Abstract
Determination of water requirements for wheat and maize under climate change is important for policy makers in Egypt. The objectives of this paper were to calculate (i) ETo and (ii) water requirements for wheat and maize crops grown in five governorates (Alexandria, Demiatte, Kafr El-Sheik, El-Dakahlia and El-Behira) located in North Nile Delta of Egypt under current climate and climate change. ECHAM5 climate model was used to develop A1B climate change scenario in 2020, 2030 and 2040. Monthly values of evapotranspiration (ETo) under the different scenarios in these governorates were calculated using Hargreaves-Samani equation (H-S). Then, these values were regressed on ETo values previously calculated by Penman-Monteith equation (P-M) and linear regression (prediction equations were developed for each governorate). The predicted ETo values were compared to the values of ETo calculated by P-M equation and the deviations between them were very low (RMSE/obs=0.04-0.06 mm and R2 =0.96-0.99). Water requirements for wheat and maize were calculated using BISm model under current climate and in 2020, 2030 and 2040. The results showed that average annual ETo would increase by low percentage in 2020 and 2030. However, in 2040 the increase would reach 8%. Water requirements are expected to increase by 2-3% for wheat and by 10-15% for maize, which would result in reduction of the cultivated area. Thus, it is very important to revise and fix the production system of wheat and maize, in terms of the used cultivars, fertilizer and irrigation application to overcome the risk of climate change.
Highlights
Climate plays an important role in the crop production
Values of evapotranspiration (ETo) under the different scenarios in these governorates were calculated using Hargreaves-Samani equation (H-S). These values were regressed on ETo values previously calculated by Penman-Monteith equation (P-M) and linear regression
There were deviations between monthly ETo values calculated from each equation in each governorate
Summary
Climate plays an important role in the crop production. Crops growth periods, crops water requirements and irrigation scheduling for crops are dependent on weather conditions in a site. The amount of applied water for a crop is associated with the calculation of reference evapotranspiration (ETo). Various equations are available for estimating ETo. Various equations are available for estimating ETo These equations range from the most complex energy balance equation requiring detailed climatological data, such as Penman Monteith (Allen et al, 1989) to simpler equations requiring limited data (Blaney & Criddle, 1950; Hargreaves & Samani, 1982, 1985). The detailed climatological data required by the P-M are not often available especially in developing countries. A reduced-weather-dataequation to calculate ETo could be more appropriate in some developing countries. Using this type of equation could reduce accuracy of calculation. Calibrating more simple equation needs limited data requirements with P-M equation could be a solution to that problem (Shahidian et al, 2012)
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