Food production as a system

A systems approach examines a system's components and the flows that connect them. Applied to food production, it shows which resources go into producing food and what losses occur along the way.

• Inputs enter the system: sunlight, rainfall, irrigation water, feed, fertilizers, fuel and labour.
• Stores hold resources: soil moisture, soil nutrients, crops, livestock and stored feed.
• Transfers move resources between components: irrigation water enters soil, plants take up water, and harvested feed goes to livestock.
• Outputs leave the system: harvested food, exported manure, wastewater, emissions and heat losses.

Comparing energy efficiency

Energy efficiency compares useful energy output with energy input. For food production, one way to express it is to divide the energy contained in edible output by the energy invested in producing it. A higher ratio indicates greater efficiency under the chosen accounting method.

Mechanized production may use substantial amounts of fuel and electricity for pumping, as well as energy to manufacture fertilizers. Heating greenhouses adds another major input. High yields alone don't show high energy efficiency. The output has to be compared with the energy needed to obtain it.

Livestock convert feed into animal products. Much of that feed energy, though, supports movement, body maintenance and respiration instead of becoming edible output. When humans eat suitable crops directly, they generally avoid this conversion loss. Grazing animals can still use vegetation on land unsuitable for cropping, so the local setting matters.

Use consistent boundaries and units when comparing systems. Edible energy output per unit of purchased energy answers a different question from kilograms of food per hectare. Comparisons must also be consistent about whether they include sunlight, feed production, transport and processing.

Comparing water footprints

A water footprint measures the freshwater consumed or polluted in producing a product. It includes water used indirectly through the product's inputs and is commonly expressed as a volume per unit of food produced.

Three components help explain why footprints differ between places:

• Green water is rainwater stored in soil and used by plants.
• Blue water is surface water or groundwater consumed, for example through irrigation.
• Grey water is the calculated volume needed to dilute pollutants to an agreed water-quality standard; it is not necessarily water actually withdrawn.

Climate, growing-season length, yield, irrigation and pollution all affect a crop's footprint. Hot, dry conditions can raise irrigation demand. Low yields spread water consumption over a smaller harvest. For animal products, the footprint also includes the water used to grow their feed.

Relative sustainability in different places

Sustainability means maintaining production over time without undermining the resources and conditions it depends on. Using resources efficiently contributes to sustainability, but doesn't establish it on its own.

Consider the same vegetable grown outdoors in a dry region and in a heated greenhouse in a cool region. The outdoor crop may need more scarce irrigation water. Growing it in the greenhouse may require more energy for heating. Neither system is automatically more sustainable.

A systems approach exposes these trade-offs and helps identify changes that could reduce resource use or losses. But a simple total can hide local consequences: consuming groundwater from a depleted aquifer is not equivalent to using rainfall in a water-abundant place. Relative sustainability also depends on soil condition, pollution, affordability and whether production can continue without exhausting essential stores.

Consumption is more than food availability

Food consumption is the quantity and types of food people eat. It differs between countries, within them and from one household to another. It also changes with the seasons or over longer periods.

Food supplies place some limits on consumption. But people must also be able to obtain and afford food, and choose to eat it. Even in a country with plentiful supplies, some households eat too little or have diets with little variety.

Physical processes

Climate, soils and water availability affect which crops and livestock people can produce locally. They also help shape traditional diets, particularly where households rely heavily on their own production or nearby markets.

Supplies fluctuate with the seasons. Before the next harvest, food stocks may run low, leaving households with smaller meals or less dietary variety. Drought can reduce crop yields and pasture productivity. Floods can destroy crops and stored food, as well as transport routes. When supply falls, prices can rise, changing what people eat even if they do not farm.

Trade, storage and irrigation can weaken the link between local conditions and local diets. The effects of physical constraints therefore vary according to a place's infrastructure and purchasing power.

Human processes

Human processes affect how much people eat and what their diets contain:

• Income and prices: as incomes rise, people can often afford more varied diets and consume more animal products. If food prices rise faster than incomes, households may cut portions or switch from expensive foods to cheaper staples.
• Urbanization and employment: urban consumers rely more on purchased food. Working hours and commuting, along with access to shops, can increase demand for convenient or prepared meals.
• Culture and religion: customary foods and religious restrictions, as well as preferences, shape what people eat even when alternatives are available.
• Trade and retail change: imports and refrigeration, together with supermarket networks, make a broader range of foods available beyond local harvests and seasons.
• Conflict and political decisions: insecurity can disrupt farming and deliveries. Subsidies, taxes and food assistance affect how affordable food is.
• Household circumstances: age, activity and health affect individual consumption, as does the way food is distributed within a household. Household averages can hide unequal access.

How factors interact across space and time

The same drought can change consumption differently from place to place. A well-connected city may replace lost domestic supplies with imports, though prices may rise. For an isolated farming household, losing both its harvest and its income may sharply reduce its ability to obtain food.

Diets can change over time as incomes grow, people migrate and retail systems change. Not everyone experiences these changes in the same way: wealthier households may diversify what they eat while poorer households remain dependent on a narrow range of staples. National averages can therefore hide important regional and social differences.

What diffusion involves

Diffusion is the spread of an innovation, characteristic or disease through space and over time. How it spreads depends on the connections between places, the contact people have with one another and the conditions at the destination.

New seed varieties, irrigation methods and cultivation practices are agricultural innovations. Awareness alone won't make them spread: farmers must be able and willing to use them. For disease diffusion, a pathogen must move, and conditions must allow transmission.

Adoption, expansion and relocation

Adoption/acquisition refers to the uptake of an innovation or the acquisition of an infection. This happens at an individual or local level; these events build into a wider diffusion pattern.

A farmer might adopt a water-saving technique after seeing a demonstration. If neighbours copy it, expansion diffusion follows. A migrating farmer who introduces the same technique elsewhere produces relocation diffusion. But adoption isn't guaranteed. Local soils may make the technique unsuitable, or it may cost too much.

Disease can spread outward locally through contacts or shared exposure. An infected traveller may carry a pathogen to a distant place; further transmission there may establish another focus. Arrival doesn't guarantee spread, though. A vector-borne infection may fail to circulate if its vector is absent.

Connections and the rate of spread

Busy transport routes and well-connected settlements often allow faster diffusion than equally distant areas with poor connections. Agricultural information may reach commercial farms with strong advisory and market links first, before spreading to less-connected farmers. Similarly, disease can move rapidly between transport hubs before it reaches nearby rural areas.

The rate of spread changes over time. Farmers may adopt slowly at first because costs and benefits are uncertain. Successful demonstrations can speed up uptake. Disease spread may accelerate as opportunities for transmission increase, then slow as fewer people remain susceptible or barriers become stronger.

Geographic barriers

• Physical barriers: mountains, deserts, seas and remoteness can reduce contact. Climate and soils may stop an agricultural practice from working. A disease vector may fail to become established where temperatures are unsuitable or breeding habitats are absent.
• Economic barriers: farmers may lack credit, equipment or affordable inputs. Poor transport and communications can slow the flow of information. Limited travel may reduce disease introductions, but once infection arrives, inadequate sanitation and healthcare can increase transmission.
• Political barriers: borders, restrictions on movement, trade rules and controls on seed imports can interrupt diffusion. Conflict can obstruct agricultural advice and disease surveillance. Displacement, meanwhile, can carry infections along new routes.

These barriers are not absolute. Air travel can bypass a mountain barrier. Financial support can make adoption possible, while political agreements can reopen connections. What matters is how each factor changes movement, uptake or transmission.

Two different transmission pathways

A living organism carries a pathogen between hosts in a vector-borne disease. A water-borne disease is acquired through water contaminated with a pathogen, commonly by swallowing that water.

Incidence counts new cases in a population during a specified period and is often expressed relative to population size. High incidence identifies intense transmission. On its own, though, it does not explain why transmission occurs or how severe its impacts are.

Geographic controls on incidence and diffusion

Temperature and moisture influence whether vectors survive and breed, as well as how pathogens develop within them. Rainfall may create breeding sites. Drought, meanwhile, may encourage households to store water, providing habitats too. Vegetation and irrigation affect how close people are to vectors, as does settlement design. These relationships vary between vectors; they don't all require the same conditions.

People moving between places can introduce pathogens to new areas. Dense settlement can increase opportunities for contact, while housing conditions influence exposure. Poverty may restrict access to screens and other prevention measures, or to treatment. Seasonal weather does not act alone: it interacts with mobility, housing and services.

For water-borne diseases, keeping drinking water separate from human waste is crucial. When sewage enters rivers, wells or distribution networks, it creates exposure. Floods can mix sewage with water supplies; drought can force households to turn to unsafe sources. Conflict and displacement may overwhelm water and sanitation services, as may rapid settlement growth.

Infected people can carry pathogens into another community. What happens next depends on contamination routes and exposure to unsafe water, rather than simply the distance from the first case. Even in densely populated places, reliable water treatment and sanitation can interrupt transmission.

Demographic and socio-economic impacts

Demographic impacts concern population characteristics and change. Disease can increase mortality and alter life expectancy. Some age groups may be affected more severely than others. The impacts depend on the disease itself, previous exposure and access to timely treatment.

Socio-economic impacts concern livelihoods, services and living conditions. Illness can reduce working time and income or interrupt education. Relatives may also need to provide care. Treatment costs put pressure on households and health services. Repeated disease can reinforce poverty; poverty, in turn, can increase exposure and delay treatment.

The same infection can have different consequences from one place to another. Rapid diagnosis and accessible care may limit mortality. Where services are weak and households are highly vulnerable, an outbreak can become a much wider livelihood crisis.

Detailed example: dengue in Singapore

Dengue is a vector-borne viral disease transmitted principally by infected Aedes mosquitoes. Singapore shows that substantial transmission can still occur in a wealthy urban place with a high level of services.

The warm climate supports mosquito activity. Around buildings and construction sites, small collections of water provide breeding opportunities, while dense urban settlement brings vectors and people close together. Travel can introduce circulating viruses. Local transmission can then follow where mosquitoes acquire and pass on infection.

Outbreaks cause illness and absence from work or school, putting pressure on healthcare. Severe dengue can be fatal. Surveillance and the removal of breeding sites reduce exposure, as does community action. Urban wealth alone, however, does not eliminate the environmental conditions that support transmission.

Detailed example: cholera in Yemen

Cholera is a water-borne bacterial disease caused by Vibrio cholerae. Yemen's major outbreak beginning in 2016 shows how conflict can turn water contamination into a widespread health emergency.

Damage to infrastructure and interrupted services weakened access to safe water, sanitation and healthcare. Displacement weakened access too. Contaminated water exposed households to infection, while people's movement and disrupted living conditions helped connect affected communities. Where sanitation was inadequate, rainfall and runoff could spread contamination further.

Severe diarrhoea causes rapid dehydration and can be fatal without treatment. Illness within households and caring responsibilities reduce earnings. At the same time, demand for treatment puts additional pressure on services that are already weakened. Insecure access to healthcare increases the risk that an otherwise treatable illness becomes deadly.

The class chooses its own detailed examples: one vector-borne and one water-borne disease. Each should connect a named place and period to the transmission pathway and to the physical and human controls on incidence and diffusion. It should also include supported demographic and socio-economic impacts. The examples above illustrate those connections; they do not prescribe the class's choices.