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流域蒸散的季节动态、陆地水文对蒸散的控制及其对区域和大陆降水的影响。该研究将验证两个假设，即(1)亚马逊地下水库可以增强根区土壤湿度和旱季ET，(2)这种增强的ET可以影响局地和下风降水。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。这些假设将分两个步骤进行检验。首先，一个综合地下水-陆地表面模型（LEAF-Hydro，由罗格斯大学团队开发）将用于模拟观测到的大气场（南美陆地数据同化系统（SALDAS））所迫使的陆地表面通量。LEAF-Hydro具有预测地下水与土壤水分耦合的水力再分配（根作为上下移动水的管道）。将模拟各种过程组合，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将被用作模拟南美洲风和湿度场的陆地模型，该模型将被用于使用亚利桑那团队开发的动态循环模型（DRM）追踪蒸汽输送路径。DRM将在空间和时间上描绘出整个大陆的源头和汇区，因此亚马逊地下水将与该大陆的气候联系起来。该研究评估了亚马逊水循环中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联系的理解。它也可能对理解世界上最大的热带雨林在森林砍伐和气候变化的当前和未来的功能有启示。森林砍伐影响气候的一个机制是深层根系的丧失，从而减少了ET和降水。该研究将揭示深层根系与地下水相互作用的功能。在预测的未来气候中，旱季会更长，一些模型预测亚马逊森林会枯死，这可能会通过正碳反馈加速变暖。提高我们对亚马逊森林如何在今天的旱季中生存下来的理解，将有助于了解它未来的发展情况。

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.