Changes and Feedbacks of
Land-use and Land-cover under
Global Change
Mingjie Shi
Physical Climatology Course,
387H
The University of Texas at
Austin, Austin, TX
November 25, 2008
Outline
1. Introduction of land-use and landcover change.
2. Changes of forests and their
feedbacks
3. Changes of tropical savanna and
their feedbacks
4. Discussion
1. Introduction of land-use and
land-cover change
Variations promoted by anthropogenic
activities include:
Substituting forests and grassland for
agriculture use,
Intensifying farmland production,
Urbanization.
Deforestation
Intensified use
Urbanization
Albedo
Land-use
and
land-cover
change
Roughness length
Leaf-area index
(LAI)
surface energy
and
water balance
1. Introduction of land-use and
land-cover change
Research methods:
Climate models (general circulation
model (GCM)),
Remote sensing,
Field study results.
Outline
1. Introduction of land-use and landcover change.
2. Changes of forests and their
feedbacks
3. Changes of tropical savanna and
their feedbacks
4. Discussion
2 Changes of forests and their
feedbacks
2.1 Tropical forest
2.2 Temperate forest
2.3 Boreal forest
2.1 Tropical forest
 Climate model
simulations show that
tropical forests maintain
high rates of evapotranspiration, decrease
surface air temperature,
and increase precipitation
compared with pastureland.
 Flux tower measurements
in the Brazilian Amazon
indicates that forests have
lower albedo compared
with pasture.
2.1 Tropical forest
 Simulations with general circulation models
(GCMs) demonstrated that changes in albedo,
roughness length, leaf-area index and
rooting depth caused by tropical
deforestation reduce precipitation and
relative humidity and increase surface
temperature and wind speed.
2.1 Tropical forest
Thinning or removal
of the forest canopy
Reduces tree cover and
prevents tree regeneration
Greater insolation
at the soil surface
Increases the air temperature
and decreases relative humidity
near the soil surface.
Increase fire risk
2 Changes of forests and their
feedbacks
2.1 Tropical forest
2.2 Temperate forest
2.3 Boreal forest
2.2 Temperate forest
Temperate forests are forest in the
temperate climate zones. They
include:
Temperate deciduous forest,
Tempereate broadleaf and mixed
forests,
Temperate coniferous forests,
Temperate rain forest.
2.2 Temperate forest
Mesoscale model simulations
Studies of eastern United States forests:
in the United States
trees maintain a warmer summer climate
in July indicated: trees
compared with crops. Lower albedo,
increase evapotranspiration
augmentation of evaporative cooling from
and decrease surface air
crops and feedbacks with the atmosphere
temperature compared
that affect clouds and precipitation.
with crops.
Flux tower analyses show:
conifer and deciduous broadleaf
forests in North Carolina have
lower surface radiative temperature
than grass fields. Greater
aerodynamic conductance
and evaporative cooling.
In western Europe, forest and
agricultural land have comparable
surface radiative temperature
when soil is moist but
respond differently to drought. .
2.2 Temperate forest
It can be seen that the net climate
forcing of temperate forests is highly
uncertain. Besides, the future of
temperate forests and their climate
services has high uncertainty.
2 Changes of forests and their
feedbacks
2.1 Tropical forest
2.2 Temperate forest
2.3 Boreal forest
2.3 Boreal forest
2.3 Boreal forest
• Boreal forests are different in energy
balance, which usually based on the
types of forest.
• Conifer forests, for example, have low
summertime evaporative fraction
(defined as the ratio of latent heat flux
to available energy), while the
deciduous broadleaf forests always
produce high rates of sensible heat
exchange and deep atmospheric
boundary layers.
2.3 Boreal forest
Surface albedo increase
(The trend of temperature
decrease)
Climate forcing raises
the fire frequency
offset
deforestation
cools climate
Carbon emission increase
(The trend of temperature
increasae)
Yet in the first year after fire, positive annual biogeochemical forcing
from greenhouse gas emission, ozone, black carbon deposited
on snow and ice, and aerosols exceeds the negative albedo forcing.
2 Changes of forests and their
feedbacks
Carbon
storage
Evaporative
cooling
Albedo
decrease
If is
replaced
by grassland or
farmland
Feedback
Tropical
forests
Strong
Strong
moderate
Trend to
warmer
and drier
the air
Positive
Temperate
forest
Strong
Moderate
Moderate
Uncertain
Positive
and
negative
(Uncertain)
Boreal
forest
Moderate
Weak
strong
Trend to
Negative
cool down
the
surface.
Outline
1. Introduction of land-use and landcover change.
2. Changes of forests and their
feedbacks
3. Changes of tropical savanna and
their feedbacks
4. Discussion
3 Changes of tropical savanna
and their feedbacks
3 Changes of tropical savanna
and their feedbacks
Degrades of tropical savanna mainly
induced by:
Expansion of agriculture
Increase of grazing
Fire frequency (result from temperature
increase)
3 Changes of tropical savanna
and their feedbacks
• Based on model and satellites research:
Degrades of tropical savanna
decrease precipitation,
increase dry season max temperature,
increase dry season maximum wind speed,
decrease dry season minimums
relative humidity
Fire risk increase
Outline
1. Introduction of land-use and landcover change.
2. Changes of forests and their
feedbacks
3. Changes of tropical savanna and
their feedbacks
4. Discussion
4 Discussion
Requirement:
Meeting immediate human needs and
maintaining the capacity of ecosystems
to provide goods and services in the
future.
Mitigate climate change induced by
CO2 emission, land-use and land-cover
changes.
4 Discussion
Strategies:
Effective policy should be promoted to
keep the balance between the current
requirements of human society and the
capacity of ecosystems.
4 Discussion
Strategies:
 Through albedo, evapotranspiration, carbon
cycle, and other processes, forests can
amplify or dampen climate change. The
interactions between all these factors are
complex, therefore extrapolation of processlevel understanding of ecosystem
functioning gained from laboratory
experiments or site-specific field studies to
large-scale climate models should be
enhanced.
4 Discussion
Strategies:
In addition, remote sensing data can be
employed in many ways to solve
environmental problems, such as
climate change and carbon cycle, loss
of biodiversity, sustainability of
agriculture, and provision of safe
drinking water.