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In a companion paper a model for the simulation of water flows in irrigation districts was formulated. The model combines a series of modules specialized in surface irrigation, open channel distribution networks, crop growth modeling, irrigation decision making, and hydrosaline balance. The objective of this paper is to calibrate, validate, and apply the model, using the Irrigation District Five of Bardenas (Spain) as a study area. Two years of study were used for the analysis, which could be classified as normal (2000) and dry (2001) from the point of view of crop water requirements. Model calibration was performed in one of the 11 hydrological sectors in which the district is divided. The control variable was the monthly water demand, while the calibration variables were related to irrigation operation and scheduling. The seasonal differences in observed and simulated water demand amounted to 0.9 and 1.9% for 2000 and 2001, respectively. Model validation was performed in the rest of the sectors, and the regression line of observed versus simulated monthly water demand could not be distinguished from a 1:1 line in both years. Model application explored scenarios based on management improvement (controlling the irrigation time) and structural improvement (increasing drainage water reuse for irrigation). These scenarios permitted one to sharply reduce water demand, halve the irrigation return flows, and reduce the daily irrigation period from 24 to 16 h. CE Database subject headings: Surface irrigation; Irrigation districts; Water management; Reservoir management; Decision support system.

Significant improvements in the profitability and sustainability of irrigated areas can be obtained by the application of new technologies. In this work, a model for the simulation of water flows in irrigation districts is presented. The model is based on the combination of a number of modules specialized on surface irrigation, open channel distribution networks, crop growth modeling, irrigation decision making, and hydrosaline balances. These modules are executed in parallel, and are connected by a series of variables. The surface irrigation module is based on a numerical hydrodynamic routine solving the Saint Venant equations, including the heterogeneity of soil physical properties. The simulation of water conveyance is performed on the basis of the capacity of the elements of the conveyance network. Crop growth is simulated using a scheme derived from the well-known model CropWat. The irrigation decision making module satisfies water orders considering water stress, yield sensitivity to stress, multiple water sources, and the network capacity. Finally, the hydrosaline module is based on a steady state approach, and provides estimations of the volume and salinity of the irrigation return flows for the whole irrigation season. The application of the model to district irrigation management and modernization studies may be limited by the volume of data required. In a companion paper, the model is calibrated, validated, and applied to a real irrigation district. CE Database subject headings: Surface irrigation; Irrigation districts; Water management; Reservoir management; Decision support systems; Water flow.

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Liberalization of agricultural markets is changing the irrigation focus from maximizing yields to maximizing profits. This study was conducted to develop a self-programmable irrigation scheduling strategy for solid sets aimed at improving profits. It is based on simulation models and water and crop prices. The economic optimization of solid-set irrigation is constrained by the fact that the efficiency is not previously known because of the unpredictability of seasonal weather and the accumulated effect of nonuniform irrigations in the soil water depletion (SWD) uniformity. Consequently, seasonal revenue and cost functions cannot be determined. The strategy addresses this constraint by (1) refilling SWD under weather conditions that minimize water losses when crop is not water stressed and SWD is high and uniform enough to prevent percolation; and (2) estimating revenue and cost functions for each irrigation event in order to determine the economically optimal water depth when SWD uniformity is so low that percolation and/or crop water stress are unavoidable. The strategy is presented in this paper and assessed under different conditions in the companion paper. [ABSTRACT FROM AUTHOR]

The companion paper presented a self-programmable profit-oriented irrigation scheduling strategy based on simulation models. This study is an assessment of the strategy and aims to contribute to the analysis of its viability. The assessment is based on the simulation of corn irrigated with a typical solid-set system under 81 scenarios that combine different conditions of weather, soil, and prices over a period of nine years. Two simpler self-programmable yield-oriented strategies serve as benchmarks for the assessment. The profit-oriented strategy achieves up to 168 euros/ha higher profit, depending on the conditions of the scenario. Lower percolation and better harnessing of initial soil water are the main drivers of the profit gap, in which the influence of prices is low because of the high efficiency achieved. This water conservation (up to 128 mm) could also deliver additional benefits that future researches should analyze. The models and a multidisciplinary approach provide a better understanding of the technical and economic processes that enable the development of advanced self-programmable strategies that lead to wiser, more situation-specific irrigation decisions. [ABSTRACT FROM AUTHOR]

This study develops an approach aimed at improving the capability of regional irrigation monitoring and evaluation to identify relevant factors and subareas influencing irrigation performance. Its objective is to contribute to improve the productivity of irrigable areas in a cost-effective manner by overcoming the lack of sufficient updated field data observed in conventional remote sensing studies. To do this, several performance indicators are calculated and analyzed by combining remote sensing with district database programs that irrigation districts use in their administrative and water management tasks. This approach was applied in Riegos del Alto Aragón (Spain), a large (124,596 ha) and heterogeneous project divided into 53 surface and sprinkler irrigation districts. The 2004 and 2005 seasons were analyzed, with the latter showing a severe water shortage. Under no water scarcity, most districts applied higher relative water supplies regardless of irrigation systems and other factors. Cropping patterns were less intensive in surface irrigation districts regardless water availability. Six districts and four main factors were identified as those most important to bridge the economic gaps that this performance implies. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of this work is to contribute to the development of a combined approach to evaluate irrigated areas based on: (1) irrigation performance analysis intended to assess the productive impacts of irrigation practices and infrastructures, and (2) water accounting focused on the hydrological impacts of water use. Ador-Simulation, a combined model that simulates irrigation, water delivery, and crop growth and production was applied in a surface irrigated area (1213ha) located in the Bear River Irrigation Project, Utah, U.S.A.. A soil survey, a campaign of on-farm irrigation evaluations and an analysis of the database from the Bear River Canal Company and other resources were performed in order to obtain the data required to simulate the water flows of the study area in 2008. Net land productivity (581US$ha−1) was 20% lower than the potential value, whereas on-farm irrigation efficiency (IE) averaged only 60%. According to the water accounting, water use amounted to 14.24Mm3, 86% of which was consumed through evapotranspiration or otherwise non-recoverable. Gross water productivity over depleted water reached 0.132US$m−3. In addition, two strategies for increasing farm productivity were analyzed. These strategies intended to improve water management and infrastructures raised on-farm IE to 90% reducing the gap between current and potential productivities by about 50%. Water diverted to the project was reduced by 2.64Mm3. An analysis based on IE could lead to think that this volume would be saved. However, the water accounting showed that actually only 0.91Mm3 would be available for alternative uses. These results provide insights to support the decision-making processes of farmers, water user associations, river basin authorities and policy makers. Water accounting overcomes the limitations and hydrological misunderstandings of traditional analysis based on irrigation efficiency to assess irrigated areas in the context of water scarcity and competitive agricultural markets. [Copyright &y& Elsevier]

Abstract: This study analyzes the effects of irrigation modernization on water conservation, using the Riegos del Alto Aragón (RAA) irrigation project (NE Spain, 123354ha) as a case study. A conceptual approach, based on water accounting and water productivity, has been used. Traditional surface irrigation systems and modern sprinkler systems currently occupy 73% and 27% of the irrigated area, respectively. Virtually all the irrigated area is devoted to field crops. Nowadays, farmers are investing on irrigation modernization by switching from surface to sprinkler irrigation because of the lack of labour and the reduction of net incomes as a consequence of reduction in European subsidies, among other factors. At the RAA project, modern sprinkler systems present higher crop yields and more intense cropping patterns than traditional surface irrigation systems. Crop evapotranspiration and non-beneficial evapotranspiration (mainly wind drift and evaporation loses, WDEL) per unit area are higher in sprinkler irrigated than in surface irrigated areas. Our results indicate that irrigation modernization will increase water depletion and water use. Farmers will achieve higher productivity and better working conditions. Likewise, the expected decreases in RAA irrigation return flows will lead to improvements in the quality of the receiving water bodies. However, water productivity computed over water depletion will not vary with irrigation modernization due to the typical linear relationship between yield and evapotranspiration and to the effect of WDEL on the regional water balance. Future variations in crop and energy prices might change the conclusions on economic productivity. [Copyright &y& Elsevier]

This article analyses the effects of irrigation modernization processes on water quantity and quality, taking the Ebro river basin (NE Spain) as a case study. The objective is to contribute to needed in-depth analysis and discussion regarding the optimization of water use in agriculture. A conceptual approach based on water accounting concepts has been applied. Results show that irrigation modernization linked to an increase in land productivity involves additional water depletion if the location of the irrigated areas and the quality of the irrigation return flows allow their re-use. Additionally, modernization reduces the volume of return flows and pollutant loads and increases the quality of the receiving water bodies. The modernization of water management will be required to maximize economic, social and environmental returns from the investment in new irrigation infrastructure. [ABSTRACT FROM AUTHOR]

This paper examines a model for estimating canopy resistance rc and reference evapotranspiration ETo on an hourly basis. The experimental data refer to grass at two sites in Spain with semiarid and windy conditions in a typical Mediterranean climate. Measured hourly ETo values were obtained over grass during a 4 year period between 1997 and 2000 using a weighing lysimeter (Zaragoza, northeastern Spain) and an eddy covariance system (Córdoba, southern Spain). The present model is based on the Penman-Monteith (PM) approach, but incorporates a variable canopy resistance rc as an empirical function of the square root of a climatic resistance r* that depends on climatic variables. Values for the variable rc were also computed according to two other approaches: with the rc variable as a straight-line function of r* (Katerji and Perrier, 1983, Agronomie 3(6): 513-521) and as a mechanistic function of weather variables as proposed by Todorovic (1999, Journal of Irrigation and Drainage Engineering, ASCE 125(5): 235-245). In the proposed model, the results show that rc/ ra (where ra is the aerodynamic resistance) presents a dependence on the square root of r*/ ra, as the best approach with empirically derived global parameters. When estimating hourly ETo values, we compared the performance of the PM equation using those estimated variable rc values with the PM equation as proposed by the Food and Agriculture Organization, with a constant rc = 70 s m−1. The results confirmed the relative robustness of the PM method with constant rc, but also revealed a tendency to underestimate the measured values when ETo is high. Under the semiarid conditions of the two experimental sites, slightly better estimates of ETo were obtained when an estimated variable rc was used. Although the improvement was limited, the best estimates were provided by the Todorovic and the proposed methods. The proposed approach for rc as a function of the square root of r* may be considered as an alternative for modelling rc, since the results suggest that the global coefficients of this locally calibrated relationship might be generalized to other climatic regions. It may also be useful to incorporate the effects of variable canopy resistances into other climatic and hydrological models. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: The surface Irrigated District V of the Bardenas Canal (Zaragoza, Spain) was evaluated, and alternatives were assessed to improve on-farm irrigation performance. Field work consisted of a soil survey and a campaign of irrigation evaluation. The results of the irrigation evaluations were extrapolated to the whole district using a hydrodynamic surface irrigation model. An average irrigation discharge of 152Ls−1 results in a relatively low irrigation time (2.8hha−1). Shallow soils, a limited conveyance network, and poor irrigation management practices determine that the application efficiency in the district is low, with an average of 49%. The district wide irrigation efficiency only reaches reasonable values when the system operates under water scarcity (49% in 2000 versus 66% in 2001). The simulation of surface irrigation indicated that the optimum irrigation time in the current situation is 1.7hha−1. The optimization of the irrigation time would lead to an average application efficiency of 76%. Improved irrigation management can therefore result in substantial water conservation in the district. [Copyright &y& Elsevier]

In this paper, daily ET0 estimates at two semiarid locations, Zaragoza and Co´rdoba, were obtained from the Penman–Monteith equation using either fixed (70 s m−1) or variable rc values. Variable rc values were computed with two models, Katerji and Perrier, and Todorovic. Daily ET0 estimates were computed from 24-h meteorological averages or from the sum of hourly estimates. Daily ET0 measured values were obtained from a weighing lysimeter (Zaragoza) and an eddy covariance system (Co´rdoba). There was a good agreement at both locations between estimated and measured ET0 values using a fixed rc value and 24-h meteorological averages. Estimates obtained from the sum of hourly estimates were somewhat worse. When 24-h meteorological averages were used, the Katerji and Perrier model for variable rc slightly improved ET0 estimates at both locations. But that improvement does not support the effort to locally calibrate that model. When daily ET0 estimates were obtained from the sum of hourly estimates, the Todorovic model improved the estimation at Zaragoza and, at a lesser degree, at Co´rdoba. Under the semiarid conditions of the two studied locations, the use of the Todorovic model is recommended to get hourly ET0 estimates from which daily estimates can be obtained. If 24-h meteorological averages are used, a fixed rc value as proposed by Allen et al. [Crop evapotranspiration: guidelines for computing crop water requirements, FAO Irrigation and Drainage Paper No. 56, FAO, Rome, 1998] should be enough for accurate ET0 estimates. [Copyright &y& Elsevier]

Abstract: In the last decade irrigation districts in the Ebro Valley of Spain have started to use database applications to enhance their management operations. Such applications often put more emphasis on administrative issues than on water management issues. A new irrigation district management software called “Ador” is presented in this paper. This database application has been designed to overcome limitations identified in an analysis of the software used in the study area. Ador can be used in irrigation districts independently of the type of irrigation system (surface, sprinkler or trickle) and the type of irrigation distribution network (open channel or pressurised). It can even be used in irrigation districts combining different types of irrigation systems and different types of irrigation distribution networks. The software can be used with minimum district information. The goals are to manage detailed information about district water management and to promote better on-farm irrigation practices. Ador is currently used to enhance management of 62 irrigation districts accounting for some 173,000 hectares in the Ebro Valley. [Copyright &y& Elsevier]

Abstract: In this paper, a contribution to the design of collective pressurised irrigation networks in solid-set sprinkler-irrigated windy areas is presented. The methodology is based on guaranteeing minimum on-farm performance, using a historical hourly wind speed database and a ballistic solid-set irrigation simulation model. The proposed method was applied to the Montesnegros Irrigation District (central Ebro basin, Spain). The district irrigates an area of 3493ha using an on-demand schedule. The average wind speed in the area is 2.8ms−1. An analysis of district water records showed that farmers often reduce water demand when the wind speed is high, but their irrigation decision making is limited by the capacity of the irrigation network and by the unpredictable character of local winds. Simulations were performed for 11 irrigation seasons, 2 triangular sprinkler spacings (18m×18m and 18m×15m), and 2 sprinkler models. The percentage of monthly suitable time for irrigation was determined for four management strategies. The first one was based on a wind speed threshold (3ms−1), while the other three were based on three levels (standard, relaxed and restrictive) of two irrigation performance parameters: the Christiansen Uniformity Coefficient (CU) and the Wind Drift and Evaporation Losses (WDEL). The standard strategy classified the time as suitable for irrigation when CU≥84% and WDEL≤20%. The thresholds limits of the irrigation parameters for the relaxed strategy were CU≥80% and WDEL≤25%. Finally, the restrictive strategy used thresholds of CU≥90% and WDEL≤15%. The suitable time for the first strategy (56%) was always lower than for the standard and the relaxed strategies (with respective average values of 75 and 86%), and higher than for the restrictive strategy (30%). In order to design the collective network, the hydrant operating time was equalled to the suitable time for irrigation. The differences in the cost of the collective network plus the on-farm equipment were particularly relevant between the restrictive strategy and the other three. Differences in suitable operating time were clear between sprinkler spacings, and less evident between sprinkler models. The application of the proposed methodology may be limited by the availability of historical wind speed records and CU estimates for different combinations of sprinkler models, sprinkler spacings and wind speed. [Copyright &y& Elsevier]