English

Abstract

High percent of the Arab countries suffer from great shortage in their water resources because it lies in hot arid and semiarid regions. However, vast areas of these regions are utilized for agricultural production, which require making essential studies regarding the determination of water requirements for irrigation purposes, i.e. determination of crops' consumptive use of water in such areas. Crops' consumptive use of water is related to reference evapo-transpiration by a coefficient called crop coefficient, which depends on type of crop and its growing stage. In addition, evaporation measurements are of great importance for irrigation systems design, irrigation rotations, and development of hydrologic models. In the present research, a seasonal regression-autoregressive model has been developed and used to simulate and estimate monthly reference evapo-transpiration in Najran Region, KSA. Actually, the present research is a part of a two-year research project, which has been planned and funded by Najran University, KSA. The performance of the developed model has been evaluated by calculating the statistical characteristics of both the estimated and measured values of monthly evapo-transpiration in each of the historical and validation periods. Analysis of results revealed the adequacy of the developed model and hence its capability of doing good estimation of monthly evapo-transpiration in Najran Region, KSA and in regions of similar climatic conditions. Keywords—Blaney - Criddle, Consumptive use of water, Dummy variables, Evapo-transpiration, S(REG_AR) model. I. 0B