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The agricultural region in the western bank of Lake Nasser is one of the new promising agricultural settlements, which has the advantage of early-season production of several high quality cash crops. The agriculture production in this region is fully-irrigated, and constrained by sever environmental, biophysical and socioeconomical conditions. Moreover, farmers have been facing several additional challenges in irrigation management due to lack of knowledge of the best practices. The aim of this study is to evaluate the current farmers’ irrigation schemes in terms of water productivity. The study examined some possible irrigation schemes in order to improve water productivity with minimum irrigation requirement and to cope with projected water shortage and temperature increase induced by climate change. The study is based on modeling approach utilizing the FAO crop model “AquaCrop” on drip irrigated tomato. It was performed (i) to calibrate AquaCrop via two field trials at two seasons, (ii) to observe and evaluate the current farmers’ irrigation schemes based on fixed application frequency, and (iii) to evaluate six irrigation schemes under current and future climate conditions. The evaluated schemes included different combinations between net irrigation application and deficit practices at two levels of 80% and 60% of net water requirements, under current and future climate conditions, based on the change in irrigation application and water productivity. The results demonstrated that the combination of deficit irrigation levels and irrigation scheduling could improve tomato water productivity to the optimal level determined under the current study conditions (2.4 kg/m 3 ), especially when deficit levels of 80 and 60% applied at both early and late stages of crop growth stages. These schemes could present acceptable adaptation options with the projected temperature increase due to climate change. *Researcher, Agricultural Engineering Research Institute (AEnRI), Agricultural Research Center (ARC) Misr J. Ag. Eng., 29 (2): 725 734 IRRIGATION AND DRAINAGE Misr J. Ag. Eng., April 2012 726 INTRODUCTION he overall objective of effective on–farm irrigation management is to maximize crop yield per each unit of applied water. Projected future temperature rises under climate change are likely to reduce the productivity of the major crops, and increase its water requirements, thereby directly decreasing crop water use efficiency. Global warming is projected to add more pressures over the Egyptian onfarm irrigation system (Attaher et al., 2006). Therefore, developing adaptation schemes for on-farm irrigation system in Egypt become one of the high national priorities. While, the vulnerability of on-farm irrigation in Egyptian agricultural regions and the acceptable adaptation measures varies according to the local regional conditions. The agricultural region in the western bank of Lake Nasser, which located in the southern part of the River Nile in Egypt, is one of the new promising and remote agricultural settlements. The region is characterized by hyper aridity and extreme hot climate. The government of Egypt is planning to resettle one million farmers around Lake Nasser by 2017 (CDS, 2007). Despite the remote location of this area, it has the advantage of early season production for several cash-crops, with high quality. The agricultural production in this region is fully-irrigated, and constrained by sever hot and arid climate, low soil fertility, labor unavailability, long distance from the markets, and high cost of production inputs. Agricultural production in this region could be very risky from the environmental prospective that the agriculture activates is very close to Lake Nasser; the strategic national water reservoir of Egypt. The farmers are tending to increase the irrigation-water, including chemicals, as practices to overcome sever environmental condition, which is projected to increase in the future. Under the current national water management scheme, water share for agriculture in this region is subject to reduction, as a national policy to protect Lake Nasser. Moreover, the irrigation time for each village is limited by certain hours per day, as the pumping energy is offered to the farmers as a type of social encouragement, which is limiting the irrigation practices beyond the actual irrigation requirements. T IRRIGATION AND DRAINAGE Misr J. Ag. Eng., April 2012 727 FAO has been developing a yield-response to water model, “AquaCrop”, which simulates attainable yields of the major crops (Steduto et al., 2008). As compared to other crop models, AquaCrop has a significantly smaller number of parameters and a better balance between simplicity, accuracy and robustness. Root zone water content is simulated by keeping track of incoming and outgoing water fluxes at its boundaries, considering the soil as a water storage reservoir with different layers. Instead of leaf area index, AquaCrop uses canopy ground cover. Canopy development, stomatal conductance, canopy senescence and harvest index are the key physiological crop responses to water stress. Evapotranspiration is simulated as crop transpiration and soil evaporation and the daily transpiration is used to derive the daily biomass gain via the normalized biomass water productivity of the crop. The normalization is for reference evapotranspiration and CO2 concentration to make the model applicable to diverse locations and seasons, including future climate scenarios. AquaCrop accommodates different water management systems, including rainfed agriculture and supplemental, deficit, and full irrigation. The objective of this study is to evaluate the current farmers’ irrigation schemes in terms of water productivity and irrigation-water use. The study also examined some possible irrigation schemes in order to improve water productivity with minimum irrigation water application, and to cope with projected water shortage and temperature increase projected under climate change. MATERIALS AND METHODS The study is based on modeling approach using the FAO crop model “AquaCrop” (Steduto et al., 2008) on “drip irrigated tomatoes” as important crop of the crop pattern of western bank of Lake Nasser. This was performed through three steps as: (i) primary calibration of the default tomato file in AquaCrop, (ii) observation and evaluation of the current farmers’ irrigation schemes, and (iii) evaluate some possible irrigation schemes under current and future climate conditions. To start with calibration, two field trials were conducted in two consequence seasons, at two reclamation villages of Kalabsha and Garf IRRIGATION AND DRAINAGE Misr J. Ag. Eng., April 2012 728 Hussein, located at western bank of Lake Nasser. For all trials, tomato crop (Lycopersicon esculentum, Adora cultivar) was manual transplanted at the middle of November, with 0.30 m between plants inter-row and 1.20 m between plant rows. The soil texture was sand, which had 13.3 vol. % field capacity and 6 vol. % wilting point. Drip irrigation system was used with line-source emitter of 0.3 m spacing and 4 L/h discharge. Irrigation water-requirements and scheduling were calculated by using "CropWat" FAO model (Smith, 1992), according to the daily weather data collected from Aswan weather station located at 23.97° N latitude, 32.78° E longitude and 199 m altitude. The crop daily management practices were set in order to avoid water and fertility stress and limitations, while the initial water conditions of the fields was at about field capacity. The development of crop canopy expansion and root depth were recorded during the trails, while the total tomato yield per unit area, fresh and dry matter of the fruits and the plant were determined at the end of the season. At the same time, Irrigation applications, irrigation time and total tomato yield were the main parameters, for about 13 farmers from the same villages, in order to determine the farmers’ irrigation schemes. Based on the calibration procedure, AquaCrop was used to evaluate six irrigation schemes under current and future climate conditions. Two schemes of farmers’ actual irrigation practices (P1 and P2) were the first two evaluation cases, whereas, the other evaluated cases were; (i) OP1: irrigation schedule based on net irrigation requirement at depletion 50% of readily available water (RAW), (ii) OP2: irrigation schedule based on 75% depletion of RAW at initial stage, 50% depletion of RAW at development and mid season stages, and 75% depletion of RAW at maturity stage, (iii) OP3: two deficit irrigation levels of 80% and 60% of actual water-requirements, at all crop growth stages, and finally (iv) OP4: two deficit irrigation levels of 80% and 60% of actual waterrequirements, at initial and maturity stages only. Five years average of daily weather data of Aswan weather station was used to represent the current climate. Air temperature raise was the climatic factor used in the evaluation procedure referring to future climate change, where CO2 response is not yet finalized in AquaCrop, IRRIGATION AND DRAINAGE Misr J. Ag. Eng., April 2012 729 and adjustments are still needed. The Maximum and the minimum monthly values of air temperature changes of Aswan were determined from a downscaled implication of IPCC SRES scenarios (IPCC, 2000) using HadCM3 GCM climate model up to year 2100 (DDC, 2010). The current and the future ETo values were determined by using FAO ETo Calculator software (Raes, 2009). In climate change simulations, the impact of air temperature increase was assessed basically on the net irrigation requirements, where the impact on the crop biomass production and the harvest index is not yet well-calibrated under the local conditions of the current study. Water productivity [WP] was calculated by using the following equation: ] [m n applicatio irrigation actual [kg] production crop actual ty productivi Water 3  RESULTS AND DISCUSSION The primary ca

DEVELOPING ON-FARM IRRIGATION SCHEMES FOR CURRENT AND FUTURE CLIMATE CONDITIONS ON THE WESTERN BANK OF LAKE NASSER