The Latiyan Dam channels the energy of the Jajeroud River in central Iran
Most of Iran is arid or semi-arid, annual precipitation averaging about 24 centimetres, or one-third the world average. One-third of all precipitation occurs in the Caspian Sea drainage area, which represents only a tenth of the total land surface, while the average rainfall in 96 per cent of Iran's land area does not exceed 20 centimetres. Worse still, much of this scanty rainfall occurs in late winter and early spring when the farmers least need it, and flash spring floods are common, with the water running to waste in the sea or desert, followed by droughts in the main growing season.
There is also a very high rate of evaporation. In Teheran, for example, where the mean annual precipitation is 22 entimetres, the potential evaporation is about 300 centimetres, or some 13 times that of actual precipitation.
In most parts of the world with such conditions, (Central Australia, for example) thereis no agriculture. Yet for most of its history Iran has been primarily an agricultural economy. Animal husbandry was possible until recently only by nomadic pastoralism, the flocks moving at fixed seasons to pastures new, while crop farming was largely dependent on the qanat system.
The qanat is an ingenious Iranian invention dating back to pre-Achaemenian times. It is an underground channel that conveys water from a highland aquifer to the surface at lower levels by gravity, commonly at distances of ten kilometres or more. From Iran the system spread to Egypt, North Africa, India, Chinese Turkestan, Arabia and even Spain and Sicily. and underground water conduits in some Saharan oases are still known as "Persian works". The highly-specialized and often dangerous work of digging qanats is still practised in most parts of Iran.
Today, although the contribution of qanats to Iranian agriculture is decliningg in relative terms, as more and more dams and wells are built, some 50,000 odd qanats are still in use, and theii total output is roughly equal to that of the Euphrates river. Left, the Dez River Dam in southern Iran
The vital necessity for Iran was to make the most efficient use of its water resources. That was underlined in October, 1967, when water nationalization was declared the tenth point of the Revolution. As the Shah told Parliament on that occasion that "the natural and climatic conditions of the country do not allow us to waste even one drop of water."
During the Fourth and Fifth Plans there has been heavy investment in water and irrigation projects. Twelve major reservoir dams, with a total capacity of over 10 billion cubic metres, became operational, five more were under construction and another five were at the planning stage. By the end of the Fifth Plan (1978) the amount of water regulated by dams reached 27 billion cubic metres per year, and the total area of irrigated land l increased to about four million hectares.
To ensure the proper utilization of groundwater resources, deep wells could only be drilled in conformity with regional plans aimed at avoiding underground reservoir depletion. The Fifth Plan called for new facilities (wells, qanats and related facilities) for the exploitation of 2.3 billion cubic metres of groundwater resources, chiefly by means of integrated systems. Other projects involved the diversion of 0.6 billion cubic metres of water from areas with plentiful supplies to arid areas.
Almost every town and most large villages had a piped water system, and the provision of safe potable water made a significant contribution to public health. Apart from conventional methods of water conservation and utilization, Iran also investigated the possibilites of modern technology, includinq cloud-seeding and desalination. Desalination plant capacity was being increased from three million to 23 million cubic metres per year during the Fifth Plan, although the high costs made it an economic proposition only in certain remote but important locations. While it was hoped that technical innovations would one day enable Iran to overcome its age-old struggle against drought, conventional systems were doing much to alleviate water shortages throughout the country.