HYDROCLIMATOLOGY OF THE MIDDLE EAST DURING LONG-TERM DROUGHTS/WET EPISODES DETERMINED FROM HOLOCENE DEAD SEA LEVEL VARIATIONS

Transferring lake levels into hydrological changes and then into parameters such as precipitation or synoptic climatology is a problematic task. The difficulties arise from age dating, modern data, and in quantifying reservoirs/fluxes in the hydrology. We conducted such a research in the Dead Sea (DS), which is a terminal lake of a large hydrological system in the Levant. It may thus be viewed as a large rain gage for the region. Its levels respond to regional climate variations and therefore we will present the newly developed late Holocene DS level curve. Then, we determine the regional hydroclimatology that affected level variations. To achieve this goal we compare between modern natural lake levels variations and instrumental rainfall record and quantify the hydrology during level rise, fall, or stability. To quantify that relationship under natural conditions rainfall data predating the artificial DS level drop since 1960s are used. In this respect, Jerusalem station (JRM) offers the longest, pre-1960s uninterrupted rainfall record. JRM rains serve as an adequate proxy for the DS headwaters rainfall because principal component analysis indicates that temporal variations of annual precipitation in all stations in Israel north of the current 200 mm yr-1 isohyet are largely synchronous and in phase. This station also represents well northern Jordan and southern Lebanon, especially during extreme droughts and wet spells. The historic levels of the DS and rainfall data are utilized to calculate the mean annual and standard deviation of JRM rainfall during natural rise (648 mm), fall (445 mm), and stable (553 mm) levels of the DS. These values can characterize Holocene rains during DS level changes. We determine a) the modern and propose the past regional paleohydrology and Eastern Mediterranean (EM) climatology that affected the severity and length of droughts/wet spells associated with multi-year episodes of DS level changes; and b) that EM cyclone tracks were different in average number and latitude in wet and dry years in JRM. The mean composite SLP and 500 mb height anomalies point that causes for wet and dry episodes span the entire EM and are rooted in anomalous Northern Hemisphere circulation. The close association of DS level changes and culture shifts in the Levant will be shortly discussed.