Evaluation of downscaled projections of present and future fire risk in the amazon basin

Abstract

Climate change and deforestation are two of the major obstacles that the Amazon Forest is facing in the 21st century. Consequently, these two factors contribute to an ideal scenario where fire occurrence becomes more frequent and more intense. Therefore, this work aimed to evaluate the effects of increasing greenhouse gases and deforestation on precipitation, temperature, and fire risk in the Amazon basin. To do this, Eta model simulations forced by three global circulation models (BESM, HADGEM-ES2 and MIROC5) were used. These simulations resulted in three different experiments, with the control experiment characterizing the current climate (1979-2005) and two experiments characterizing the future climate (2070-2100). The simulations of the future climate were based on two scenarios, the first with only increasing atmospheric CO2 concentrations (RCP8.5_DEF15) and the second with the combination of high CO2 emissions and deforestation (RCP8.5_DEFTOT). Fire risk was calculated via the simulations of precipitation and maximum temperature using the Keetch-Byram drought index (KBDI). To better understand the behavior of the simulations, validation of the control experiment was performed for the dry period (July, August and September). In general, the maximum temperature and the temperature at 2 meters were underestimated in the simulations throughout the basin, and precipitation was overestimated. For the KBDI, the use of the multi-model ensemble method showed an advantage over individual members and, despite the biases found in the previous variables, the KBDI did not show a tendency to reach extreme values. For the future climate, using greenhouse gas emissions and deforestation scenarios, precipitation was reduced and the maximum temperature increased in both the dry and rainy periods. However, the largest impacts were observed during the dry period, and especially in the RCP8.5-DEFTOT scenario. For the KBDI, in the RCP8.5-DEF15 experiment, it was found that its values increase in both periods, and are concentrated to the north in the rainy period and are generalized in the basin area in the dry period. For RCP8.5-DEFTOT, the KBDI anomaly is greater, and shows that in a scenario of climate change and deforestation, the forest loses its ability to suppress conditions that are favorable to fire. Furthermore, in the extreme years of the RCP8.5-DEF15 and RCP8.5-DEFTOT experiments, respectively, 40% and 58% of the basin area present a risk of extreme fire in the dry period. Therefore, the results of this research reaffirm the importance of reducing greenhouse gases and deforestation so that fire occurrence is not a threat to the biodiversity and ecosystem services of the world’s largest tropical forest.