|AUTHORS||AM Ramos (1), RC Blamey (2), R Tomé (1), PM Sousa (1), MLR Liberato (1,3), CJC Reason (2), RM Trigo (1)|
- Instituto Dom Luiz, Faculdade Ciências, U. Lisbon, Lisbon, Portugal
- Department Oceanography, University of Cape Town, Rondebosch, South Africa
- Universidade de Trás-os-Montes e Alto Douro, Vila Real, Portugal
|ABSTRACT||The Mediterranean climate is usually characterized by warm and hot summers intermingled with mild and rainy winters. Besides being coined for the Mediterranean basin area, it also characterizes the climate of other important areas of the planet, including California, southwestern South Africa, Central Chile or southwestern Australia.
Recently, it has been suggested that another common feature shared by all Mediterranean climate regions is the occurrence of Atmospheric Rivers (ARs) and their related weather-driven extremes. ARs are relatively narrow and elongated filaments of high water vapour transport, which are associated with tropical moisture exports and often occur in combination with the passage of strong extratropical cyclones. Such structures transport more than 90% of the total mid-latitude vertically integrated water vapour and can lead to intense precipitation episodes due to its interaction with topography or ascent in the Warm Conveyor Belt.
A detection algorithm allowed the identification and a comprehensive characterization of the major North Atlantic AR events that affected the Iberian Peninsula since 1948 (Ramos et al., 2015). The relationship between ARs and extreme precipitation events in western Iberian river basins (Minho, Tagus, and Duero) is noteworthy, while for eastern and southern basins (Ebro, Guadiana, and Guadalquivir) the impact of ARs is reduced.
A similar climatology for Southern Atlantic was developed recently evaluating the role played by ARs bound for the western coast of South Africa since 1979, during the austral winter months (April–September) (Blamey et al., 2018). Meteorological stations positioned in areas of high topography present the highest percentage of persistent ARs contribution to rainfall, whereas stations downwind of the major topographic barriers show the lowest contributions. We show that around 70% of the top 50 daily winter rainfall extremes in South Africa were linked to ARs.
Finally, we show that several recent major drought episodes in both settings are related to the dislocation of ARs impacting Iberia (e.g. 2004-2005) and South Africa (e.g. 2015-2017).
' Blamey, R.C.; Ramos, A.M.; Trigo, R.M.; Tomé, R.; Reason, C.J. (2018) The influence of Atmospheric Rivers over the South Atlantic on Winter Rainfall in South Africa. Journal of Hydrometeorology, 19, 127–142.
' Ramos, A.M; Trigo, R.M.; Liberato, M.L.R.; Tomé, R. (2015) Daily Precipitation Extreme Events in the Iberian Peninsula and Its Association with Atmospheric Rivers, Journal Hydrometeorology, 16:579–597.
This work was supported by the project IMDROFLOOD funded by Fundação para a Ciência e a Tecnologia, Portugal (FCT, WaterJPI/0004/2014). Alexandre M. Ramos was also supported by an FCT postdoctoral grant (FCT/DFRH/SFRH/BPD/84328/2012).|