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Impact of deforestation in the Amazon basin on cloud climatology

Shallow clouds are prone to appear over deforested surfaces whereas deep clouds, much less frequent than shallow clouds, favor forested surfaces. Simultaneous atmospheric soundings at forest and pasture sites during the Rondonian Boundary Layer Experiment (RBLE-3) elucidate the physical mechanisms responsible for the observed correlation between clouds and land cover. We demonstrate that the atmospheric boundary layer over the forested areas is more unstable and characterized by larger values of the convective available potential energy (CAPE) due to greater humidity than that which is found over the deforested area. The shallow convection over the deforested areas is relatively more active than the deep convection over the forested areas. This greater activity results from a stronger lifting mechanism caused by mesoscale circulations driven by deforestation-induced heterogeneities in land cover.

Plain English Discussion

In Rondonia in the southwestern Amazon, some of the forest has been converted to pasture. It is warmer and drier over the pasture than the nearby forest. This tends to favor more shallow cumulus clouds over the pasture and deeper clouds that rain more over the forest.

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Wang, J., F. J. F. Chagnon, E. Williams, A. K. Betts, N. O. Renno, L. A. T. Machado, G. Bisht, R. Knox and R. L. Bras (2009), Impact of deforestation in the Amazon basin on cloud climatology. PNAS, 106, 3670-3674. doi:10.1073/pnas.0810156106 http://www.pnas.org/content/106/10/3670.full.pdf+html