Adjusting the irrigation water demand projection module to be viable in central Jordan Valley

Abstract

In 2004, the Jordan National Water Master Plan (NWMP) was developed, which includes a number of water demand projection modules for assessing the existing water resources, and predicting demands on water for all uses; municipal, industrial, tourist and irrigation. The Irrigation Demand Module was tested with historical data and comparisons were made between the predicted demands as obtained by the module, and the recorded water use provided by relevant institutions. Serious imbalances appeared, totaling the irrigation water demands of more than 1.5 times the recorded irrigation water use. The purpose of this study was to verify the viability of the functional part of the Irrigation Demand Module, namely the Net Irrigation Requirements Calculator (NIR-Calculator) in terms of functions, factors, and data used for the calculations. Results show that the original NIR-Calculator overestimated the values of NIR in the initial growth stage, Kci, by almost 55 %, because Cuenca Formula is used in the original version to calculate the initial crop coefficient, while FAO-56 Formula is used in the modified version. When taking the Jordan climatic characteristic into consideration, the original NIR-Calculator underestimated the values of the mid growth stage crop coefficient, Kcm, by 1.7–3.5 %, as well as the values of the end growth stage crop coefficient, Kce, by 2.2–8.0 %. The original NIR-Calculator overestimated the effective rainfall by 66.5, 44.8 and 34 % for dry, medium and wet scenarios, respectively. The NIR values obtained by the original NIR-Calculator differed than the modified NIR-Calculator by 5.2, 6.2 and 8.6 % for dry, medium and wet scenarios respectively. Finally, the irrigation demand volume for Deir Ala area obtained by the original NIR-Calculator differed than the modified NIR-Calculator by 2.0, 3.5 and 9.3 % for dry, medium and wet scenarios respectively. In conclusion, although there is a difference between these two versions of the NIR-Calculator, this difference is not enough to cause the 1.5 imbalance in the Irrigation Demand Module. This imbalance can’t be attributed only to the NIR-Calculator and further investigation is required to determine why the imbalance exists.