Introduction

The world’s food, water and energy resources are nowadays experiencing significant stress and it is expected rapidly increasing demands for these resources in the coming years Water, energy, and food will become scarce in future (Bizikova et al. 2013; Hoff 2011). With limited resources, inadequate energy supply, and growing water stress, the challenge of providing enough water and energy to grow enough food for the growing population will be faced (Bizikova et al. 2013; Hoff 2011). Water, energy and food are vital for human well-being, poverty decline and sustainable expansion (FAO 2014a, b). An approach based on the water–food–energy nexus helps explain the complex and dynamic interrelationships involved and provides support for decisions to allocate the limited resources. It can do this by offering an informed and clear framework for determining and undertaking trade-offs to meet increasing demand without threatening sustainability (Bonn 2011).

Food, water, and energy are interconnected. Managing one of them cannot be considered in isolation but should be seen as part of an integrated system (Giampietro et al. 2013). The interactions among water, food, and energy are numerous and substantial. Water is used for food production (i.e. irrigation of food and feed crops and food processing). Water is used for energy production (i.e. cooling of thermoelectric power-plants, hydroelectric power-plants). Energy is used throughout the food supply chain, from the manufacture and application of agricultural inputs, such as fertilizers and irrigation, processing, and distribution services. Energy is used for food production (i.e. production of fertilizers, operation of machines, pumping irrigation water). Energy is used for water production (i.e. pumping and extraction of water, water and west water treatment, desalination). To meet increasing water demand, a substantial amount of energy is needed for pumping, treating and delivering water (Rutschmann 2013).

Due to the interaction among the three sectors, any strategy that focuses on one sector without considering its interconnections with other sectors may lead to acute unpremeditated consequences (Bizikova et al. 2013). Therefore, it is necessary to take a nexus approach when developing strategies. The nexus approach illustrates how and where the three systems interconnect (Hanlon et al. 2013). Using a nexus approach to steward water resources sustainably in energy supply chains and food supply chains is seen as a promising approach (Allan et al. 2015).

Recently, researchers, organization, and decision makers have considered the significance of the multifaceted relationships between water, energy, and food (Arent et al. 2011; Siddiqi and Anadon 2011; Bizikova et al. 2013; Gulati et al. 2013; Lele et al. 2013; Peyman et al. 2013; Finley and Seiber 2016; Biggs et al. 2015; Nielsen et al. 2015; El Gafy et al. 2017; Keairns et al. 2016; Paul and Tenaiji 2016). The nexus is broadly considered as a suggesting approach to settling the sustainable management of natural resources and ecosystems with the needs of development, including the growing demand for energy, food, and water (Bonn 2011; FAO 2014b). The nexus approach allows for more integrated and effective policy-making, planning, monitoring and evaluation related to the different nexus sectors (Giampietro et al. 2013).

A set of comparative performance indices were applied to evaluate water sustainability and progress and priorities for water policies intervention. Among of them are the water availability index, the Water scarcity index, the Water Resources Vulnerability Index, Social Water Stress Index, Water Stress Indicator (WSI), and the Water Poverty Index (WPI) (Molle and Peter 2003; Juwana et al. 2010; Brown 2011; The United Nations Educational, Scientific and Cultural Organization (UNESCO) 2014; El-Gafy 2015). However, there is a need to produce an index that considers the water and energy and not concentrate only in one sector such as the previous indices.

The objective of the current research is providing a method to decision makers to analysis Water–food–Energy Nexus (WFEN) of the crop’s production system. The current research applies the proposed method to analysis the water–food–energy nexus of 42 Egyptian food crops under different crop categories (cereal, legumes, sugar crops, oil crops, vegetable, and fruit).

Methodology

Through the current research the following were carried out: (1) six indicators, as illustrated in Fig. 1, were proposed to be applied as a tool to quantify the nexus and help in drawing strategies in the area of the crop production system, (2) based on these indicators, a Water–food–Energy Nexus Index (WFENI) was performed, and (3) WFEN and WFENI of 42 Egyptian main crops in Egypt were determined based on the performed WFENI and its indicators. WEFNI can be applied to developed strategies for the optimal cropping pattern that minimizing the water and energy consumption and maximizing their productivity. WEFNI can be applied as a holistic tool to evaluate the progress in the water and agricultural national strategies.

Fig. 1
figure 1

Water–food–energy assessment method

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Water and energy consumption indicators

Indicator (1): water consumption indicator (W c,t ), is the water consumption per hectare of crop c at time t.

Indicator (2): Energy consumption indicator (E c ), is the energy consumption per hectare of crop c. Energy consumption for the crop food production can be categorized into direct and indirect energy use. Crop production uses energy directly, as fuel or electricity, to operate machinery and equipment and indirectly as in the energy consumed in producing the fertilizers and chemicals that are used in the farm [Zahedi et al. 2015]. E c is calculated applying Eq. 1.

$$E_{c,t} = \sum\nolimits_{{}}^{{}} \begin{aligned} q_{h} h_{(c,t)} + q_{m} m_{(c,t)} + q_{d} d_{(c,t)} + q_{f} f_{(c,t)} \hfill \\ + q_{p} p_{(c,t)} + q_{s} s_{(c,t)} + q_{w} w_{(c,t)} \hfill \\ \end{aligned}$$
(1)

where: q h , q m , q d , q f , q p , q s , and q w are the energy equivalents of human labor (J/h), machinery (J/h), diesel oil (J/L), fertilizer (J/kg), pesticides (J/kg), seeds (J/kg), and irrigated water (J/m3) inputs in crop c production. h (c,t), m (m,t), d (d,t), f (c,t), p (c,t), s (c,t), and w (c,t) are human labor (h/ha), machinery (h/ha), diesel fuel (L/ha), electricity (kWh/ha), fertilizer (kg/ha), pesticides (kg/ha), seeds (kg/ha), irrigated water (m3/ha) inputs in crop c production at time t.

Water and energy mass productivity indicators

Indicator (3): water mass productivity at time t (W pro,t , ton/m3) is calculated applying Eq. (2).

$$W_{{{\text{pro}},t }}= {\raise0.7ex\hbox{${Y_{c,t} }$} \!\mathord{\left/ {\vphantom {{Y_{c,t} } {w_{c,t} }}}\right.\kern-0pt} \!\lower0.7ex\hbox{${w_{c,t} }$}}$$
(2)

where: \(Y_{c,t}\) is the yield of crop c (ton/ha) at time t, \(w_{c,t}\) is the water consumption per hectar of crop c (m3/ha) at time t.

Indicator (4): energy mass productivity at time t (E pro,t , ton/J) is calculated applying Eq. (3).

$$E_{{{\text{pro}},t }}= {\raise0.7ex\hbox{${Y_{c,t} }$} \!\mathord{\left/ {\vphantom {{Y_{c,t} } {E_{c,t} }}}\right.\kern-0pt} \!\lower0.7ex\hbox{${E_{c,t} }$}}$$
(3)

where: \(E_{c,t}\) is the energy consumption per ha of crop c at time t (J/ha).

Water and energy economic productivity indicators

Indicator (5): the economic water productivity of irrigation water at time t (W EV,t , $/m3) is calculated applying Eqs. 4.

$$W_{{EV,t }} = {{N_{{c,t}} - C_{{c,t}} } \mathord{\left/ {\vphantom {{N_{{c,t}} - C_{{c,t}} } {w_{{c,t}} }}} \right. \kern-\nulldelimiterspace} {w_{{c,t}} }}$$
(4)

where: Nc,t is the return per ha from crop c ($/ha) at time t and C c,t is the cost of inputs used per ha for cultivating crop c at time t.

Indicator (6): the economic productivity of energy c at time t (E EV,t ,$/J) is calculated applying Eqs. 5.

$$E_{{EV,t }} = {{N_{{c,t}} - C_{{c,t}} } \mathord{\left/ {\vphantom {{N_{{c,t}} - C_{{c,t}} } {E_{{c,t}} }}} \right. \kern-\nulldelimiterspace} {E_{{c,t}} }}$$
(5)

Water–food–energy nexus index

Through the current research a preliminary WFENI was proposed. The index gives a picture to the decision makers about the performance of the water–food–energy nexus management. WFENI is calculated applying Eq. 6:

$${\raise0.7ex\hbox{${WEFNI_{t} = \mathop \sum \nolimits_{i = 1}^{n} w_{i} X_{i} }$} \!\mathord{\left/ {\vphantom {{WEFNI_{t} = \mathop \sum \nolimits_{i = 1}^{n} w_{i} X_{i} } {\mathop \sum \nolimits_{i = 1}^{n} w_{i} }}}\right.\kern-0pt} \!\lower0.7ex\hbox{${\mathop \sum \nolimits_{i = 1}^{n} w_{i} }$}}$$
(6)

The indicators of WFENI were normalized to exclude the inflection of different dimensions applying the Min–Max normalization technique applying Eqs. 7 and 8 approach as (Juwana et al. 2010). Equation 7 is used when the \({\text{Min}} \left( {x_{i} } \right)\) of the indicator is the least preferred value and \({\text{Max}} \left( {x_{i} } \right)\) is the most preferred value, where Eq. 8 is used for the opposite situation.

$$X_{i} = \frac{{x_{i} - {\text{Min}}\left( {x_{i} } \right)}}{{{\text{Max}} \left( {x_{i} } \right) - {\text{Min}}\left( {x_{i} } \right)}}$$
(7)
$$X_{i} = \frac{{{\text{Max}} \left( {x_{i} } \right) - x_{i} }}{{{\text{Max}} \left( {x_{i} } \right) - {\text{Min}}\left( {x_{i} } \right)}}$$
(8)

where: \(X_{i}\) refers to normalized indicator,\(x_{i}\) actual value of the indicator, \({\text{Min}}\left( {x_{i} } \right)\) and \({\text{Max}} \left( {x_{i} } \right)\) are the minimum and maximum values of the indicator, \(w_{i}\) is the weight applied to each indicator and n is the number of WFENI indicators. The highest value 1 is taken to be the best situation while 0 is the worst.

Total water and energy consumption footprint

Total water (W t , m3/year) of the crops production per year is calculated according to Eq. 9.

$$W_{t} = \mathop \sum \limits_{c = 1}^{v} A_{c,t} \times w_{c,t}$$
(9)

Total energy (E t , J/year) of the crop production per year is calculated according to Eq. 10 v is the number of crops under study.

$$E_{t} = \mathop \sum \limits_{c = 1}^{v} A_{c,t} \times E_{c,t}$$
(10)

where: \(A_{c,t}\) is the cultivated area of crop c at time t.

Case study

Agriculture consumes the largest amount of the available water in Egypt, with its share exceeding 85% of the total demand for water. Energy used for agricultural is used for pumping irrigation water, producing fertilizers and pesticides, operation of machines, and transportation. Through the current research the water–food–Energy nexus of 42 Egyptian food crops was analyzed. The determination method of WFENI and its indicators for the case study was summarized in Table 1.

Table 1 The determination method of water–food–Energy nexus index and its indicators for the case study
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Table 2 Numbers of irrigation pumps according to their powers
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Table 3 Food–water–energy nexus index of a number of studied food crops and its normalized indicators
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Table 4 Total food–water–energy nexus of the studied food crops in 2010
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Results and discussion

Determination of the proposed indicators for the case study

Calculated water and energy consumption indicators

The calculated water and energy consumption per hectare indicators, indicators 1 and 2, are illustrated in Fig. 2. The energy of human labor, machinery, diesel oil, fertilizer, pesticides, and irrigated water inputs per hectare in the crop’s production system are consider in the calculation of energy consumption. Annex a Table 5.a illustrates the different energy inputs per hectare for the studied crops.

Fig. 2
figure 2

Water–energy–food nexus: water and energy consumption indicators of the main food crops at the study year (The energy of human labor, machinery, diesel oil, fertilizer, pesticides, and irrigated water inputs per hectare in the crop’s production system were illustrated in Appendix: Table 5)

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According to the energy used for irrigation, as shown in Fig. 3, the energy used for irrigating one hectare of fruits, sugar crops, oil crops, cereal, and vegetables represent 14, 11, 10, 7, and 6% of the total energy use for the production of each category, respectively. Rice, sugar can, lintel, okra, olive, and mango are the highest energy consumption for irrigation in the cereal, sugar, legume, oil, vegetables, and fruits categories, respectively, as shown in Table 5.

Fig. 3
figure 3

Contribution of agricultural inputs categories to the total energy used for the food crops production

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Calculated water and energy productivity indicators

The calculated water and energy productivity indicators, indicators 3 and 4, are illustrated in Fig. 4. As shown in Fig. 4, having the highest water productivity does mean that the crop should have the highest energy productivity. As an example, potato is the highest energy productivity crop in the vegetable category while garlic is the highest water productivity one in this category.

Fig. 4
figure 4

Water–energy–food nexus: Water and energy mass productivity indicators of the main food crops at the study year

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Calculated economic water and energy productivity indicators

Economic water and energy productivity indicators of summer crops are shown in Fig. 5. As shown in the previous figure, onion has the highest economy productivity among the summer crops. Due to the data availability for some crops, a complete analysis of the economic indicators did not conceder through the current research.

WEFNI of the main food crops

The WFENI of summer crops, as an example, were calculated. The indicators of the water–energy consumption, mass, and economic productivity, as illustrated in Table 3, of the summer crops were first calculated. Based on the previous indicators, the WFENI of the summer crops for year 2010 were determined, Table 3. A comparative analysis among the crops base on their WFENI was carried out. The study showed that the calculated WFENI of the summer crops have scores that range from 0.21 to 0.79, as shown in Table 3. Comparing to onion (the highest scoring WFENI), rice has the lowest WFENI among the summer crops. WFENI could be applied yearly to evaluate the performance of the water–food–energy nexus management. WEFN index can be applied to developed strategies for the optimal cropping pattern that minimizing the water and energy consumption and maximizing their productivity.

Fig. 5
figure 5

Water–energy–food nexus: water and energy economic productivity indicators of the main food crops at the study year

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Analysis of Water-Food-Energy nexus of the studied food crops in 2010

The WFEN of each food crop under study was determined, Table 4. The analysis of The WFEN of the food crops’ production and consumption for year 2010 showed that:

  • The total production of the food crops is about 71 Mt (29% cearal, 33% sugar, 0.40% oil, 0.40% legume, 26% vegetables, 11% fruits).

  • The water and energy consumed for cultivating the studied food crops in 2010 (study year) was about 41 Billion Cubic Meter (BCM) (54% cereal, 17% vegetables, 14% fruits, 10% sugar crops, 2.4% oil crops, and 1% legume) and 2,14,217 TJ (59% for cereal, 23 vegetables, 8% fruits, 2% oil crops, 1% legumes), respectively.

  • The energy consumed for irrigation is about 15,800 TJ which is representing about 7.4% of the total energy for the studied crops.

Conclusion

The current research is providing a method to decision makers to analysis the Water-food-Energy Nexus (WFEN) of the crop’s production system. The research applied Water–Food–Energy Nexus Index (WFENI) that considers the water and energy and not concentrated only in one sector. This index integrates a number of aspects that refract major concerns in the nexus. Where, WFENI composite indicators for Water-Energy consumption (the energy of human labor, machinery, diesel oil, fertilizer, pesticides, and irrigated water inputs in the crop’s production system were considered), water–energy mass productivity, and water–energy economic productivity.

WFENI and its indicators were applied to analysis the water–food–energy nexus of the crop production system of 42 Egyptian main food crops cultivated in year 2010 in Egypt.

The study showed that the calculated WFENI of the studied Egyptian crops have scores that range from 0.21 to 0.79. Comparing to onion (the highest scoring WFENI) rice has the lowest WFENI among the 42 food crops. The WFE nexus of each food crop under study was determined. Analyzing the WFEN of the food crops’ production for year 2010 shown that: the total production of the food crops is about 71 Mt, The water and energy consumption for cultivating the studied food crops in 2010 (study year) were about 41 BCM and 2,14,217 TJ, respectively. The energy consumed for irrigation is about 15,800 TJ which is representing about 7.4% of the total energy of the studied crops.

Understanding WFE nexus allows for more integrated planning, development, policy-making, monitoring and evaluation related to the nexus sectors. The water food energy nexus should be considered when developing development projects. The WFE nexus should be considered when developing the stagey of the country and not only focuses on one sector. The proposed indicators/indices should be applied for comparing the change in the water–energy–food nexus of the agriculture production system over years. WFENI could be applied yearly to evaluate the performance of the water–food–energy nexus management. WEFNI can be applied to developed strategies for the optimal cropping pattern that minimizing the water and energy consumption and maximizing their productivity. Other indicators could be considered within the index according to the availability of the data, the use of the index, and the level of its application.