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.