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Effects of Land Cover Change on local and regional climate Ann Thijs Physical Climatology December 1, 2005 Tropical deforestation, Borneo
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Outline The Litvak Lab just a bit of my own research Land Cover Change Deforestation tropical forest Deforestation boreal forest Urban development
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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
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Litvak Lab Theme: Biogeochemical cycles: Biosphere-Atmosphere exchange of energy, water and CO 2 (importance for carbon cycle and local / regional climate) Soil processes: nitrogen cycle, carbon sequestration
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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 CO 2 levels, altered precipitation regimes, nitrogen pollution 1965 1975 1990 1995
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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.
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Eddy covariance tower
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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
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Land Cover Changes Deforestation tropical forest Deforestation boreal forest Urban development: UHI
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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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Tropical deforestation Snyder et al, 2004
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Tropical deforestation Snyder et al, 2004
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Tropical deforestation Snyder et al, 2004
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Tropical deforestation Snyder et al, 2004 - 30 % +0.6 -- +3.8 °C -1.0 – 1.6 mm/day
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Deforestation of tropical forest Mostly changes in water balance Model Results: Decreased surface roughness oReduced ET, latent heat flux oIncreased surface temperatures oPrecipitation decreases Increased albedo, lower net radiation (smaller effect)
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Boreal deforestation Snyder et al, 2004
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Boreal deforestation Snyder et al, 2004
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Boreal deforestation Snyder et al, 2004 156 % increase -2.8°C +9%
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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
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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
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visibleearth.nasa.gov
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Urban Heat Islands Increased minimum temperature at night Small increase or decrease maximum temperature during day Decrease in diurnal range of temperatures
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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
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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
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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
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