Extreme precipitation events in the Mediterranean area: contrasting Lagrangian and Eulerian models for moisture sources identification

Abstract

Abstract. Concern about heavy precipitation events has increasingly grown in the last years in Southern Europe, especially in the Mediterranean region. These occasional episodes can result in more than 200 mm of rainfall in less than 24 h, producing flash floods with very high social and economic losses. To the better understanding of this phenomena, a correct identification of the origin of the moisture must be found. However, the contribution of the different sources is very difficult to estimate from observational data, so numerical models are usually used to this end. Here, we present a comparison between two complex methodologies for the quantification of the moisture sources in two infamous events occurred during October and November 1982 in the Western Mediterranean area. In a previous study, using an Eulerian approach it was determined the contributions of moisture evaporated in: 1) Western Mediterranean; 2) Central Mediterranean; 3) North Atlantic ocean and 4) tropical and subtropical Atlantic and tropical Africa. Now, we use the Lagrangian model FLEXPART-WRF to quantify the role played by these sources. Considering the results provided by the Eulerian analysis as the virtual reality, we validated the performance of the Lagrangian model. Results show that the Lagrangian method has an acceptable performance in identifying local (Western Mediterranean) and medium-distance (Central Mediterranean and North Atlantic) sources. However, remote moisture sources, like tropical and subtropical areas, are underestimated by the Lagrangian approach. Notably, for the October event, the tropical and subtropical area reported a relative contribution six times below than the Eulerian method. In contrast, the FLEXPART-WRF overestimates the contribution of some sources, especially from the Sahara. We argue that such an inconsistent contribution is associated with the fact that the Lagrangian method does not consider moisture phase changes. These overand underestimates should be taken into account by other authors when drawing conclusions from the Lagrangian analysis.

Moisture Sources for Precipitation Associated With Major Hurricanes During 2017 in the North Atlantic Basin

“…(2012)). Lagrangian approaches have proven powerful tools for identifying moisture sources and studying anomalous atmospheric moisture transport in global and regional studies (Knippertz et al., 2013; Miralles et al., 2016; Nieto et al., 2014; Stohl & James, 2004, 2005; Vázquez et al., 2020), meteorological systems such as extra TCs (Cloux et al., 2021; Liberato et al., 2012), or low‐level jets and atmospheric rivers (Algarra et al., 2019, 2020; Braz et al., 2021; Ramos et al., 2016, 2019). However, these techniques have rarely been used for TCs.…”