Chapter Two
Topography And Climate
Topography
A Digital Elevation Model (DEM) containing Z-value with pixel size of 100m is created for Nablus district. This model 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 three dimensional lines with varying elevation .
Figure 2.1 represents the producing DEM, which is themed using the threshold table with an interval of 100m. Themes are colored values that give a quick and effective method for identifying features and areas that meet specified criteria. The threshold table is simply tells the GIS software which color to use when displaying certain pixels.
A contour map based on the created digital elevation mode is constructed with contour interval of 100m (Figure 2.2 ). The highest point in the district reaches 918m above sea level at Jabel 'Ibal, while the lowest elevation is 349m below sea level at the southeast corner of the district.
A three dimension model for Nablus district is created using the perspective model of the Pamap GIS software version 4.2 (Figure 2.3). The view is facing to south east and an exaggeration factor of 10 is used.
The topography of Nablus district can be divided into four parts: Jordan Valley, the eastern slopes, mountain crests and western slopes. The Jordan Valley is located between Jordan river and the eastern slopes with elevation ranges between 349m below sea level to 100m above sea level. 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 wadi El Badan. 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, with elevation ranges between 250500 meters above sea level.
Two main drainage systems are distinguished in Nablus district (Figure 2.4). The first system is run to the west such as wadi Qana, wadi Rabah, wadi Khalifa and wadi Mas-ha. While the second system is run to the east or south east, such as wadi el Maleh, wadi Dura, wadi el Far'a and wadi el Ahmar
Climate
Nablus district is located at the northern latitude earth grid 3213`, it has hot, dry summers and moderate, rainy winters. Table 2.2 shows the long term variation in different climatic parameters in Nablus district (1970-1992). This data was adopted from the Nablus Meteorological Station.
Table 2.1: Long term annual rainfall for the period 1970-1993.Year Rainfall (mm) Year Rainfall (mm) 1970-1971 633.2 1982-1983 1118.7 1971-1972 671.2 1983-1984 555.5 1972-1973 430.3 1984-1985 467.3 1973-1974 774 1985-1986 527.4 1974-1975 553.3 1986-1987 756.6 1975-1976 588.1 1987-1988 843.9 1976-1977 606.4 1988-1989 566.6 1977-1978 508.4 1989-1990 588.7 1978-1979 350.3 1990-1991 504.9 1979-1980 894.6 1991-1992 1391.5 1980-1981 643.3 1992-1993 816.4 1981-1982 653.2
Table 2.2: Long term average of different climatic parameters in Nablus district, 1970-1992.Month Rainfall(mm) Max. Temp(°C) MinTemp R.H. % Wind (Km/day) E. pan(mm/month) Sunshine (hours)
January 148.38 13.08 6.21 67.21 209.19 49.6 4.7
February 144.04 14.4 6.72 67.25 226.81 67.2 4.75
March 101.26 17.21 8.77 62.25 240.39 99.2 6.4
April 32.38 22.15 12.04 53 244.06 149.1 8.16
May 6.77 25.73 14.87 50.72 257.19 202.7 8.9
June 0.15 27.88 17.37 54.96 288.1 225.9 8.36
July 0 29.07 19.26 60.65 298.71 237.9 9.6
August 0.09 29.36 19.54 64.83 281.47 218.2 10.9
September 1.68 28.42 18.53 64.43 247.01 177.6 10.16
October 18.53 25.84 16.24 57.43 183.82 131.1 9.83
November 67.02 20.22 12.14 57.32 186.17 74.4 7
December 143.29 14.62 7.83 67.26 183.82 48.6 4.76
Average 663.59 22.3 13.3 61 237 1681 7.8
Table Notes: "R.H: Relative Humidity," Max.: Maximum Min.: Minimum E.Pan: Pan Evaporation.
Wind:
The southwest and northwest winds are the prevailing winds in this area with an annual average wind speed of 237 km per day. During the summer, wind moves with relatively cooler air from the Mediterranean towards the north, with an average wind speed of 298.71 km per day in June. At night, the land areas become cooler, causing diurnal fluctuations in wind speeds due to the reduction of the pressure gradient. In winter, the wind moves from west to east over the Mediterranean, bringing westerly rain bearing winds of average wind speed 209.19 km per day in January.The Khamaseen, desert storm, may occur during the period from April to June. During the Khamaseen, the temperature increases, the humidity decreases, and the atmosphere becomes hazy with dust of desert origin.
Temperature:
The geographical position of Nablus district in the northern part of the West Bank gives it a comparatively lower temperature range than the other districts. During January, the coldest month, the average maximum temperature reaches 13.1°C, and average minimum temperature reaches 6.2°C. During August, the hottest month, the average maximum temperature is 29.4 and the average minimum temperature is 19.5. Figure 2.5 shows the variation of maximum and minimum temperature during the period 1970-1992.
Humidity:
The mean annual relative humidity of Nablus district is 62%. During the Khamaseen period, the relative humidity decreases to reach its minimum value of 50.72% (in May). Maximum humidity of 67% is usually registered in December, January and February. This value increases gradually at night, as shown in Figure 2.6.
Rainfall:
Rainfall in Nablus district is limited to the winter and spring months, from October to May. The annual mean rainfall is 663.6 mm. Figure 2.7 shows the variation in the average monthly rainfall for the period 1970-1992. In 1978/1979 rainfall reached only 350.3 mm while in 1991/92 rainfall reached a maximum of 1391.4 mm. Nearly 81% of the annual rainfall occurs between December and March, while July is totally dry. Some showers, however, were registered at Nablus Meteorological Station in June and August (Table 2.2). No data is available on hail or snow in Nablus district. It does periodically snow and hail, but these events are rare.
Evaporation:
Pan Evaporation is used to reflect the evaporation rate in Nablus district. The evaporation rate is particularly high in the summer due to strong insulation. It can reach 237.9mm/month (July), while in the winter it reaches only 48.6mm/month (December). During the spring and autumn, the evaporation is 100-150 mm per month. In December, January, February and March, precipitation exceeds the rate of evaporation as shown in Figure 2.8.
Sunshine Radiation:
The annual average solar radiation received in Nablus district is 17.8MJ/m2/day (calculated by Penman method). During August, the district receives an average of 11 hours/day of sunshine, with an average maximum solar radiation of 25MJ/m2/day. In December, the district receives an average of only 5 hours/day of sunshine and an average maximum solar radiation of 9MJ/m2/day.These values can differ from one place to another in Nablus district, depending on the cloud cover. The cloud cover in Nablus district is usually greatest around Burin village due to its position and altitude, therefore there is less sunshine and lower solar radiation. Figure 2.9 shows the variation of average monthly radiation from 1970-1992.
