To evaluate the individual and combined impacts of increasing greenhouse gases and deforestation on extreme precipitation events in the Amazon Basin, we carried out 4 numerical experiments with the regional Eta model forced from the initial and boundary conditions of the global HadGEM2-ES model: (1) control experiment (CTRL); (2) RCP8.5 scenario; (3) DEFOREST scenario; and (4) RCP8.5+DEFOREST scenario. To analyze changes in extreme rainy events associated with the increase in greenhouse gases, deforestation, and their combined effect, anomalies were calculated from the sensitivity and control experiments. In the RCP8.5 scenario, there was an increase in the maximum number of consecutive dry days (CDD), a reduction in the maximum number of consecutive wet days (CWD), a reduction in total annual precipitation (PRCPTOT), and an increase in the maximum precipitation accumulated in 5 consecutive days (RX5Day). The DEFOREST scenario evidenced an increased CDD, and a reduction in the other indices (CWD, PRCPTOT, and RX5Day). Furthermore, the RCP8.5+DEFOREST scenario exhibited an increased CDD, and a reduction in the other indices (CWD, PRCPTOT, and RX5Day), but with more intense increases and reductions than observed in the DEFOREST scenario. In general, towards the end of the 21st century, the 3 scenarios are projected to increase the drought period, mainly on the boundary between the Brazilian states of Amazonas and Pará.

Deforestation in the Amazon has accelerated in recent years, making it increasingly important to understand the physical processes that occur after forest removal. This study investigates how deforestation at different spatial scales alters the climate in the Amazon. Using the Eta regional climate model, 3 deforestation scenarios were simulated: a scenario with the Amazon basin totally covered by forest (FLOR); a second scenario with projected deforestation for the year 2050 (DF50); and a third scenario in which the Amazon forest is entirely replaced by degraded pasture (DFTOT). The results show that both deforestation scenarios caused a reduction in precipitation (0.10 mm d-1 for DF50 and 0.35 mm d-1 for DFTOT during the wet season), due mainly to reduced evapotranspiration in the forest (0.28 mm d-1 for DF50 and 0.96 mm d-1 for DFTOT during the wet season). Despite the increase in moisture flux convergence, it was not sufficient to increase the precipitation in the region. Deforestation resulted in increased upward motion in the lower troposphere, creating a potentially more convective environment, but not enough to produce more cloudiness and precipitation over the Amazon basin. Regardless of the considered deforestation scenario, significant changes were observed in radiation, energy and water balances, atmospheric conditions, and convective potential across much of the Amazon basin during the dry and wet seasons. However, the most significant impacts occur in scenarios of complete deforestation, indicating a direct relationship between the spatial scale of deforestation and the impact on regional climate.