Within Libya as many as five different climatic zones have been recognized, but the dominant climatic influences are Mediterranean and Saharan. In most of the coastal lowland, the climate is Mediterranean, with warm summers and mild winters. Rainfall is scanty, and the dry climate results in a year-round 98-percent visibility. The weather is cooler in the highlands, and frosts occur at maximum elevations. In the desert interior the climate has very hot summers and extreme diurnal temperature ranges.
Less than 2 percent of the national territory receives enough rainfall for settled agriculture, the heaviest precipitation occurring in the Jabal al Akhdar zone of Cyrenaica, where annual rainfall of 400 to 600 millimeters is recorded. All other areas of the country receive less than 400 millimeters, and in the Sahara 50 millimeters or less occurs. Rainfall is often erratic, and a pronounced drought may extend over two seasons. For example, epic floods in 1945 left Tripoli under water for several days, but two years later an unprecedentedly severe drought caused the loss of thousands of head of cattle.
Deficiency in rainfall is reflected in an absence of permanent rivers or streams, and the approximately twenty perennial lakes are brackish or salty. In 1987 these circumstances severely limited the country's agricultural potential as a basis for the sound and varied economy Qadhafi sought to establish. The allocation of limited water is considered of sufficient importance to warrant the existence of the Secretariat of Dams and Water Resources, and damaging a source of water can be penalized by a heavy fine or imprisonment.
The government has constructed a network of dams in wadis, dry watercourses that become torrents after heavy rains. These dams are used both as water reservoirs and for flood and erosion control. The wadis are heavily settled because soil in their bottoms is often suitable for agriculture, and the high water table in their vicinity makes them logical locations for digging wells. In many wadis, however, the water table is declining at an alarming rate, particularly in areas of intensive agriculture and near urban centers. The government has expressed concern over this problem and because of it has diverted water development projects, particularly around Tripoli, to localities where the demand on underground water resources is less intense. It has also undertaken extensive reforestation projects .
There are also numerous springs, those best suited for future development occurring along the scarp faces of the Jabal Nafusah and the Jabal al Akhdar. The most talked-about of the water resources, however, are the great subterranean aquifers of the desert. The best known of these lies beneath Al Kufrah Oasis in southeastern Cyrenaica, but an aquifer with even greater reputed capacity is located near the oasis community of Sabha in the southwestern desert. In the late 1970s, wells were drilled at Al Kufrah and at Sabha as part of a major agricultural development effort. An even larger undertaking is the so-called Great Man-Made River, initiated in 1984. It is intended to tap the tremendous aquifers of the Al Kufrah, Sarir, and Sabha oases and to carry the resulting water to the Mediterranean coast for use in irrigation and industrial projects.
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