The Effects of Amazonian Deforestation on Regional and Global Climate

Using the GISS Model II Global Climate Model, we simulate an extreme Amazon deforestation to see what effects such a change will have on the climates of Amazonia and North America. We have run the model twice: a control run with the vegetation set to its 1950 level (a mixture of several vegetation types), and a deforested run in which the rainforest in Amazonia is converted to a mixture of shrubs and grassland. Each is run out 12 years, and two complete realizations are done.

The effect of deforestation in the Amazon is substantial, with summertime precipitation and evaporation both reduced significantly. The annual cycle of precipitation-evaporation (P-E, an indicator of moisture convergence in the column) is reduced in amplitude, with a corresponding change in ground temperature and soil wetness (drier, warmer summer/cooler, wetter winter). The reason for the change in summer is the reduction in convection and the consequent reduction in large-scale moisture convergence.

The effects of Amazon deforestation in North America were strongest in the North Central region of the United States. We see the largest effects in the warmer, rainier months, with the largest reductions of precipitation and evaporation in June. The reductions were statistically weak, however. We do see that the deforested runs show a stronger relationship between precipitation and divergence aloft, suggesting a teleconnection may be operating in the deforested run.