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Month Day Topic C,M&M

Jan. 6 Introduction8 History of EE 1

10 Earths climate system 2

13 Energy balance 4

15 Water balance 4

17 Climate/vegetation 4

20 HOLIDAY!

22 Soils I 3

24 Soils II 3

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Bowen ratio

Can range from 10 (desert)

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Outline

Water outputs

Measurements

Vegetation and climate

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Transpiration drives water

movement through plant

Water moves in continuous column from

film on soil particles to leaf cells

Moves upward because of strong

cohesive forces among water molecules

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Plants have some water storage capacityQuite limited in most plants (2 hours in this graph)

Most of water must come from soil (not plant storage)

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Water loss from leaves Driving force is vapor pressure gradient

Depends on temperature and water vapor

in bulk air

Stomata are major resistance

Stomatal conductance depends on Soil moisture

Vapor pressure of air (in some species)

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Rate of water loss from leaves

depends on water supply

Influences water potential gradient

Plants adjust stomatal conductance to

match water supply

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Water inputs to ecosystem

determines water outputs

P + S = ET + R

P = Precipitation

S = Storage

ET = Evapotranspiration

R = Runoff

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Controls over ET

Interception

Boundary layer conductance

Physicalcontrol over water loss Depends on vegetation structure and wind

THE majorvegetationcontrolwhensoilsaremoist

Surface conductance

Depends on stomatal conductance

Becomes increasingly important as soils dry

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Streamflow is the leftovers

after storage and ET are met

Over long term, runoff depends on ppt

and ET

Runoff = (P + S) ET

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In moist ecosystems, ET is relatively insensitive to ppt.

Precipitation directly regulates streamflow

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Converting the Amazon to pasture

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Consequences of deforestation 25-40% of ppt in Amazon basin comes from

within-basin ET

Dry air = decreased transport of ocean air tobasin

Permanent reduction in ppt

Favors grasses/savannah vegetation/fire

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Positive feedback to grass/fire

q Rooting depth

q ET/LE

oAirT

o H

q Humidity

q ppt

o Grass/fire

+

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Forests absorb more radiation (lower albedo)

Forests transfer more sensible heat to atmosphere

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Air over forest is warmer and more humid at any give height

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Positive feedback to migration of treeline

o Trees

o H

qAlbedo

(earlier spring)

o Rnet

oAirT

Warmer climate

+

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Energy

Measurements Rnet

Storage

Ground heat flux

Sensible heat flux

Latent heat flux