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Effects of Land Cover Change on local and regional climate

Effects of Land Cover Change on local and regional climate. Ann Thijs Physical Climatology December 1, 2005. Tropical deforestation, Borneo. Outline. The Litvak Lab just a bit of my own research Land Cover Change Deforestation tropical forest Deforestation boreal forest

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Effects of Land Cover Change on local and regional climate

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  1. Effects of Land Cover Change on local and regional climate Ann Thijs Physical Climatology December 1, 2005 Tropical deforestation, Borneo

  2. Outline • The Litvak Lab • just a bit of my own research • Land Cover Change • Deforestation tropical forest • Deforestation boreal forest • Urban development

  3. 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

  4. 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

  5. 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

  6. 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.

  7. Eddy covariance tower

  8. 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

  9. Land Cover Changes • Deforestation tropical forest • Deforestation boreal forest • Urban development: UHI

  10. Deforestation and forest degradation Hotspots: Tropical: Amazon basin Southeast Asia Boreal: Siberia Main areas of forest-cover change over 20 years (1980-2000) (Lepers et al, 2005)

  11. Tropical deforestation Snyder et al, 2004

  12. Tropical deforestation Snyder et al, 2004

  13. Tropical deforestation Snyder et al, 2004

  14. - 30 % +0.6 -- +3.8 °C Tropical deforestation -1.0 – 1.6 mm/day Snyder et al, 2004

  15. Deforestation of tropical forest • Mostly changes in water balance • Model Results: • Decreased surface roughness • Reduced ET, latent heat flux • Increased surface temperatures • Precipitation decreases • Increased albedo, lower net radiation(smaller effect)

  16. Boreal deforestation Snyder et al, 2004

  17. Boreal deforestation Snyder et al, 2004

  18. Boreal deforestation 156 % increase -2.8°C +9% Snyder et al, 2004

  19. 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

  20. Urban growth Highest densities: India China Java Major cities: Western Europe East coast US India East Asia Growth: Tropical belt Population density in 1995 and most populated and changing cities over 750000 inhabitants between 1980 and 2000 (Lepers et al, 2005)

  21. visibleearth.nasa.gov

  22. 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

  23. 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

  24. Urban Heat Islands • 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)

  25. 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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