Propagation of hydro-geomorphic disturbances through continental-scale river basins: Future evolution of the Amazon River and its floodplain

数以亿计的人生活在世界各大河流附近，并依赖这些河流获得水、食物、交通和维持繁荣的生态系统。然而，这些河流越来越容易受到各种自然和人为干扰的影响，包括气候变化、大型水坝建设、河流工程、森林砍伐、农业集约化和采矿活动。在过去的20年里，气候变化和森林砍伐对亚马逊河流域的水文和沉积物通量产生了影响。然而，亚马逊河仍然是少数几个基本上未受水坝影响的大型河流系统之一。这种情况正在迅速改变，因为巴西、玻利维亚、秘鲁和厄瓜多尔广泛建设的水电站大坝现在威胁着该盆地，计划或正在建设的水坝有100多座。预计这些水坝将在整个流域引发严重的水文物理和生态干扰，包括向亚马逊低地及其洪泛区输送的沉积物和营养物质大量减少，河床和河岸严重退化，河流水位和洪水发生重大变化，以及对人类赖以生存的河流和洪泛区生态系统产生不利影响。最近一些引人注目的研究强调，需要采取国际行动来评估和减轻这些影响，无论是在亚马逊还是在其他地方。然而，我们这样做的能力受到定量模型的严重限制，这些模型无法预测环境扰动如何通过大河和洪泛平原，跨越大陆距离，以及十年到百年的时间周期传播。至关重要的是，由水坝、气候和土地覆盖变化驱动的环境扰动促进了河流的动态响应（例如，河流宽度、深度、坡度、泥沙大小、分支程度和洪泛区改造速度的变化），这反过来又控制了洪水输送和下游泥沙输送的变化。尽管在短距离（<100公里）的河流动力学建模方面取得了进展，但应用于大陆尺度流域的水文模型将河流和洪泛平原视为静态管道。因此，这些模式无法代表或预测环境变化对洪水、泥沙通量或河流和洪泛平原功能的未来影响。这个项目将使我们的建模、预测和理解世界大河如何受到环境变化的影响以及如何应对环境变化的能力发生重大变化。我们将通过实施一项涉及六个要素的研究策略来实现这一目标：首先，我们将开发一种新的多尺度数值模拟方法，使河流动力学对通过大陆尺度流域的环境扰动传播的影响得以模拟。其次，我们将开发一套环境情景，代表整个亚马逊流域近期（1985-2015）和未来（至2200年）的气候和土地覆盖变化以及大坝建设。第三，我们将在亚马逊河上的站点收集新的现场数据集，这些站点需要测试模型的关键组件。第四，我们将与一个由项目伙伴组成的国际团队合作，收集高分辨率的实地、卫星和模型数据集，量化整个亚马逊流域的河道和洪泛平原过程，以及河流形态和动态。第五，我们将利用这些数据对我们的新模式进行严格的测试。第六，我们将应用该模型预测亚马逊河及其支流在各种环境变化情景下的未来演变，并量化大型流域内水文地貌扰动传播的控制因素。我们将与项目合作伙伴共同努力，将我们的模型代码、数据集和项目成果传播给国内和国际上的非学术利益相关者。

Hundreds of millions of people live close to, and depend upon, the world's large rivers for water, food, transport and the maintenance of a thriving ecosystem. However, these rivers are increasingly vulnerable to the effects of a wide range of natural and human-induced disturbances, including climate change, construction of large dams, river engineering works, deforestation, agricultural intensification, and mining activity. Over the past 20 years, climate change and deforestation have impacted on the hydrology and sediment fluxes within the Amazon River Basin. However, the Amazon has remained one of the few large river systems that has been largely unaffected by dams. This situation is changing rapidly, because widespread hydropower dam construction in Brazil, Bolivia, Peru and Ecuador now threatens the basin, with >300 dams planned or under construction. These dams are expected to trigger severe hydro-physical and ecological disturbances throughout the basin, including massive reductions in sediment and nutrient delivery to the lowland Amazon and its floodplains, substantial degradation of river beds and banks, significant changes in river water levels and flooding, and adverse impacts on river and floodplain ecosystems, on which the human population depends. Recent high profile studies highlight the need for international action to assess and mitigate these impacts, both in the Amazon and elsewhere. However, our capacity to do this is severely restricted by an absence of quantitative models that can predict how environmental disturbances propagate through large rivers and floodplains, over continental distances, and decadal to centennial time periods. Critically, environmental disturbances driven by dams, climate and land cover change promote dynamic river responses (e.g., changes in river width, depth, slope, sediment size, degree of branching and rate of floodplain reworking), which in turn control changes in flood conveyance and downstream sediment delivery. Despite advances in modelling of river dynamics over short distances (<100 km), hydrological models that are applied to continental-scale drainage basins treat rivers and floodplains as static conduits. Consequently, such models are unable to represent or predict the future impacts of environmental change on flooding, sediment fluxes or river and floodplain functioning. This project will deliver a step-change in our ability to model, predict and understand how the world's large rivers are impacted by, and respond to, environmental change. We will achieve this by implementing a research strategy that involves six elements: First, we will develop a new multi-scale numerical modelling approach that enables the effects of river dynamics on environmental disturbance propagation through continental-scale drainage basins to be simulated. Second, we will develop a suite of environmental scenarios representing climate and land cover changes and dam construction throughout the Amazon Basin for the recent past (1985-2015) and future (up to 2200). Third, we will collect new field datasets at sites on the Amazon River that are required to test key components of the model. Fourth, we will work with an international team of project partners to assemble high-resolution field, satellite and model datasets that quantify channel and floodplain processes, and river morphology and dynamics throughout the Amazon Basin. Fifth, we will use these data to carry out rigorous testing of our new model. Sixth, we will apply the model to predict the future evolution of the Amazon River and its tributaries for a wide range of environmental change scenarios, and quantify the controls on hydro-geomorphic disturbance propagation within large drainage basins. We will work with our project partners to disseminate our model code, datasets and project outcomes to non-academic stakeholders, both nationally and internationally.