LIFE in desert areas requires intensive use of scarce water. So development beyond that of nomadic societies is difficult.
But faith in the power of technology has fostered recurrent attempts to establish cultures alien to the desert, each resulting in failure and destruction of the environment.
Wherever nature has indicated a scarcity or environmental decline, different technologies have been enlisted to import more water or increase yields from beleaguered aquifers.
Some underground aquifers and recycled water exist in the desert, but the main source is rainfall. Desert rainfall, however, is an erratic phenomenon of high intensity and short duration, which can cause erosion instead of runoff surplus. And long periods of drought mean percolation to groundwater aquifers is relatively small.
Water-resource assessments are difficult because verifying information about rain intensity, distribution, and probability is a serious challenge even where reliable observations and measurements are available.
The phrase "efficient water use" can have different meanings depending on the location involved and its stage of development. In one case it may mean subsistence conditions. In another, such as Israel's Negev Desert, it may mean the ability to attain higher standards of living.
Primeval inhabitants of the Negev increased their water harvest by increasing collection of storm runoff, diverting it from sloping areas to saturate their lands.
Modern water harvesting is designed to increase runoff for saturation of woodlands. In the Negev, however, efficient use of water means maximizing net income per water unit.
Agricultural production in the Negev is an integral part of an international marketing system, and maximizing profits requires the most efficient use of water for the crops that are in demand on the national and world markets.
In the Negev and some other regions, special importance is attached to the use of brackish water because of the presence of a deep aquifer that will last for years if carefully utilized. Research has led to the adoption of drip irrigation, the only method for using brackish water. Crop varieties resistant to salinity have been developed and attempts to adapt other crops continue.
Large-scale irrigation requires the following elements:
* Profitable use of all types of water - fresh, brackish, and reclaimed effluents;
* Efficient fertilizer use;
* Avoidance of damage to foliage from poor-quality water;
* Minimum water losses;
* Flexibility, enabling irrigation at any time and swift transition between crops;
* Little environmental damage.
Each of the irrigation systems in use today has its advantages and disadvantages. Based on experience in the Negev, there are four general irrigation methods: surface irrigation, sprinkler irrigation, machine-sprayer irrigation, and drip irrigation.
Surface irrigation has been largely abandoned because of its low efficiency and high water loss. Sprinkler irrigation gives higher yields and is easy to automate. Sprayers are useful for supplemental irrigation of large areas, but can cause runoff.
Today drip systems - both surface and subsurface - are rapidly becoming the dominant irrigation system in the Negev. Their advantages include easy fertilizer application; low soil and air pollution; minimal evaporation; high flexibility; less-restrictive water-quality standards; and ease of automation. Subsurface systems also protect the plastic piping from weather and wildlife.
Irrigation requires investment that can only be justified in the context of efficient agriculture and suitable markets. But the Israeli experience indicates that advanced technologies can be transferred to uneducated farmers if they understand the inherent opportunities and the risks are minimized. The desertification process can be arrested, but the causes must be identified in time and halted.