Lecture 3: Water and food 2 Flashcards
Urbanised society
Urbanisation increasing particularly in developing countries
Majority of population not self sufficient for food/water
Thus dependent on operational Ag. infrastructure and technology
Greater urbanisation and access to markets leads to more complex supply chains
Greater supply chain complexity
Farm door prices/profits driven down
More transportation of food
Virtual water imports/exports
Food waste
Significant losses at all stages
Differ with food type (greatest for fresh fruit+veg)
30%-50% of food produced is never consumed (greater for some crops)
Higher post-harvest losses for developing countries (pests,storage)
Highest losses in developed countries at retailer/consumer level
Consumption patterns
Have been changing in developing countries
More meat and/or milk as GDP increases (exceptions)
Society has treated water as an inexhaustible resource but:
There is a limited amount of rainfall available globally at any one time
Natural cleansing and renewing functions of hydrologic cycle do not work properly if systems are overloaded or damaged (see ecosystem services lecture)
‘Renewal’ of water takes time through hydrological cycle
Rate at which we are now using water is sometimes faster than it can be renewed
Difference between:
Withdrawal - total amount of water taken from a source
Consumption - fraction of withdrawn water made unavailable for other purposes (not returned to its source).
Degradation - change in water quality due to contamination making it unsuitable for desired use. Much water that is not consumed is nevertheless degraded.
Green water
Green water – goes through vegetation and is thus productive (producing biomass/crops) through (evapo- transpiration)
Blue water
Blue water – flows in rivers – not productive of plant biomass but productive in other ways (e.g. fisheries, hydropower)
green and blue water process
Rainfall returns to atmosphere either as green water (via land ET) or blue water (via sea ET).
Where water is evaporated for crop production it is not available downstream for crop production or other uses (see virtual water flows)
Though water is a renewable resource - at any one time there is a finite amount in the terrestrial sphere that can be used, hence the restriction
Agriculture uses huge amount of water
> 70% of global water use is for Ag.
Rainfed Ag. is the greatest global water use
24% or croplands are irrigated delivering 34% of Ag. Production
Without irrigation cereal production would decrease globally by 20%
Crops vary greatly in the calories delivered per litre of water evaporated (water productivity)
crops and irrigation
Crop production highly dependent on irrigation
Irrigated areas up to 100% in some regions
Irrigation in many areas unsustainable (withdrawals»recharge)
Irrigation can be inefficient.
Flood or furrow irrigation
Half of water can be lost through evaporation.
Flood irrigation sometimes used to remove salts from field, but salt then contaminates streams
Sprinklers have high evaporation losses esp. when used at wrong time of day.
Drip (trickle) irrigation releases water near roots, conserving water.
Global distribution of irrigation is concentrated in developed world
Development loans for irrigation projects peaked in the 1980s and led to declining food prices (dependable “rainfall”)
Drivers for chronic food insecurity
Increasing population;
Changing and converging consumption patterns;
Increasing per capita incomes, leading to increased resource consumption;
Growing demand for livestock products (meat and dairy), particularly those fed on grain;
Growing demand for biofuels;
Increasing water and land scarcity;
Adverse impacts of climate change;
Slowing of increases in agricultural productivity.
Into the future…
Once we hit 9.5 billion and, if development continues, across the developing world pop. pop growth rates will likely decline
This will reduce pressure
But, increasing living standards (incl. diets) for all will mean pressure still very much on.
