1.74 | Fall 2020 | Graduate

Land, Water, Food, and Climate

SECTION 2 | Food and Natural Resources: Demand and Supply, Current and Projected

S5. Food and Natural Resource Demands

Food Energy and Protein Demands

The following calculations provide estimates of the 2050 food energy and protein demands for the globe and for East Africa, based on data from FAOSTAT and the assumptions listed below.

Global food demand is of interest because a necessary (but not sufficient) condition for universal food security is that the global supply of food energy and protein must meet the global demand. If this condition is not met some portion of the global population will not have adequate nutrition. Of course, some groups may not have adequate nutrition due to an uneven distribution of supply, even if the global supply exceeds the global demand. That has been the case in the recent past, as illustrated by plots in S4.

East African food demand is of particular interest because this region has an unusually high rate of population growth as well as widespread undernutrition. Taken together, these two factors require an especially large increase over current values in the food energy and protein needed to provide adequate nutrition to the entire population. In regional analyses such as the one done here for East Africa the estimated 2050 energy and protein demands could be supplied by a mix of locally grown food and imports.

The calculations given below for the globe and East Africa are expressed in terms of the ratio of demand in 2050 to the demand in 2010, which serves as a baseline date. The following assumptions are made:

  • The population growth ratios are based on the median UN estimates for 2010 and 2050:

Global = 9.6 109/ 6.9 109 = 1.4                       (persons)
East Africa = 0.9 109/0.35 109 = 2.6               (persons)

  • Energy and protein growth ratios are based on increasing 2050 per capita consumption levels to those reported in 2010 for a typical southern European diet:

                   Global energy= 3300/2900 =  1.15                      (Kcal person-1 day-1)
                   East Africa energy = 3300/2100 = 1.6                 (Kcal person-1 day-1)
                   Global protein= 105/80  = 1.3                             (g person-1 day-1)
                   East Africa protein = 105/60 = 1.8                      (g person-1 day-1)

  • The global food loss ratio is assumed to be 0.9, reflecting a significant decrease in food waste, primarily at the consumer end. The East Africa food loss ratio is also assumed to be 0.9, primarily reflecting a decrease in food loss at the producer end. These food loss figures are just illustrative and are difficult to predict.

The expressions for the increases in energy and protein are:

Global demand:
  2050 Energy =  (2010 Energy) (Pop Δ) (Calorie Δ) (Loss Δ)
     1.5                          1               1.4          1.15          0.9
  2050 Protein  =  (2010 Protein) (Pop Δ ) (Protein Δ) (Loss Δ)
     1.7                          1               1.4          1.3            0.9

East Africa demand:
  2050 Energy  =  (2010 Energy) (Pop Δ) (Calorie Δ) (Loss Δ)
     3.7                          1                2.6          1.6            0.9
  2050 Protein  =  (2010 Protein) (Pop Δ ) (Protein Δ) (Loss Δ)
     4.2                          1                 2.6          1.8           0.9

These simple calculations reveal the relative roles played by population growth and diet and also show the difference between global and East African conditions. The increase in global food demand is a significant concern but the very large increase in East African demand presents a major challenge for the region. It is also consistent with the UN’s prediction that most of the global increase in food demand will occur in developing countries in Africa and parts of Asia, where population growth will be high and diets need to be improved to provide adequate nutrition. This conclusion can be investigated further with analyses similar to the one presented above by comparing average growth rates for two groups: all developed countries vs. all developing countries.

Natural Resources Required to Meet Food Demands with a Given Technology

The resource demands implied by the above food demand estimates depend on 1) the mix of crops included in the diet, 2) their nutritional (e.g. energy and protein) content and 3) a number of technological factors that determine how much land, water, and nutrients are needed to meet specified energy and protein demands. The following expressions give the land area, water volume, and mass (dry weight) of a particular nutrient (e.g. reactive nitrogen) needed to grow a given mass (dry weight) of a particular grain crop:

\begin{eqnarray*} Land(m^2) = \frac{Production(kgG)}{Yield(kgG \;m^{-2})} \end{eqnarray*} \begin{eqnarray*} Water(mW^3) = \frac{Production(kgG)}{HI(kgG \;kgB^{-1})WUE(kgB \;mW^{-3})} \end{eqnarray*} \begin{eqnarray*} Nutrient(kgN) = \frac{Production(kgG)}{HI(kgG \;kgB^{-1})NUE(kgB \;kgN^{-1})} \end{eqnarray*}

\(Yield =\) crop yield \(= kg\) grain dry weight harvested per \(m^2\) of cropland
\(HI =\) crop harvest index \(= kg\) grain dry weight harvested per \(kg\) plant biomass dry weight
\(WUE =\) water use efficiency \(= kg\) total plant biomass dry weight produced per \(m^3\)water applied to the field
\(NUE =\) nutrient use efficiency \(= kg\) total plant biomass dry weight produced per \(kg\) nutrient dry weight applied to the field

These are macroscopic relationships that do not account, for example, for temporal differences in plant water or nutrient requirements over the season. However, they do show that resource requirements depend not only on the production required but also on various input efficiencies that depend on management practices and technology, such as the method and schedule used to apply water or nutrients to the field. In most applications of these efficiency relationships the production value is the mass of crop harvested after losses to pests. If pest losses can be reduced the production increases and the yield and other efficiency factors increase proportionately. Care should be taken to confirm units and calculation assumptions when using the efficiencies introduced above, since definitions vary.

To explore the consequences of these relationships, suppose that :

  1. The yields, harvest indices, and water and nutrient efficiencies in the above resource requirement expressions remain fixed (indicating current management practices and technology apply)
  2. Production of each crop in the average diet increases equally to meet the 1.5X increase in global calorie demand estimated earlier.

Then we will require an increase of 1.5X in the land, water, and nutrients needed for agriculture to meet caloric requirements. A similar calculation applies for protein. The readings from Classes 3 and 4 suggest that such large increases in land and water inputs are not likely. This implies that we will need to raise crop yields and efficiencies to meet demand. We consider this challenge further in Sections 3 and 4.

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