Title: Changes and Feedbacks of Land-use and Land-cover under Global Change
1Changes 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
2Outline
- 1. Introduction of land-use and land-cover
change. - 2. Changes of forests and their feedbacks
- 3. Changes of tropical savanna and their
feedbacks - 4. Discussion
31. 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.
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5 surface energy and water balance
Land-use and land-cover change
61. Introduction of land-use and land-cover change
- Research methods
- Climate models (general circulation model (GCM)),
- Remote sensing,
- Field study results.
7Outline
- 1. Introduction of land-use and land-cover
change. - 2. Changes of forests and their feedbacks
- 3. Changes of tropical savanna and their
feedbacks - 4. Discussion
82 Changes of forests and their feedbacks
- 2.1 Tropical forest
- 2.2 Temperate forest
- 2.3 Boreal forest
92.1 Tropical forest
- Climate model simulations show that tropical
forests maintain high rates of evapo-transpiration
, 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.
102.1 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.
112.1 Tropical forest
Thinning or removal of the forest canopy
Greater insolation at the soil surface
Increases the air temperature and decreases
relative humidity near the soil surface.
Reduces tree cover and prevents tree
regeneration
Increase fire risk
122 Changes of forests and their feedbacks
- 2.1 Tropical forest
- 2.2 Temperate forest
- 2.3 Boreal forest
132.2 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.
142.2 Temperate forest
Studies of eastern United States forests trees
maintain a warmer summer climate compared with
crops. Lower albedo, augmentation of
evaporative cooling from crops and feedbacks
with the atmosphere that affect clouds and
precipitation.
Mesoscale model simulations in the United
States in July indicated trees increase
evapotranspiration and decrease surface air
temperature compared 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. .
152.2 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.
162 Changes of forests and their feedbacks
- 2.1 Tropical forest
- 2.2 Temperate forest
- 2.3 Boreal forest
172.3 Boreal forest
182.3 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.
192.3 Boreal forest
Surface albedo increase (The trend of temperature
decrease)
Climate forcing raises the fire frequency
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.
202 Changes of forests and their feedbacks
Carbon storage Evaporative cooling Albedo decrease If is replaced by grass-land 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 cool down the surface. Negative
21Outline
- 1. Introduction of land-use and land-cover
change. - 2. Changes of forests and their feedbacks
- 3. Changes of tropical savanna and their
feedbacks - 4. Discussion
223 Changes of tropical savanna and their feedbacks
233 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)
243 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
25Outline
- 1. Introduction of land-use and land-cover
change. - 2. Changes of forests and their feedbacks
- 3. Changes of tropical savanna and their
feedbacks - 4. Discussion
264 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.
274 Discussion
- Strategies
- Effective policy should be promoted to keep the
balance between the current requirements of human
society and the capacity of ecosystems.
284 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 process-level understanding of
ecosystem functioning gained from laboratory
experiments or site-specific field studies to
large-scale climate models should be enhanced.
294 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.
30Thank you!