Topic 4: Water World
The Global Hydrological Cycle
· Made up of a series of stores and transfers
· A global system – water is transferred through winds and oceans
· A closed system – water cannot enter/leave the system as the Earth doesn’t get wetter or dryer
The Drainage Basin
· The drainage basin is an open system – water can enter and leave the system
· Surface run off can occur when the ground is impermeable so the water doesn’t sink into it
Infiltration: movement of water into soil from the surface
Percolation: movement of water into underlying rocks
Transpiration: water coming though and off the leaf
Groundwater storage: water stored in rocks through percolation
Saturation: when water is full of moisture
Water table: the level saturation occurs within the ground
The drainage basin in the area of land drained by a river and its tributaries. The hydrological cycle operates as an open system within the drainage basin.
When precipitation falls from the atmosphere it may get to the river in several ways. If it falls directly into the river it is called chemical precipitation, if rain falls onto vegetation it is known as interception. Vegetation can also release water to the air via the process of transpiration. Rain that falls directly onto the ground may soak down via infiltration whereas, if the soil is already saturated it may follow the ground as surface run off.
Rain that soaks into the soil may move toward a river, through pore spaces or animal burrows, by the process of through flow. It may soak down further via percolation to beneath the water table where the ground is permanently saturated. It then becomes rainwater and moves slowly via groundwater flow.
When water reaches a stream or river it becomes channel from and will eventually flow into a lake or the ocean. At any stage water may be heated and evaporate, returning to the atmosphere where it cool and condenses into clouds and the cycle begins again.
Where is water stored?
Sea water – 97.5%
Fresh water – 2.5% - ice 0.3%, underground 30.8% and lakes and rivers 68.9%
The majority of water on Earth is stored in our oceans. Freshwater is therefore limited. Rivers, lakes and ice from the main stages o freshwater although access to water is often difficult (e.g. ice is frozen, lakes may not always fill and groundwater is often difficult to extract)
What impact might the distribution of water resources have on the population of certain countries?
India has a high population but not as much as access to water resources. South Africa also has a high population but not as many water resources. Parts of Russia have a high freshwater resource however the population is not…