Effects of Land Cover Change on local and regional climate

Ann Thijs

Physical Climatology

December 1, 2005Tropical deforestation, Borneo

Outline

The Litvak Lab just a bit of my own research

Land Cover Change Deforestation tropical forest Deforestation boreal forest Urban development

Litvak Lab Theme

How does vegetation change alter biogeochemical cycles?

Vegetation Changes studied: Succession after fire in boreal forest Effect of burn season in savanna grasslands Effect of invasive grass KR Bluestem Woody encroachment in Texas savannas Woody encroachment in New Mexico Pinon-Juniper

woodlands

Litvak Lab Theme:

Biogeochemical cycles:

Biosphere-Atmosphere exchange of energy, water and CO2

(importance for carbon cycle and local / regional climate)

Soil processes: nitrogen cycle, carbon sequestration

My own research: Savannas

One eighth of global land surface Continuous herbaceous layer and a discontinuous stratum

of shrubs and trees Woody encroachment: “the addition of woody canopies

without major losses of herbaceous cover” Causes: chronic overgrazing, disturbance of the natural fire

cycle, rising CO2 levels, altered precipitation regimes, nitrogen pollution

1965 1975 1990 1995

Juniper encroachment in Texas savannas

Altered ecosystem function: Energy balance:

decreased albedo ??? higher latent and sensible heat exchange ??? lower surface temperatures ???

Water balance: increased evapotranspiration ??? lower groundwater recharge ???

Carbon balance: Considered a carbon sink, but remains one of the

largest unknowns in the North American carbon balance.

Eddy covariance tower

Land Cover Changes

Environmental Issue of global significance – 35 % land surface already altered

Linked to other global issues: Biodiversity Climate System and Carbon Cycle Sustainability of agriculture Provision of safe drinking water Infectious diseases

Land Cover Changes

Deforestation tropical forest Deforestation boreal forest Urban development: UHI

Deforestation and forest degradation

Main areas of forest-cover change over 20 years (1980-2000) (Lepers et al, 2005)

Hotspots:

Tropical:

Amazon basin

Southeast Asia

Boreal:

Siberia

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Snyder et al, 2004

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Snyder et al, 2004

Tro

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Snyder et al, 2004

Tro

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Snyder et al, 2004

- 30 %

+0.6 -- +3.8 °C

-1.0 – 1.6 mm/day

Deforestation of tropical forest

Mostly changes in water balance Model Results:

Decreased surface roughnesso Reduced ET, latent heat flux

o Increased surface temperatureso Precipitation decreases

Increased albedo, lower net radiation (smaller effect)

Boreal deforestation

Snyder et al, 2004

Boreal deforestation

Snyder et al, 2004

Boreal deforestation

Snyder et al, 2004

156 % increase

-2.8°C

+9%

Deforestation of boreal forests

Mostly changes in surface energy balance Especially in winter/spring: removal of

vegetation exposes snow surfaces and increase albedo, leading to lower net radiation and lower surface temperatures

Climate response can be amplified by a SST / sea ice / albedo positive feedback

Urban growth

Population density in 1995 and most populated and changing cities over 750000 inhabitants between 1980 and 2000 (Lepers et al, 2005)

Highest densities:

India China Java

Major cities:

Western Europe East coast US India East Asia

Growth:

Tropical belt

visibleearth.nasa.gov

Urban Heat Islands

Urban Heat Islands Increased minimum temperature at night Small increase or decrease maximum

temperature during day Decrease in diurnal range of temperatures

Urban Heat Islands

Traditional method Innovative method:

Time series from weather stations

Time series from NCEP/NCAR-DOE re-analysis (R-1 or R-2) (estimate of surface T solely dependent on atmospheric measurements - independent of surface cover

Contribution of warming due to land cover change or increased greenhouse effect Zhou et al, 2004

Traditional estimate warming effect: 0.06-0.15°C per century in the US

Estimate using innovative method 0.37°C per century in eastern US (Kalnay

and Cai, 2003) 0.5°C per century in China (Zhou et al,

2004)

Urban Heat Islands

Conclusions

Land Cover Change extensive and has demonstrated impact on climate

Study methods: Very localized empirical measurements - e.g.

eddy covariance, FLUXNET Modeling approaches – mostly coupled

atmosphere-biosphere models; need to use coupled atmosphere-biosphere-ocean models

Time series analysis – e.g. UHI