Chap 3 - Water & its Spatial Distribution (geog)

Where does water come from?

Freshwater - Saltwater

glaciers oceans

rivers

lakes

groundwater

soils

Distribution of Earth's Water

• 97.5% of Earth's water is saltwater, while only 2.5% is freshwater.

• Of that freshwater, only 1.2% is accessible for human use.

• Of the accessible surface freshwater, only 21.39% is readily available for humans.

IS water renwable?

Water is renewable because it is recycled by the water cycle, which is powered by the Sun.

However, fresh water can still become scarce if it is overused or polluted faster than it can be naturally replenished.

what is infiltration

Infiltration is the physical process involving movement of water through the boundary area where the atmosphere interfaces with the soil.

what is percolation?

Percolation (takes place after infiltration) is the movement of

water through the soil, and its layers, by gravity and capillary forces. The prime moving force of groundwater is gravity.

what is a catchment area?

A catchment is an area of land where water collects when it rains, often bounded by hills.

Do we have an unlimited supply of water to drink? (yes and no) must know both

yes - Water cycle is a continuous process

Water is a renewable source – it is naturally replenished over time within the same time period when it is used

No- Most of the Earth’s water is saltwater – Not suitable for drinking

Most freshwater is inaccessible –Around 68% is locked in ice caps and glaciers; some is deep underground and hard to reach

Pollution (Chap 4) reduces usable water – Human activities pollutes freshwater stores, making less clean water available for use.

What is a Water Budget? and waht is the equation

A water budget equation describes the flow of water in and out of a catchment area (area that receives water, and also contributes water to rivers)

Net change in water storage= input minus output

input-Processes that increase the amount of water in a catchment area (i.e. precipitation)

what does input mean?

input-Processes that increase the amount of water in a catchment area (i.e. precipitation)

what does output mean?

Processes that decrease the amount of water in a catchment area (i.e. evaporation)

What happens when there is more or less input

than output?

Water surplus = input more than output

water deficit= input less than output

Is the water budget of this area balanced? (surplus / deficit)

This is a deficit because:

-Rainfall inputs are lower than water outputs (demand +

releases)

-Soil and reservoirs are losing water faster than they are

replenished.

Based on today’s weather – is it water surplus or deficit in

Singapore’s catchment area?

Can’t tell as this is only input. No output stated.

An area receives 1000mm of rain per year. 700mm evaporates back to the atmosphere, and 200mm flows away as runoff to another area.

1. What is the storage change?

2. What would this storage change mean for this area?

3. If this was Singapore’s water budget where would the extra 100 mm of stored water likely go?

4. What might happen to this water budget during a very dry year?

5. If an area needs 150mm stored water to avoid shortages, is this area water-secure?

1. What is the storage change?

Storage change = 1000 - 700 - 200 = +100 mm

2. What would this storage change mean for this area?

+100mm is a positive storage change, means the water level would rise.

3. If this was Singapore’s water budget where would the extra 100 mm of stored water likely go?

It’ll go to reservoirs and underground storage.

4. What might happen to this water budget during a very dry year?

This would make storage change less positive or even negative.

5. If an area needs 150mm stored water to avoid shortages, is this area water-secure?

No, they only store 100mm but need 150mm, so they have a 50mm deficit and may face water shortages