1.7 Hydrologic (Water) Cycle

Water Cycle Overview

Movement of H₂O (in different states) b/w sources & sinks

State of matter (Solid/Liquid/Gas) as well as where water is moving are key in H₂O cycle

Energy from sun drive H₂O cycle

• Heat from sun → Liquid water in oceans becomes a gas (evaporation) in atm

Ocean = largest Water Reservoir

Ice caps & groundwater are smaller reservoirs, but contain fresh, usable water for humans

Evaporation & Evapotranspiration

2 main sources of water (process that cycles it from liquid on earth back into the atm)

• Sometimes called “vaporization” since liquid water becomes water vapor (gas) in atm.

Both processes are driven by enegy from the sun

Transpiration

Process plants use to draw groundwater from roots up to their leaves

• Leaf openings called stomata open, allowing water to evaporate. into atm. from leaf

• Movement. of H₂O out of the leaf creates low H₂O potential in leaf, pulling H₂O up from roots

Evapotranspiration

Amount of H₂O that enters atmosphere from transpiration & evaporation combined

Runoff & Infiltration

Precipitation (rain) either flows over earth’s surface into a body of water (runoff) or trickles through soil down into groundwater aquifers (infiltration)

Groundwater (aquifers) & surface waters (lakes/rivers) are important freshwater reservoirs for humans and animals

• Precipitation recharges groundwater through infiltration, but only if ground is permeable (able to let water pass through)

  • Runoff recharges surface waters, but can also carry pollutants into water sources