Abstract
Abstract. Atmospheric rivers (ARs) – long and narrow structures of anomalously high water vapor flux located in the warm sector of extratropical cyclones – have been shown to be closely related to extreme precipitation and flooding. In this paper we analyze the connection between ARs and flooding in the northwestern Spanish region of Galicia under a variety of synoptic conditions represented by the so-called “weather types”, a classification of daily sea-level pressure patterns obtained by means of a simple scheme that adopts the subjective procedure of Lamb. Flood events are identified from official reports conducted by the Spanish emergency management agency (Protección Civil) from 1979 to 2010. Our results suggest that, although most flood events in Galicia do not coincide with the presence of an overhead AR, ARs are present in the majority of severe cases, particularly in coastal areas. Flood events associated with ARs are connected to cyclonic weather types with westerly and southwesterly flows, which occur mostly in winter months. The link between ARs and severe flooding is not very apparent in inland areas or during summer months, in which case heavy precipitation is usually not frontal in nature but rather convective. Nevertheless, our results show that, in general, the amount of precipitation in flood events in Galicia more than doubles when an AR is present.
Highlights
Atmospheric rivers (ARs) are narrow, elongated structures that carry high quantities of water vapor in the lower troposphere
The climatological characteristics of ARs have been recently reviewed by Guan and Waliser (2015), who proved that they exhibit a mean length of about 3700 km and have average integrated vapor transport (IVT) fields of 375 kg m−1 s−1
Flood events (FEs) during summer months are mostly associated with anticyclonic situations (NE, A, AE) that block the arrival of fronts and ARs
Summary
Atmospheric rivers (ARs) are narrow, elongated structures that carry high quantities of water vapor in the lower troposphere. The climatological characteristics of ARs have been recently reviewed by Guan and Waliser (2015), who proved that they exhibit a mean length of about 3700 km and have average integrated vapor transport (IVT) fields of 375 kg m−1 s−1. ARs are usually found in the warm sector of extratropical cyclones and are associated with the meridional transport of latent and sensible heat from the (sub)tropics to the midlatitudes (Newell et al, 1992; Zhu and Newell, 1998; Gimeno et al, 2010; Gimeno et al, 2014; Gimeno et al, 2016; Ralph and Dettinger, 2011; Lavers and Villarini, 2013; Matrosov, 2013; Neiman et al, 2013; Rutz et al, 2014; Garaboa-Paz et al, 2015; Waliser and Guan, 2017). Despite the fact that discrepancies in the finer details of their detection remain, all algorithms in the literature rely on an analysis of the integrated water vapor column (IWV) and IVT fields.
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