4.1 Water Systems

Importance of water

• essential for life - acts as solvent in our cells for chemical reactions to take place

What drives the hydrological cycle?

• solar radiation and gravity

Evaporation is

Process where the heat from the sun provides energy to convert liquid to vapour

What is released during condensation

Latent hear which warms the atmosphere and drives furher air movement

Factors affecting rate of infiltration

• soil permeability

• vegetation cover

Why is hydrological cycle a system?

Has matter and energy that undergo transfers and tranformations

Is hydrological cycle open or closed system

open locally, closed globally (no matter loss)

Main stores of hydrological cycle

• Oceans (97%)

• Glaciers and ice caps (1.7%)

• ground water (1.7%)

• surface freshwater (0.02%)

• atmosphere (0.001%)
  

Transfers in hydrological cycle

• advection

• infiltration

• percolation

• precipitation

Transformations in hydrological cycle

• evaporation

• condensation

• freezing

• melting

• sublimation

• transpiration

Turnover time

time take for a molecule of water to enter/leave part of a system ;

Main turnover times

• oceans 37 000 years

• ice caps 16 000 years

• ground water 300 years

• rivers 15 days

• atmosphere 9 days

What does renewability of water depend on

• Storage and extraction rate

• groundwater becomes non-renewable when depleted faster than recharged

Water budget

a quantitative estimate of the amounts of water in stores and flows of the water cycle

Human activities that disrupt water cycle

• Withdrawal - domestic or agriculture

• discharges - chemicals, sewage

• deforestation

• Urbanisation - impermeable surfaces, less infiltration, flash flooding

• Agriculture

Effects of reduced evapotranspiration

• decreased atmospheric moisture and disrupted rainfall patterns

Agriculture expanded

• 72% of water use

• Irrigation and livestock

• Runoff - pesticides and excess nutrients

• Machinery compacts soil - less infiltration

• harvest season - no vegetation cover - flooding

Aral Sea

• intense irrigations stopped river flow into the sea and lowered sea level

• area decreased by 75%

• volume of water fell by 90%