lecture 2: use and availability Flashcards
What is the water footprint?
a measure of humanity’s appropriation of fresh water in volumes of water consumed and/or polluted.
it measures the amount of water used to produce each of the goods and services we use. it can be measured for a single process, such as growing rice, for a product, such as a pair of jeans, for the fuel we put in our car, or for an entire multi-national company.
- the water footprint can also tell us how much water is being consumed by a particular country- or globally- in a specific river basin or from an aquifer.
How can the water footprint be measured?
- cubic meters
- per tonne of production
- per hectare of cropland
- per unit of currency
- and in other functional units
the water footprint helps us understand for what purposes our limited freshwater resources are being consumed and polluted.
the impact it has depends on where the water is taken from and when
if it comes from a place where water is already scarce, the consequences can be significant and require action.
What is the green water footprint?
is the water from precipitation that is stored in the root zone of the soil and evaporated, transpired or incoproated by plants. it is particular relevant for agricultural, horticultural and forestry products
What is the blue water footprint?
is the water that has been sources from surface or groundwater resoures and is either evaporated, incoprotaed into a product or taken from one body of water and retruned to another, or returned at a different time. Irrigated agriculture, industry and domestic water use can each have a blue water footprint.
What is the grey water footprint?
is the amount of freshwater required to assimilate pollutants to meet specific water quality standards. The grey water footprint considers point-source pollution discharges to a freshwater resource directly through a pipe or indirectly through runoff or leaching from the soil, impervious surfaces, or other diffuse sources.
what substance uses the most amount of water?
Proteins
plus land and energy
- feedstock cultivation
- livestock farming
- food processor
- retailer
- consumer
(all have direct water footprints)
(it takes nine times as much water to produce 1kg of beef compared to that required to produce 1kg of chicken).
(synthetic rubber production is also very water consuming- 3000l/kg)
here are some examples of the global/ national crop water footprint?
Global crop water footprint Wc,g = Wc (m3/ton) x Pc,g (M tons/year) Global rice water footprint: Wrice,g = 2291 m3/ton x 593 M ton/yr = 1,358,563 M m3/yr = 1358 km3/yr Annual rice production in Thailand: Price,Thailand = 18 M tons Rice water footprint: Wrice,Thailand = 2291 m3/ton * 18 M tons = 41238 M m3/yr = 41 km3/yr Annual rainfall over Thailand, R = 1750 mm/yr Area of Thailand, A = 513,120 km² Volume of rainfall, V = R x A = 1750 / (1000*1000) x 513,120 = 898 km3/yr Wrice,Thailand = ~5% Total renewable water resources = 438 km3/yr Wrice,Thailand = ~10% Internal renewable water resources = 225 km3/yr Wrice,Thailand = ~20%
Water use depends not only on the application but also the location
Czech republic: calculated water footprint for litre of beer (45L)
SA: (155L)
The water footprint allows us to answer a broad range of questions for companies, governments and individuals
Where is the water dependence in my company’s
operations or supply chain?
How well are regulations protecting our water
resources?
How secure are our food or energy supplies?
Can I do something to reduce my own water footprint
and help us manage water for both people and nature?
UK domestic water use: where is potable water quality required?
- bath/ shower
- dishwasher
- drinking
define: internal renewable water resources
what is produced within a region
Define: external renewable water resources
what is produced outside of a region
define: total renewable water resources
internal + external
Dependency ratio
- percentage of total renewable water resources originating outside of countru = 100% x external/ total
what are the blue planet statistics?
- Total volume of water on Earth (100%) = 1,386,000,000 km3
- Total freshwater (2.5%) = 35,000,000 km3
- Available freshwater (0.015%) = 200,000 km3
what is the salt constraint?
saltwater 97%
freshwater 2.5%
glaciers and permenant snow cover 68.9%/ groundwater 30.8%, lakes and river storage 0.3%
what is the hydrological cycle residence time constraint
Residence time: average travel time for water to pass through a subsystem of the hydrologic cycle (e.g. river or aquifer)
Tr = S/ Q
Tr= residence time S= storage Q= flow rate- a function of natural flows and human management
Residence time dictates the renewability of water resources
Residence time of global atmospheric moisture
Volume (storage) of atmospheric water: 13,000km3
Flow rate of moisture from the atmosphere as precipitation= 502,000km3/yr
Tr=13,000/502,000= 0.026yr~9 days
(this is one reason why weather cannot be forecast accurately more than a few days ahead).
What are the following residence times of:
- water vapour over sea
- sea
- rivers
- glaciers and snow
- wetlands
- Groundwater
1 week 100s years 1-3weeks 1000s years (1000-10000) 10s years 1000s years (2 weeks to 10000)
Residence time dictates how renewable water resources are. A water resource that is renewed within a few years could be considered to be renewable and sustainable.
What is the third constraint of water: spatial variability of water?
renewable freshwater resources are not evenly distributed globally
- huge global variation in volume by continent
- global variation in worlds surface water: evaporation and runoff