• Energy Research

Abstract 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 15–55% 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.

AbstractLand cover changes may affect climate and the energy balance of the Earth through their influence on the greenhouse gas composition of the atmosphere (biogeochemical effects) but also through shifts in the physical properties of the land surface (biophysical effects). We explored how the radiation budget changes following the replacement of temperate dry forests by crops in central semiarid Argentina and quantified the biophysical radiative forcing of this transformation. For this purpose, we computed the albedo and surface temperature for a 7‐year period (2003–2009) from MODIS imagery at 70 paired sites occupied by native forests and crops and calculated the radiation budget at the tropopause and surface levels using a columnar radiation model parameterized with satellite data. Mean annual black‐sky albedo and diurnal surface temperature were 50% and 2.5 °C higher in croplands than in dry forests. These contrasts increased the outgoing shortwave energy flux at the top of the atmosphere in croplands by a quarter (58.4 vs. 45.9 W m−2) which, together with a slight increase in the outgoing longwave flux, yielded a net cooling of −14 W m−2. This biophysical cooling effect would be equivalent to a reduction in atmospheric CO2 of 22 Mg C ha−1, which involves approximately a quarter to a half of the typical carbon emissions that accompany deforestation in these ecosystems. We showed that the replacement of dry forests by crops in central Argentina has strong biophysical effects on the energy budget which could counterbalance the biogeochemical effects of deforestation. Underestimating or ignoring these biophysical consequences of land‐use changes on climate will certainly curtail the effectiveness of many warming mitigation actions, particularly in semiarid regions where high radiation load and smaller active carbon pools would increase the relative importance of biophysical forcing.

AbstractThe FLUXNET2015 dataset provides ecosystem-scale data on CO2, water, and energy exchange between the biosphere and the atmosphere, and other meteorological and biological measurements, from 212 sites around the globe (over 1500 site-years, up to and including year 2014). These sites, independently managed and operated, voluntarily contributed their data to create global datasets. Data were quality controlled and processed using uniform methods, to improve consistency and intercomparability across sites. The dataset is already being used in a number of applications, including ecophysiology studies, remote sensing studies, and development of ecosystem and Earth system models. FLUXNET2015 includes derived-data products, such as gap-filled time series, ecosystem respiration and photosynthetic uptake estimates, estimation of uncertainties, and metadata about the measurements, presented for the first time in this paper. In addition, 206 of these sites are for the first time distributed under a Creative Commons (CC-BY 4.0) license. This paper details this enhanced dataset and the processing methods, now made available as open-source codes, making the dataset more accessible, transparent, and reproducible.