4.1 Introduction to Water Systems

What percentage does fresh water make up of Earth’s water storages?

2.5%

Where is the fresh water stored?

• 68.7% in glaciers and ice sheets

• 30% in groundwater

• 1.3% in rivers, lakes and the atmosphere

What type of system is the hydrological system?

A closed system

What is the hydrological cycle?

A series of processes in which water is constantly recycled through the system

What are the main processes occuring within the hydorlogical cycle?

• Evaporation - sun evaporates surface water into vapour

• Condensation - water vapour condenses and precipitates

• Flows - water runs off the surface into streams and reservoirs or beneath the surface as ground flow

What does the hydrological cycle lead to?

Local temperature fluctuations because of energy exchange

Explain how the hydrological cycle leads to temperature fluctuations

1. As water evaporates, it absorbs energy from its surroundings

2. This cools the environment

3. The reverse happens when water condenses

4. This heat exchange influences the local climate

What are the storages in the hydrological cycle?

• Rivers, lakes, oceans

• Groundwater (aquifers)

• Soils

• The atmosphere

• Glaciers and ice caps

• Organisms

What are the flows in the hydrological cycle?

• Evapotranspiration

• Sublimation

• Evaporation

• Condensation

• Advection

• Precipitaion

• Melting

• Freezing

• Flooding

• Surface run-off

• Infiltration

• Percolation

• Stream-flow or currents

Define evaporation

The process by which liquid water changes into a gaseous state (water vapour) and enters the atmopshere from water bodies such as oceans, lakes and rivers

Define transpiration

The process by which plants absorb water from the soil through their roots and release it as water from the soil through stomata

Define evapotranspiration

The combined process of water vaporisation from the Earth’s surface and the release of water vapour by plants through transpiration

Define sublimation

Solid to vapour without melting

Define condensation

The process in which water vapour in the atmosphere transforms into liquid water, forming clouds or dew, as a result of cooling

Define advection

The horizontal movement of water vapour, clouds or precipitation caused by the prevailing wind patterns

Define precipitation

The process of water falling from the atmosphere to the Earth’s surface in the form of rain, snow, sleet or hail

Define melting

Solid to liquid

Define freezing

Liquid to solid

Describe flooding

Overflow of water onto dry land, caused by heavy rainfall, melting snow or dam failure

Define surface run-off

The movement of water over the Earth’s surface, typically occurring when the ground is saturated or impermeable, leading to excess water

Define infiltration

The process of water seeping into the soil from the surface, entering teh soil layers and becoming groundwater

Define percolation

The downward movement of water through the soil and underlying rock layers, eventually reaches aquifers or groundwater reservoirs

Stream-flow or currents

Describe stream-flow or currents

The movement of water in streams, rivers or other water bodies, driven by gravity and the slope of the land, ultimately leads to oceans/lakes

What are the human impacts on the hydrological cycle?

• Agriculture e.g. irrigation

• Deforestation

• Urbanisation

What is irrigation?

The process of artificially supplying water to agricultural crops

Directly impacts hydrological cycle by modifying the water distribution and availability in a region

What does increased irrigation lead to?

• Artificially high evapotranspiration rates as more water is supplied to plants than would occur naturally,

• Increased atmospheric moisture levels

• Increases in precipitation downwind of irrigated areas

  • Altering rainfall patterns in the region

What is caused by excessive irrigation?

Increased surface run-off

• When water is applied faster than soil can absorb, it flows over surface

  • Carries sediments, fertilisers, pesticides

  • Leads to water pollution and nutrient imbalances

Define deforestation

Clearing/removal of forests for agriculture, logging or urban development purposes

What role do forests play in the hydrological cycle?

• Absorb rainfall

• Facilitate infiltration

  • Recharges groundwater

  • Maintains stream flows

What happens when forests are cleared?

Surface runoff increases

• Without tree canopy and vegetation to intercept and slow down rainfall, more water reaches the ground surface

Reduces evapotranspiration rates

• As trees removed, less transpiration and evaporation occurring, resulting in reduced moisture release into the atmosphere and increased erosion

How does urban development alter the hydrological cycle?

• Replace permeable surfaces with impermeable surfaces

  • Prevent infiltration

  • Lead to reduced groundwater recharge

  • Rainfall becomes surface runoff, which can cause flooding downstream

Why do urban areas have higher temperatures?

Urban heat island effect

• Concentration of buildings and paved surfaces, increases evaporation rates, altering local precipitation patterns

What is ocean circulation driven by?

Differences in temperature and salinity

What does this resulting difference in density do?

Drives the ocean conveyor belt, which distributes heat around the world and affects climate

What do ocean currents do?

Redistribute heat energy around the globe

Where do cold currents move?

Towards the equator

Where do warm currents move?

Towards the poles

How are ocean currents formed?

By prevailing surface winds created by global atmospheric circulation

Explain the convection current that maintains ocean circulation

• Polar cold waters contain denser, saltier sea water, which sinks to the ocean floor

• Water then flows above it, which forms a current

• The deep ocean currents flow towards Antartica along the western Atlantic basin, before splitting off into the Indian and Pacific Oceans where the water begins to warm up

• The warming makes the water less dense so it loops back up to the ocean surface in the South and North Atlantic Ocean

• The warmed surface waters continue to flow around the glove and eventually return to North Atlantic, where cycle begins again

Define thermohaline circulation

Movement of water, which drives the ocean conveyor belt