ENVIRSC 1A03 Lecture Notes - Hydrosphere, Water Cycle, Permanent Wilting Point
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ENVIR SCI 1A03 February 12, 2014
Hydrologic Cycle and Water Balance
What is the Hydrosphere?
•All of Earth’s water.
•Ocean – 97% of all water, freshwater – most in glaciers and ice caps,
surface freshwater are in streams or lakes.
oOver the ocean – 86% evaporation, clouds will form and cloud will
move from over ocean to land and the transfer between land and
atmosphere are going to be balanced.
oThe movement on the land by slopes balances the net transfer
between the atmosphere and the land.
Where does Rainwater go on Land?
•Water can be absorbed by plants or evaporated = evapotranspiration
•Can infiltrate the ground and percolate downward and fill pore spaces and
recharge water table and form water table
•Move at the surface – runoff as overland flows, inter flow is just beneath
the ground surface
What is a Water Balance?
•Represents: hydrological cycle at the local state
•Accounts for interactions with the available energy and moisture at the
•Take into account moisture and latent heat
•Take a look at all the energy the system provides – output, input and
What is the Water Balance Equation?
•P = (PE – D) + S +/- ΔST
•D = PE – AE
•P – precipitation, PE – potential evapotranspiration (amount of moisture
that could potentially evaporate at a given temperature), D – deficit
(moisture shortage), S - surplus (oversupply, soil moisture at its full
capacity), ΔST- soil moisture storage change (moisture saving, snowpack,
reservoirs), AE – actual evapotranspiration, if all demand is satisfied
•Deficit and Surplus
oDeficit occurs when PE cannot be satisfied through P, soil moisture
oif growing crops, you need to find additional water for crops and
irrigation is needed
oUnder ideal conditions: AE and PE are close
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