Collaborative Research: The Amazon Groundwater and Its Impact on Evapotranspiration and the Climate of South America

本项目重点研究亚马逊蒸发蒸腾(ET)的季节动态，它受陆地水文学的控制，以及它对区域和大陆降水的影响。它将检验两个假说，(1)亚马逊地下水库可以增加根区土壤水分和旱季ET，(2)这种增强的ET可以影响局地和下风向降水。地下水位观测表明，地下水足够浅，足以影响陆地表面，文献表明亚马逊ET是区域降水的关键驱动因素。这些假设将分两步进行检验。首先，将使用一个地下水-陆面综合模式(由罗格斯团队开发的LEAFE-HELDRO)来模拟由观测到的大气场(南美陆地数据同化系统(SALDAS))强迫的陆面通量。叶-水通过水力再分配(根作为上下移动水分的管道)将地下水与土壤水分耦合在一起。将模拟各种工艺组合，以隔离更深的模型土壤、更深的根、水力再分配和地下水的存在的影响。其次，WRF-Hydro将被用作陆地模型来模拟南美洲的风场和湿度场，这将被用来使用由亚利桑那州团队开发的动态循环模型(DRM)来追踪蒸汽传输路径。DRM将在空间和时间上描绘大陆上的源和汇区域，因此亚马逊地下水将与大陆的气候联系在一起。研究评估了亚马逊水循环中的一个潜在的基本过程：地下水在ET中的作用，从而提高了我们对陆地水储存之间的联系的理解。它还可能对理解世界上最大的雨林在当前和未来在森林砍伐和气候变化下的功能产生影响。森林砍伐影响气候的一个机制是深层根部的丧失，因此ET和降雨量减少。这项研究将有助于揭示深层根系与地下水相互作用的功能。在预计未来气候将出现更长旱季的情况下，一些模型预测亚马逊森林将会枯死，这可能会通过碳的正反馈加速变暖。提高我们对亚马逊森林如何在今天的旱季中生存的理解，将有助于我们了解它未来的表现。

This project focuses on the seasonal dynamics of Amazon evapotranspiration (ET), its control by land hydrology, and its consequences on regional and continental precipitation. It will tests two hypotheses, (1) the groundwater reservoir under the Amazon can enhance root-zone soil moisture and dry-season ET, and (2) this enhanced ET can influence local and downwind precipitation. Water table observations suggest that the groundwater is sufficiently shallow to influence the land surface, and the literature suggest that Amazon ET is a key driver of regional precipitation. These hypotheses will be tested in two steps. First, an integrated groundwater-land surface model (LEAF-Hydro, developed by the Rutgers Team) will be used to simulate land surface fluxes forced by observed atmospheric fields (South American Land Data Assimilation System (SALDAS)). LEAF-Hydro has a prognostic groundwater coupled to the soil moisture with hydraulic redistribution (roots as conduits to move water up and down). Various process combinations will be simulated to isolate the effect of deeper model soil, deeper roots, hydraulic redistribution and the presence of the groundwater. Second, the WRF-Hydro will be used as the land model to simulate the wind and humidity fields over South America, which will be used to trace vapor transport pathways using the Dynamic Recycling Model (DRM, developed by the Arizona Team). DRM will delineate, in space and time, the source and sink regions over the continent, and hence the Amazon groundwater will be linked to the climate of the continent.The research evaluates a potentially fundamental process in the Amazon water cycle: the role of groundwater in ET, and thus improves our understanding of the linkages among terrestrial water stores. It may also have implications to understanding the functions of the world's largest rainforest at the present and in the future under deforestation and climate change. A mechanism whereby deforestation affects the climate is the loss of deep roots and hence a reduced ET and precipitation. This study will shed lights on the functions of deep roots interacting with the groundwater. Under projected future climate with a longer dry season, some models have predicted an Amazon forest die-down, which, via positive carbon feedbacks, may accelerate warming. Improving our understanding of how the Amazon forest survives the dry season today will shed lights on how it may fare in the future.