Parameters for accounting for water balance on irrigation projects have evolved over the past century. Development of the classic term irrigation efficiency is summarized along with recent modifications such as effective irrigation efficiency. The need for terms that describe measurable water balance components of irrigated agriculture is very important, as demands and competition for available renewable water supplies continue to increase with increasing populations. Examples of irrigation efficiency studies conducted during the past few decades are summarized along with related irrigation terminology. Traditional irrigation efficiency terminology has served a valid purpose for nearly a century in assisting engineers to design better irrigation systems and assisting specialists to develop improved irrigation management practices. It still has utility for engineers designing components of irrigation systems. However, newer irrigation-related terminology better describes the performance and productivity of irrigated agriculture. On a river-basin level, improved terminology is needed to adequately describe how well water resources are used within the basin. Brief suggestions for improving irrigation water management are presented.
Rising demand for food, fiber, and biofuels drives expanding irrigation withdrawals from surface water and groundwater. Irrigation efficiency and water savings have become watchwords in response to climate-induced hydrological variability, increasing freshwater demand for other uses including ecosystem water needs, and low economic productivity of irrigation compared to most other uses. We identify three classes of unintended consequences, presented here as paradoxes. Ever-tighter cycling of water has been shown to increase resource use, an example of the efficiency paradox. In the absence of effective policy to constrain irrigated-area expansion using "saved water", efficiency can aggravate scarcity, deteriorate resource quality, and impair river basin resilience through loss of flexibility and redundancy. Water scarcity and salinity effects in the lower reaches of basins (symptomatic of the scale paradox) may partly be offset over the short-term through groundwater pumping or increasing surface water storage capacity. However, declining ecological flows and increasing salinity have important implications for riparian and estuarine ecosystems and for non-irrigation human uses of water including urban supply and energy generation, examples of the sectoral paradox. This paper briefly considers three regional contexts with broadly similar climatic and water-resource conditions - central Chile, southwestern US, and south-central Spain - where irrigation efficiency directly influences basin resilience. The comparison leads to more generic insights on water policy in relation to irrigation efficiency and emerging or overdue needs for environmental protection.
Increasing irrigation efficiency has been suggested as a solution in water scarce areas but its potential rebound effect (increased ex-post water consumption) is receiving growing attention; paradoxically, although improved irrigation efficiency may reduce water use, it may also increase water consumption. This paper undertakes an analytical review of the microeconomic foundations of the effects of water-saving investments and the resulting irrigation efficiency on water use and consumption. Moreover, it analyses the relationship between irrigation efficiency, water demand and water pricing. Findings show that improving efficiency would significantly reduce water use, though the impact on water consumption would be negligible even if there is a radical increase in water cost. Thus, the potential rebound effect would not be related to irrigation efficiency, but rather to other factors such as irrigated area expansion, crop-mix changes, and market forces.
Irrigation efficiency (IE) and water-saving potential (WSP) are two fundamental parameters for assessing water use and management in irrigation systems. A new calculation method was proposed herein to accurately estimate the IE and WSP in irrigation systems. The proposed method considers the reuse of return flow. A modified Soil and Water Assessment Tool (SWAT) was used to simulate hydrological processes under various water-saving scenarios for the Yangshudang (YSD) watershed within the Zhanghe Irrigation System (ZIS) in Hubei Province, China. The dry year of 2010 was chosen as a study case. Based on simulation results, the traditional irrigation efficiency ( ) and water-saving potential ( ) as well as the irrigation efficiency taking into account the reuse of return flow ( ) and water-saving potential considering the reuse of return flow ( ) were calculated for various scenarios. The relationships between the two IE indicators and the cause thereof, as well as the two WSP values, were analyzed and explored. The results showed that both IE and WSP were improved with the enhancement of water saving. As long as there was the reuse of return flow, must be greater than . Moreover, in terms of water-saving approaches that improved the reuse rate of return flow, was determined to be greater than , thereby suggesting that the traditional method underestimated the WSP. However, for water-saving approaches that reduced the reuse rate of return flow, was determined to be less than , which suggested that the traditional method overestimated the WSP. The relationship between and was attributed to the fact that was calculated by subtracting the amount of the water saved by the reuse of return flow on the basis of , and this difference can be either positive or negative. Therefore, the managers of irrigation systems should use as the actual IE but not , and use instead of to evaluate the actual WSP.
Within scenarios of water scarcity, the irrigation efficiency plays an increasingly strategic role. In this paper, a method that uses an advance-infiltration model based on four field measurements and the soil particle size distribution is proposed to estimate border-irrigation efficiencies. This method was applied to fifteen irrigation events and the application, storage and distribution efficiencies were estimated. The advance-infiltration model was validated against soil moisture measurements. The field-scale saturated hydraulic conductivity was estimated by model fitting to the measured depth of water infiltration. The sensitivity of the modelled irrigation efficiency to the operational surface irrigation parameters was evaluated by simulating seven irrigation scenarios based on field-collected data. The infiltration profiles obtained by the proposed method were in agreement with the soil moisture measurements. The maximum difference between simulated and measured infiltration depth was 0.018 m. The field-scale saturated hydraulic conductivity values were in agreement with the infiltrometer tests results. The analysis of both simulated scenarios and monitored irrigation events highlighted the need for farmers to reduce the flow rates and increase the duration of irrigation events, in order to improve the irrigation efficiencies.
Water and land are the two most critical resources for food production and they are intricately linked. Irrigation expansion, population growth, and climate change are threatening the sustainability of water-land nexus system (WLNS). In this study, a possibilistic-flexible chance-constrained programming (PFCP) method that is capable of addressing multiple uncertainties expressed as possibilistic distributions, flexible variables, and probabilistic distributions existed in WLNS is developed. PFCP can help gain in-depth analysis of the tradeoffs between system benefit and reliability of satisfying constraints. Then, the proposed PFCP method is applied to the lower reaches of Amu Darya River basin for assessing the impact of irrigation efficiency on the WLNS management, where 1080 scenarios are analyzed in association with different irrigation schemes, violation risk levels, and satisfactory degrees. A number of water and land resources allocation alternatives for different irrigation districts and crops are generated. Results indicate that the advanced irrigation modes (e.g., sprinkle and drip) can improve irrigation efficiency and raise unit water benefit from 0.15 US$/m to 0.24 US$/m . Irrigation mode with efficiency of about 0.61 is an effective option in adaption to changed water availabilities, which is beneficial for pursuing balance between water and land relationships. These findings can support decision makers implementing comprehensive agricultural management strategies (e.g., the advancement of irrigation modes as well as the optimization of water and land allocation patterns) in responding to variations in water availability, electricity consumption, and market price.