Amazonian Deforestation and Regional Climate Change

TLDR

Amazonian deforestation of tropical forests to pasture or crops can alter regional climate and affect neighboring areas. The study employed a coupled atmosphere–biosphere GCM and an empirical bioclimatic soil‑moisture stress index to simulate the climatic effects of large‑scale deforestation and the resulting shift of the savanna‑forest boundary. Model results show that replacing Amazon forests with pasture raises mean surface temperature by ~2.5 °C, cuts evapotranspiration, precipitation, and runoff by 30 %, 25 %, and 20 % respectively, amplifies dry‑season extremes, reduces moisture convergence, and lengthens the dry season in the southern basin, threatening forest regeneration.

Abstract

Large-scale conversion of tropical forests into pastures or annual crops could lead to changes in the climate. We have used a coupled numerical model of the global atmosphere and biosphere (Center for Ocean-Land- Atmosphere GCM) to assess the effects of Amazonian deforestation on the regional and global climate. We found that when the Amazonian tropical forests were replaced by degraded grass (pasture) in the model, there was a significant increase in the mean surface temperature (about 2.5°C) and a decrease in the annual evapo-transpiration (30% reduction), precipitation (25% reduction), and runoff (20% reduction) in the region. The differences between the two simulations were greatest during the dry season. The deforested case was associated with larger diurnal fluctuations of surface temperature and vapor pressure deficit; such effects have been observed in existing deforested arms in Amazonia. The calculated reduction in precipitation was larger than the calculated decrease in evapotranspiration, indicating a reduction in the regional moisture convergence. There was also an increase in the length of the dry season in the southern half of the Amazon Basin, which could have serious implications for the reetablishment of the tropical forests following massive deforestation since rainforests only occur where the dry season is very short or nonexistent. An empirical bioclimatic scheme based on an integrated soil moisture stress index was used to derive the movement of the savanna-forest boundary in response to the simulated climate change produced by large-scale deforestation. The implications of possible climate changes in adjacent regions are discussed.