In the first half of the 20th century, Lebanon had regained its past agricultural boom where almost one-fourth of its land had been cultivable (the highest proportion in the Arab world). After the 1950s and the prosperous decades that followed, agriculture faced a decline with the beginning of the Lebanese Civil War and especially after the Israeli invasion in the early 1980s. In the latter period, the government prepared plans to irrigate an additional 60,000 hectares, and by 1984 studies were under way on 6 major irrigation projects, all designed to be carried out as part of the 1982-91 reconstruction plan. However, with the Israeli invasion came a continuous diversion of water from rivers mainly located in the south. Even in the relative calm between 1978 and 1981, about 1,100 hectares of tobacco were destroyed, 300 hectares of agricultural land were abandoned because of land mines, and 51,000 olive trees and 70,000 fruit trees were destroyed, according to the United Nations High Commissioner for Refugees. By the mid-1980s Lebanon had become one of the world's most prominent narcotics trafficking centers, with the prosperous phase that it witnessed (especially in the Beqaa valley). Before 1975 much of this trade was exported by air from small airstrips in the Beqaa Valley. After the valley came under Syrian control, the drug crop left the country by sea through Christian-controlled ports to Cyprus, overland to Syria or sometimes through Israel to Egypt.