Abstract
Abstract. Reducing the water footprint (WF) of the process of growing irrigated crops is an indispensable element in water management, particularly in water-scarce areas. To achieve this, information on marginal cost curves (MCCs) that rank management packages according to their cost-effectiveness to reduce the WF need to support the decision making. MCCs enable the estimation of the cost associated with a certain WF reduction target, e.g. towards a given WF permit (expressed in m3 ha−1 per season) or to a certain WF benchmark (expressed in m3 t−1 of crop). This paper aims to develop MCCs for WF reduction for a range of selected cases. AquaCrop, a soil-water-balance and crop-growth model, is used to estimate the effect of different management packages on evapotranspiration and crop yield and thus the WF of crop production. A management package is defined as a specific combination of management practices: irrigation technique (furrow, sprinkler, drip or subsurface drip); irrigation strategy (full or deficit irrigation); and mulching practice (no, organic or synthetic mulching). The annual average cost for each management package is estimated as the annualized capital cost plus the annual costs of maintenance and operations (i.e. costs of water, energy and labour). Different cases are considered, including three crops (maize, tomato and potato); four types of environment (humid in UK, sub-humid in Italy, semi-arid in Spain and arid in Israel); three hydrologic years (wet, normal and dry years) and three soil types (loam, silty clay loam and sandy loam). For each crop, alternative WF reduction pathways were developed, after which the most cost-effective pathway was selected to develop the MCC for WF reduction. When aiming at WF reduction one can best improve the irrigation strategy first, next the mulching practice and finally the irrigation technique. Moving from a full to deficit irrigation strategy is found to be a no-regret measure: it reduces the WF by reducing water consumption at negligible yield reduction while reducing the cost for irrigation water and the associated costs for energy and labour. Next, moving from no to organic mulching has a high cost-effectiveness, reducing the WF significantly at low cost. Finally, changing from sprinkler or furrow to drip or subsurface drip irrigation reduces the WF, but at a significant cost.
Highlights
In many places, water use for irrigation is a major factor contributing to water scarcity (Rosegrant et al, 2002; Mekonnen and Hoekstra, 2016), which will be worsened by increasing demands for food and biofuels (Ercin and Hoekstra, 2014)
The current paper introduces the method for developing marginal cost curves (MCCs) for water footprint (WF) reduction in irrigated agriculture, and shows how the MCCs can be applied to achieve a certain WF reduction target, like reducing the WF to a certain WF permit level or WF benchmark level
The method is innovative by employing a model that combines soil water balance accounting and a crop growth model and assessing costs and WF reduction for all combinations of irrigation techniques, irrigation strategies and mulching practices
Summary
Water use for irrigation is a major factor contributing to water scarcity (Rosegrant et al, 2002; Mekonnen and Hoekstra, 2016), which will be worsened by increasing demands for food and biofuels (Ercin and Hoekstra, 2014). Chukalla et al.: Marginal cost curves for water footprint reduction individual users than fit within the cap This would urge water users to reduce their blue WF to a level that is sustainable within the catchment. In order to increase water use efficiency, Hoekstra (2014) proposes water footprint benchmarks for specific processes and products as a reference for what is a reasonable level of water consumption per unit of production. This would provide an incentive for water users to reduce their WF per unit of product down to a certain reasonable reference level. A relevant question though is how much it costs to reduce the WF of crop production to a certain target such as a WF benchmark for the water consumption per tonne of crop or a WF permit for the water consumption per area
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