Key Questions

1
HEAT

• Key Questions
• What controls lake temperature?
• What controls heat inputs from specific sources,
  and how do these vary in time and space?

2
Heat and temperature

• Heat
• Heat is total amount of energy in something
• Heat flux is quantifiable

• Temperature
• Temperature is related to average heat content
• Mass independent
• Material dependent

Heat content H mass temp specific heat
3
Intrinsic properties of water

• Water - high specific heat (strong H-bonding)
• Absorbs heat well
• Increase temperature and lose heat slowly- heat
  storage
• High heat of vaporization large heat loss by
  evaporation
• Heat of fusion relatively small importance of
  ice?

4
Heat Budget

• Birgean Heat required to account for annual
  change in lake temperature, cal or J/cm2/yr

5
Heat Sources and Sinks

• Sun/atmosphere
• - Longwave
• - Shortwave
• Air
• - Conduction
• (sensible)
• Inflow
• - Surface Flow
• Groundwater
• Sediments

• Atmosphere
• - Evaporation (latent)
• - Longwave radiation
• - Sensible
• Outflow
• - Seepage and
• Surface Flow
• Sediments

Which are most important?
6
Atmospheric sources and sinks

• Losses
• Longwave ? T4
• Latent heat ?
• LvEvaporation
• Sensible heat ?Tair - Tlake, Wind

Latent heat
- Sources radiation (lw sw)
From Horne and Goldman 1994
What are terms affected by current global warming?
7
Catchment Inputs/Outputs

• Inflow, outflow, sediment heat inputs ?
  hydrology, morphometry
• Importance varies seasonally

8
Some heat budgets
9
Lake
Air
Temp Pressure Wind SW Rad LW Rad
Temp Net Radiation Latent heat Sensible
heat Heat change
10
Conclusions

• Lake Morphometry strongly controls net (Birgean)
  heat budget of lakes
• Inputs of heat to lakes is dominated by
  atmospheric radiation
• Heat outputs are primarily via evaporation and
  secondarily sensible heating
• Small, shallow lakes can have important heat
  inputs from the catchment and sediments.
• Lake Temperature balance of heat inputs and
  outputs and is less variable than air temperature