Increased frequency of torrential rainstorms during a regional late Holocene eastern Mediterranean drought

Abstract

Identifying climates favoring extreme weather phenomena is a primary aim of paleoclimate and paleohydrological research. Here, we present a well-dated, late Holocene Dead Sea sediment record of debris flows covering 3.3 to 1.9 cal ka BP. Twenty-three graded layers deposited in shallow waters near the western Dead Sea shore were identified by microfacies analysis. These layers represent distal subaquatic deposits of debris flows triggered by torrential rainstorms over the adjacent western Dead Sea escarpment. Modern debris flows on this escarpment are induced by rare rainstorms with intensities exceeding >30 mm h−1 for at least one hour and originate primarily from the Active Red Sea Trough synoptic pattern. The observed late Holocene clustering of such debris flows during a regional drought indicates an increased influence of Active Red Sea Troughs resulting from a shift in synoptic atmospheric circulation patterns. This shift likely decreased the passages of eastern Mediterranean cyclones, leading to drier conditions, but favored rainstorms triggered by the Active Red Sea Trough. This is in accord with present-day meteorological data showing an increased frequency of torrential rainstorms in regions of drier climate. Hence, this study provides conclusive evidence for a shift in synoptic atmospheric circulation patterns during a late Holocene drought.

Predicting Extreme-Precipitation Effects on the Geomorphology of Small Mountain Catchments: Towards an Improved Understanding of the Consequences for Freshwater Biodiversity and Ecosystems

“…Instrumental as well as historical [2] data clearly suggest that extreme rainfall events are increasing in the northern Apennines, in good agreement with the international literature [6][7][8][9][10][11][12]. This trend will, unfortunately, most likely be confirmed, and our case studies/observations suggest that there might be consequences also for the biodiversity, structure, and function of mountain freshwater ecosystems.…”

“…Furthermore, changes in the hydrological cycle of the Alps and Apennines are not only due to extreme events that increase in frequency and intensity [2][3][4][5][6][7][8][9][10][11][12], but also to heat waves and droughts, which are increasingly intense and prolonged, respectively. The combined action of these two factors can and will have important effects on the biodiversity of mountain surface and groundwater environments.…”

“…Meteorological events characterized by extreme rainfall intensity have recently struck the hilly and mountainous territory of the northern Apennines (Italy) [1,2] and the Emilia-Romagna region in particular [3][4][5], as well as many other geographic areas of the world [6][7][8][9][10][11][12].…”

Changing flood frequencies under opposing late Pleistocene eastern Mediterranean climates

“…Other synoptic-scale systems capable of generating floods are Active Red Sea troughs (ARST) and Tropical Plumes (also named Subtropical Jet-related disturbances) 20 , 27 . Active Red Sea troughs are associated with short-duration heavy-precipitation storms 10 , 28 – 31 , that mostly generate low-volume, scattered local floods 31 , 32 , whereas tropical plumes are rare, and generate widespread floods throughout the region 33 – 36 . The relationship between Dead Sea levels and modern regional winter rainfall, dictated by eastern Mediterranean climatology has been shown to stretch into the Holocene 15 , 16 , thus suggesting that elevated lake levels during the Last Glacial Maximum (Fig.…”

“…However, pinpointing flood occurrence and quantifying short-term hydroclimatic variability from geological records remains difficult, and is rarely achieved through the analyses of high-resolution archives 7 – 9 . Furthermore, associating synoptic-scale atmospheric circulation patterns with paleofloods is only possible where flood generation is strongly correlated with specific synoptic atmospheric patterns 10 . Determining flood frequencies during changing climate and examining if the relationship between mean climate and flood frequency holds for past climates is a crucial task for properly describing climate and preparing for the possible outcomes of climate change on in situ hydrology.…”