The 1990s have witnessed a dramatic shift in the priorities for water resource allocations and development. Irrigation, which was once seen as the essential factor for securing sufficient food production, is now seen as a "low-value" use of water compared to its municipal, industrial, and even the environmental uses. Irrigation no longer receives priority either in the allocation of funds for project developments or in the allocation of water itself.

Dry areas occupy over 95 percent of the total lands of West Asia and North Africa (WANA) region. The area is dominated by a Mediterranean-type climate characterized by cool and rainy winters and temperate dry summers. Mediterranean sub-climates are usually differentiated by the length of the summer drought period and the temperatures during winter and summer.

The world is facing severe and growing challenges in maintaining water quality and meeting the rapidly growing demand for water resources. New sources of water are increasingly expensive to exploit, limiting the potential for expansion of new water supplies. Water used for irrigation, the largest use of water in most developing countries, will likely have to be diverted to meet the needs of urban areas and industry whilst remaining a prime engine of agricultural growth.

Rice is the staple food for nearly half of the world's population, most of whom live in developing countries. The crop occupies one-third of the world's total area planted to cereals and provides 35-60 percent of the calories consumed by 2.7 billion people. More than 90 percent of the world's rice is produced and consumed in Asia (Barker and Herdt 1985, IRRI 1989).

Traditionally, the main aims of hydrological research have been to provide an understanding of the water balance operating in catchments,1 the processes and mechanisms that control water movement, and the impacts of land use change on water quantity and quality.

The relationship between land use and hydrology is of interest worldwide. In many developing countries, extensive areas are undergoing land use change. The largest changes in terms of land area, and arguably also in terms of hydrological impacts, often arise from afforestation and deforestation activities (Calder 1992a) .

Salinity has been associated with irrigated agriculture since its early beginnings. One reason is that irrigation often exacerbates the effects of salinity, which occurs naturally because of weathering of saline parent material derived from sea water deposits or other sources.

All science depends on its concepts. These are ideas which receive names. They determine the questions one asks, and the answers one gets. They are more fundamental than the theories which are stated in terms of them.