Medvigy: The Amazon: A resilient natural system, or the ebb of the green ocean?
The Amazon:A resilient natural system, or the ebb of the green ocean?
Amazon deforestation Expansion of the cattle and soy industries in the Amazon basin has increased deforestation rates and will soon push all-weather highways into the region’s core. RED: already deforested YELLOW and By 2050, current trends in agricultural expansion will ORANGE: deforested eliminate a total of 40% of Amazon forests. by 2050 Red is projected to be deforested by the year 2050. (Soares-Filho et al. 2006)
Characteristics of the landscape: vegetation Other Wooded grassland Agriculture Short grass Water Tropical rainforest N/A Deciduous shrubNote the river; the large expanse of tropical rainforest; several large areas of agriculture.
Characteristics of the landscape: topography1. Andes Mountains -- very high! -- very narrow in the north -- somewhat wider in the south2. Guyanan Highlands3. Brazilian Highlands1. Note that the Amazon is relatively flat.
Spatial patterns of rainfall in the Amazon mm/day 1. Northwest Amazon gets a lot of rain. • There is another rainfall maximum near the mouth of the river. • Note the northwest-to- southeast gradient. 1. The Andes are generally dry, though Eastern slopes can be very wet. • Driest desert on Earth• Wettest city on Earth (Atacama Desert, Chile) (Quibdo, Columbia; 8+ meters rain/year) (Data from TRMM)
Seasonality of Amazon precipitation January July 0 5 10 15 20 mm/d (Data from TRMM)
Interannual variability: Amazon River flooding Flood area, % deviation from mean Total flood area No statistically significant long-term trend in river discharge (Davidson et al. 2012)
Tropical rainforests and carbon: 1. Forests take up carbon through photosynthesis 2. Forests release carbon through respiration Is there a net effect? 3. What is the net effect in the wet season? The dry season?
Seasonality of the Carbon Cycle: 1 site in eastern Amazonia Wet season: Dry season: ecosystem loses carbon ecosystem gains carbon(Saleska et al. 2003)
Different answers at different sites North: Evaporation is not seasonal South: Evaporation is reduced in the dry season (da Rocha et al. 2009)
How about long-term droughts: rainfall exclusion experiments Soil moisture at the control siteTarps cover ground, preventing infiltration of water to soil (da Costa et al. 2010)
1. Trees die2. Surviving trees don’tgrow as much
Recent mega-droughts: 2005, 2010 (Lewis et al. 2011)
The origin of Amazon precipitation In the atmosphere above the Amazon, water exits as rain. Water enters either through (1) winds that transport moist, marine air; or (2) evaporation from the Clouds land surface.Andes Winds blow moist, marine air Rain over the continent Evaporation Vegetation/Land Atlantic Ocean Water is neither created nor destroyed: Rain = Evaporation + Moisture transport.
How will deforestation affect the Amazon?1. Traditionally, atmospheric General Circulation Models (GCMs) have been used to infer the effects of deforestation.• The most commonly considered scenario is the most extreme: what if all tropical rainforests were converted to pasture?
Tropical deforestation reduces evapotranspiration (Findell et al. 2006)
Tropical deforestation increases surface air temperatures
Tropical deforestation leads to changes in rainfall Simulated reductions in rainfall [mm] with 2 different models. Results are for January-February(Ramos da Silva et al. 2008)
Is total deforestation realistic?What if only small portions of the tropics were deforested?What if there was somecomplicated mosaic of land cover?Current deforestation: 20%Projected 2050 deforestation: 40%Max projected deforestation: 60% (Walker et al. 2009)
Trends in rainy season onset(Four stations with long time series in the deforested area)(No stations had a significantly earlier start to the rainy season)(Trends > 0.5 days/year)
No significant changes in precipitation totals
The Ocean-Land-Atmosphere Model (OLAM): A multiple-resolution Earth System Model Staggered C Grid; Shaved, Cartesian coordinates IcosahedronOLAM solves a finite-volume analogof the full compressible Navier-Stokes equations in conservation form,and exactly conserves mass andmomentum. Unstructured Grid; No overlapping grid cell; No special nest communication; Each cell communicates directly with its neighbor independently of resolution
Changes in extreme “cold” events(Medvigy et al., in press)