The water scarcity situation in WANA is getting worst every day. It is projected that the vast majority of the nineteen WANA countries will reach the severe water poverty level by the year 2025; ten of them are already below that level. Over the coming years this situation will worsen with increasing demand, given the fact that the possibility of new supplies is limited. The increasing pressure on this resource will, unless seriously tackled, escalate conflicts and seriously damage the already fragile environment in the region. In many countries of the world, the challenge, as set by the CGIAR challenge program, is to retain diversions of water to agriculture not higher the 2000 level. For the dry areas the question is how fast the share for agriculture is dropping.
As a result of unfavourable rainfall characteristics, soil moisture does not satisfy crop needs over the whole season. I will take wheat as an example here. In the wet months (Dec to Feb) stored rain is ample, crop sown at the beginning of the season are in early growth stages, and water extraction rate from root zone is very low. Usually little or no moisture stress occurs during this period. However, in early spring, crops grow faster demanding high rate of evapotranspiration and soil moisture depletion. Usually, at that time chances of rain become little while soil moisture drops below critical levels. Thus, a stage of increasing moisture stress starts and continues until the end of the season. This moisture stress occurs in all Mediterranean-type rainfed areas with no exception but varies in its starting time and severity. As a result rainfed yields are very low in all countries of the region. Potential yields are much higher and are attainable if soil moisture stress during dry spills is alleviated.
Supplemental irrigation is an effective response to this problem. It is the addition of essentially rainfed crops of small amounts of water during times when rainfall fails to provide sufficient moisture for normal plant growth, in order to improve and stabilize yields.
Average WUE of rain in producing wheat in the dry areas of WANA range from about 0.35 to 1-kg grain/m3. However, water used in supplemental irrigation can be much more efficient. ICARDA found that a cubic meter of water applied at the right time (when crops suffer from moisture stress) and good management could produce more than 2.5 kg of grain over the rainfed production. This extremely high WUE is mainly attributed to the effectiveness of a small amount of water in alleviating severe moisture stress during the most sensitive stage of crop growth. The stress usually causes a collapse in the crop development and seed filling and reduces the yields substantially. When SI irrigation water is applied before such conditions occur, the plant may reach its high potential. In comparison to the productivity of water in fully irrigated areas (rainfall effect is negligible) we find greater advantage with SI. In fully irrigated areas with good management, wheat grain yield is about 6 t/ha using a total amount of 800 mm of water. This makes WUE about 0.75 kg/m3, one third of that under SI with similar management. This suggests that water resources may be better allocated to SI when other physical and economic conditions are favourable.
Managing water resources under scarcity and climate change Theib Oweis Director, Integrated water and Land Management program, ICARDA, Aleppo, Syria For IFAD-ICARDA knowledge and technology exchange in NENA region, October 2009
Real vs. paper water losses Storage Irrigation Precipitation Runoff recoverable Transpiration Evaporation Losses To ground water recoverable Deep percolation Drainage Partially recoverable Quality losses Seepage recoverable
Dependence on green and blue water August 2006 Areas in green: agriculture mainly under rainfed Areas in blue: agriculture mainly under irrigation Circles depict total crop depletion Why rainfed systems?