Wet Spells and Associated Moisture Sources Anomalies across Danube River Basin

Abstract

Abstract:The Danube River Basin is the second longest catchment basin in Europe and exhibits intense climatological diversity. In recent decades, the frequency and intensity of daily precipitation extremes have suffered from an increment in many parts of the world, including Central and Eastern Europe. Wet spells are defined by the number of consecutive rainy days with different thresholds. The identification of wet spells and their trends in the rainfall time is very important for many sectors, such as agriculture, ecology, hydrology and water resources. Wet spells can lead to extreme events and cause floods and other disasters. In this study, we will attempt to characterise global precipitation in the context of wet spells and associated precipitation depth of wet spells in the Danube River Basin area using daily precipitation data, as well as analysing different approaches to identifying wet spells. The ten most intense wet spells were detected, and the most intense, which occurred on 23 September 1996, was studied in depth in terms of precipitation and associated anomalies, the synoptic situation and the anomalous transport of moisture using a Lagrangian approach. The existence of a marked west-east dipole in the field of sea level pressure between the Atlantic Ocean and the eastern Mediterranean leads to the anomalous moisture transport from the Northern Atlantic Ocean to the Mediterranean Sea, where a higher available amount of moisture existed, and subsequently penetrated within the low positioned over the Danube River Basin. In addition, an Atmospheric River was also responsible for the wet conditions in the Danube River Basin. The combination of all these factors was responsible for the extreme precipitation linked with the wet spell.

Contribution of Moisture from Mediterranean Sea to Extreme Precipitation Events over Danube River Basin

“…Many studies have investigated extreme precipitation events in the Danube basin region [19][20][21][22]. Ciric et al [22] ranked extreme precipitation events with different durations in the Danube River basin by considering all days within the period 1981-2015.…”

“…Many studies have investigated extreme precipitation events in the Danube basin region [19][20][21][22]. Ciric et al [22] ranked extreme precipitation events with different durations in the Danube River basin by considering all days within the period 1981-2015. Their study analysed the most extreme precipitation event (23 September 1996), investigated the moisture sources and synoptic conditions leading to this extreme precipitation, and determined that the Mediterranean Sea is one of the most important moisture sources in the region [4,22] and for certain adjacent areas, such as the Balkan Peninsula [23,24] and the Southern Alpine region [25].…”

“…Ciric et al [22] ranked extreme precipitation events with different durations in the Danube River basin by considering all days within the period 1981-2015. Their study analysed the most extreme precipitation event (23 September 1996), investigated the moisture sources and synoptic conditions leading to this extreme precipitation, and determined that the Mediterranean Sea is one of the most important moisture sources in the region [4,22] and for certain adjacent areas, such as the Balkan Peninsula [23,24] and the Southern Alpine region [25]. It is important to note the importance of the Mediterranean Sea as a source of moisture at a global scale, being one of the major oceanic sources to continental precipitation [26].…”

“…In this paper, we use the ranking of extreme precipitation events developed by Ciric et al [22] to analyse the contribution from the Mediterranean Sea (as a source of moisture) to the 100 most intense precipitation events recorded over the Danube River basin and obtained from the Climate Hazards Group Infra-Red Precipitation with Station dataset (CHIRPS) [27], which have different durations of 1, 3, 5, 7, and 10 days. Using the outputs of the Lagrangian dispersion model FLEXPART V9.0, which was initially developed by Stohl and James [28,29], and was fed with ERA-Interim reanalysis dataset from the ECMWF (European Centre for Medium-Range Weather Forecast) [30].…”

<span>The Mediterranean moisture supply in the genesis of climatological and extreme monthly continental precipitation</span>

“…Large-scale precipitation events in the western, central and eastern Mediterranean are related with local anomalies of high moisture over the Mediterranean Sea [9], and those are influenced by remote positive sources anomalies [10]. Many works pointed out the important role of remote sources for extreme precipitation events in the area of Mediterranean basin [10][11][12][13].…”