Atmospheric Rivers Increase Future Flood Risk in Western Canada's Largest Pacific River

Curry, Charles L.; Islam, Siraj ul; Zwiers, Francis W.; Déry, Stephen J.

doi:10.1029/2018gl080720

Cited by 35 publications

(31 citation statements)

References 54 publications

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“…For snowpack to melt during a ROS, in addition to the energy advected by rain, it is necessary the contribution from turbulent sensible and latent heat transfer associated with condensation and sublimation under saturated conditions and with high air and dew point temperatures [15,60,61]. Some of the big precipitation events in the Iberian Peninsula occur as atmospheric rivers [62] and these may bring moist air that substantially increases longwave radiation that enhances snowmelt [63]. Since our research focused on the regional characteristics of flooding, we did not explore the energy balance components of the snowpack during the flood events.…”

Section: Discussionmentioning

confidence: 99%

Hydro-Meteorological Characterization of Major Floods in Spanish Mountain Rivers

Morán-Tejéda

Fassnacht

Lorenzo‐Lacruz

et al. 2019

Water

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Spain, one of the most mountainous countries in Europe, suffers from frequent river flooding due to specific climatic and topographic features. Many headwaters of the largest rivers in Spain are located in mountainous areas of mid-to-high elevation. These include the Pyrenees, the Central System, and the Cantabrian mountains, that have a sustained snowpack during the winter months. Most previous research on flood generation in Spain has focused on intense rainfall events, and the role of snowmelt has been ignored or considered marginal. In this paper we present a regional-scale study to quantify the relative importance of rainfall versus snowmelt in the largest floods recorded in mountain rivers in Spain during the last decades (1980–2014). We further analyzed whether catchments characteristics and weather types may favor the occurrence of rainfall or snowmelt induced floods. Results show that in 53% of the 250 analyzed floods the contribution of rainfall was larger than 90%, and in the rest of events snowmelt contribution was larger than 10%. Floods where snowmelt was the main contributor represented only 5% of the total events. The average contribution of snowmelt represents 18% of total runoff in floods that were analyzed. The role of snowmelt in floods, rather than triggering the event, was usually amplifying the duration of the event, especially after the peak flow was reached. In general, the importance of snowmelt in floods is greater in catchments with characteristics that favor snow accumulation. However, this does not apply to floods where contribution of snowmelt was larger than 90%, which tend to occur at catchments at mid-elevations that accumulate unusual amounts of snow that melt rapidly. Floods were more frequent under both cyclonic and anticyclonic synoptic situations over the Iberian Peninsula, as well as under advection of western and eastern flows. Our results contribute to the ongoing improvement of knowledge about the role of snow in the hydrology of Spanish rivers and on the importance of mountain processes on the hydrology of downstream areas.

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Section: Discussionmentioning

confidence: 99%

Hydro-Meteorological Characterization of Major Floods in Spanish Mountain Rivers

Morán-Tejéda

Fassnacht

Lorenzo‐Lacruz

et al. 2019

Water

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“…By the end of the 21st century under RCP 8.5, peak flow in this basin is increasingly decoupled from springtime snowmelt due to the decline in winter snowpack, and, instead, coupled to AR-related precipitation extremes 148 . Further work suggests that the increased frequency and intensity of projected ARs affecting this basin manifests as more frequent and larger wintertime flows, and an increase in the likelihood of flooding 149 . Similar results were found on the Salt River and Verde River basins in Arizona 150 .…”

Section: Greenland/arcticmentioning

confidence: 97%

Responses and impacts of atmospheric rivers to climate change

Payne

Demory

Leung

et al. 2020

Nat Rev Earth Environ

250

240

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Atmospheric rivers (ARs) are synoptic-scale features characterized by their striking geometry-extending thousands of kilometres in length and an order of magni tude less in width 1-and vertically coherent low-level moisture transport concentrated in the bottom 3 km of the atmosphere 2 (Fig. 1). In total, ARs are estimated to accomplish as much as 90% of poleward moisture transport 3,4 , which, in the North Pacific, averages 700 kg m −1 s −1 (Fig. 1b), more than twice the mean annual discharge found at the mouth of the Amazon River 5. ARs do not describe continuous moisture transport. Rather, they are continually evolving pathways that incorporate moisture from local convergence and evaporation along their track 6,7 or, in select cases, from distant source regions in the tropics or subtropics 8-12. Owing to the complexity of their evolution, our baseline knowledge of AR characteristics at the global scale is uncertain due to the dependency on identification algorithms (Box 1), with factors such as genesis, development and termination only recently being explored 13,14. However, ARs are known to operate as one part of a larger, synoptic-scale dynamical system driving the poleward transport of sensible and latent heat 4,15. They are generally found in the vicinity of extratropical cyclones. Over the North Pacific, for example, 85% of ARs are paired with extratropical cyclones 16 , consistent with their observed relationship with baroclinic instabilities and the mid-latitude storm track 3,6. However, this relationship is nuanced; only 45% of extratropical cyclones over the same region are associated with an AR 16. Similar non-linear relationships are observed in the North Atlantic, where the evolution and life cycle of a single AR can span that of several cyclones 9. While the phenomena are clearly related, their relationship is interactive, with potential implications on the inten sification of storms and the severity of precipitation impacts on land 17,18. Indeed, given their intense moisture transport and moist-neutrality, ARs exhibit conditions that are ideal for forced precipitation, either through interaction with topography or ascent along a warm conveyor belt or frontal boundary 19. Thus, when ARs make landfall, they can have a range of hydrological impacts, including precipitation extremes and related hazards,

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“…Over the past 60 years, mean annual surface air temperature in the FRB has risen by 1.4 • C, modifying the FRB's natural water cycle (Kang et al, 2014). Impacts of this warming include reductions in snow accumulation (Danard and Murty, 1994), declines in the contribution of snow to runoff generation (Kang et al, 2014) and earlier melt-driven runoff with subsequent reductions in summer flows (Kang et al, 2016). The corresponding changes in mean flow (Danard and Murty, 1994;Morrison et al, 2002;Ferrari et al, 2007;Kang et al, 2014Kang et al, , 2016 have been accompanied by considerable amplification in the interannual variability over recent decades across many streams and rivers in the FRB (Déry et al, 2012).…”

Section: Study Domainmentioning

confidence: 99%

Quantifying projected changes in runoff variability and flow regimes of the Fraser River Basin, British Columbia

Islam

Curry

Déry

et al. 2019

Hydrol. Earth Syst. Sci.

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Abstract. In response to ongoing and future-projected global warming, mid-latitude, nival river basins are expected to transition from a snowmelt-dominated flow regime to a nival–pluvial one with an earlier spring freshet of reduced magnitude. There is, however, a rich variation in responses that depends on factors such as the topographic complexity of the basin and the strength of maritime influences. We illustrate the potential effects of a strong maritime influence by studying future changes in cold season flow variability in the Fraser River Basin (FRB) of British Columbia, a large extratropical watershed extending from the Rocky Mountains to the Pacific Coast. We use a process-based hydrological model driven by an ensemble of 21 statistically downscaled simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5), following the Representative Concentration Pathway 8.5 (RCP 8.5). Warming under RCP 8.5 leads to reduced winter snowfall, shortening the average snow accumulation season by about one-third. Despite this, large increases in cold season rainfall lead to unprecedented cold season peak flows and increased overall runoff variability in the VIC simulations. Increased cold season rainfall is shown to be the dominant climatic driver in the Coast Mountains, contributing 60 % to mean cold season runoff changes in the 2080s. Cold season runoff at the outlet of the basin increases by 70 % by the 2080s, and its interannual variability more than doubles when compared to the 1990s, suggesting substantial challenges for operational flow forecasting in the region. Furthermore, almost half of the basin (45 %) transitions from a snow-dominated runoff regime in the 1990s to a primarily rain-dominated regime in the 2080s, according to a snowmelt pulse detection algorithm. While these projections are consistent with the anticipated transition from a nival to a nival–pluvial hydrologic regime, the marked increase in FRB cold season runoff is likely linked to more frequent landfalling atmospheric rivers in the region projected in the CMIP5 models, providing insights for other maritime-influenced extratropical basins.

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Atmospheric Rivers Increase Future Flood Risk in Western Canada's Largest Pacific River

Cited by 35 publications

References 54 publications

Hydro-Meteorological Characterization of Major Floods in Spanish Mountain Rivers

Hydro-Meteorological Characterization of Major Floods in Spanish Mountain Rivers

Responses and impacts of atmospheric rivers to climate change

Quantifying projected changes in runoff variability and flow regimes of the Fraser River Basin, British Columbia

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