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  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 CO 2 (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 CO 2 levels, altered precipitation regimes, nitrogen pollution

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 ( ) (Lepers et al, 2005) Hotspots: Tropical: Amazon basin Southeast Asia Boreal: Siberia

Tropical deforestation Snyder et al, 2004

Tropical deforestation Snyder et al, 2004

Tropical deforestation Snyder et al, 2004

Tropical deforestation Snyder et al, % °C -1.0 – 1.6 mm/day

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)

Boreal deforestation Snyder et al, 2004

Boreal deforestation Snyder et al, 2004

Boreal deforestation Snyder et al, % 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 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  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:  °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