The hydrology and paleohydrology of the Dead Sea tributaries

The Dead Sea (drainage area of ̃42,200 km ² ) is a terminal lake fed from the north by the Jordan River. The main water source into the Dead Sea is runoff, and its level is highly sensitive to the annual rainfall in the upper Jordan River drainage Basin. Here, we summarize relevant data about present and past surface-water hydrology in the drainage Basin and water input into the Dead Sea. The lower Jordan River, with a natural mean annual discharge of ̃1100 10 ⁶ m ³ yr ^-1 , drains Mediterranean to semiarid areas in northern Israel, Jordan, Syria, and Lebanon. Additional water is contributed from tributaries such as the Zarqa River (64 10 ⁶ m ³ yr ^-1 ). The diversion of water from these and other sources since the 1960s to an inflow of only ̃210 10 ⁶ m ³ yr ^-1 caused a 20 m decline of the Dead Sea level. The ephemeral Nahal Arava drains hyperarid areas south of the Dead Sea and contributes small volumes of water (̃5 10 ⁶ m ³ yr ^-1 ) but experiences occasional large floods (up to 1000 m ³ s ^-1 ); the smaller, steep ephemeral tributaries west of the Dead Sea produce relatively large floods (up to 775 m ³ s ^-1 ) due to their wetter headwaters, but their volumes are relatively small (<3 10 ⁶ m ³ ). The annual inflow (̃200 10 ⁶ m ³ yr ^-1 ) to the Dead Sea from the eastern, semiarid tributaries is divided between base flows (̃65% of annual discharge) and winter floods. In the arid part of the Basin, transmission losses and recharge into the shallow alluvial aquifers and probably also to the deeper aquifers during floods are directly related to flow volume. Transmission losses in Nahal Zin decrease with flood magnitude from ̃86% to 100% in small floods of <10 m ³ s ^-1 to ̃10% for large floods of up to 1500 m ³ s ^-1 . During the largest floods, the volume of these losses can exceed 4 10 ⁶ m ³ . Rare paleofloods during the past 2000 yr in the Negev were 2-3 times larger than present-day measured floods. The temporal distribution of paleofloods shows that periods with a high frequency of large floods alternate with periods of few large floods. Periods with a high frequency of large floods correlate with high Dead Sea levels, and a low frequency of floods correlates with low lake levels.