5.1C: The Global Water Budget
The global water budget limits water available for human use and water stores have different residence times; some stores are non-renewable (fossil water or cryosphere losses)
The global water budget takes into account all the water that is held in stores and flows of the global hydrological cycle. The most significant feature of the budget is that only 2.5% of it is freshwater; the rest is in oceans. Even more remarkable is that only 1% of all freshwater is 'easily accessible surface freshwater'. Nearly 70% is locked up in glaciers and ice sheets.
Although water is constantly circling around the hydrological cycle, each store has a residence time. This is the average time a molecule of water will spend in one of the stores. Residence times vary from 10 days in the atmosphere to 3,600 years in the oceans and 15,000 years in an ice cap. It is claimed that two water stores, fossil water and cryosphere are non-renewable.
Fossil Water
From a human viewpoint, the most critical feature of the global water budget is that accessible surface water is a mere 1% of all the world's freshwater, and this is the major source of water for human use.
The smallness of this figure emphasises the important point that water is not the abundant resource so many think it is. Indeed, it is a scarce resource needing careful management.
Figures:
All water:
Although water is constantly circling around the hydrological cycle, each store has a residence time. This is the average time a molecule of water will spend in one of the stores. Residence times vary from 10 days in the atmosphere to 3,600 years in the oceans and 15,000 years in an ice cap. It is claimed that two water stores, fossil water and cryosphere are non-renewable.
Fossil Water
- Ancient, deep groundwater made from pluvial (wetter) periods in the geological past
- Made up of those areas of the world where water is frozen into snow or ice
- Is it non-renewable? This is to be questioned because, come another glacial period, more water will once again be locked in glaciers and ice sheets.
From a human viewpoint, the most critical feature of the global water budget is that accessible surface water is a mere 1% of all the world's freshwater, and this is the major source of water for human use.
The smallness of this figure emphasises the important point that water is not the abundant resource so many think it is. Indeed, it is a scarce resource needing careful management.
Figures:
All water:
- 97.5% in oceans
- 2.5% freshwater
- 69% in ice caps and glaciers
- 30% in groundwater
- 1% as easily accessible surface water
- 52% in lakes
- 38% as soil moisture
- 8% as atmospheric water vapour
- 1% in rivers
- 1% as accessible water in plants