Ecole Normale Supérieure, Geosciences Department and Laboratoire de Météorologie Dynamique, Paris, F-75230, France.
Potsdam Institute for Climate Impact Research, Potsdam, 14473, Germany.
Sci Rep. 2017 Jan 25;7:41489. doi: 10.1038/srep41489.
The Amazon rainforest has been proposed as a tipping element of the earth system, with the possibility of a dieback of the entire ecosystem due to deforestation only of parts of the rainforest. Possible physical mechanisms behind such a transition are still subject to ongoing debates. Here, we use a specifically designed model to analyse the nonlinear couplings between the Amazon rainforest and the atmospheric moisture transport from the Atlantic to the South American continent. These couplings are associated with a westward cascade of precipitation and evapotranspiration across the Amazon. We investigate impacts of deforestation on the South American monsoonal circulation with particular focus on a previously neglected positive feedback related to condensational latent heating over the rainforest, which strongly enhances atmospheric moisture inflow from the Atlantic. Our results indicate the existence of a tipping point. In our model setup, crossing the tipping point causes precipitation reductions of up to 40% in non-deforested parts of the western Amazon and regions further downstream. The responsible mechanism is the breakdown of the aforementioned feedback, which occurs when deforestation reduces transpiration to a point where the available atmospheric moisture does not suffice anymore to release the latent heat needed to maintain the feedback.
亚马逊雨林被认为是地球系统的一个关键因素，由于雨林部分地区的砍伐，整个生态系统有可能枯萎。这种转变背后的可能物理机制仍在进行辩论。在这里，我们使用专门设计的模型来分析亚马逊雨林与大气水汽输送之间的非线性耦合，这种水汽输送从大西洋到南美洲大陆。这些耦合与亚马逊地区的降水和蒸散向西级联有关。我们研究了森林砍伐对南美季风环流的影响，特别关注以前被忽视的与雨林上凝结潜热有关的正反馈，这大大增强了来自大西洋的大气水汽流入。我们的研究结果表明存在一个临界点。在我们的模型设置中，跨越临界点会导致亚马逊西部和下游地区未砍伐森林部分的降水减少多达 40%。造成这种情况的原因是上述反馈的崩溃，当森林砍伐导致蒸腾作用减少到一定程度，以至于可用的大气水汽不足以释放维持反馈所需的潜热时，就会发生这种情况。
