Is Improving Field Irrigation Efficiency the Panacea for Water Scarcity? the Case of Egypt

Water is becoming scarce resource throughout the world with the Mediterranean Sea basin as one of the most water limiting regions in the world. Desalinization and improving irrigation efficiency are two of the possibilities mentioned for decreasing water scarcity. In this presentation we will use Egypt as an example to explore the effect of improving field irrigation efficiencies. In Egypt and the economy with 83 million people entirely depends on the Nile of which 85% of the water originates in Ethiopia. The water in the Egypt is regulated by Lake Nasser smoothing out the runoff peaks to an even flow of approximately 0.16 BCM per day. This water is mainly used for irrigation, industrial and municipal uses. Approximately between 5.4 and 6 million ha are irrigated along the Nile and in the delta. Less than 20% of the Nile flow at the Aswan dam enters the Mediterranean Sea and is highly polluted. Irrigation practices in Egypt are highly inefficient with field efficiencies in the order of 70%. It has been suggested that increasing efficiencies will increase water availability down stream. In order to understand if this is possible, we considered the fate of the irrigation water. Part of the water applied to the field evaporates and the remaining water percolates downward and recharges the aquifer. The aquifer supplies base flow to the Nile and provides water for irrigation. Thus the only loss of the system is the evaporation from the crop in the field. Using this fact we can estimate the overall irrigation efficiency of the irrigation in the Nile. If we assume that 98% of the cultivated land are irrigated with an average evaporation rate of 1150 mm we find that the agricultural water use is at the same order as the water released at the Aswan dam. Assuming that all other uses are also conservative (i.e. use the water and return it back to the Nile with some pollution), we see that the overall use is over 100% during some years. This is not possible so not all land is double cropped and some are water short. Many estimates are available for the number of times that the water is reused in the Nile basin. From the simple calculations presented before we find that the reuse is a function of the irrigation efficiency. A field irrigation efficiency of 75 % can result in a reuse factor of four and is greater than any of the current estimates. In addition these calculations put into question if water allocated to Egypt decrease, improving field irrigation efficiency can increase the acreage that can be irrigated. Increasing production may only be achieved by increasing the yield per unit water evaporated. Finally, it is doubtful if the Nile outflow to the Mediterranean can be decreased because of salt contents in the drainage water of agricultural fields is greater than what can be used to grow agricultural crops. The salt content in the drainage water is still much less than that in the Mediterranean Sea and desalinization of this water will therefore be more economical then using the Mediterranean water. So in the future the Nile might become a closed basin in which all water is being used and only the salt enters the Mediterranean Sea.