Marginal cost curves for water footprint reduction in irrigated agriculture: guiding a cost-effective reduction of crop water consumption to a permit or benchmark level

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 costeffectiveness 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 m 3 ha −1 per season) or to a certain WF benchmark (expressed in m 3 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 cropgrowth 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.

Trade‐off between nutritive value improvement and crop water use for an alfalfa–grass system

“…After estimating the total cost and revenue, the MC of additional revenue over the grass‐only control (benchmark) was calculated for each treatment as the change in total cost per additional revenue from the alfalfa–grass mixtures (Equation ), analogous to the MC for WF reduction (Chukalla, Krol, & Hoekstra, 2017): …”

Groundwater saving and quality improvement by reducing water footprints of crops to benchmarks levels

“…Formulating WF reduction targets for crop production, as a general national policy, and to downscale targets per climate zone to specific targets at farm level still await practical implementation. The field is still in its infancy, with only a few earlier studies available for total blue WF benchmarks ( Hoekstra, 2013;Mekonnen and Hoekstra, 2014;Chukalla et al, 2015Chukalla et al, , 2017Zhuo et al, 2016b ) or grey WF benchmarks Chukalla et al, 2018 ). Further studies, using different models and remote sensing, and validating findings based on field data, will be necessary to assess uncertainties in more detail, and test the feasibility of lowering the WFs of crops to benchmark levels at large scale.…”

“…A promising strategy to save water and reduce water pollution in the agricultural sector is to formulate benchmark levels for water footprints of crop production ( Zwart et al, 2010;Brauman et al, 2013;Hoekstra, 2013;Mekonnen and Hoekstra, 2014;Zhuo et al, 2016b;Chukalla et al, 2017 ). A water footprint refers to the volume of water that is consumed or polluted to produce a tonne of product.…”

“…If grey WFs in crop production are reduced, worldwide, to the level of the best 25% of current global production, water pollution would be reduced by 54%. Chukalla et al, (2015Chukalla et al, ( , 2017 studied the reduction potential of blue and green WFs for cereals by developing benchmarks for different alternative irrigation techniques, irrigation strategies, and different alternative mulching practices. Their results demonstrate that integrating drip irrigation with deficit irrigation and synthetic mulching may cause a 29% reduction in consumptive WF compared to conventional farming practices.…”

Water and Land Footprints and Economic Productivity as Factors in Local Crop Choice: The Case of Silk in Malawi

“…Water footprints (WF) and land footprints (LF) of crop production represent the volume of water (m 3 ) and area of land (m 2 ) that are appropriated to produce a crop (kg) [12]. Footprints inform the farmer how much water and land the intended crop requires in absolute terms, or, if compared to a benchmark footprint for that crop, in relative terms [13,14]. Economic water productivity (EWP, in € m −3 ) and economic land productivity (ELP, in € m −2 ) address economic considerations, by showing how much money each cubic meter of water or square meter of land generates.…”