Hydrological extremes and feedbacks in the changing water cycle

未来几十年气候将发生重大变化，这意味着社会必须紧急面对水循环变化的影响，特别是极端洪水和干旱带来的风险日益增加。迫切需要为决策者提供指导，以支持对这些风险的适应，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可能发生的程度以及它们预计发生的频率的能力仍然有限。这主要是由于在如何最好地利用现有数据和模型的知识方面存在差距；特别令人关切的是，气候和水文模型产生现实极端情况和变化的水文行为的能力有限。例如，区域气候模式产生的数据通常需要缩小到更精细的分辨率，但问题是，缩小后的数据的哪些属性是关键的，以及应该如何缩小尺度。另一个例子是，干旱规划需要准确地表示年际和区域间的降雨和蒸发，然而，关于如何利用现有模式在未来气候下最好地实现这一点，几乎没有指导。此外，在水文模拟（例如地下水储存、河流流量和蒸发）方面也存在弱点，这是开发下一代气候模式的障碍；特别是目前用于模拟从地球表面到大气的反馈的模式，忽略了重要的水文过程。该提案将产生解决这些问题所需的科学和模型，整合气候和水文科学，使影响建模超越目前的技术水平。具体来说，建议是：1。利用当代气候科学和统计方法，改进和加强对10至60年时间尺度上水文相关指标潜在变化的预测，特别是极端的强降水和干旱；2. 建立在历史数据分析的基础上，以提高对气候变率的水文响应的极端和非平稳性的科学认识和开发创新方法；3. 力求改善地表模式中水文过程的表现，特别是加强地表和地下过程的模式，以模拟陆地-大气反馈。为了解决这些知识上的差距，拟议的项目将跨越NERC变化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集水区和伊甸园集水区。这些集水区广泛代表了英国的低地和高地，具有来自NERC和DEFRA-EA实验项目的大量气候和水文数据集。该项目将考虑地方到流域的尺度，并认为由此产生的科学和模型最终将集成到全球尺度模型中。主要项目产出将是：1)改进英国水文相关尺度上降水和蒸发的未来变率和极值的量化；2)改进了水文水循环对这些极端条件的响应模型，明确纳入了非平稳条件；3)在气候模式中纳入地-气反馈过程及其影响，特别是对非饱和带和地下水储流量的识别和纳入。在所有情况下，将开发新的建模工具来测试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.