Hydrological extremes and feedbacks in the changing water cycle

未来几十年气候发生重大变化的前景意味着，社会必须紧急面对不断变化的水循环的影响，特别是极端洪水和干旱带来的风险增加。迫切需要为政策制定者提供指导，以支持适应这些风险并支持应对气候变化的缓解战略。然而，气候科学家和水文学家预测洪水和干旱的可能程度以及预计发生的频率的能力仍然有限。这在很大程度上是由于在如何最好地利用现有数据和模型方面的知识差距；特别令人关切的是，气候和水文模型产生现实极端情况和改变水文行为的能力有限。例如，区域气候模型产生的数据往往需要缩小到更精细的分辨率，但关于缩小后的数据的哪些属性是关键的以及应该如何进行缩小的问题出现了。作为另一个例子，干旱规划要求准确地表示年度间和区域间的降雨量和蒸发量，但几乎没有关于如何在未来气候下使用现有模型最好地实现这一点的指导意见。此外，在水文学模拟(例如地下水储存、河流流动和蒸发)方面也存在弱点，这是开发下一代气候模型的障碍；特别是目前用于模拟从地球表面到大气的反馈的模型忽视了重要的水文过程。这项提议将产生解决这些问题所需的科学和模型，将气候和水文科学结合起来，使影响建模超越当前的技术水平。具体地说，该提案：1.利用当代气候科学和统计方法，改进和加强对10至60年时间尺度上与水文有关的指标的潜在变化的预测，特别是强降水和干旱的极端情况；2.以对历史数据的分析为基础，增进对气候变化的水文反应的极端和非平稳性建模的创新方法；3.力求改进在陆面模型中的水文过程的表示，特别是改进用于模拟陆地-大气反馈的地表和次表层过程的建模。在解决这些知识差距的过程中，拟议的项目将涉及国家环境研究中心改变水循环方案的所有四个主题：陆地-大气相互作用；降水模拟；对变化的理解；以及评估后果的创新方法。案例研究将包括泰晤士河流域和伊甸园流域。这些集水区广泛代表低地和高地英国，拥有来自NERC和DEFRA-EA实验方案的大量气候和水文数据集。该项目将考虑从地方到集水区的尺度，认为由此产生的科学和模型最终将纳入全球尺度模型。主要项目成果将是：1)改进对联合王国未来降水和蒸发在水文相关尺度上的变异性和极端情况的量化；2)改进对这些极端情况的水文水循环响应模型，明确纳入非平稳条件；3)将地球-大气反馈过程及其影响纳入气候模型，特别是认识和纳入非饱和带和地下水储存和排放。在所有情况下，都将开发新的建模工具，以检验气象水文功能的想法。

The prospect of significant climate change over the next decades means that society must urgently face up to the implications for the changing water cycle, in particular increasing risks from extreme floods and droughts. Guidance for policy-makers to support adaptation to these risks and to support mitigation strategies to combat climate change is urgently required. However, the ability of climate scientists and hydrologists to predict the possible magnitudes of floods and droughts, and the frequency with which they are expected to occur, is still limited. This is due largely to gaps in knowledge of how best to use available data and models; of particular concern is the limited ability of climate and hydrological models to produce realistic extremes and changing hydrological behaviour. For example, regional climate models produce data which often requires to be downscaled to finer resolutions, but questions arise about what properties of the downscaled data are critical and how the downscaling should be done. As another example, drought planning requires inter-annual and inter-regional rainfall and evaporation to be represented accurately, however there is little guidance about how this can best be achieved under future climate using available models. In addition, there are weaknesses in the simulation of hydrology (for example, groundwater storage, river flows and evaporation) which act as hurdles to development of next generation climate models; in particular models currently used to simulate feedbacks from the earth surface to the atmosphere neglect important hydrological processes. This proposal will produce the science and models needed to address these questions, integrating climate and hydrological science to take impact modelling beyond the current state of the art. Specifically, the proposal: 1. exploits current generation climate science and statistical methods to improve and enhance projections of potential change in hydrologically-relevant metrics over a time-scale of 10 to 60 years, in particular extremes of heavy precipitation and drought; 2. builds on the analysis of historical data to improve scientific understanding and develop innovative methods for the modelling of extremes and non-stationarity in the hydrological response to climate variability; 3. seeks to improve the representation of hydrological processes in land surface models, in particular, the enhanced modelling of surface and subsurface processes for simulation of land-atmosphere feedbacks. In addressing these gaps in knowledge, the proposed project will cross all four themes of NERC's Changing Water Cycle programme: land-atmosphere interactions; precipitation modelling; understanding of change; and innovative ways to assess consequences. Case studies will include the Thames catchment and the Eden catchment. These catchments are broadly representative of lowland and upland UK with substantial climate and hydrological datasets from NERC and DEFRA-EA experimental programmes. This project will consider local to catchment scales, with the view that the resulting science and models will ultimately be integrated into global scale models. The main project outputs will be: 1) improved quantification of future variability and extremes of precipitation and evaporation over hydrologically relevant scales in the UK; 2) improved models of the hydrological water cycle response to these extremes, with the explicit inclusion of non-stationary conditions; 3) the inclusion of earth-atmosphere feedback processes and their effects in climate models, in particular the recognition and inclusion of unsaturated zone and groundwater storage and discharge. In all cases, new modelling tools will be developed to test the ideas of meteo-hydrological functioning.