Unit 4. Water, Food production systems and society
4.1. Introduction to water systems
Water budget: an estimate of the amounts of water in storages and flows on the water
cycle.
Most of the water is salt water (97%)
0.3 % of the total fresh water is on the surface
The Water Cycle
Storages of water and flows of water between the storages. These flows can be¨
Transfers: stays in the same state
o Flooding
o Infiltration
Transformations: changes state
o Evapotranspiration: liquid to water vapour
o Condensation: water vapour to liquid
o Freezing: into solid snow and ice
Driven by energy form solar radiation and the force of gravity
Human impact on the water cycle
1) Withdrawals – taking out water
2) Discharges – adding pollutants to water
3) Changing the speed at which water can flow
4) Diverting rivers
Ocean currents and energy distribution
Ocean currents: movements of water both on the surface and in deep water that move
in specific directions
Important role in the global distribution
Two types:
o Surface currents
o Deep water currents
Due to differences in water density (salt and temperature)
Cold water holds more salt than warm water
Cold ocean currents:
o Benguela current
o Humboldt current
Warm ocean current:
o Gulf stream
, o Angolan current
4.2. Access to fresh water
Water as a critical resource
Water is mostly saline
Desalination can be implemented but it requires too much energy
o Salt extracted form desalination is returned to the ocean
Water scarcity: the lack of sufficient available water resources to meet the demands
of water usage within a region
Water scarcity will only increase
Sustainability of freshwater resources
allows full natural replacement of the resources exploited
sources of fresh water: surface freshwater and underground aquifers - a layer
of porous rock (holds water) sandwiched between two layers of impermeable
rock
global fresh water consumption is increasing -> human pop. is increasing
o leads to water scarcity and water degradation (water quality deteriorates)
Issues:
Low water levels in rivers
Slow water flow in the lower courses of rivers -> sedimentation
Fresh water becomes contaminated
Irrigation results in soil degradation -> dissolved minerals remain in the top
layer -> salinization
Fertilizers and pesticides pollute rivers
Industries release pollutants into surface
Solutions:
Increase fresh water supplies by:
o Desalination plants
o Rainwater harvesting system
o Artificially recharging aquifers
Reduce domestic use of freshwater
o Water-efficient showers
Reduce the amount of pesticides and fertilizers used
Grey-water recycling – water from showers and baths can be reused for garden
irrigation or WCs
Highly selective pesticides instead of generic pesticides
Industries can remove pollutants from their wastewater with water treatment
plants
4.1. Introduction to water systems
Water budget: an estimate of the amounts of water in storages and flows on the water
cycle.
Most of the water is salt water (97%)
0.3 % of the total fresh water is on the surface
The Water Cycle
Storages of water and flows of water between the storages. These flows can be¨
Transfers: stays in the same state
o Flooding
o Infiltration
Transformations: changes state
o Evapotranspiration: liquid to water vapour
o Condensation: water vapour to liquid
o Freezing: into solid snow and ice
Driven by energy form solar radiation and the force of gravity
Human impact on the water cycle
1) Withdrawals – taking out water
2) Discharges – adding pollutants to water
3) Changing the speed at which water can flow
4) Diverting rivers
Ocean currents and energy distribution
Ocean currents: movements of water both on the surface and in deep water that move
in specific directions
Important role in the global distribution
Two types:
o Surface currents
o Deep water currents
Due to differences in water density (salt and temperature)
Cold water holds more salt than warm water
Cold ocean currents:
o Benguela current
o Humboldt current
Warm ocean current:
o Gulf stream
, o Angolan current
4.2. Access to fresh water
Water as a critical resource
Water is mostly saline
Desalination can be implemented but it requires too much energy
o Salt extracted form desalination is returned to the ocean
Water scarcity: the lack of sufficient available water resources to meet the demands
of water usage within a region
Water scarcity will only increase
Sustainability of freshwater resources
allows full natural replacement of the resources exploited
sources of fresh water: surface freshwater and underground aquifers - a layer
of porous rock (holds water) sandwiched between two layers of impermeable
rock
global fresh water consumption is increasing -> human pop. is increasing
o leads to water scarcity and water degradation (water quality deteriorates)
Issues:
Low water levels in rivers
Slow water flow in the lower courses of rivers -> sedimentation
Fresh water becomes contaminated
Irrigation results in soil degradation -> dissolved minerals remain in the top
layer -> salinization
Fertilizers and pesticides pollute rivers
Industries release pollutants into surface
Solutions:
Increase fresh water supplies by:
o Desalination plants
o Rainwater harvesting system
o Artificially recharging aquifers
Reduce domestic use of freshwater
o Water-efficient showers
Reduce the amount of pesticides and fertilizers used
Grey-water recycling – water from showers and baths can be reused for garden
irrigation or WCs
Highly selective pesticides instead of generic pesticides
Industries can remove pollutants from their wastewater with water treatment
plants
