Physiography

The Dead Sea is the terminal lake of the Jordan Rift Valley. It is the lowest point on the surface of the earth, and the waters have the highest density and salinity of any sea in the world. The east and west shores of the Dead Sea are bounded by towering fault escarpments that form part of the African-Syrian rift system. The valley slopes gently upward to the north along the Jordan River, and to the south along the Wadi Araba.

Map 1. Topography of the Dead Sea Basin

          The Dead Sea extends from 35^o30’00 to 35^o34’05 East and 30^o58’01 to 31^o46’01 North. Its total area is 634 km², while its perimeter is approximately 148 km . It lies some 1,357 feet (418 meters) below sea level-the lowest elevation and the lowest body of water on the surface of the Earth.  The total surface area of the Dead Sea catchment is approximately 40,700 km². The major Wadis in the Dead Sea catchment are Wadi Mujib, Wadi Wala, Wadi Hasa, Wadi Draja, Wadi Arugot, Wadi Ze'elim, Wadi Zohar, Wadi Zin and Wadi Arava (see Map 1).  The elevation ranges from 418 below sea level to 1,605 m (The mean elevation is approximately 440 m above sea level), and slopes range from 0 to 87 degrees (65% of the study area has a slope of less than 10 degrees). The coastal areas of the Dead Sea Basin exhibit complex relief characteristics with steep slopes. The highest point, the highlands around Al Tafila (1,605 m), lies near the South-eastern side of the basin.

Figure 1: Terrain Slope Histogram of the Dead Sea Basin

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Surface Geology and Soil

            Approximately, 28% of the study area is composed of Coniacian-Camparian and Camparian Chalk and Chert formations, 27% is composed of Turonian and Cenomanian limestone, marl and dolostone formations while 16% is composed of Sandstone, siltstone, dolostone and limestone formations. Dolostone, clay, sand loess and gravel make up the remaining 29% (Map 2).

Map 2. Lithology Map of the Dead Sea Basin

          The soil depth varies widely depending on surface geology, relief and vegetation density.  The soil types in the study area include Brown Lithosols and loessial Arid Brown Soils, Dark Brown Soils, Brown Randzinas and Pale Randzinas, Terra Rossa, Bare Rocks and Desert Lithosols, Brown Lithosols and Loessial Serozems.

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Climate

          The climate of the study area is highly variable.  Average annual precipitation  decreases along two geographical gradients; namely the latitudinal gradient as rainfall decreases from north to south and the altitudinal gradient as rainfall decreases along with the decrease in elevation.  The maximum average annual rainfall of 594 mm/yr occurs in the north-western part of the study area (East Jerusalem) and the minimum average annual rainfall of 80 mm/yr occurs along a small hyper-arid longitudinal zone running along the Dead Sea coast.  The mean annual precipitation in the study area is approximately 200 mm/yr (Map 3), of which approximately 60% falls in the three months of December, January and February (Figure 2).

Map 3. Average Annual Precipitation in the study area

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Figure 2.  Monthly precipitation distribution in the study area showing precipitation patterns in the wet and dry areas of the Basin.

          Temperatures vary from an annual average of 17 degree centigrade in the Western side of the Basin to 24 degrees centigrade along the Salting lakes coastal area. In the western part of the study area, the dry hot season (xerothermic period) starts in April and lasts for 6-7 months up to mid October whereas in the arid eastern part of the study area the dry hot season lasts for 10-11 months from February to mid November.

          Based on the above, the combination of hot, dry summers and wet winters satisfy the conditions required to classify the climate of the Dead Sea Basin as a Mediterranean climate.  Furthermore, the Emberger (1971) method was used to define the subclasses of the Mediterranean bioclimate of the Dead Sea Basin.  It was found to range from temperate and sub-humid (Al A’rrub Weather Station Readings) to hot and desert (Jericho Weather Station Readings).

          Potential evaporation (pan evaporation) in the study area varies from 1,700 mm/year in the north-western part to 2,300 mm/year in the northern Arava valley. Figure 3 shows the monthly values of potential evapotranspiration in the Dead Sea Basin.  Average potential evaporation over the Dead Sea is approximately 1,980 mm/yr whereas average potential evaporation over the salting lakes is approximately 2260 mm/yr.  Actual evaporation from the surface of the Dead Sea  ranges between 1,300-1,600 mm/yr and depends on several climatic variable (e.g. wind speed, relative humidity, temperature) and surface water temperature and water salinity. 

Figure 3.  Minimum and Maximum observed values of total monthly pan evaporation in different areas in the Dead Sea Basin

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