Hot, arid deserts are among the adverse environments which man can now consider for
future expansion. According to Eckholm and Brown (1977, 1), one-third of the world's land
area is arid or semi-arid desert. The expansion into adverse desert environment is practically
inevitable in countries which are totally contained in desert zones, Saudi Arabia, for example,
and many other countries in the arid Middle East region. Figure 1.1 shows the world
distribution of "cold deserts," north and south of 60° latitude, and "hot deserts," particularly
near 30° north and south. The largest expanse of desert is that occupied by the geographic
region of the Arab World in North Africa and the Arabian Peninsula (Eckholm and Brown
1977). Approximately 6 per cent of Saudi Arabia is semi-arid, 84 per cent is arid, and 10 per
cent is extremely arid deserts (Dregne 1970, 4; McGinnies and Goldman 1968, xxiv).