Nutritional water productivity and diets
D. Renault
a,*,1,2, Professor W.W. Wallender
baIrrigation Engineer, International Water Management Institute, P.O. Box 2075, Colombo, Sri Lanka bDepartments of Land, Air and Water Resources (Hydrology Program) and Biological and Agricultural
Engineering, University of California, Davis, CA 95616, USA
Accepted 26 October 1999
Abstract
The increase in water productivity is likely to play a vital role in coping with the additional requirement for food production and the growth of the uses of water other than in agriculture in the coming century consistent with the shift from productivity per unit land to productivity per unit water, the nutritional productivity of water is calculated as energy, protein, calcium, fat, Vitamin A, iron output per unit water input.
Nutritional productivity is estimated in the agricultural context of California for the main crops and food products. In general vegetal products are much more productive than animal products. Four crops emerge as highly productive for one or several key nutrients: potato, groundnut, onion and carrot. A balanced diet based on these four crops requires a consumption of water (evapotranspired) of 1000 l per capita per day, while the current needs for the diet in the USA is 5400 l, and 4000 l for developed countries.
On the basis of nutritional productivity analysis it is further demonstrated that a signi®cant part of the additional water resource to produce food for the next century population can be generated by changes in food habits. A reduction of 25% of all animal products in the developed countries' diet generates approximately 22% of the additional water requirements expected by the year 2025. #2000 Elsevier Science B.V. All rights reserved.
Keywords:Water productivity; Nutrition; Diet; Food Production; Water requirements Agricultural Water Management 45 (2000) 275±296
*Corresponding author. Tel.:33-38824-8224; fax:33-383388-248284.
E-mail addresses: d.renault@engees.u-strasbg.fr, d.renault@cgiar.org (D. Renault), wwwallender@ucdavis.edu (W.W. Wallender)
1Tel.: 94-1-867404; fax: 94-1-866854.
2ENGREF. Montprllier, France, for the early stages of this study.
1. Introduction
At the turn of the third millennium there is a growing awareness that water is one of the crucial limiting factors for increased food and fiber production to supply an ever growing number of people under increasing competition with other users of water (municipal, industrial, environmental, etc.). The fundamental question, which underlies current debates in many forums is: how many people can the planet sustain, given our limited availability of natural resources?
The answer will obviously depend to a large extent on the availability of water for both rainfed and irrigated agriculture, the size of the human population and ultimately the water requirements to grow crops and produce food. The irrigated areas contribute a major fraction of the global food supply. However, the possibility of expanding the irrigated areas is becoming rare and costly (Carruthers et al., 1997), therefore, improving productivity within the existing irrigated areas and within the rainfed agriculture is crucial. The concept of productivity has, in recent decades shifted from `Crop per unit area' to `Crop per unit volume of water'. The step sustaining the human population is nutrition per water volume.
In this paper, nutrition per water volume is quantified in the context of improving human food production given our limited water resources and modified diets are evaluated. Water productivity is expressed in kg/m3 whereas nutritional water productivity is expressed in nutritional units/m3(nutritional units being energy, protein, calcium).
2. Water productivity
The concept of productivity, i.e. production per unit input, focuses on limiting factors or constraints. In the mid-70s, for example, the petroleum crisis highlighted the importance of energy in agriculture and the productivity of energy became popular. In areas where labor is constrained, due to rural migration, the concept of labor productivity is used. Water is also a limiting resource and various productivity measures have been suggested.
The concept of water productivity is certainly not new. There is a long history of the development of efficient techniques for managing scarce water in arid areas. Even the case of the Indus basin development in the 19th century, relies on the concept of water productivity. In this case, the water delivery was purposely designed to meet only 1/3 of the command area water requirements because the operational goal was to reach as many farmers as possible within the available water resource. The productivity indicator of the development was then the number of farmholdings per unit of water.
The development of large projects after World War II, temporarily led to the illusion that water is limitless. During the 1970s, the world community again realized that water resources are limited. It was at this time that, for example, breeders and geneticists developed a better understanding of the water use during photosynthesis (Stone, 1975). The difference in water use between C3 and C4 plants and the consequences on total water use were documented. A C3 plant (wheat, barley, rice, potato) produces 1 tonne of
dry matter with 600 tonnes of water, while a C4 plant (maize, sorghum, sugarcane) requires only 300 tonnes (Tinus, 1975). The ratio of the photosynthesis and the transpiration expresses the water-use efficiency of the crop. This ratio is related to both the gradient of CO2at the leaf surface between the inside and outside, and the resistance of the mesophyll for carbon dioxyde. C4 plants have a higher gradient and a lower re-sistance than C3 plants, and therefore, a much better water-use efficiency (Feddes, 1988). Agronomists evaluate the productivity of water through water use efficiency (WUE), the ratio of yield to water consumed (kg/m3) by the crop through evapotranspiration at the field scale (Doorenbos and Kassam, 1979) or as the yield per unit depth of water depth per area (kg/ha/mm) (Gregory, 1991). Biomass yield may also include straw and roots when the latter have an economic value (Gregory, 1991).
Water use efficiency concepts have been applied in diverse contexts for both rainfed and irrigated agricultures (Shalhevet et al., 1992). Water productivity in irrigation was debated during the late 70s and early 80s in India (Sundar and Rao, 1984; Chambers, 1985). More recently, studies on water efficiency and productivity have expanded to include `real' or `virtual' water savings, and the necessity to analyze the problem at the water basin level (Seckler, 1996) as well as advocating a consistent approach of water accounting (Molden, 1997; Young and Wallender, 1999).
In a water scarce country such as Israel, water productivity has significantly increased from 1.60 kg/m3in 1949 to 2.32 in 1989 (Stanhill, 1992). This has been made possible by increases in the water application efficiency at the field scale. Stanhill then identifies plant breeding as the main avenue to further increase water productivity.
2.1. Models
Productivity may be estimated as the ratio of the output of an economic unit and the inputs:
PRODUCTIVITYOUTPUTS
INPUTS (1)
Herein, assume water is the limiting input and calculate output. Water productivity is based on the ratio of mass produced (actual yield, Ya) to the water consumed (actual evapotranspiration ETa). This productivity is often expressed in kg/m3and is increasingly used to measure performance for irrigation systems. A more comprehensive approach for productivity (Molden et al., 1998) introduces the economical value of the agricultural production ($/unit of water). Performance comparisons among irrigation systems producing different crops in different environments are thus possible.
2.2. Average and marginal productivity
Productivity is estimated as an average value for the whole cropping season, i.e. actual yield (Ya) divided by actual water evapotranspired (ETa) as follows:
Average Productivity Ya ETa
(2)
Although the average productivity facilitates a comparison between crops and products, it is not suf®cient to fully express the yield response to water. The marginal productivity, in contrast, re¯ects the productivity of an additional unit of water, as follows:
Marginal Productivity dYa d ETa
(3)
The marginal productivity of water is crucial in determining the optimal allocation of scarce water. In a rainfed system, an increment of water can be applied either as supplemental preventative irrigation or as an emergency irrigation to avoid crop failure. In an irrigated system when shortages occur, more sensitive crops and yield sensitive periods have ®rst priority.
2.3. Water input
In general water productivity is a function of water applied which depends on space scale and generally increases from small plots to large agricultural domains at a basin scale because applied water is recycled and reused. Herein, the domain under consideration is the field scale. We consider water supply through direct precipitation and/or through irrigation and we are interested in the fraction of applied water which is consumed by evapotranspiration. We assume crop transpiration and direct soil evaporation as the water input of the process. Other components such as runoff and percolation, or losses along the water delivery infrastructure are not accounted for.
2.4. Yield
The yield response to water is highly dependent on the yield response factor (ky) linking evapotranspiration to yield. The relationship between relative yield decline and relative evapotranspiration deficit is linear for a range of deficits which do not lead to crop failure. This relationship is (Doorenbos and Kassam, 1979):
1ÿYa
whereYais the actual harvested yield,Ymthe maximum harvested yield,kyyield response factor, ETathe actual evapotranspiration, and ETcthe potential crop evapotranspiration. The yield response factor (ky) varies from one crop to another, and from one vegetative period to another. Doorenbos and Kassam (1979) states that maize is much more sensitive to water stress (ky1.25) than groundnut (ky0.7). Therefore, in the case of water shortages priorities for water distribution should be based on the yield response factor along with other considerations such as market prices. For crops having a yield response factor below unity, the maximum water productivity is obtained for a water supply and a yield less than the maximum values, as recorded by Maozheng and Wang (1992) for a winter wheat in north China. For most crops the yield response factor reaches a peak during the flowering period.
2.5. Interventions for improving water productivity
Classically productivity improvements can result from raising the efficiency of the input (better timing, minimizing process losses) and increasing the output, as it can be seen in Eq. (1). One input intervention is to minimize non-beneficial water depletion, i.e. reducing direct evaporation at the field level particularly during the early stages of crop development when ground cover is incomplete. For example, DeTar et al. (1996) compared the productivity of different techniques of irrigation on potatoes. In the same environment and for the same climatic year they recorded productivity values ranging from 6 kg/m3 for sprinkler irrigation to 10.5 kg/m3 for subsurface drip irrigation (accounting in both cases for a limited contribution of rainfall). Another input intervention is precisely timing water stress. For certain crops the optimum yield quantity and/or quality occurs when water needs are met at 100% except for a slight water stress at later stages of development. Another intervention on the water supply is to increase the reliability of the deliveries to the field. This reduces productivity decline linked to fluctuating and unpredictable inputs which may occur in rainfed agriculture and unreliable irrigation systems.
On the other term of the productivity function (output) intervention should consist of minimizing the effect of other limiting factors (nutrients, pest control) and closing or optimizing the gap between actual yield (Ya) and maximum possible yield (Ym). It should also consider developing varieties better adapted to the rainfall pattern to avoid water stress, and introducing more productive varieties (increaseYm), crops better adapted to the environment, and/or with a higher economical value.
As mentioned earlier there are situation for which the priority should be to reduce the gap between (Ya) and (Ym) with improved management of all the inputs including water (reliability). Herein we assume (Ya) is already optimized, which generally means close to but not necessary equal to (Ym) and we specifically investigate the improvement of water productivity in terms of nutritional outputs.
3. Transition to nutritional water productivity
The meaning of water productivity and the decisions related to the concepts of productivity vary significantly from the point of view of a farmer, an irrigation manager, an agricultural professional, and a policy maker at national or international levels. In an open market, the productivity in kg/UW (unit of water), Gross product/UW, Net benefit/ UW are certainly relevant for farmers and local managers and ultimately positive net benefit is required.
For national policy makers kg/UW or $/UW are worthy variables to maximize. In an open market, one strategy is to domestically produce and export high value crops and import low value crops. Alleviation of malnutrition is an issue of production and of distribution as well as poverty. Nutritional productivity becomes important for some strategic products and/or in situations of crisis, e.g. whenever the circulation of food is locally reduced by the closure of boundaries, or if the surplus of the staple food from the producing countries is no longer able to match the demand. The food shortages at the
beginning of the seventies, with the rapid increase of basic food prices led to starvation of the poorest of the poor (Islam, 1995).
For international policy makers, the focus should be more on a comprehensive approach of productivity, balancing kg/m3, $/m3and ultimately nutritional productivity. Furthermore, consideration of the sustainable human population on this planet should focus on diet and its relation to scarce water resources. The agricultural and dietary policy are center stage in the strategy for agricultural outputs and nutritional yields, and on the water requirements per capita.
3.1. Nutrition productivity
Altering yield objectives from weight to nutritional values involves the consideration of numerous nutritional components of food. It is quite common in nutrition guidelines and food surveys to consider three metrics: energy, protein and fat (FAO, 1990). In addition experts list vitamin components, 10 mineral components, four indicators for lipids, and finally 18 amino acid components (Dunne, 1990).
In this study we purposely limit the approach to the three major components: energy, protein, and calcium, with additional consideration of fat, iron and Vitamin A. Energy and protein are the most common components considered in food studies. Calcium, iron and Vitamin A are considered herein because most nutrition studies show growing evidence linking malnutrition to deficiencies in these elements. We fully admit that this approach limited to six components may not be sufficient in some cases, but the method is expandable.
Although the average productivity per crop or product is assumed, further detailed investigations should be made using marginal productivity of water with respect to nutritional outputs for each component. For example a decrease in mass may not lead to a similar decrease in nutritional outputs and vice versa.
3.2. Water requirements
The estimates of water productivity refer to values of crop yield and water consumption measured or assessed in California. This agricultural domain is considered one of the more productive in the world. Therefore, figures for yields must be considered, in most cases, as representative of the practical maximum sophisticated infrastructure. Other inputs also do not generally limit yield. Water productivity in this region is not necessarily representative of a situation where water is more scarce however. It might be more representative of a standard situation with a good irrigation system. Results are derived from a database and a spreadsheet model built in 1993 (Barthelemy, 1993). The Reference Evapotranspiration is estimated using the FAO `CROPWAT' program (FAO, 1993) and planting dates and crop coefficients from the University of California Cooperative Extension Leaflets (Snyder et al., 1989). Estimates were made for crops which were planted on more than 5% of each county's total area. The state average for each crop was estimated from the county values. For crops not grown in California, water consumption was estimated as if they were grown in the state. Maximum yield estimates were found in California (California Agricultural Statistics Source, 1991a, 1991b, 1992)
and US statistics (US Department of Commerce, Bureau of Census, 1989) publications. For animal products, water consumption for each end product, has been computed considering each feed component entering the diet during the different stages of the life cycle of the animal (Barthelemy, 1993). Water productivity (kg/m3) is computed first for each feed component, including irrigated pasture, rangeland, hay, by-product and cereals. Then all the water consumed in feed and direct consumption during the life cycle of the animal is added. This completes the first step of estimating the water requirements which, along with the yield, allow the evaluation of the water productivity in kg/m3or the water requirements in m3/kg. Water productivity in kg/m3for each product and food category is given in Tables 1 and 2.
4. Nutritional water productivity
4.1. Model
Nutritional water productivity is:
NWP Ya
ETa
NP (5)
where NWP is the nutritional water productivity (nutrition unit/m3of water),Yathe actual harvested yield (kg/ha), Etathe actual evapotranspiration (m3/ha), and NP is the nutrition content per kg of product (nutrition unit/kg).
In estimating NWP, one source of uncertainty is the ratio yield per water consumed (Ya/ ETa). Another source of uncertainty is the nutrition content of the product (NP) in which there are significant deviations between data sets. For example the energy content of cereals varies from 2700 kcal/kg (FAO Balance sheets, 1995) to 3500 kcal/kg (Dunne, 1990) for the US. Part of the variation is explained by differences in processing (raw product, partially processed, after cooking). Unfortunately most values reported in the literature are given without any clear specification of level of processing. To overcome this inconsistency relative nutrition values and relative water savings generated by a change of diet are used to study policy changes. The values used in the FAO Balance Sheets are typically 20% lower than those published by Dunne (1990). One possible reason is that the FAO data set accounts for losses between the raw product and the consumed product.
To be consistent, the California agricultural context used the same data source for production, diet and nutrition (FAO, 1998). For components not incorporated in the FAO database (calcium, iron and Vitamin A) we used values from Dunne (1990), multiplied by the same correcting factor (0.8) linking the two data sets (energy). Meat productivity is the average nutritional value considering different parts of the carcass.
4.2. Energy
Energy (kcal/m3) productivity is given in Table 3 and displayed in Fig. 1 for the main food products usually considered in the FAO balance sheets. It is not surprising that the
Table 1
Crop evapotranspiration, yield, water use ef®ciency estimates for Californiaa
Crops Estimates for
Water use efficiency (WUE) California estimates versus other for WUE
Rice 1200 8.5 6±8 6.7±7.8 Same 0.71 0.7±1 0.94 Same
Maize 696 9.8 6±9 9.5 6.6±10 Same 1.41 0.8±1.6 1.44 1.20 Same
Roots
Potatoes 425 40.4 15±35 25 27±30 HIGHER 9.51 4±7 10.00 6.40 HIGHER except
for BRLd
Sugar beet 1112 57.6 40±60 60 Same 5.18 6±9 SLIGHTLY LOWER
Other
Cotton 873 2.2 4±5 3.2 LOWER 0.25 0.4±0.6 0.50 LOWER
Sugarcane 2491 97.4 50±150 107±120 Same 3.91 5±8 6.50 LOWER
Soybean 803 2.6 1.5±2.5 3.25 2.8±3.0 Same 0.32 .4 to .7 0.76 0.90 LOWER
Beans 548 2.7 1.5±2 2.5 1.2±1.5 HIGHER 0.59 0.3±0.6 0.89 0.60 Same than FAO
Vegetables
Tomatoes 622 47.8 45±65 60 Same 7.69 10±12 13.13 LOWER
Onions 711 49.2 35±45 44 30±40 HIGHER 6.94 8±10 9.30 12.00 LOWER
Fruit and Nut
Orange 973 25.7 25±40 30 Same 2.65 2±5 Same
Lemon 973 28.3 25±40 30 Same 2.91 2±5 Same
Grapefruit 935 32.6 25±40 30 Same 3.49 2±5 Same
Apples 1037 26.8 27 Same 2.58 2.40 Same
Grapes 850 18.7 15±30 18 11±19 Same 2.20 2±4 6.00 3.30 Same than FAO lower
than IWMI
Banana 1597 32.0 40±60 Same 2.00 2.5±4 LOWER
Groundnut 655 2.6 3.5±4.5 3.5±4.7 LOWER 0.39 0.6±0.8 LOWER
Forages
Alfalfa (dry) 1238 13.7 13 Same 1.11 1.5 to 2 1.59 LOWER
Maize silage (green)
696 50.4 7.24
Small grain hay(dry)
606 5.1 0.84
Irrig. Pasture (dry)
1244 9.0 0.72
Rangeland 1244 2.2 0.72
aFAO 33 after Doorenbos.
bBRL: Data recorded in the South-east of France (BRL, 1985).
energy productivity of animals is low (between 100 kcal/m3 for bovine meat to about 400 kcal/m3 for pork meat and 660 kcal/m3 for milk) and conversely cereals are high (from 2300 kcal/m3for wheat to 3900 for maize). Potatoes (5600 kcal/m3) are the most productive.
If a person requires an average of 2700 kcal/day then maize and potatoes cover the daily needs with much less than 1 m3per capita daily. Wheat, rice, sugarbeet, groundnut and onions require little more than 1 m3to produce the daily energy requirement.
4.3. Protein
Estimated protein productivity is given in Table 3 and displayed in Fig. 2. It is no surprise that the meat group is more productive in protein than in energy. It ranges from 10 g/m3for bovine meat, i.e. 13% of the daily requirements (75 g of protein), to about 40 g/m3for egg and milk, i.e. 53% of the daily requirements. Potatoes again appear to be by far the most productive protein source (150 g/m3). It supplies the daily protein requirements with only 0.5 m3of water. Wheat, maize, pulses, groundnut and vegetables including tomatoes, onion and others supply the daily requirement using less than one cubic meter of water. Rice is lower than wheat in protein (49 g/m3) and is equivalent to eggs and milk.
4.4. Calcium
The situation for calcium productivity is quite different from the previous metrics (Fig. 3). Onions (1673 mg/m3) produce by far the most calcium per unit of water used, twice the daily need of 800 mg/m3. There are other vegetables such as cabbage, cauliflower and leeks, which exceed 1500 mg/m3(not shown in Fig. 3). One product high in calcium is milk (1233 mg/m3) and all the derived milk products are high in calcium per unit of water used.
4.5. Fat
There are no recommendations for fat as a whole, although one can find specific recommendations for some particular lipid components. For example Dunne
Table 2
Water requirements per kg and per type of food product (reference to California)
Type of food product Water requirement (m3/kg)
Vegetables 0.15
Cereals 0.7±1.4
Fat products 11±18
Fruits 0.45
Nuts 2.5±4.8
Milk 0.8
Poultry and Pork 4.3
Bovine meat 13.5
Table 3
Nutrient content (NP) and nutritional water productivity (NWP) for main food products
Product Water inputs per kg prod (l/kg)
Productivity (kg/m3)
Nutrition entry tablea Nutritional productivity
Outputs per kg product Nutrional Ouputs per water m3
Cal
Wheat 1159 0.863 2641 86 10 324 2279 74 9 279
Rice 1408 0.710 2800 69 7 186 1989 49 5 132
Maize 710 1.408 2738 55 12 44 3856 77 17 63
Potatoes 105 9.524 591 16 1 57 5626 150 9 543
Sugar beet 1408 0.710 3548 0 0 808 2520 0 0 574
Pulses (beans) 2860 0.350 3397 218 12 1353 1188 76 4 473
Treenut 4768 0.210 2482 66 215 377 521 14 45 79
Groundnut 2547 0.393 6067 283 526 753 2382 111 206 296
Soybean oil 15240 0.066 8337 0 939 7 547 0 62 0
Cotton seed oil 11542 0.087 8320 0 936 0 721 0 81 0
Tomatoes 130 7.692 184 8 1 26 1416 65 11 200
Onions 147 6.826 331 12 0 245 2259 85 0 1673
Orange 378 2.646 250 5 0 210 663 13 0 556
Bovine meat 13500 0.074 1376 135 89 39 102 10 7 3
Pork meat 4600 0.217 1879 97 162 33 408 21 35 7
Poultry meat 4100 0.244 1354 135 86 59 330 33 21 14
Eggs 2700 0.370 1402 110 98 448 519 41 36 166
Milk 790 1.266 521 32 30 974 659 40 38 1233
Butter 18000 0.056 7280 13 816 191 404 1 45 11
aNutritional contents are taken from FAO Balance Sheets (USA 1995) for Energy, protein and fat and from Dunne (1990) for calcium (with a correcting factor).
Fig.
1.
W
ater
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for
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Kcal/m
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for
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Fig.
2.
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(1990) recommends that linoleic acid should provide about 2% of the total energy and mentions that nutritionists suggest that an intake of fat providing 25±30% of the energy is compatible with good health. As a whole in developed countries there is no deficit in fat intake but rather it seems that fat intake is far too high in many developed countries.
4.6. Vitamin A
Deficiency in Vitamin A is considered one of the major causes of malnutrition. It leads to severe vision problems and blindness (Pellet, 1989) in hundreds of thousands of children worldwide. Therefore, a systematic check of the Vitamin A content has been made in all the investigated diets.
Vitamin A is measured in international units (IU) and the recommended daily intake for adults is 4±5 kIU/day (kIU1000 IU). Two major sources of Vitamin A are vegetables, in particular carrots (280 kIU/kg), sweet potatoes (200 kIU/kg) and onions (50 kIU/kg), and animal livers, ranking from 200 kIU/kg for poultry to 350 kIU/kg for beef liver and 500 kIU/kg for lamb. The productivity of water for Vitamin A has been analyzed only for significant products for which data were available. It shows that productivity ranks from 26 to 49 kIU/m3, respectively for beef and poultry liver, to 340 kIU/m3for onion and 1440 kIU/m3for carrots.
4.7. Iron
Iron is vital for the production of hemoglobin, the vehicle for oxygen transport. Deficiency in iron leads to anemia; women are much more sensitive to iron deficiency than men. Leslie (1995) stated that iron deficiency is `the most widespread nutritional problem among women.' As a consequence, the recommendations for iron are higher for women (18 mg/day) than for men (10 mg/day).
An average of 15 mg/day has been considered as the requirement in this study. Iron is found mostly in vegetables and in animal livers. Considering the water productivity for iron, it was found that potatoes provided (57 mg/m3), vegetables (25±36 mg/m3); cereals (20±30 mg/m3), liver poultry (20 mg/m3). These were the main iron sources and diets optimized for the other factors were adjusted if necessary to reach at least the minimum requirements.
5. Diets and water requirements
In this section we consider different diets and estimate the water requirements to produce the corresponding food. As mentioned above estimates are based on California crop yields and water productivity, and the diet reported for USA is considered as the reference.
5.1. Diet 0: USA reference
The data used for the analysis correspond to the main components of the diet recorded in USA for 1995 (FAO Balance Sheets, 1998). They include six animal products and 24 vegetal products. Sea and fish products, which contribute 6% of the protein availability, and alcoholic beverages (beer, wine) which provide 6% of the total energy are not included in the computation of water requirements.
As mentioned above, the FAO estimates of food availability discount for losses in the storage, transportation, delivery and cooking. To estimate the carrying capacity of the planet one needs to be aware of the difference between nutrition production from raw product versus that realized by humans. However, the relative values and the relative water savings that might be generated by a change of diet are instructive in guiding policy changes.
Food intake per capita in USA categorized by food type and with the corresponding relative water inputs are given in Table 4. The total water requirements to produce the food is estimated to be 5.4 m3 per capita per day with nearly half required for meat (46%). The reference values for nutrients per day (not considering sea, fish and alcoholic products) are 3400 kcal of energy, 104 g of protein, 146 g of fat, 960 mg of calcium, 5 kIU of Vitamin A and 17 mg of iron. Unless specified otherwise, the water requirements for each simulated diet presented below achieves at least the same values as the reference diet for energy, protein, calcium, Vitamin A and iron. The fat intake is allowed to fluctuate provided it is greater than the value recorded for Japan (80 g/day) which has the lowest fat intake within the developed countries.
5.2. Diet 1: Animal products reduced by 25% and replaced by vegetal products
This scenario corresponds to a significant reduction of all animal products (milk-eggs-meat) by 25%, and their replacement by an increase in highly nutritious vegetal products. The water required for this diet falls to 4.6 m3/day.
5.3. Diet 2: 50% beef replaced by poultry together with an adjustment of vegetal products
In this scenario, poultry replaces 50% of the beef required for the protein and energy needs. The water required for this diet is estimated to be 4.8 m3/day.
5.4. Diet 3: 50% red meat replaced by vegetal products
In this scenario, vegetal products (potatoes and groundnuts) replace 50% of red meat (beef and pork). Sugar intake is slightly reduced to match the target level for energy. The water required for this diet is estimated to be 4.4 m3/day.
5.5. Diet 4: Animal products reduced by 50% and replaced by vegetal products
This scenario corresponds to an important reduction of all animals products by 50% and their replacement by highly nutritious vegetal products (potatoes, groundnuts and onions). A further reduction of oil products is made to reduce the energy intake to the target value. The water required for this diet is 3.4 m3/day.
5.6. Diet 5: Vegetarian
In this scenario, we consider a vegetarian diet, with suppression of all meat. Eggs and butter components are maintained as in Diet 0. Milk is reduced to 70% of Diet 0. Balance is obtained by increasing the highly nutritious vegetal products. The estimated water requirement falls to 2.6 m3/day.
Table 4
Food intake for the reference Diet 0 corresponding to the food consumption in the USA in 1995
Product Annual consumption (kg) Fraction of water budget (%)
Vegetables 178 2
Fruits 121 2.5
Cereals 113 6.5
Sugar products 67 8
Milk eggs and butter 277 18
Oil 29 17
Meat 117 46
5.7. Diet 6: Survival
This scenario explores an extreme diet, based only on the most productive products for each nutrient considered. Only four products are necessary to achieve the targeted intakes for energy, protein, fat, calcium and Vitamin A. They are potatoes, groundnut, onions and carrots. The goal here is to bound the domain of water savings by defining an absolute minimum water requirement given biological needs. For several reasons, this diet is not at all realistic. It is certainly not sufficiently diverse or as nutrient rich as the other six con-sidered. It also implies that large quantities of the same product would be consumed. This would be quite difficult to implement. For example the quantities of potatoes and onions per day are estimated to be 2 kg. However, further progresses in food processing can be expected, and we cannot discard the possibility of future improvements in extracting nutrients from current products. This diet requires a modest 1.0 m3of water per day.
The above diets (1±6) define the range of water requirements for food and the water savings that can be generated by a change in food consumption. It is somehow reassuring to know that there is a high potential for water savings between the two opposite diets (0 and 6). Diet 0 is the rich diet whereas Diet 6 is the extreme opposite which still meets the nutrition targets. Intermediate solutions include reducing some known excesses in current diets such as a diminution of sugar and vegetable oil by 50% in Diet 0 will save 650 l per day per capita. Daily water requirements per capita are summarized in Table 5 along with the gain in water productivity resulting from a change in diet from Diet 0.
6. Nutritional water productivity and population
The challenge for feeding the population in the coming century is to find a balance between the growth of the population, the evolution of diets and the likely availability of water resources.
6.1. Population growth
Optimistically we assume it is more likely that the population will follow the lower scenario of the well known United Nations projections for the year 2025 (from 7.6±9.4
Table 5
Per capita productivity of water (reference to California)
Type of DIET Water requirements
m3-day person
Increase in water productivity from Diet 0 (%)
Diet 0 reference diet 5.40 0
Diet 1 25% reduction of animal product 4.60 17 Diet 2 Poultry replaces 50% beef 4.80 11 Diet 3 Vegetal products replaces 50% red meat 4.40 22 Diet 4 50% reduction of animal product 3.40 59
Diet 5 Vegetarian 2.60 103
Diet 6 Survival 1.00 440
billions). In the following we assume that world population will increase during the next 30 years by about 33% from 5.7 billions in 1995 (FAO data for year 1995) to some 7.60 billions in 2025. Population in developed countries was 1.29 billion in 1995 and is likely to reach 1.45 billion in 2025. The remaining world population will increase from 4.4 billion in 1995 to 6.16 billion in 2025.
6.2. Diet changes
In the developed countries diets are rich or even excessive while in the developing countries diets are fair or poor with sometimes important specific deficiencies, e.g. low calcium intake. Various scenario of diets and intensiveness in the agricultural production sector have been investigated on a regional basis by Penning de Vries et al. (1995). They came to the conclusion that to relax the stress on food and on environment at the horizon 2040, some changes in diets, i.e. less affluent, are desirable in many developed countries.
Alleviating malnutrition in developing countries will require an increase in the food intake. Furthermore, economic growth may also create an increase in the demand for high-input food products as forecasted by Brown (1995) for China. Therefore, reducing the wide gap between actual and maximum yields in developing countries is absolutely crucial to meet the increase of the food supply requirements.
6.3. Water requirements
Using the same values of water productivity and yield for California, the daily per capita water requirements in developed countries is estimated at 4 m3, in sharp contrast to water requirements in developing countries of 1.3 m3. However, water productivity recorded in California might not be appropriate for the developing countries where yield and productivity are known to be lower. To take that effect into account we consider the ratio of average yield for cereals in developing and in developed countries (2400 and 3300 kg/ha). If the ratio is applied, the water requirement for developing countries increases from 1.3 to 1.8 m3per day per capita.
The global water requirement estimate for 1995 is 13.1 billion m3/day (4790 km3/year) and the projected need for 2025 is 16.9 billion m3/day (6190 km3/year). Without any change in productivity and diets, the additional water needed to supply food is estimated to be 3.8 billion m3/day (1400 km3/year), which represents an increase of 29% above 1995 requirements.
6.4. Global water demand and diet
Changes in developed countries diets from high-input to low-input foods might significantly affect the world water balance. Table 6 contains estimates of water savings and the contribution of these savings to meet the increases in global water demand by the year 2025. Approximately 13% of the increase in water demand is met when poultry replaces 50% of the beef meat and 81% is met for a change to the vegetarian diet, and even more for the survival diet (not shown).
These estimates for the first time present a quantitative framework for a global debate on water policy related to nutrition and population. How realistic are these scenarios? For many social, political and religious reasons the vegetarian scenario may not be desirable nor realistic. Substituting vegetables for 50% red meat and 50% reduction of all animal product intakes, scenarios 3 and 4, respectively, seems to be more practical in the long term. This generates a 23±39% of the additional water requirements by 2025.
Its is noteworthy to acknowledge that some of the changes in diet are already under way in developed countries. It is estimated that water requirements for food have dropped between 1990 (4.4 m3/day/capita) and 1995 (4. m3/day/capita). This corresponded to a global reduction in meat consumption and for a short period (5 years) a reduction of the total intake; energy intake fell 4% and protein intake by 3%. Increasing awareness of the relationship between health and diet played a central role. The consumption of meat in the developed countries increased steadily to 78 kg/capita/year in 1990, more likely due to the growth of income and productivity gains, but thereafter the trend reversed and the latest data available (1996) shows a significant decrease to 72 kg/capita/year. The downward trend for developed countries may continue.
The second change in diet is the replacement of beef and pork with poultry. Red meat consumption peaked in the 1970s, and significantly decreased after 1990 as shown in Fig. 4. For France, the break point started earlier in 1980. In developed countries, the decrease of red meat is partially compensated by a continuing growth of poultry consumption. Thus the current trend corresponds to a scenario similar to Diet 2, which might ultimately generate 13% of the additional water requirements by 2025. Therefore, it is realistic to think that greater awareness of consumers in developed countries of water resource requirements to produce food, and also a more strict adherence to the real cost of water might reinforce the current trend and lead to further savings.
Table 6
Impact of diet change in developed countries on water availability in 2025
DIET in developed
25% reduction of animal product (309)
Diet 2 3.7 0.50 13
Poultry replaces 50% beef (182)
Diet 3 3.40 0.88 23
Vegetal products replaces 50% red meat (320)
Diet 4 3.00 1.5 39
50% reduction of animal product (545)
Diet 5 1.90 3.10 81
Vegetarian (1130)
The possibility of switching from one product to another is driven by site specific agriculture conditions. It might be possible to convert some agriculture lands from forage to cereals or vegetables for human consumption but impossible to convert mountain pasture to a vegetable production system. Animal products and particularly milk are essential particularly as a major source of calcium. In contrast confinement animal agriculture for these contexts might not be appropriate and might even be harmful for the environment in the long term.
The battle for water in the next century will be won on many fronts, such as improving the efficiency and reliability of water delivery systems, minimizing non-beneficial water use, optimizing the gap between actual and maximum yield, and, as suggested herein, improving nutritional water productivity. The enormous advantages of water savings via changes in diet are that production, medical, and environmental costs are reduced. Therefore, it would be wise to promote water saving by increasing the awareness of consumers of the true cost of water in food products.
Acknowledgements
The study owes much to F. Barthelemy (Ms.C student from ENGREF France in 1993) who contributed to the earlier phases and developed the water consumption model for crop and animal products. The authors are also thankful to David Seckler for his helpful comments at various stages of the writing.
References
Bailey, R., 1990. Irrigated Crops and Their Management. Farming Press Books, Ipswich, UK, 192 pp. Barthelemy, F.D., 1993. Water for a sustainable human nutrition: inputs and resources analysis in arid areas. MS
Thesis. Ecole Nationale du GeÂnie Rural, des Eaux et des ForeÃts, Stage de ®n d'eÂtudes, Paris, France, 120 pp (unpubl.).
Brown, L.R., 1995. Who will feed China: Wake-up Call for a Small planet. W.W. Norton & Company. 163 pp. BRL Memo d'irrigation, 1985. Technical lea¯ets for irrigation, Compagnie Nationale du Bas Rhone et du
Languedoc, 685 Route d'Arles BP 4001 Nimes France.
Carruthers, I.M., Rosegrant, W., Seckler, D., 1997. Irrigation and food security in the 21st century. Irrig. Drainage Syst. 11, 83.
Chambers, R. 1985. Food and water as if poor people mattered: a professional revolution in water and water policy in world food supplies. Proceedings of the Conference, Texas A & M University, College Station, May 26±30.
DeTar, W., Browne, G.T., Phene, C.J., Sanden, B.L., 1996. Real-time irrigation scheduling of potatoes with sprinkler and subsurface drip systems. In: Camp, C.R., Sadler, E.J., Yoder, R.E. (Eds.), Evapotranspiration and Irrigation Scheduling, pp. 812±824. Proceedings of the International Conference, November 3±6, 1996, San Antonio Convention Center, San Antonio, TX, St. Joseph, MI, ASAE.
Doorenbos, J., Kassam, A.H., 1979. Yield response to water. Food and Agriculture Organization, Irrigation and Drainage Paper 33, Rome, Italy pp. 1±193.
Dunne, J.L., 1990. Nutrition Almanac, 3rd Edition. McGraw-Hill, New York, pp. 120±125. FAO Balance Sheets. 1998. www.fao.org.
Feddes, R.A., 1988. Modeling and simulation in hydrologic systems related to agricultural development: state of the art. Agric. Wat. Manage. 13, 235±248.
Gregory, P.J., 1991. Concepts of water use ef®ciency. In: Harris, H.C., Cooper, P.J.M., Pala, M. (Eds.), Soils and Crop Management for Improved Water Use Ef®ciency in Rainfed Areas, pp. 9±20. Proceedings of an International Workshop, May 15±19, 1989, Ankara, Turkey. Aleppo, Syria.
Islam, N., 1995. Population and Food in the Early Twenty-First Century: Meeting Future Food Demand of an Increasing Population. International Food Policy Research Institute, Washington, DC, pp 1±239. Leslie, J., 1995. Improving the nutrition of women in the third world, child growth and nutrition In: Andersen
et al. (Eds.), Developing Countries: Priorities For Action, Pinstrup. Cornell University Press, Ithaca, New York, 1995, pp. 1±447.
Maozheng, Y., Wang, H., 1992. A study of water use ef®ciency of winter wheat in the north china plain. In: Shalhevet, J., Liu, C., Xu, Y. (Eds.), Water Use Ef®ciency in Agriculture. Priel Publishers, Rehovot, Israel, pp.1±297.
Molden, D., 1997. Accounting for water use and productivity, SWIM Part 1, International Water Management Institute, Colombo, Sri Lanka.
Molden, D., Sakthivadivel, R., Perry, C.J., de Fraiture, C., Koezen, W.H., 1998. Indicators for comparing performance of irrigated agricultural systems. Research Report 20. International Water Management Institute, Colombo, Sri Lanka.
Pellet, P.L., 1989. Nutrition, health, and agricultural development. In: Clubb, D., Ligon, P.C., (Eds.), Food, Hunger, and Agricultural Issues Nutrition, Health, and Agricultural Development. Winrock International Institute for Agricultural Development, Morrilton, AR, 240 pp.
Penning de Vries, F.W.T., Van Keulen, H., Rabbinge, R., 1995. Natural resources and limits of food production in 2040. In: Bouma, J. et al. (Eds.), Eco-regional Approaches For Sustainable Land Use and Food Production. Kluwer, Dortrecht, The Netherlands, pp. 65±87.
Shalhevet, J., Liu, C., Xu, Y., (Eds.) 1992. Water use ef®ciency in agriculture. Proceedings of the Binational China-Israel Workshop, Beijing, China, 22±26 April 1991 Priel Publishers, Rehovot, Israel, 297 pp.
Seckler, D., 1996. The new era of water resources management: from `dry' to `wet' water savings. Research Report 1. International Water Management Institute, Colombo, Sri Lanka.
Stanhill, G., 1992. Water Use Ef®ciency. In: Shalhevet, J. et al. (Eds), Agriculture. Priel Publishers, Rehovot, Israel, 1992, pp. 1±297.
Stone, J., 1975. Plant Modi®cation For More Ef®cient Water Use. Elsevier, Amsterdam, The Netherlands, 320 pp.
Sundar, A., Rao, P.S., 1984. Productivity and equity in irrigation tanks. In: Pant, N. (Ed.), Productivity and Equity In Irrigation Systems. Ashish Publishing House, New Delhi, India, pp. 163±177.
Tinus, R.W., 1975. Impact of CO2requirement on plant water use. In: Stone, J. (Ed.), Plant Modi®cation For More Ef®cient Water Use. Elsevier, Amsterdam, The Netherlands pp. 1±320.
Young, C.A., Wallender, W.W., 1999. High resolution irrigation district hydrology balance: 1. water balance. J. Irrig. Drain. Eng.
