ATS 761 Land-Atmosphere Interaction 2014 Dynamic Vegetation

Scott Denning CSU ATS 1

Dynamic Vegetation

Please read Bonan Chapters 22-25

Simple Climate Classification

Simple Vegetation Classification Biogeography

ATS 761 Land-Atmosphere Interaction 2014 Dynamic Vegetation

Scott Denning CSU ATS 2

Somewhat More Sophisticated

Radiation vs the ratio of radiation to precipitation

“Paint by Numbers”

PET/

PPT

“bio

tem

pera

ture

”

Succession

•  This is an ecological progression, not climate change •  The paint-by-numbers approach would never do this

Alaskan Succession after Fire

ATS 761 Land-Atmosphere Interaction 2014 Dynamic Vegetation

Scott Denning CSU ATS 3

Agricultural Land Use

•  Insufficient to consider only climate and succession

•  People intentionally replace vegetation for our gain

•  Not just for agriculture!

Cropland in USA

Historical Land-Use Changes

•  Westward ho!

•  Abandonment of previously-cultivated land produces secondary forest

•  Also suburbia!

Vegetation Changes since

the Last Glacial

Maximum •  Reconstructed

primarily from fossil pollen

•  Huge changes!

•  Paint-by-numbers not too bad for this process

•  Very slow changes

ATS 761 Land-Atmosphere Interaction 2014 Dynamic Vegetation

Scott Denning CSU ATS 4

Natural Vegetation

Changes Since Warm Climate at 6000 BP

Dynamic Global Vegetation Modeling

(DGVM)

Vegetation Forcing of

Climate Change

albedo

roughness

Climate Effects of Vegetation

Removal

ATS 761 Land-Atmosphere Interaction 2014 Dynamic Vegetation

Scott Denning CSU ATS 5

Climate-Vegetation Feedback:

Desertification (Charney, 1975)

•  No longer paint-by-numbers, because the “paint” affects the “numbers!”

•  Changes in vegetation cause changes in energy balance

•  Δ Energy balance causes Δ climate

•  Δ climate causes change in potential vegetation

Coupled Vegetation-Climate Models

(1)  Equilibrium climate differences …

Coupled Vegetation-Climate Models

(2) Iterated transient simulations

Coupled Vegetation-Climate Models (3) Fully interactive!

ATS 761 Land-Atmosphere Interaction 2014 Dynamic Vegetation

Scott Denning CSU ATS 6

Dynamic Vegetation

and Interannual Variability over Sahel •  Decadal

rainfall changes not well predicted unless vegetation interacts with climate!

dry wet

dry wet

Sahelian Desertification and Roots

Deep roots let water from rainy season sustain latent heat flux into following dry season … fuels convection & winds!

Coupled Vegetation and Future

Climate Change