Expansion of soybean plantations into new agricultural frontiers may worsen the climatic impacts of deforestation in the Amazon Basin

Abstract

Over the past 20 years, soybean cultivation has expanded rapidly across the Amazon Basin. There has been growing evidence that the conversion from forest to croplands can worsen the climatic impacts of deforestation, in comparison to other land use conversions, such as forest to rural settlements, or pastures. This research applied process model simulations to clarify the biophysical mechanisms of regional climatic changes associated with the most common land use transitions in the Amazon Basin.  Our results suggest that soybean plantations, due to their minimal vegetation cover and/or seasonal bare land at harvest or planting periods, transmit more longwave radiation to the atmosphere than pastures or forests, leading to an increase in atmospheric temperature. Although the vegetation properties of the soybean plantations tend to increase the surface heat flux, resulting in a stronger surface heat lifting effect, due to the reduction of the water vapor content in the boundary layer, the regional precipitation will also be affected and reduced. Changes in atmospheric boundary layer elements are more pronounced over soybean plantations than in pastures, thereby confirming previous research that large-scale commodity crops will exacerbate regional climatic change in the Amazon Basin. Furthermore, we provide evidence that large-scale soybean plantations have more pronounced climatic impacts in the northern and western Amazon Basin, suggesting that as large-scale soybean plantations continue to expand into new agricultural frontiers, climatic changes associated with it are likely to be magnified.