In rising the air expands and discharges some of its moisture in the form of rain. The result is that the western slopes of the Syrian highlands annually receive the largest amount of precipitation, which decreases as one goes from west to east and from north to south. Thus Beirut averages about 36 inches of rain a year, Jerusalem about 26 and Damascus only 10. On the whole the Palestine-Lebanon coast receives more than twice as much precipitation as the corresponding coast of southern California.
The mean annual temperature in Beirut is 68° F., but temperatures above 107° and below 30° have been recorded there. Humidity reaches its maximum, strangely enough, in July with an average of 75 per cent, its minimum in December with an average of 60 per cent. In winter the dense, cold, dry anticyclonic influences of Central Asia spread over the eastern plateau region of Syria, giving it frost and snow, a phenomenon hardly ever experienced along the coast. There the temperature is moderated by the influence of the sea, which is warmer in winter and cooler in summer than the land. The mountains prevent the cooling sea breezes from reaching the interior, while dust-laden desert winds cause the summer heat in such cities as Damascus and Aleppo to become intense. Most dreaded of the hot winds from the east or south-east is the simoom, or sirocco, which is particularly oppressive and dry, with a humidity at times under 10 per cent, making it difficult to breathe. It is frequent through spring and autumn, when it often reaches the coast and announces the coming of rain. On the fringe of the desert it is often laden with fine penetrating sand, increasing the discomfort of man and beast.
Much of the rain water percolates through large expanses of limestone rock and is thus lost. Some of it gathers in subterranean channels and gushes out in the form of springs. The prevalence of limestone in Lebanon and Palestine thus introduces another unfavourable factor in addition to the minor one of a shimmering dusty landscape, mentioned
