Surface albedo raise in the South American Chaco: Combined effects of deforestation and agricultural changes.

Deforestation affects climate and the energy balance of the Earth not only through the release of greenhouse gases but also through shifts in the physical properties of the surface. These physical effects can be strongly dependent not only on the deforestation event but on the land use choices and management that follow it. Here we explored how the albedo and radiation balance of the dry subtropical Chaco forests of South America changed over the last decade in response to both deforestation and land use/management. For the whole region we analyzed changes in the mean annual albedo derived from MODIS imagery and their relation with the dominant land use trajectories for a 12-year period (2000-2012). In two focal areas we identified how specific land uses and management shifts affected the seasonality of surface albedo and green vegetation cover, quantifying their associated radiation budget changes and radiative forcing effects. Deforestation accounted for 83% of the regional albedo increase observed in Chaco, yet, land use and land management changes were also a main driver of albedo shifts, explaining the rest of the albedo rise occurred in the region. Albedo raises increased the mean annual outgoing shortwave energy flux at the top of the atmosphere producing a biophysical cooling effect which was strongly dependent on the land use choice and agricultural management, ranging from -8 W m-2 in silvopastoral systems to -17 W m-2 under single annual cropping schemes. These values are equivalent to a reduction in atmospheric CO2 of 12-27 Mg C ha-1, or 15 to 55% of the typical emissions that accompany deforestation in this region. Land use and management choices in the Chaco region produce strong divergences in the resulting albedo seasonality that should not be ignored in the assessment of their net climatic effects and the discussion of possible mitigation actions.

Highlights

In the last decade, deforestation and agricultural shifts raised regional albedo.
Management had a greater effect on albedo than the land use choice after deforestation.
Seasonality of albedo is strongly dependent on land use and management.
Albedo increases grow from silvopastoral systems to pastures to annual crops.
Land use and management choices determine the net effect of deforestation over albedo.