Climate

The UAE is a tropical / subtropical hot desert country with high temperatures and low rainfall. Its arid climate is characterised by two distinct seasons: a long dry summer season (April - November) with very high temperatures and short winter season (December - March) with mild to warm temperatures and low precipitation rates (Al Assam, 1992). The UAE is influenced by the subtropical anticyclon; thus it has little chance of rain. The mean total annual rainfall over the whole country is 119 mm. However, like other arid countries, this total can be highly variable between one year and another. The rainfall distribution within the UAE is of ecological interest, with low precipitation rates in the South West, where the annual total can be less than 5 mm, and generally much higher rates in the North East, where the maximum rates can exceed 480 mm. The mean annual air temperatures are 270° C, with maximum temperatures exceeding 49° C, and minimum temperatures around 4° C. Air humidities are high in the coastal areas, whereas the inland regions are usually very dry. Winds in the UAE tend to be light to moderate with mean annual wind speeds of less than 10 knots, though wind gusts have been recorded with maximum speeds of over 160 km/h. The evaporation rates vary between 4 mm and 13 mm per day throughout the year, with a total of about 3300 mm, against a mean annual rainfall of 119 mm (Embabi 1993). Following FAO et al. (1977), Satchell (1978) and B°er (1995, 1997) the UAE may be classified into three bioclimatic zones: a hyperarid zone (P/E = 0 - 0.03), an arid zone (P/E = 0.03 - 0.20) and a semi - arid zone (P/E = 0.20 - >0.5). Table 1 provides climatological data of various UAE and GCC states.