Water as a Limiting FactorBy Andrew & Joanna

Global Water Supply97.4% of the Earth’s water is saltyMost of the remaining 2.6% of fresh water is

not readily available to humans; trapped as ice in polar caps.

Only 0.014% of global water supply is readily available to humans and other life forms.

Recycling is therefore important to maintain this supply of water

The Water CycleThe water cycle

involves evaporation and precipitation.

Although most of the evaporated water returns directly to the sea some of it falls in rivers and lakes etc and can be used by humans.

Increasing Demand for WaterAgriculture:

73%Industry: 22%Domestic Usage: 5%

As technology and world population increases, the need for more water also increases and water is becoming more and more a limiting factor.

Global Uses Of Water

Agri-cultureIndustryDomestic Usage

Meeting the Increased DemandAs the need for more water increases, water

management techniques must be efficient at keeping water consumption to a minimum.

About 90% of water from industrial and domestic usage can be returned to waterways and reused if managed carefully.

Effective techniques to Manage Water ConsumptionMicro Irrigation: This new technique uses

perforated pipes to “drip feed” crops with water, thus only using necessary volumes of water.

Dams: Allows slight control over the water cycle and provides sufficient water for a specific area. Also prevents flooding. However irrigation channels may carry deadly parasites and malaria carrying mosquitoes may breed in the shallow waters.

Unpredictability of SupplyIn Developed countries

there is normally a continuous supply of clean and safe water

Many developing countries cant depend on a reliable source of water; some regions have a permanent shortage of water and in others rainfall is random and erratic.

The world’s water supply is unevenly distributed

ClimateThe climate of a region is the result of

interactions between the atmosphere, land mass, oceans and geographical locations of the region.

The climate of a region changes over time and can affect the availability of the water supply to the area.

Short Term Climate ChangeBrief, extreme

changes in a regions climate occur occasionally.

These short-lived changes can have devastating effects on the region.

ErosionErosion is the loss of the fertile top soil by the

action of water or wind on the land.Erosion rarely occurs in areas well covered

by vegetation.Erosion can be prevented on farmland by

building terraces to grow rice and by ploughing sloping fields round the contours of hills.

DeforestationThe complete

clearing away of a forest.

The destruction of these areas can have terrible effects on the water cycle.

Effects of Deforestation on Water CycleEffect of deforestation ConsequenceLoss of forest’s “sponge” effect;

flow of water no longer regulated.

Erosion of top layer of soil by fast moving water.

Less water vapour returned to atmosphere by evaporation.

CO2 produced during burning of the forest.

Rivers fail to supply consistent supplies of water needed by humans or flooding of low-lying areas.

Soil fertility reduces; rivers and lakes become blocked with silt; water becomes undrinkable.

Reduction in rainfall so climate becomes drier.

Extra CO2 may contribute to the “green-house effect”

DesertificationThere are many area

of the world covered by desert. When it is caused by human actions it is named desertification.

Desertification