• Countries receiving 100 to 300 mm annually with 40 to 70 days of rain, Jordan (111 mm), Kuwait (121 mm), Oman (125 mm), Turkmenistan (161 mm), Yemen (167 mm), Tunisia (207 mm), Iraq (216 mm), Djibouti (220 mm), Iran (228 mm), Syria (252 mm), Somalia (282 mm)
• Countries receiving less than 100 mm each year with fewer than 30 days of rain: Egypt (51 mm), Libyan Arab Jamahiriya (56 mm), Saudi Arabia (59 mm), Qatar (74 mm), United Arab Emirates (78 mm), Bahrain (83 mm), Algeria (89 mm), Mauritania (92 mm)

Rainfall in almost the entire region is intense, producing flash floods. Evaporation and transpiration cause much water loss from the surface. Potential evapotranspiration ranges from 1500 to 3000 mm per year. The Arabian Peninsula, which has almost one-fourth of CWANA's hyperarid zone, has annual precipitation deficits between 1700 to 2500 mm. A way to examine the consequences for agricultural systems in CWANA is to divide the region into aridity zones (Table 1-1):

• The hyperarid zone covers about 0.9 billion ha, over 86% in CWANA. Except for irrigated areas, such as in Egypt, few nomads live in this zone.
• In the arid zone the natural vegetation of short grass and sparse thorn scrub provides some grazing for sheep, goats, cattle and camels. Some wildlife, mostly gazelles and reptiles, live in this zone. Opportunistic rainfed cropping of sorghum and pearl millet is practiced in depressions and foothills. Nomadic groups live in this zone, which has a low carrying capacity.

• The semiarid zone has both animal and rainfed husbandry and therefore supports millions of rural people and major agricultural industries.
• The subhumid zone contains luxuriant vegetation, from savanna to broken woodland. Productive arable farming is the primary use.

Three more aridity zones occupy small areas:

• The coastal zones have various landscapes, coastal salty marshes, a series of medium-high hills lying a few kilometers away from the sea and open plains traversed by rocky sediments. While arid ecosystems dominate, fertile deltas of agricultural value exist.
• Swamps cover considerable areas in the region. In Sudan, the Sud swamps cover about 12 million ha. These swamps are inundated permanently or seasonally. The seasonally inundated parts are vast meadows of almost pure grass, which maintain much livestock.
• Mountain meadows occur on shallow soil at the higher altitudes and have high rainfall, high humidity and low temperatures. The meadows are rich in grasses, herbs and trees. Plants vary with the altitude, up to about 3500 m. Some of Central Asia and the Caucasus have 1-5 m snowfall. The climate has a short growing season and long, cold winters.