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ABSTRACT
Numerical models have long predicted that the deforestation of the Amazon would lead to large regional changes in precipitation and temperature, but the extratropical effects of deforestation have been a matter of controversy. This paper investigates the simulated impacts of deforestation on the northwest United States December-February climate. Integrations are carried out using the Ocean-Land-Atmosphere Model (OLAM), here run as a variable-resolution atmospheric GCM, configured with three alternative horizontal grid meshes: 1) 25-km characteristic length scale (CLS) over the United States, 50-km CLS over the Andes and Amazon, and 200-km CLS in the far-field; 2) 50-km CLS over the United States, 50-km CLS over the Andes and Amazon, and 200-km CLS in the far-field; and 3) 200-km CLS globally. In the high-resolution simulations, deforestation causes a redistribution of precipitation within the Amazon, accompanied by vor- ticity and thermal anomalies. These anomalies set up Rossby waves that propagate into the extratropics and impact western North America. Ultimately, Amazon deforestation results in 10%-20% precipitation re- ductions for the coastal northwest United States and the Sierra Nevada. Snowpack in the Sierra Nevada experiences declines of up to 50%. However, in the coarse-resolution simulations, this mechanism is not resolved and precipitation is not reduced in the northwest United States. These results highlight the need for adequate model resolution in modeling the impacts of Amazon deforestation. It is concluded that the de- forestation of the Amazon can act as a driver of regional climate change in the extratropics, including areas of the western United States that are agriculturally important.
1. Introduction
Many numerical models have predicted that Amazon deforestation would lead to local increases in surface temperature and decreases in precipitation (Henderson- Sellers et al. 1993; Lean and Rowntree 1993; Gash and Nobre 1997; Hahmann and Dickinson 1997; Costa and Foley 2000; Gedney and Valdes 2000; Werth and Avissar 2002; Avissar and Werth 2005; Findell et al. 2006; Sampaio et al. 2007; Hasler et al. 2009; Medvigy et al. 2011). Using numerical models, some studies have con- cluded that Amazon deforestation can impact extra- tropical climate (Gedney and Valdes 2000; Werth and Avissar 2002; Medvigy et al. 2012); however, other modeling studies have not found a statistically significant response (Findell et al. 2006). Using observations to di- rectly...