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Changes and Feedbacks of Changes and Feedbacks of Land-use and Land-cover under Land-use and Land-cover under
Global Change Global Change
Mingjie ShiMingjie ShiPhysical Climatology Course, 38Physical Climatology Course, 38
7H7HThe University of Texas at AustiThe University of Texas at Austi
n, Austin, TXn, Austin, TXNovember 25, 2008November 25, 2008
OutlineOutline1. Introduction of land-use and land-1. Introduction of land-use and land-
cover change.cover change.
2. Changes of forests and their 2. Changes of forests and their feedbacksfeedbacks
3. Changes of tropical savanna and 3. Changes of tropical savanna and their feedbackstheir feedbacks
4. Discussion4. Discussion
1. Introduction of land-use and 1. Introduction of land-use and land-cover changeland-cover change
Variations promoted by anthropogenic Variations promoted by anthropogenic activities include:activities include:
Substituting forests and grassland for Substituting forests and grassland for agriculture use, agriculture use,
Intensifying farmland production,Intensifying farmland production, Urbanization. Urbanization.
Deforestation
Intensified use
Urbanization
Land-use and
land-cover change
surface energy and
water balance
Albedo
Roughness length
Leaf-area index (LAI)
1. Introduction of land-use and 1. Introduction of land-use and land-cover changeland-cover change
Research methods: Research methods: Climate models (general circulation Climate models (general circulation
model (GCM)),model (GCM)), Remote sensing, Remote sensing, Field study results. Field study results.
OutlineOutline1. Introduction of land-use and land-1. Introduction of land-use and land-
cover change.cover change.
2. Changes of forests and their 2. Changes of forests and their feedbacksfeedbacks
3. Changes of tropical savanna and 3. Changes of tropical savanna and their feedbackstheir feedbacks
4. Discussion4. Discussion
2 Changes of forests and their 2 Changes of forests and their feedbacksfeedbacks
2.1 Tropical forest2.1 Tropical forest
2.2 Temperate forest2.2 Temperate forest
2.3 Boreal forest2.3 Boreal forest
2.1 Tropical forest2.1 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.
2.1 Tropical forest2.1 Tropical forest
Simulations with general circulation models Simulations with general circulation models (GCMs) demonstrated that changes in albedo,(GCMs) demonstrated that changes in albedo, roughness length, leaf-area index and rootin roughness length, leaf-area index and rooting depth caused by tropical deforestation g depth caused by tropical deforestation redreduceuce precipitation and relative humidity and precipitation and relative humidity and inincreasecrease surface temperature and wind speed. surface temperature and wind speed.
2.1 Tropical forest2.1 Tropical forest
Greater insolation at the soil surface
Increases the air temperature and decreases relative humidity
near the soil surface.
Increase fire risk
Reduces tree cover and prevents tree regeneration
Thinning or removal of the forest canopy
2 Changes of forests and their 2 Changes of forests and their feedbacksfeedbacks
2.1 Tropical forest2.1 Tropical forest
2.2 Temperate forest2.2 Temperate forest
2.3 Boreal forest2.3 Boreal forest
2.2 Temperate forest2.2 Temperate forest
Temperate forests are forest in the Temperate forests are forest in the temperate climate zones. They temperate climate zones. They include:include:
Temperate deciduous forest,Temperate deciduous forest, Tempereate broadleaf and mixed Tempereate broadleaf and mixed
forests, forests, Temperate coniferous forests, Temperate coniferous forests, Temperate rain forest.Temperate rain forest.
2.2 Temperate forest2.2 Temperate forestStudies 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 broadleafforests 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 forest2.2 Temperate forest
It can be seen that the net climate It can be seen that the net climate forcing of temperate forests is highly forcing of temperate forests is highly uncertain. Besides, the future of uncertain. Besides, the future of temperate forests and their climate temperate forests and their climate services has high uncertainty.services has high uncertainty.
2 Changes of forests and their 2 Changes of forests and their feedbacksfeedbacks
2.1 Tropical forest2.1 Tropical forest
2.2 Temperate forest2.2 Temperate forest
2.3 Boreal forest2.3 Boreal forest
2.3 Boreal forest2.3 Boreal forest
2.3 Boreal forest2.3 Boreal forest• Boreal forests are different in energy Boreal forests are different in energy
balance, which usually based on the balance, which usually based on the types of forest. types of forest.
• Conifer forests, for example, have low Conifer forests, for example, have low summertime evaporative fraction summertime evaporative fraction (defined as the ratio of latent heat flux (defined as the ratio of latent heat flux to available energy), while the to available energy), while the deciduous broadleaf forests always deciduous broadleaf forests always produce high rates of sensible heat produce high rates of sensible heat exchange and deep atmospheric exchange and deep atmospheric boundary layers.boundary layers.
2.3 Boreal forest2.3 Boreal forest
Climate forcing raises the fire frequency
Surface albedo increase(The trend of temperature
decrease)
Carbon emission increase(The trend of temperature
increasae)
offset deforestation cools climate
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 2 Changes of forests and their feedbacksfeedbacks
Carbon Carbon storagestorage
Evaporative Evaporative coolingcooling
Albedo deAlbedo decreasecrease
If is If is replaced replaced by grass-by grass-land or land or farmlandfarmland
FeedbackFeedback
Tropical Tropical forestsforests
StrongStrong StrongStrong moderatemoderate Trend to Trend to warmer warmer and drier and drier the airthe air
Positive Positive
Temperate Temperate forestforest
StrongStrong ModerateModerate ModerateModerate UncertainUncertain PositivePositive and and negativenegative (Uncertain)(Uncertain)
Boreal Boreal forestforest
ModerateModerate WeakWeak strongstrong Trend to Trend to cool down cool down the the surface. surface.
NegativeNegative
OutlineOutline1. Introduction of land-use and land-1. Introduction of land-use and land-
cover change.cover change.
2. Changes of forests and their 2. Changes of forests and their feedbacksfeedbacks
3. Changes of tropical savanna and 3. Changes of tropical savanna and their feedbackstheir feedbacks
4. Discussion4. Discussion
3 Changes of tropical savanna 3 Changes of tropical savanna and their feedbacksand their feedbacks
3 Changes of tropical savanna 3 Changes of tropical savanna and their feedbacksand their feedbacks
Degrades of tropical savanna mainly Degrades of tropical savanna mainly induced by:induced by:
Expansion of agriculture Expansion of agriculture Increase of grazing Increase of grazing Fire frequency (result from temperature Fire frequency (result from temperature
increase)increase)
3 Changes of tropical savanna 3 Changes of tropical savanna and their feedbacksand their feedbacks
• Based on model and satellites Based on model and satellites research: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
OutlineOutline1. Introduction of land-use and land-1. Introduction of land-use and land-
cover change.cover change.
2. Changes of forests and their 2. Changes of forests and their feedbacksfeedbacks
3. Changes of tropical savanna and 3. Changes of tropical savanna and their feedbackstheir feedbacks
4. Discussion4. Discussion
4 Discussion4 Discussion Requirement:Requirement: Meeting immediate human needs and Meeting immediate human needs and
maintaining the capacity of ecosystems maintaining the capacity of ecosystems to provide goods and services in the to provide goods and services in the future.future.
Mitigate climate change induced by Mitigate climate change induced by CO2 emission, land-use and land-cover CO2 emission, land-use and land-cover changes.changes.
4 Discussion4 Discussion Strategies:Strategies: Effective policy should be promoted to Effective policy should be promoted to
keep the balance between the current keep the balance between the current requirements of human society and the requirements of human society and the capacity of ecosystems. capacity of ecosystems.
4 Discussion4 Discussion
Strategies:Strategies: Through albedo, evapotranspiration, carbon Through albedo, evapotranspiration, carbon
cycle, and other processes, forests can amplicycle, and other processes, forests can amplify or dampen climate change. The interactionfy or dampen climate change. The interactions between all these factors are complex, thers between all these factors are complex, therefore extrapolation of process-level understaefore extrapolation of process-level understanding of ecosystem functioning gained from lnding of ecosystem functioning gained from laboratory experiments or site-specific field staboratory experiments or site-specific field studies to large-scale climate models should budies to large-scale climate models should be enhanced.e enhanced.
4 Discussion4 Discussion
Strategies:Strategies: In addition, remote sensing data can be In addition, remote sensing data can be
employed in many ways to solve employed in many ways to solve environmental problems, such as environmental problems, such as climate change and carbon cycle, loss climate change and carbon cycle, loss of biodiversity, sustainability of of biodiversity, sustainability of agriculture, and provision of safe agriculture, and provision of safe drinking water. drinking water.