Impacts of future deforestation and climate change on the hydrology of the Amazon Basin: a multi-model analysis with a new set of land-cover change scenarios

Abstract

Abstract. Deforestation in Amazon is expected to decrease evapotranspiration (ET) and to increase soil moisture and river discharge under prevailing energy-limited conditions. The magnitude and sign of the response of ET to deforestation depend both on the magnitude and regional patterns of land-cover change (LCC), as well as on climate change and CO2 levels. On the one hand, elevated CO2 decreases leaf-scale transpiration, but this effect could be offset by increased foliar area density. Using three regional LCC scenarios specifically established for the Brazilian and Bolivian Amazon, we investigate the impacts of climate change and deforestation on the surface hydrology of the Amazon Basin for this century, taking 2009 as a reference. For each LCC scenario, three land surface models (LSMs), LPJmL-DGVM, INLAND-DGVM and ORCHIDEE, are forced by bias-corrected climate simulated by three general circulation models (GCMs) of the IPCC 4th Assessment Report (AR4). On average, over the Amazon Basin with no deforestation, the GCM results indicate a temperature increase of 3.3 °C by 2100 which drives up the evaporative demand, whereby precipitation increases by 8.5 %, with a large uncertainty across GCMs. In the case of no deforestation, we found that ET and runoff increase by 5.0 and 14 %, respectively. However, in south-east Amazonia, precipitation decreases by 10 % at the end of the dry season and the three LSMs produce a 6 % decrease of ET, which is less than precipitation, so that runoff decreases by 22 %. For instance, the minimum river discharge of the Rio Tapajós is reduced by 31 % in 2100. To study the additional effect of deforestation, we prescribed to the LSMs three contrasted LCC scenarios, with a forest decline going from 7 to 34 % over this century. All three scenarios partly offset the climate-induced increase of ET, and runoff increases over the entire Amazon. In the south-east, however, deforestation amplifies the decrease of ET at the end of dry season, leading to a large increase of runoff (up to +27 % in the extreme deforestation case), offsetting the negative effect of climate change, thus balancing the decrease of low flows in the Rio Tapajós. These projections are associated with large uncertainties, which we attribute separately to the differences in LSMs, GCMs and to the uncertain range of deforestation. At the subcatchment scale, the uncertainty range on ET changes is shown to first depend on GCMs, while the uncertainty of runoff projections is predominantly induced by LSM structural differences. By contrast, we found that the uncertainty in both ET and runoff changes attributable to uncertain future deforestation is low.

Modelling the Effects of Historical and Future Land Cover Changes on the Hydrology of an Amazonian Basin

“…The manual adjustment of parameters, prior to the automatic calibration, based on previous knowledge of the physiographic characteristics of the basin, helped in defining the optimal parameter set and improve the reliability of the simulations. Although small, the deforestation that occurred in the basin between 1973 and 2012 was sufficient to depict a trend of increases in the streamflow at a monthly time-scale analysis ( Figure 5), corresponding to the increase in deforested areas, which is in accordance with the findings from previous studies in Amazon basins and other tropical regions [29,30,89,90]. This trend was more clearly displayed when simulating discharge during the high-flow season corresponding to the future BAU_2050 and GOV_2050 scenarios (Figure 4c).…”

“…SurfQ was the only WBC that showed a substantial increase in the annual average values, following the increase of deforestation (Figure 6), indicating that the SurfQ was the main component responsible for the slight increase in Q AA throughout the scenarios. Forest removal in tropical Basins typically reduces interception and ET, and increases SurfQ and Q during the rainy season [29,90,91]. However, during the dry season, Q is reduced when deforested areas increase (Figure 4c).…”

Forests, atmospheric water and an uncertain future: the new biology of the global water cycle

“…Complexity has increased as additional phenomena and their associated sub-models are added and refined. Various aspects of vegetation cover, such as leaf area phenology, canopy roughness and rooting depth are generally included with varying levels of sophistication (Bonan 2008;Guimberteau et al 2017).…”

Future Climate and Land Use Change Impacts on River Flows in the Tapajós Basin in the Brazilian Amazon

“…Earth's Future Sorribas et al, 2016;Guimberteau et al 2017). The selection of the two extreme ESMs allowed to analyze the range of variability accounting for the uncertainty linked to the choice of climate models.…”

“…Several bias correction methods applied to hydrological simulations of future climate scenarios have been used in previous studies (e.g., Eisner et al, 2012;Hempel et al, 2013;Muerth et al, 2013;Rojas et al, 2012). One approach has been to downscale and bias correct the meteorological inputs, typically precipitation and temperature (e.g., Guimberteau et al, 2017;van Vliet et al, 2013). As discussed in Hashino et al (2007), several techniques are being applied to bias correct meteorological forcing data: simple approaches calculate a "delta factor" (e.g., Diaz-Nieto & Wilby, 2005), but other more sophisticated statistical approaches also exist (e.g., Fang et al, 2015;Moghim et al, 2016).…”