WHAT CAN DEAD SEA SEDIMENTS TEACH US ON THE IMPACT OF CLIMATE CHANGE ON FLOOD FREQUENCY AND HYDROCLIMATIC VARIABILITY IN THE LEVANT?

Determining flood frequency under changing climates of the past is rarely achieved, although storms and floods are dominant components of aridland hydroclimatology. This is because the understanding of the impact of mean climate states on flood occurrences requires determination of both independent climate and flood occurrences, which is hard to come by in the same hydroclimatic system. The sedimentary record of the Dead Sea provides a high-resolution archive of the late Pleistocene hydroclimate in the eastern Mediterranean-Levant. Mean centennial to millennial climate changes are manifested in Dead Sea lake level, which reflect mean hydrological changes. These mean conditions are composed of sub-seasonal rainstorms, born out of key synoptic circulation patterns that govern freshwater inflow into the lake and also produce floods in the large tributaries into the Dead Sea. Late Pleistocene varve sequences provide a rare record of seasonal floods, and therefore provide information on the annual frequency of causative synoptic circulation patterns within a single season. Two ~700-year-long seasonally resolved flood time series were extracted from late Pleistocene (30-15 ka) varved sediment. They are contemporaneous with significant Dead Sea lake-level variations, reflecting contrasting long-term changes in its hydrological budget, where one interval represents lake-level rise, and the other a lake-level drop. In both intervals, floods are non-uniformly distributed and cluster into periods of intense flooding. Within clusters, flood frequency increases by +75% and +20% above their respective background frequencies during rising and falling lake-levels, respectively. These series demonstrate that changes in mean centennial precipitation in the eastern Mediterranean are coupled with drastic changes in flood frequency. Contemporary observations, point to the link between these drastic changes in flood frequencies and changes in the track, depth, and frequency of eastern Mediterranean cyclones during wetter and drier regional climatic conditions.