FOR 5288: Fast and invisible: Conquering Subsurface Stormflow through an Interdisciplinary Multi-Site Approach

下雨的时候水会流向哪里？洪水是在哪里产生的，又是如何产生的？在比赛期间，是什么控制着溪流的水质？从工程和防洪到水和生态系统管理以及全球变化影响的预测，这些问题对许多领域都很重要。在这些问题背后的过程集合中最难以捉摸的过程是地下风暴流(SSF)，它是由横向地下水流触发的快速事件响应。SSF很普遍，而且是一个比通常所考虑的更重要的过程，因为仍然缺乏基于跨规模和跨地点的系统研究的基本理解。然而，只有通过系统的研究，才有可能通过发现SSF运作的一般原则来真正增进我们的理解，并为其评估提供方案和最佳做法，无论是在实验方面还是在建模方面。在许多自然景观中，SSF，即响应降水事件而发生的任何地下水流，在径流产生中发挥着重要作用：要么直接促成径流，要么通过产生饱和区域或返回径流，后者是饱和过量陆面径流的根本原因。因此，我们在过程线上看到的许多事件响应可能是SSF的直接或间接结果。SSF的放电信号，包括水流中的间接触发响应，很可能比我们通常假设的要大。虽然源头的重要性可能是最大的，但源头占水系网络的70%，对下游水和溶质的供应和运输有很大影响。然而，由于以下几个原因，SSF难以捉摸，也很难解释，因为测量很困难：地下无法进入，空间变异性和异质性很大，来源可变，而且这是一个只在某些事件期间发生的阈值驱动过程。因此，缺乏对SSF的系统研究，这主要是由于难以量化。我们建议对不同环境、不同规模的SSF进行这样一种系统的研究，并使用包括新方法在内的精心设计和重复的方法选择。随后将对方法和可能的代理进行系统评价，并对模型进行相互比较、评价和改进。因此，我们将集中于4个挑战：1)新的实验方法的发展，2)SSF的空间模式，3)SSF的阈值和级联效应，4)SSF的影响。当标准的单个研究项目在特定地点调查这一谜题的一部分时，该研究单位提供了将大量拼图拼接在一起的独特机会。这个研究单位将把重点放在四个不同测试集水区的实验工作上，然后直接提供给协作建模工作，这反过来又在迭代过程中影响实验设计。

Where does water go when it rains? Where are floods generated and how? What controls stream water quality during events? These questions are important to many fields from engineering and flood protection to water and ecosystem management and prediction of impacts of global change. The most elusive processes in the process-ensemble underlying these questions is subsurface stormflow (SSF), the fast event response triggered by lateral subsurface flow. SSF is prevalent and a more important process than generally accounted for because a basic understanding based on systematic studies across scales and sites is still lacking. However, only with systematic studies will it be possible to really advance our understanding by discovering general principles of SSF functioning and to provide protocols and best practices for its assessment, both experimentally and with respect to modelling. In many natural landscapes, SSF, i.e. any subsurface flow that occurs in response to a precipitation event, plays a major role in runoff generation: either by contributing directly to streamflow or by producing saturated areas or return flow, which then is the underlying cause of saturation excess overland flow. Therefore, much of what we see as event response in the hydrograph might be the direct or indirect result of SSF. It is likely that the discharge signal of SSF, including the indirectly triggered response in the stream, is larger than we generally assume. While its importance is probably largest in the headwaters, headwaters make up 70% of the stream network and greatly influence the supply and transport of water and solutes downstream. However, SSF is elusive and poorly accounted for as measurements are difficult for several reasons: the inaccessibility of the subsurface, the large spatial variability and heterogeneity, the variable sources and the fact that it is a threshold-driven process that only occurs during certain events. Thus, systematic studies of SSF are lacking, mainly due to difficulties of quantification. We suggest such a systematic study of SSF in different environments, across scales, and using a well-designed and replicated selection of approaches including novel approaches. This will be followed by a systematic evaluation of methods and possible proxies as well as model intercomparison, evaluation and improvement. Thereby, we will focus on 4 challenges: 1) Development of novel experimental methods,2) Spatial patterns of SSF, 3) Thresholds and cascading effects of SSF, 4) Impacts of SSF.Whereas standard single research projects investigate part of this puzzle at a specific location, this Research Unit provides the unique opportunity of fitting a large number of puzzle pieces together. This Research Unit will have a strong emphasis on experimental work in four different test catchments that then directly feeds into a collaborative modelling effort, which in turn influences experimental design in an iterative process.