lecture 20- appropriation of fresh water Flashcards
What does water availability depend on?
- Residence time in the reservoir
- Temporal availability
- Spatial availability
- Proximity to human need
- Availability vs access
What is residence time? Why can they be deceiving?
The length of time water remains in a reservoir differs.
- Different reservoirs of the same type can have different residence times
- Different parts of a reservoir can have different residence times
Based on residence time, freshwater is classified as either:
Renewable:
* Water in the reservoir is continuously recharged (<1yr)
* Significant withdrawals do not typically cause depletion within the reservoir- how much we can withdraw without impacts/depleting the reservoir.
* Renewable freshwater can be depleted if withdrawals
are significant enough
Non-renewable:
* Reservoirs that are not recharged on human time scales, or recharge so slowly that significant withdrawals will cause depletion within the reservoir
Explain the temporal availability of freshwater.
Not all freshwater is equally accessible year-round
* Rainfall patterns vary seasonally
Major changes in seasonal rainfall patterns:
* Rainy season and dry season
Explain the spatial availability of freshwater.
1- Rainfall patterns differ globally - most precipitation occurs in equatorial regions.
2- The frequency of terrestrial reservoirs differs: both for green and blue water.
3- Local proximity: location of freshwater resources must be within reach of human activities requiring the water resources
What is available water?
How much water is available for potential usage.
What is accessible water?
How much available water we can actually access for use.
* Spatial and temporal location
* Economic access
* Culturally and politically acceptable access
What is the equation that describes the water sources available in a steady state?
RFWSland = Pland = ETland + R
- RFWSland: terrestrial renewable fresh water supply
- Pland: precipitation over land
- ETland: evapotranspiration from land (green water)
- R: runoff to sea (blue water)
What are the classifications of water usage?
1- Water for survival:
* Water needed for basic survival
* Drinking, cooking, hygiene
2- Water for economic purposes:
* Agriculture, industry
3- Environmental water:
* Water needed to support ecosystems
* Services and species
Explain water for survival:
Many people globally don’t have access to safe drinking water. Access to safe drinking water is not shared globally.
Water distribution even occurs in technologically advanced countries. Lack of investment in water infrastructure is a major issue. For example, lack of investment into existing water purification infrastructure in Jackson, Mississippi.
Lack of safe drinking water has been used as a political tool.
Explain water for economic usage.
Many of the world’s largest rivers now run dry at some point during the year. Often a result of mismanagement and overallocation.
Agricultural fields in many places around the globe are unproductive for lack of water. Fields don’t get enough water and can’t grow or produce anything.
* Lying fallow
Explain environmental water.
Demands on freshwater resources for human use:
* Placing pressure on natural systems.
Explain the impact on California’s environmental water.
Unprecedented low levels of groundwater in central California:
* Identified as being the primary cause of mass mortality event in mature oaks ( ~ 200 years old)
* Groundwater levels receded so deeply, roots could no longer reach water
* Caused by excessive anthropogenic groundwater pumping
Explain the process of saltwater intrusion as a consequence of environmental water:
Where rivers dry up at the freshwater/marine interface: saltwater infiltration occurs in areas previously occupied by freshwater.
Freshwater pressure generated by flow:
* Holds back saltwater.
* Reduced freshwater flow: salt water moves into terrestrial areas → saltwater intrusion.
Salt water is generally fatal to freshwater species. It can also infiltrate
groundwater sources.
What is allocation?
How much water is allowed to be withdrawn by a party along the river.
