Physical characteristics of West Bank and Gaza
Despite its small geographical area, the West Bank is characterised by a great variation in topography (Map 7). This variation directly reflects on climate and the distribution and diversification of agricultural patterns, from irrigated agriculture in the Jordan Valley, the lowest area in the world, to rainfed farming in the mountains. The population distribution and centres of urbanisation are affected by the topography of the West Bank. The maximum concentration of built-up areas are found on the mountain ranges where climate is more suitable for human life than in the hot climate of the Jordan Valley. Furthermore, most of the West Bank rangelands are found on the arid Eastern Slopes.
The West Bank is divided into five major phytogeographical, geomorphologic and topographical parts: the Jordan Valley, Eastern Slopes, Central Highlands and the Semi-Coastal Region. The mountainous area of the West Bank serves as the main rainfall collection and replenishment area for the underground water aquifers. Many drainage and valley systems are spread in and among the above mentioned four parts
Gaza is located on the coast of the Mediterranean Sea, north of the Sinai Peninsula and southwest of Jerusalem, on a road that links Egypt with central Israel. Gaza Strip forms part of the coastal forshore plain bordering the hebron Mountains in the north-east, the Northern Negev desert in the south-east, and the Northern Sinai desert in the south. It is situated in the shadow of the Nile Delta and Northern Sinai. The curve in the coastal starting from El Arish towards north of Gaza. The topography of the coastal plain is determined by the exposure of Kurkar ridges. The age of these ridges increases from the coastline eastwards. In the north of the Gaza Strip there are four ridges: the coastal ridge (20 m MSL), the Gaza ridge (up to 50 m MSL), the El Muntar ridge (80 m MSL), and the Beit Hanun ridge (90 m MSL). The ridges are separated by deep depression (20-40 m MSL) with alluvial deposits. There is evidence that there are at least three to four younger Kurkar ridges on the continental shelf, parallel to the present coastal line and several kilometers offshore.
Kukar ridges of calcareous sandstone appear all along the coast positioned in a south-west-northerly direction parallel to the coast. The influence of these Kurkar ridges on sedimentation and erosion processes is however limited to local disruption of waves and currents.
Active Dunes
Active dunes can be found near the coast, especially in the southern part between Deir El Balah and Rafah. More inland (west of Khan Younis) are older dunes stabilized by vegetation penetrating an area 4-5 km inland. There is gradual transition from a sandy dune landscape towards the rolling loess plains of the North-western Negev. The sands and sandstones were covered by fine windblown dust materials originating from sources in the Southern Negev and Sinai desert. Loess deposition in areas with over 300 mm rainfall has been a continuous process at a rate of one meter in 10 000 years. Areas with a large accumulation of loess can be found 15 km south-west of the Gaza where these layers reach a thickness of eight meters.
West Bank
The geographical location of the West Bank between the 31°21` and 32°33` latitude and between 34°52` and 35°32` longitude, makes the area highly influenced by the Mediterranean climate. The Mediterranean climate is characterized by a long, hot, dry summer and short, cool, rainy winter. Rainfall is limited to the winter and spring months. It usually starts in the middle of October and continues up to the end of April. Snow and hail, although uncommon, may occur anywhere in the area especially to the west of and over the highlands (Rofe & Raffety, 1965).
Temperature:
The climate of Palestine as a whole, and the West Bank in particular, is of the Mediterranean type, marked by a mild, rain winter and a prolonged dry and hot summer. The annual amount of rainfall decreases from north to south. Temperatures, on the other hand, increase from north to south. In a west to east direction, annual rainfall and mean temperatures undergo similar but less regular changes. Also, there is a gradual decrease in the annual, monthly, and diurnal averages of relative humidity from north to south and from west to east throughout the whole area.
Annual temperature isotherm in the West Bank shows the lowest temperatures in the mountain region. The northern mountains at Nablus register an annual average temperature of 17.8°C, while the higher southern mountains in Hebron, register an annual average of 15.5°C.
Humidity
The mean annual relative humidity is 61% in Nablus, 69.6% in Tulkarm and 52% in Jericho. Relative humidity reaches its highest in winter, when the average humidity is 67.2% in Nablus, 73% in Tulkarm, and 68.5% in Jericho.
Evaporation is particularly high in summer, due to therise in temperatures, intensive sunshine and the low humidity. The mean monthly evaporation rates from June to August are 215.1 mm/month in Hebron, 277.3 mm/month in Nablus and 284.9 mm/month in Jericho. Towards the coastal plain, the rate of evaporation decreases because of the year around exposure to the humid sea breeze. Evaporation rate is relatively low during the winter months when the solar radiation is lowest. The mean monthly evaporation rates from December to February are 55.1 mm/month in Nablus, 69.4 mm/month in Hebron and 70.9 mm/month in Jericho.
Gaza Strip
The Gaza Strip is located in a transitional zone between the arid desert climate of the Sinai Peninsula and the temperature and semi-humid Mediterranean climate along the coast. According to the Koppen system the Gaza Strip has a Mediterranean dry summer sub-tropical climate with mild winters.
Temperature
The average daily mean temperature ranges from 25 0C in summer to 13 0C in winter. Average daily maximum temperatures range from 29 0C to 17 0C and minimum temperature from 21 0C to 9 0C in the summer and winter respectively.
Humidity
Daily relative humidity fluctuates between 65% in the daytime and 85% at night in the summer, and between 60% and 80% respectively, in winter.