation of a Multi-Year Fractional Surface Water Data Set Derived from Active/Passive Microwave Remote Sensing Data

“…This result is consistent with the approach taken by Whitcomb et al [88] which takes advantage of the U.S. National wetlands inventory data to map wetlands with SAR. Water ponding and flooding of waterlogged, arable land following heavy rainfall periods in Western Europe could have explained the occurrence of small inundated areas during winter months [138] that were not detected by the independent data. Interestingly, these areas were also detected by GIEMS, but with FW that was 10-30 times as large, thus inadvertently biasing forward calculations of methane emission for the region [16] including recent efforts of downscaling GIEMS [49,50,139].…”

Climate-driven changes in UK river flows

“…Recent studies (Lavers et al 2011;2012) have demonstrated the importance of Atmospheric Rivers (ARs), narrow bands along which a large flux of moisture is transported from the subtropics to mid-latitudes, causing winter flooding and extreme rainfall in the north and west of the UK. ARs are expected to become more frequent in the future under anthropogenic warming (Lavers et al, 2012), but so far there has been no analysis of whether there is any anthropogenic contribution to the prevalence of ARs in the observed record.…”