Changes and Feedbacks of Land-use and Land-cover under Global Change - PowerPoint PPT Presentation

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Changes and Feedbacks of Land-use and Land-cover under Global Change

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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 – PowerPoint PPT presentation

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Title: Changes and Feedbacks of Land-use and Land-cover under Global Change


1
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

2
Outline
  • 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

3
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.

4
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5
surface energy and water balance
Land-use and land-cover change
6
1. Introduction of land-use and land-cover change
  • Research methods
  • Climate models (general circulation model (GCM)),
  • Remote sensing,
  • Field study results.

7
Outline
  • 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

8
2 Changes of forests and their feedbacks
  • 2.1 Tropical forest
  • 2.2 Temperate forest
  • 2.3 Boreal forest

9
2.1 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.

10
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.

11
2.1 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
12
2 Changes of forests and their feedbacks
  • 2.1 Tropical forest
  • 2.2 Temperate forest
  • 2.3 Boreal forest

13
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.

14
2.2 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. .
15
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.

16
2 Changes of forests and their feedbacks
  • 2.1 Tropical forest
  • 2.2 Temperate forest
  • 2.3 Boreal forest

17
2.3 Boreal forest
18
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.

19
2.3 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.
20
2 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
21
Outline
  • 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

22
3 Changes of tropical savanna and their feedbacks
23
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)

24
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
25
Outline
  • 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

26
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.

27
4 Discussion
  • Strategies
  • Effective policy should be promoted to keep the
    balance between the current requirements of human
    society and the capacity of ecosystems.

28
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 process-level understanding of
    ecosystem functioning gained from laboratory
    experiments or site-specific field studies to
    large-scale climate models should be enhanced.

29
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.

30
Thank you!
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