Conditions of Natural and Human Resources 29

Chapter 2 Conditions of Natural and Human Resources

Continuous or sustainable social development can only be achieved when a society’s resources are appropriately controlled, used and distributed, since the resources given to a society are limited. The oasis society is particularly so, because of the severe natural circumstances that characterize a desert region. This chapter deals with the natural and human conditions pertaining to resources, specifically water and population, and with the relationship between water, population and land use in the region of Dakhla Oasis, to which Rashda belongs, in order to examine the human activities and the resource conditions under which Rashda lived.

Climate and Hydrogeology

The climate of is characterized by a hot season from March to September and a cold season from October to February, although the northern winds moderate the temperatures slightly (Robaa, 2008). In the coastal regions along the Red Sea and Mediterranean Sea coasts, average annual temperatures range from a maximum of 37°C to a minimum of 14°C. The most humid area in Egypt is along the Mediterranean coast, where the average annual rainfall is about 200 mm. Rainfall decreases drastically towards the south. It may only once in several years in many desert locations (Robaa, 2008). Temperatures vary greatly in the inland desert areas, especially in summer, when the diurnal range is from 7°C at night to 43°C during the day. During winter, temperatures in the desert fluctuate less dramatically, but they can be as low as 0°C at night and as high as 18°C during the day. The average annual temperature increases towards the south from the Delta in the north to the Sudanese border, where temperatures are similar to those of the open deserts to the east and west. Solar radiation has a magnitude of 12 to 30 MJ/m2/day, and there are between 3,500 and 4,500 sunshine hours per year (Tadros, 2000). All Egypt is character- ized by clear skies during summer (June to August) and partially cloudy skies during the transitional seasons of spring (March to May) and autumn (September to November) (Robaa, 2008). In winter, most of Egypt is character- ized by cloudy sky, especially the northern part, while coverage decreases from north to south. A phenomenon of Egypt’s climate is the hot spring wind that blows across the country. The winds, known to Europeans as the “Sirocco”

© Koninklijke Brill NV, Leiden, 2016 | doi 10.1163/9789004317390_004 30 Chapter 2 and to Egyptians as the “Khamasin”, usually arrive in April but occasionally occur in March and May. Unobstructed by geographical features, the winds reach high velocities and carry great quantities of sand and dust from the des- erts. These sandstorms, often accompanied by winds with speeds of up to 39 m/s, can cause temperatures to rise by as much as 20°C in two hours. The winds blow intermittently and may continue for days, causing illness in people and animals, harming crops and occasionally damaging houses and infrastruc- ture (Robaa, 2008). Dakhla Oasis is one of the major oases in the Western Desert and is located on low-level ground ranging from 0 to 200 metres above sea level (the sur- rounding altitude is above 200 metres). The aridity index (AI) used by the United Nations Environment Program (UNEP, 1997) indicates that this area is hyperarid. Here, AI is defined as the ratio of annual rainfall to potential evapo- transpiration. Potential evapotranspiration is the amount of water that would be removed from the land surface by evaporation or transpiration if the amount of water already present in the land surface were not a limiting factor. In other words, the potential evapotranspiration over the desert is very great because the amount of evaporation that could take place there is huge. However, because there is no water there to evaporate, the evapotranspiration that actually takes place is quite small. In Dakhla Oasis, the annual rainfall is extremely scarce and insignificant (~1 mm/year). Potential evapotranspiration is 1,773 mm to 1,950 mm, calcu- lated using data from the Dakhla meteorological station. This means that the evaporation rate is extremely high in Dakhla Oasis. Thus, the areas around the oasis are bare of vegetation except for very isolated clumps of plants such as Acacia or Tamarix, which survive on the little moisture that is contained in blown sand and is derived from dew, isolated showers, and frontal storms (Brookes, 2001). The climate of Dakhla Oasis is mainly controlled by the Harmattan, a dry wind that blows hot air from the Sahara at high pressure. From 1990 to 2005, the relative sunshine duration, which is defined as the percentage of actual sunshine duration to possible sunshine duration, was at a high level of 87% (a low of 82% occurred in January; it peaked at 90% in June) at the Kharga meteorological station 120 km from Dakhla (Robaa, 2008). According to the distribution of annual solar radiation around the world, the highest levels of solar radiation can be found around the southern part of the Western Desert in Egypt (Budyco, 1956). Although the wind direction frequencies were almost all northerly, there was a slight westerly skewing, probably reflecting a topographic indraft of northern winds into the Dakhla depression (Brookes, 2001). The annual