4.1 INTRODUCTION TO WATER SYSTEMS
Significant ideas
● The hydrological cycle is a system of water flows and storages that may be disrupted by human
activity.
Applications and skills
● Discuss human impact on the hydrological cycle.
● Construct and analyse a hydrological cycle diagram.
Understandings
1. Solar radiation drives the hydrological cycle.
2. Freshwater makes up only a small fraction (approximately 2.6% by volume) of the Earth’s water
storages.
3. Storages in the hydrological cycle include organisms, soil and various water bodies, including oceans,
groundwater (aquifers), lakes, rivers, atmosphere, glaciers and ice caps.
4. Flows in the hydrological cycle include evapotranspiration, sublimation, evaporation, condensation,
advection (wind-blown movement), precipitation, melting, freezing, flooding, surface runoff, infiltration,
percolation, and stream-flow or currents.
5. Human activities such as agriculture, deforestation and urbanization have a significant impact on
surface runoff and infiltration.
6. Ocean circulation systems are driven by differences in temperature and salinity. The resulting
difference in water density drives the ocean conveyor belt, which distributes heat around the world,
and thus affects climate.
The Earth's water budget
A quantitative estimate of the amounts of water in storages and flows of the water cycle.
About 70% of the Earth’s surface is covered by water.
● ~2.6% is freshwater.
● 97% is ocean water (saltwater).
,Freshwater is in short supply.
● 68.7% is in the polar ice caps and glaciers.
● 30.1% in groundwater.
● 0.3% is in lakes, rivers and swamps.
● only 0.001% of the total Earth’s water volume is as water vapour in the atmosphere.
● according to the US Geological Survey, if all of the water in the atmosphere rained down at once, it
would only cover the ground to a depth of 2.5 cm.
The turnover times (time it takes for a molecule of water to enter and leave that part of the system) are very
variable.
● Oceans: 37,000 years.
● Icecaps: 16,000 years.
● Groundwater: 300 years.
● Rivers: 12–20 days.
● Atmosphere: only 9 days.
Water can be considered a renewable resource or a nonrenewable resource depending on where it is stored.
, The water (hydrological) cycle
Energy from solar radiation and the force of gravity drive the water cycle. The water cycle drives the world’s
weather systems.
Transfers:
Flows of water when it stays in the same state.
● advection (wind-blown movement)
● flooding
● surface run-off
● infiltration and percolation (when water runs into and through soil or rocks)
● stream flow and current
Transformations:
When it changes state to or from liquid water.
● evapotranspiration – liquid to water vapour.
● condensation – water vapour to liquid.
● freezing – into solid snow and ice.
Storages:
● oceans
Significant ideas
● The hydrological cycle is a system of water flows and storages that may be disrupted by human
activity.
Applications and skills
● Discuss human impact on the hydrological cycle.
● Construct and analyse a hydrological cycle diagram.
Understandings
1. Solar radiation drives the hydrological cycle.
2. Freshwater makes up only a small fraction (approximately 2.6% by volume) of the Earth’s water
storages.
3. Storages in the hydrological cycle include organisms, soil and various water bodies, including oceans,
groundwater (aquifers), lakes, rivers, atmosphere, glaciers and ice caps.
4. Flows in the hydrological cycle include evapotranspiration, sublimation, evaporation, condensation,
advection (wind-blown movement), precipitation, melting, freezing, flooding, surface runoff, infiltration,
percolation, and stream-flow or currents.
5. Human activities such as agriculture, deforestation and urbanization have a significant impact on
surface runoff and infiltration.
6. Ocean circulation systems are driven by differences in temperature and salinity. The resulting
difference in water density drives the ocean conveyor belt, which distributes heat around the world,
and thus affects climate.
The Earth's water budget
A quantitative estimate of the amounts of water in storages and flows of the water cycle.
About 70% of the Earth’s surface is covered by water.
● ~2.6% is freshwater.
● 97% is ocean water (saltwater).
,Freshwater is in short supply.
● 68.7% is in the polar ice caps and glaciers.
● 30.1% in groundwater.
● 0.3% is in lakes, rivers and swamps.
● only 0.001% of the total Earth’s water volume is as water vapour in the atmosphere.
● according to the US Geological Survey, if all of the water in the atmosphere rained down at once, it
would only cover the ground to a depth of 2.5 cm.
The turnover times (time it takes for a molecule of water to enter and leave that part of the system) are very
variable.
● Oceans: 37,000 years.
● Icecaps: 16,000 years.
● Groundwater: 300 years.
● Rivers: 12–20 days.
● Atmosphere: only 9 days.
Water can be considered a renewable resource or a nonrenewable resource depending on where it is stored.
, The water (hydrological) cycle
Energy from solar radiation and the force of gravity drive the water cycle. The water cycle drives the world’s
weather systems.
Transfers:
Flows of water when it stays in the same state.
● advection (wind-blown movement)
● flooding
● surface run-off
● infiltration and percolation (when water runs into and through soil or rocks)
● stream flow and current
Transformations:
When it changes state to or from liquid water.
● evapotranspiration – liquid to water vapour.
● condensation – water vapour to liquid.
● freezing – into solid snow and ice.
Storages:
● oceans
