Abstract
An intensive investigation has been undertaken to assess the negative impacts of irrigated agriculture in the Northwestern region of Libya. A total irrigated area of 90 thousand hectares has been cultivated with more than 15 major crops with a total irrigation water demand of no less than 730 million cubic meters per year (m3 /y). The analysis of water sample hydrological data collected from more than 90 wells representing the whole region shows clearly those groundwater resources are depleting at an alarming and increasing rate. The negative economic and environmental impacts of this excessive groundwater depletion have been reflected in severe water level and piezometric head declines, intensive and extensive irreversible seawater intrusions, deteriorating water quality, soil salinization, and exposure to nitrate pollution and reduced crop productivity. To prevent any further deterioration, the gap between the renewable water supplies of 200 million m3 /y and the agricultural water demand of 730 million m3 /y must be closed through the diversion of no less than 500 million m3 /y from phase two of the Man-made River Project (MRP) at the cost of 0.34-0.83 US$/m3 . This water supply will have to be subsidized, however, since irrigated agriculture is unable to pay back even 10% of this cost. The other alternative is to limit the irrigation water demand to the renewable water supplies through the importation of virtual water, reducing the irrigated area and the cultivation of crops that have the highest economic crop water productivity values.