Effects of Land Cover Change on local and

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

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

Litvak Lab Theme n How does vegetation change alter biogeochemical cycles? n 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 n n 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

Juniper encroachment in Texas savannas n Altered ecosystem function: ¡ Energy balance: n n n ¡ Water balance: n n ¡ decreased albedo ? ? ? higher latent and sensible heat exchange ? ? ? lower surface temperatures ? ? ? increased evapotranspiration ? ? ? lower groundwater recharge ? ? ? Carbon balance: n Considered a carbon sink, but remains one of the largest unknowns in the North American carbon balance.

Eddy covariance tower

Land Cover Changes n n 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 n n n Deforestation tropical forest Deforestation boreal forest Urban development: UHI

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)

Snyder et al, 2004 Tropical deforestation

Snyder et al, 2004 Tropical deforestation

Snyder et al, 2004 Tropical deforestation

Tropical deforestation - 30 % +0. 6 -- +3. 8 °C -1. 0 – 1. 6 mm/day Snyder et al, 2004

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

Boreal deforestation Snyder et al, 2004

Boreal deforestation Snyder et al, 2004

Boreal deforestation 156 % increase -2. 8°C +9% Snyder et al, 2004

Deforestation of boreal forests n n n 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 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)

visibleearth. nasa. gov

Urban Heat Islands n 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 n n Traditional method Innovative method: ¡ ¡ ¡ Time series from weather stations Time series from NCEP/NCAR-DOE reanalysis (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

Urban Heat Islands n Traditional estimate warming effect: ¡ n 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)

Conclusions n n 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