Topography

A Digital Elevation Model (DEM) containing Z-value with pixel size of 100 m was created for Ramallah District. In generating the DEM, the GIS unit at ARIJ depends on the topographic maps of the US Army Crops of Engineers and the British maps produced in 1942. It was constructed using the finite difference technique of the Topographer Model of the Pamap GIS software version 4.2. The finite difference technique is considered to be suitable for using trend data as the input data. The trend data represents the overall shape of the terrain. It is usually contour lines but can also be represented by three dimensional lines with varying elevation.

Figure 2.1 shows the produced DEM, which is themed using the threshold table with an interval of 100 m. Themes are colored values that give a quick and effective method for identifying features and areas that meet specified criteria. A contour map based on the created digital elevation model was constructed with contour intervals of 50 m (Figure 2.2).

Figure 2.1

Figure 2.2

A three dimensional model for Ramallah District is created using the perspective model of the Pamap GIS software version 4.2, (Figure 2.3). The view is facing to southeast with exaggeration factor of 15.

Figure 2.3

 

The topography of Ramallah District can be divided into three parts: the eastern slopes, mountain crests and western slopes. The eastern slopes are located between the Jordan Valley and the Mountains. They are characterized by steep slope which contribute to forming young wadis such as wadi El-Maquk. Mountain crests form the watershed line and separate the eastern and western slopes. Elevation ranges on average between 750 and 800 meters above sea level. Western slopes, characterized by gentle slopes, and have elevation ranges between 250­500 meters above sea level. The highest point in Ramallah District is 1022 m above sea level at Tal A'sur, and the lowest elevation is 24 m below sea level at the southeast corner of the district.

Two main drainage systems are distinguished in the Ramallah District (Figure 2.4). The first system runs to the west towards the Mediterranean such as wadi Sarida, wadi El-Shamiyah, wadi El-Durlb, wadi Salman and wadi El-Kabeir. The second system runs to the east towards the Jordan River, such as wadi El-Maquk and Wadi El-Ein.

Figure 2.4:Drainage system in the Ramallah District

Climate

The Ramallah District is influenced by the Mediterranean climate, a rainy winter and dry summer. Little climatic data are available for the Ramallah District. The climatic data from October 1994 up to September 1995 were taken from the recently installed weather station at Bir Zeit University, and the rainfall data for the past 20 years were obtained from the Ramallah Department of Agriculture.

Temperature

Ramallah District is part of the Hill Regions which have lower temperatures than other places in the West Bank. Table 2.1 shows the variation in temperature for the year 1994/95. Like other districts in the West Bank, January is the coldest month and August is the hottest. During the 1994/95, the highest temperature was registered at 37.5 ⁰C in May 1995 and the lowest at 1.2 ⁰C in February 1995. The mean annual temperature ranges between 15-20 ⁰C. The temperature of the coldest month (January) is 6-12 ⁰C, while the hottest month (August) ranges between 22-27 ⁰C. Figure 2.5 shows the variation of average monthly temperature throughout the year.

Rainfall

Winds from the west and southwest which are saturated with moisture from the Mediterranean Sea precipitate a mean annual rainfall of 694 mm on the Ramallah District. This amount is distributed over an average of 59 days; and almost 85% of the total rainfall occurs between November and February. Table 2.2 shows the variation of long term annual rainfall for a period of 20 years (1974-1994) and the number of rainy days per year. In years of extreme rain, such as 1982/83 and 1991/92, floods and extensive soil erosion is likely to occur because of the intensity of the rainfall. The steep slopes of Bir Zeit and Bitunia receive most of the precipitation ranging between 400-900 mm. The areas that are wide spread on or near mountain summits like Beit U'r Tihta have an annual precipitation ranges from 300-700 mm. Figure 2.6 shows the variation of the monthly rainfall among the year.

Figure 2.6: Monthly rainfall for 1994 /95.

Little data are available on the amount of snow in the Ramallah District. There is infrequent snow fall during the winter period. The largest snowfall on record came on February 9, 1920 when one and quarter meters of snow fell on Ramallah.

Figure 2.7: Annual rainfall in mm for 1974-94.

Humidity

The mean humidity level in 1994/95 was 70.2% in the Ramallah District. The minimum relative humidity was registered in May at 57.2% and the maximum in December with a value of 77.1%. Figure 2.8 shows the variation of monthly relative humidity in 1994/95.

Figure 2.8 Monthly relative humidity for 1994/95

Evaporation

The high temperature in the summer time, the intensive insulation under a cloudiness sky, with 306.3 wattm² as maximum energy reached to the soil surface in June, and the low air humidity results in a high evaporation rate. The evaporation rate decreases in the winter due to high humidity, and low radiation of 98.3 wattm² reached to the soil surface in December. The monthly variation in radiation for the year 1994/95 is shown in Figure 2.9

Figure 2.9: Monthly radiation for 1994/95

Wind

During the summer, the area is influenced by regional winds with an average daily wind speed of 216 km in August. During the winter season, the rain-bearing winds move in a general west-east direction with an average daily wind speed of 294 km in December, causing precipitation. Between April and June the area is influenced by Khamseen winds which blow frequently from the Arabian Desert, full of sand and dust. This wind brings high temperature and reduced humidity.