Water supply

Water supply

Water Supply
1. Climate
  1. For example, regions near to the equator receive high levels of annual precipitation, while some tropical areas suffer recurring drought.
  2. The distribution of water globally is related to the Earth’s climatic zones.
  3. Rainfall may also vary with the seasons. Equatorial areas such as the Amazon lowlands have two distinct periods of wet weather per year, whereas the monsoon lands of southeast Asia have one very distinct wet season
  4. High mountains with snowpack hold vast reserves of water, some of which is released in late spring and during the summer.
2. River systems
  1. The world’s major rivers store large quantities of water and transfer it across continents.
  2. The Amazon, for instance, produces an average discharge of 219,000 m3 s−1 from a catchment area of 6,915,000 km2.
  3. This is 20% of all the river water entering the world’s oceans.
  4. River flow generally increases downstream as tributaries feed into the main river, though high temperatures can lead to considerable water loss by evaporation.
  5. Seasonal changes in climate can also create significant variations in discharge and produce distinctive river regimes.
3. Geology
  1. Where the rocks underlying a river basin are impermeable, water will remain on the surface as runoff, creating a high drainage density.
  2. Permeable soils and rocks such as limestone may allow water to pass into underground drainage systems.
  3. Aquifers such as chalk and porous sandstones can store vast quantities of water under- ground.
  4. The Ogallala aquifer, in the High Plains region of the USA, is one such water source.
  5. Groundwater may create springs or provide the baseflow of rivers.
4. Finite resource
  1. A fundamental issue for water supply is that the amount of water available is finite.
  2. The world’s oceans hold an estimated 1,386 million km3 of water, and this accounts for 97.5% of the global water store
  3. So only 2.5% of the store is potentially available as freshwater, and almost 80% of that is trapped in ice, snow and permafrost.
  4. Most of the remaining 20% is groundwater.
  5. Only 1% is easily accessible freshwater held in lakes, ecosystems, the atmosphere and rivers
Green water flow involves either the interception and transpiration of water by vegetation or its evaporation from a variety of surfaces.
1. These processes have important ecological as well as hydrological functions.
Blue water flow is the visible part of the system, namely water running on the surface and supplying rivers or travelling underground, recharging aquifers.
1. This water is potentially available and recyclable.
The familiar model of the hydrological system makes use of the terms inputs, stores, outputs and flows to explain how water moves through the environment. Within this framework, we are able to identify important elements such as precip- itation, groundwater, evapotranspiration and surface runoff.

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	Created by Jodie Goodacre over 10 years ago