Energy consumption for crop irrigation in a semiarid climate (south-eastern Spain)
Introduction
Water is a critical natural resource upon which all social and economic activities and ecosystem functions depend. Agriculture accounts for 70% of all water withdrawal by the combined agricultural, municipal and industrial sectors in the world, with crop irrigation being the prevailing use. Irrigated agriculture plays a crucial role in the global food production system, accounting for more than 40% of the world's production on less than 20% of the cultivated land. Irrigated crop yields are about 2.7 times higher than those of rainfed farming at worldwide scale [1]. In Spain, the role of irrigation is even higher since the agriculture sector uses approximately 75% of the total water resources [2]; about 60% of total production comes from just 20% of cropland that is irrigated [3]; and irrigated crops yields are about six times those of rainfed farming [4].
Water and energy are coupled in an intimate way. Many technical processes of harnessing, extracting, and producing energy utilise water, and energy is also required to make use of water at every phase of its extraction, distribution and usage processes [5]. This interdependence, which is often referred to as the ‘water–energy nexus’, has been increasingly highlighted as an important issue for future planning and strategic policy considerations [6]. Moreover, water scarcity is forcing nations to use non-traditional water sources such as desalinated and recycled water; choices that need to be sensitive to the environmental impacts of the required electricity [1].
Global energy demands are expected to grow by as much as 55% by 2030, according to the International Energy Agency [7]. The water–energy nexus is one of the reasons for this, since water is becoming scarce, not only in arid and drought prone areas but also in regions where rainfall is abundant, and new water sources with higher energy requirements should be incorporated to the supply systems. Thus, the embodied energy associated with water provision and the environmental impacts associated with water supply are also increasing with growing water scarcity [8].
The current importance of crop irrigation in total water consumption makes it clear that the sustainable use of water is a priority for agriculture in water stressed regions. To comply with this statement, Spanish irrigation systems have experienced profound transformations in the last decades, including a modernisation process since 2002 aimed to improve management performance and water use efficiency. As a result, while water consumption per hectare was reduced by 21% between 1950 and 2008, energy demand increased by 657% [3]. Therefore, although the amount of water diverted for irrigation to farms has been considerably reduced, the energy for pumping pressurised systems is much greater now compared to the gravity-fed systems used previously. Consequently, from now on it is necessary to manage energy resources more efficiently to control the increasing energy demand for crop irrigation [9].
At farm level, the concept of productivity can be defined as the production per unit input, and it is focused on limiting factors such as water and energy. Several productivity indicators have been suggested to analyse water use performance for irrigation [10], [11]. Other studies have stressed the need to study the energy consumption and energy output of different fruit and vegetable crops [12], [13], [14], some of them extrapolating the productivity concept to take into account the water–energy nexus and to analyse its footprint in irrigated crop production [15]. Indicators that capture the combined effect of water and energy inputs for measuring the potential environmental impacts of crop production have also been proposed [16].
This work is focused on the analysis of the interdependence between water and energy consumption in pressurised distribution and irrigation systems under the semi-arid conditions of south-eastern Spain. The study assesses energy consumption for irrigation throughout a 10-year period, particularising for different management levels and locations in the study area. The quantification of water and energy use in the Mediterranean region is interesting for planners and managers in water agencies and collective irrigation associations, especially if irrigation district modernisation processes and different water scarcity intensities have occurred throughout the study period. The results can also be useful for formulating recommendations for rationalising water and energy use in irrigated crop production.
Section snippets
Materials and methods
The methodology for developing this study was structured into several steps. First a suitable set of indicators for characterising the relationship between the water and energy use was selected. Next, the value of these indicators was calculated throughout a 10-year study period (2002–2011) in three irrigation districts (IDs) under the semi-arid conditions of south-eastern Spain. To calculate the performance indicators it was necessary to obtain data by: (a) consulting the manager and the
Water and energy consumption
Table 3 presents the average value and the variation range for the study period of the specific energy (EacVs) consumed in each management level and ID. EacVs in the basin level was considered as the addition of energy consumption weighted according to the percentage of water supplied from each source shown in Table 2.
Conclusions
Different water management levels are involved in providing water for crop irrigation. The right analysis of energy use at each management level is required in order to know the real value of energy performance indicators in crop production, as well as for making local or regional comparative analysis (benchmarking). There are three management levels that are involved in the water supply for irrigation in south-eastern Spain: basin, irrigation district (ID), and farm.
From the present work it
Acknowledgements
The authors acknowledge the European Community's Seventh Framework Research Programme for the financial support of this study through the grant agreement n. 245159 project SIRRIMED (Sustainable use of IRRIgation water in the MEDiterranean region, FP7-KBBE-2009-1-2-03, www.sirrimed.org). The collaboration of the staff of “Comunidad de Regantes del Campo de Cartagena”, “Comunidad de Regantes de Miraflores” and “Comunidad de Regantes del Transvase Tajo-Segura Comarca de Calasparra Cieza” and
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