Nonlinear interactions between the Amazon rainforest and the atmospheric moisture circulation in South America: Possible impacts of ongoing deforestation

亚马孙雨林通过降水和蒸散(ET)与大气交换大量水分，对南美洲上空的低层大气环流产生强烈影响。这个循环系统将水汽从热带大西洋输送到亚马逊盆地，并进一步向亚热带地区输送。因此，可以认为正在进行的森林砍伐会严重影响大气水分含量，从而影响非洲大陆大部分地区的降雨量。利用非线性动力学和复杂网络的概念，我打算从概念的角度对生态系统和大气之间最相关的耦合机制进行建模，并将结果与使用耦合区域气候模式获得的相应结果进行比较。将特别着重于涉及的反馈机制：我首先计划量化ET与维持大气传输路线上的水分含量的相关性。然后，将详细分析亚马逊盆地上空凝结引起的潜热释放产生的正反馈及其与维持循环系统的相关性。这种加热导致来自邻近海洋的低层水汽流入加速，并应强烈影响系统对ET率变化的敏感性。在这些问题得到回答后，我打算调查正在进行的亚马逊雨林砍伐和由此导致的ET下降将如何影响水流下游的水分可获得性，同时考虑到由于正反馈而产生的耦合的特殊敏感性。该项目将分三个后续步骤进行：第一，将制定一个一维概念模型，其中包括与上述三个问题有关的地球物理机制。其次，我计划在之前工作的基础上，从气候数据中推导出功能网络，以便将该模型扩展到两个空间维度。然后，在第一步中得到的方程将沿着代表南美洲主要水汽输送路线的网络的链接进行求解。第三，将这一概念性方法的结果与使用耦合区域气候模型获得的相应结果进行比较。

By exchanging large amounts of moisture with the atmosphere through precipitation and evapotranspiration (ET), the Amazonian rainforest strongly influences the low-level atmospheric circulation over South America. This circulation system conveys moisture from the tropical Atlantic ocean to the Amazon basin and farther towards the subtropics. Ongoing deforestation can therefore be assumed to significantly impact the atmospheric moisture content and thus precipitation over large parts of the continent. Using concepts from nonlinear dynamics and complex networks, I intend to model the most relevant coupling mechanisms between the ecosystem and the atmosphere from a conceptual point of view, and to compare the results with corresponding ones obtained using a coupled regional climate model. Special focus would be put on the involved feedback mechanisms: I first plan to quantify the relevance of ET for maintaining the moisture content along the atmospheric transport route. A positive feedback arising from condensation-induced latent heat release over the Amazon basin, and its relevance for maintaining the circulation system, shall then be analysed in detail. This heating leads to an acceleration of the low-level moisture inflow from the adjacent ocean, and should strongly affect the systems sensitivity to changes in the ET rates. After these questions are answered, I intend to investigate how ongoing deforestation of the Amazon rainforest and the resulting decrease in ET will impact the moisture availability downstream of the flow, taking into account the particular sensitivity of the coupling due to the positive feedback. The project would be carried out in three subsequent steps: First, a one-dimensional conceptual model incorporating the geophysical mechanisms relevant for the above three questions would be formulated. Second, I plan to build upon prior work on deriving functional networks from climatological data in order to extend the model to two space dimensions. The equations obtained in the first step shall then be solved along the links of a network representing the main moisture transport routes over South America. Third, results from this conceptual approach shall be compared with corresponding results obtained using a coupled regional climate model.