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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 vorticity 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 reductions 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 deforestation 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.

This study investigates the possibility of changes in daily scale solar radiation and precipitation variability. Coefficients of variation (CVs) were computed for the daily downward surface solar radiation product from the International Satellite Cloud Climatology Project and the daily precipitation product from the Global Precipitation Climatology Project. Regression analysis was used to identify trends in CVs. Statistically significant changes in solar radiation variability were found for 35% of the globe, and particularly large increases were found for tropical Africa and the Maritime Continent. These increases in solar radiation variability were correlated with increases in precipitation variability and increases in deep convective cloud amount. The changes in high-frequency climate variability identified here have consequences for any process depending nonlinearly on climate, including solar energy production and terrestrial ecosystem photosynthesis. To assess these consequences, additional work is needed to understand how high-frequency climate variability will change in the coming decades.

This study investigates how future deforestation in the Amazon may alter precipitation statistics in South America using a variable-resolution GCM. The model’s grid mesh is set up to cover South America and nearby oceans at mesoscale (25 km) resolution, and then to gradually coarsen and cover the rest of the world at 200-km resolution. Because of the computational efficiency of this approach, it was possible to carry out the first decadal-scale simulations of Amazon deforestation at mesoscale resolution. Unlike traditional mesoscale models, this approach does not require lateral boundary conditions. The results indicate that deforestation reduces simulated precipitation in the Amazon, but this reduction is much smaller than that seen in most previous GCM studies. Furthermore, a subcontinental redistribution of precipitation is found whereby the northwest Amazon becomes drier and the southeast Amazon becomes wetter. During most of the year, these changes are driven by changes in the mean intensity of precipitation events; however, in September–November, changes in precipitation frequency are also important. Large changes in June–August hydroclimate were also found, with extreme cold events becoming more common. These changes have consequences for agriculture, natural ecosystems, and surface hydrology.