STORMY-WEATHER: Plausible storm hazards in a future climate

气候变化可以说是本世纪人类面临的最大挑战，极端气候和水文的强度和频率的变化将对我们的社区产生巨大影响。2017年气候变化风险评估确定洪水和风暴可能对英国的关键基础设施部门产生强烈影响。极端降雨随着变暖而变得更加强烈，风暴中的短时间爆发似乎以更高的速度增加。然而，我们仍然不知道大规模大气模式的变化，风暴路径，蒸发和其他因素释放的能量将如何影响风暴的时间分布以及它们的频率和持续时间。这部分是由于大多数科学研究都集中在固定持续时间内的“峰值强度”变化，例如每天，多日，每小时等，除此之外，大多数研究都着眼于可能的变化范围，即使最重要的风险很少在这个范围内。相反，最重要的风险往往与“可能的最坏情况”有关。在STORMY-WEATHER中，我们正在根据不同的“风暴”类型制定一种新的方法，以了解变化背后的驱动因素，并制定一套物理上合理的高影响风暴危险故事情节和指标，供人们用于规划未来。这些将使用最新的气候预测。我们使用气候模型来告诉我们未来的天气会是什么样的，这些计算机模型是基于基本的物理定律和复杂的数学方程，这些数学方程必然会简化真实的过程。其中一个似乎真正重要的简化是深对流（想象一下导致雷暴的过程类型）。然而，现在的计算机是如此强大，我们能够产生在越来越小的尺度上工作的模型，最近我们已经开发了我们称之为“对流允许”的模型，在那里我们不再使用这些对深对流的简化。这些“允许对流”的模式不一定更好地模拟平均降雨量或降雨发生，但它们更好地模拟短时间内（不到一天）的强降雨，导致洪水，特别是山洪事件。这些新的模式也能更好地模拟我们所能观测到的随着气温上升而增加的强降雨量，因此我们对它们预测未来强降雨量的变化更有信心。我们将使用这些新的模式以及更常用的全球气候模式来评估我们预测未来的不确定性。我们将考虑将温度变化作为风暴灾害变化的潜在驱动力，包括降水和风作为联合灾害。我们的风暴型方法将有助于澄清不同降雨机制的危害及其随温度的缩放率，以及风暴造成的风雨综合危害，以及它们随变暖而变化的性质;对规划影响至关重要的特征（例如洪水，基础设施故障，运输和能源系统等）。对风暴特性的关注与了解大尺度环流模式的潜在变化对风暴灾害的影响的需要相平衡，例如频率/持续性变化，特别是环流驱动的跨区域主要事件类型变化的可能性。我们需要更好的信息，了解未来极端天气事件可能如何变化，以便做出适应性决策和风暴-WEATHER打算提供这一重要的进展，同时将这些信息转化为用于适应气候变化的有用工具和指标。

Climate change is arguably the biggest challenge facing people this century, and changes to the intensity and frequency of climatic and hydrologic extremes will have large impacts on our communities. The 2017 Climate Change Risk Assessment identified floods and windstorms as likely to have a strong impact on key infrastructure sectors in the UK with climate change. Extreme rainfall is becoming more intense with warming, and short-duration bursts within storms appears to be increasing at a higher rate. However, we still don't understand how changes in large scale atmospheric patterns, the storm track, the release of energy from evaporation and other factors will influence the profile of the storm in time and as well as their frequencies and how long they last for. This is partly due to the fact that most scientific studies have concentrated on 'peak intensity' changes over fixed durations, e.g. daily, multi-day, hourly, etc. Alongside this, most studies look at the likely range of change even though the most important risks rarely lie within this range. Instead, the most important risks are often associated with the 'plausible worst case' scenario. In STORMY-WEATHER we are producing a new methodology based on different 'storm' types to understand the drivers behind the changes and to produce a set of physically-plausible high-impact storm hazard storylines and metrics that people can use to plan for the future. These will use the latest climate projections. We use climate models to tell us about what weather in the future will be like and these computer models are based on fundamental physical laws and complicated mathematical equations which necessarily simplify real processes. One of the simplifications that really seems to matter is that of deep convection (imagine the type of processes that cause a thunderstorm). However, computers are so powerful now that we are able to produce models that work on smaller and smaller scales, and recently we have developed models which we call "convection-permitting" where we stop using these simplifications of deep convection. These "convection-permitting" models are not necessarily better at simulating mean rainfall or rainfall occurrence but they are much better at simulating intense rainfall over short time periods (less than one day) which cause flooding, in particular flash-flood events. They are also better at simulating the increase in heavy rainfall with temperature rise that we can observe; therefore we are more confident in their projections of changes in heavy rainfall for the future.We will use these new models as well as global climate models more commonly used to assess the uncertainty in our projections of the future. We will consider changing temperatures as the potential driver of change to storm hazards, including precipitation and wind as joint hazards. Our storm-type approach will help clarify hazard from different rainfall mechanisms and their scaling rates with temperature, alongside combined wind and rain hazard from storms, as well as their changing nature with warming; characteristics that are vital for planning for impacts (e.g. flooding, infrastructure failure, transport and energy systems, etc.) The focus on storm properties is balanced against the need to understand the impact of potential changes to large-scale circulation patterns on storm hazards, e.g. frequency/persistence changes, and, in particular, the possibility of circulation-driven changes to the dominant event type across regions.Ultimately, we need better information on how extreme weather events might change in the future on which to make adaptation decisions and STORMY-WEATHER intends to provide this important advance, alongside translating this information into useful tools and metrics for use in climate change adaptation.