Elsevier

Science of The Total Environment

Volume 670, 20 June 2019, Pages 188-199
Science of The Total Environment

Understanding agricultural water footprint variability to improve water management in Chile

https://doi.org/10.1016/j.scitotenv.2019.03.127Get rights and content

Highlights

  • Basin-scale agricultural water consumption was assessed considering climate variability.

  • A geographic variable (upper, middle, lower basin) was added to identify local changes.

  • The WFagricultural WFblue and WFgray were greatest in the dry year and WFgreen in a normal year.

  • Avocados, olives and corn had the greatest WFagricultural, in contrast to onions.

  • The integration of these results would allow rational water allocation.

Abstract

Understanding water consumption is crucial for sustainable management of water resources. Under climate change scenarios that project highly variable water availability, the need for public policies that assure efficiency and equity in water resources is increasing. This work analyzes the case of the Cachapoal River agricultural basin (34°S 71°W), which presents temperature increases and a precipitation deficit, with a drought period that began more than eleven years ago having significantly decreased water availability. Water consumption in the basin for food production was determined from the agricultural water footprint (WFagricultural), using the green (WFgreen), blue (WFblue) and gray water footprint (WFgray) indicators, which were measured in the upper, middle and lower basin under conditions of climate variability (dry, wet and normal years). The greatest WFagricultural was established in the dry year, with a total of 18,221 m3 t−1, followed by 15,902 m3 t−1 in the wet year and 14,091 m3 t−1 in the normal year. Likewise, the greatest WFblue and WFgray, of 12,000 m3 t−1 and 4934 m3 t−1, respectively, were also observed in the dry year. The greatest WFgreen, 2000 m3 t−1, was calculated for a normal year. The 63% of agricultural area of the basin was covered by avocado (Persea americana), olive (Olea europaea), corn (Zea mays) and grape (Vitis sp) crops, which presented the greatest WFagricultural. This water footprint data provides a quantitative basis for the assessment of water consumption and degradation, considering agricultural production and its multiple variables. The success of the application of these results lies in the use of indicators to understand change processes and complement future water allocation plans with more rational water management models.

Introduction

Climate variability and competing water intake flows or demands make water a scarce, vulnerable resource (Hejazi et al., 2014; Hoekstra et al., 2016; Miglietta et al., 2018). The water footprint (WF) is an indicator of water resources use that allows the volume of water directly or indirectly consumed or polluted for the production of a good or service to be determined (De Miguel et al., 2015; Pellicer-Martínez and Martínez-Paz, 2018). Thus, it is a useful tool for addressing the imbalance between the supply of and demand for various water flows (Chukalla et al., 2017; Qian et al., 2018).

The water footprint (WF) requires information on water flows, vegetation dynamics and human needs. River runoff and groundwater infiltration are known as the blue water flow. The green water flow is the precipitation that is temporarily stored in the soil and on top of vegetation. The gray water flow is the water necessary to replenish the environmental carrying capacity after a human intervention (Hoekstra, 2014; Liu et al., 2017). Globally, it is estimated that around three fifths of precipitation takes the green path and two fifths the blue (Lovarelli et al., 2016). Consequently, the three components of the WF are: 1) WFblue, which is the volume of blue flow water taken up for industrial, domestic and agricultural irrigation purposes; 2) WFgreen, which is the consumption of green flow water that sustains the production of crops, pasture land, forestry plantations and ecosystems; and 3) WFgray, which is the volume of water required to assimilate or dilute pollutant or fertilizer inputs (Cazcarro et al., 2015; Hoekstra et al., 2016; Hoekstra, 2017).

The WFcrop is defined as the water consumed as a result of evapotranspiration, irrigation requirements and fertilizers applied during the growing period, according to climate and soil characteristics and crop parameters; the sum of the water consumption of each crop ultimately determines the WFagricultural of the basin (Salmoral et al., 2011; Schyns et al., 2015; Chukalla et al., 2018).

Establishing water consumption in a river basin contributes to the sustainable and efficient management of water resources. The unconsumed portion of the extracted water returns to the system and remains available for downstream use; thus, water quality and the destination of the returned water are important (Hoekstra et al., 2012). Nonetheless, there are few studies that address the assessment of the WFagricultural in river basins, particularly in the case of mediterranean regions, where agriculture requires irrigation to compensate for drought periods (Billib et al., 2009; Cortés et al., 2012; Pellicer-Martínez and Martínez-Paz, 2018). In such areas, blue and green water availability is variable, due precisely to rainfall irregularity; thus, agriculture in these areas is the greatest water consumer (Ercin et al., 2013). Switzerland (Hoekstra, 2015) and California (Fulton et al., 2012) are examples.

In the last 25 years of research on water management in agriculture, the greatest efforts have been made mainly in Asia (China, India), North America (United States), Oceania (Australia) and Europe (Germany), while in Latin America the field is still emerging (Velasco-Muñoz et al., 2018).

The economy of Chile, a Latin American country rich in mediterranean landscapes, is based on the use and extraction of natural resources, including water (Donoso, 2006; Cortés et al., 2012). Agriculture accounts for 80% of consumptive extractions of water, allowing the irrigation of over 1.1 million hectares; the irrigated area has increased annually, especially into previously unused areas, an expansion aided by the application of technology (Donoso et al., 2016; DGA, 2016). Global climate change trends will also produce greater vulnerability as increasing water demands become more difficult to meet, with projections for 2040 indicating general water reduction in central Chile (32°S to 33°S), where the largest amount of cropland is concentrated (Iglesias and Garrote, 2015; Pino et al., 2015; Chartzoulakis and Bertaki, 2015). Added to these trends is the drought period that began on 2007, with a precipitation deficit of 30% and temperature increases between 0.5 °C and 1.5 °C above the historical average (Boisier et al., 2016; Valdés-Pineda et al., 2016).

The foregoing suggests the need for public policies that ensure efficiency and equity in water resources (Jaramillo and Destouni, 2015). Water regulation in Chile is a major challenge. It is based on a market model governed by the Water Code of 1981 (DFL 1.122), which entails a combination of a (centralized) distribution system and (freely transferable) water use rights (Hearne and Donoso, 2014; Rivera et al., 2016). In this model, water is a “national good of public use,” but water use rights are private property (Guiloff, 2012; Hearne and Donoso, 2014). Thus, Chile is an example of an extreme unitary legal system, as the state has limited power to intervene and promote the maintenance of continental aquatic systems, with minimum environmental protections incorporated belatedly and independent of local ecosystems and a large percentage of water already allocated (OECD – UN ECLAC, 2016). This last situation has led to over-granting of water use rights in many agricultural regions in the central macro zone (30°–35° S), with consumptive and non-consumptive surface flows of 7271.932 m3/s granted (DGA, 2016).

Thus, this study contributes to water-use planning in a region of the Southern Hemisphere that, due to its geographical particularities, exhibits high-value, high-quality agricultural production (Aguilera et al., 2019; Fernández et al., 2018), and where regional fruit exports increased 33% in 2018 and are estimated at 1609.4 MMUS$, in contrast to other agricultural exports, which decreased by 22%, to 8.7 MMUS$ (INE, 2018). These changes are attributed to instances of climate change, droughts and fires (Henríquez et al., 2016), in addition to decreases in sales to China, Brazil and Japan (INE, 2018).

It is therefore a priority to calculate indicators that assess agricultural water demands and allow the impacts of climate phenomena to be quantified and change processes to be interpreted (Lathuillière et al., 2018), through a holistic approach that includes technical, environmental, and socio-economic aspects in an innovative and manner, as achieved by water footprint assessment (Zhang et al., 2018).

Current basin-level water management practices make agricultural production dependent on irrigation type and climate characteristics (Billib et al., 2009; Cortés et al., 2012; Valdés-Pineda et al., 2016), leading to questions such as the following: What component of the WFagricultural (WFblue,WFgreen, WFgrey) explains the greatest water consumption? Does the area in which crops are grown influence the water requirement? Is it possible to determine the differences in agricultural water consumption as a function of local climate variability? What percentage of water consumption of crops is given by WFblue, WFgreen and WFgrey?

The hypothesis is that the greatest WFagricultural will occur in dry periods, even though water resources are diminished then. The primary objective of this study is to determine the water consumption of the main crops produced in a central Chilean river basin by calculating the water footprint of agriculture considering climate variability (dry, wet and normal years) and the green, blue and gray water footprint indicators in order to modify future water allocation plans and complement them with more rational water management models.

Section snippets

Materials and methods

To analyze the WF, the Cachapoal River basin was selected as representative of a central Chilean basin because it accounts for 78% of the cropland in one of the administrative regions of the area. Agribusinesses are located along its banks, contributing to water pollution (Novoa et al., 2016, Novoa et al., 2019). There is increasing soil erosion (moderate, severe and very severe) in 44% of the total basin area, environmental damage resulting from poor practices in the forestry, farming and

Agricultural water footprint

The analysis of the climatic behavior of the Cachapoal River basin in the 34 years studied and at the weather stations selected as a reference showed that precipitation and effective precipitation revealed higher values in 2005 (representative of a wet year), with 969 ± 3.1 mm and 625 ± 8.1 mm, respectively. The opposite was observed in 2007 (representative of dry conditions), in which precipitation (420 ± 3.4 mm) and effective precipitation (212 ± 8.2 mm) were lower, with a decrease of 43%

Discussion

The study of the water footprint on a drainage-basin scale is carried out through the development of increasingly complex indicators, allowing a large variety of factors that determine the water cycle to be considered and their dynamics to be simulated, in addition to permitting spatial variations to be included as input data (Chukalla et al., 2018; Vanham et al., 2018). Multiple climate variables, soil characteristics and crop properties, as well as evapotranspiration estimates and irrigation

Conclusions

Climate variations are determinant in the water requirements of agricultural activities, particularly in a Latin American basin with a mediterranean climate, since the water flow is related to various types of consumption, that is, in a year with drought conditions (this is, 43% decrease in precipitation relative to 34 years of records) the greatest WFagricultural and WFblue were estimated, while in normal conditions the greatest WFgreen was determined. The WFgray, however, was directly

Nomenclature

SymbolUnitExplanation
ARkg/ha/mass/areaApplication rate of a chemical (fertilizer or pesticide) per unit of land
ΑLeaching-run-off fraction, i.e. fraction of applied chemicals reaching freshwater bodies
AWP$/m3Apparent water productivity
CWUbluem3 ha−1/volume/areaBlue crop water use
CWUgreenm3 ha−1/volume/areaGreen crop water use
CWRmm month−1/length/timeCrop water requirement
Cmaxkg m3/mass/volumeMaximum acceptable concentration of a chemical in a receiving water body
Cnatkg m3

Acknowledgements

The authors express their gratitude to the Conicyt National Commission for Scientific and Technological Research for the funding provided through the CRHIAM Conicyt/Fondap/15130015 project, the Conicyt Advanced Human Capital Program of the Government of Chile, the National Doctorate Grant-2011, and FONDECYT projects 11150424 and 1150459. Dr. Ahumada-Rudolph expresses his gratitude to the post-doctoral program of the Directorate of Research, University of Bío-Bío.

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