Assessment of connections between atmospheric planetary waves and extreme rainfall events

NERC:Anna Whitford:NE/ s007512 /1极端降雨事件被认为会造成重大的社会经济损失和生命损失，因为强降雨会产生危险的洪水，特别是在陡峭的小集水区和城市地区。这些极端降雨事件是由局地和区域尺度上的热力学（与温度有关）和动力（与大气环流有关）力量共同驱动的。虽然近年来的研究已经揭示了极端降雨的热力学驱动因素，但我们对动力驱动因素仍有很多不了解（Westra et al., 2014）。这些动力驱动的范围从非常大的行星尺度大气波（罗斯比波）到非常局部的小尺度对流流。在这个项目中，我们专注于大尺度的大气驱动因素，特别是罗斯比波和极端降雨事件之间的关系。以前的研究表明，这些大尺度大气波是极端热浪事件和5至7天极端降雨事件的驱动因素。这些连接既发生在匿名的高振幅波中，也发生在非常慢的移动（准静止）波中（Petoukhov等人，2013；Wolf等人，2018；Kornhuber等人，2019）。因此，我们的目标是确认这些联系是否也发生在较短的多日（3天或更少）极端降雨事件中，然后调查是否也存在与日和次日极端事件的联系。中纬度波导是大气中出现的高空风（喷流）的窄带，可以有效地捕获波导纬度带内的罗斯比波。中纬度波导已被发现与异常高的准平稳波活动和极端热事件一起发生（Petoukhov等人，2013;White, 2019），这表明它们对有利于异常罗斯比波发展的条件的发展有影响。该项目旨在确定极端降雨事件中是否存在相同的波导-罗斯比波关联。一旦确定了罗斯比波和极端降雨之间的任何联系，我们将使用季节性到亚季节性气候预报模型和罗斯比波指数的输出来研究是否有可能根据罗斯比波活动在季节性时间尺度上对极端降雨事件的发生进行预测。研究表明，由于气候变化，支持异常RWs发展的条件频率增加（Petoukhov等人，2013；Kornhuber等人，2019）。与此同时，由于全球变暖，极端降雨的强度和频率增加的证据（Trenberth et al., 2003）表明，我们迫切需要了解这些破坏性事件背后的驱动因素。因此，提高我们对异常RWs如何影响极端降雨的理解对于提高我们对这些事件和任何相关洪水的预测和准备能力至关重要。该项目最终将为这一认识提供关键的研究，其结果将有助于提高我们预测未来极端事件频率的能力。该项目的成果可能会对保险业以及地方和国家政府机构（如英国环境署）产生巨大的积极影响。能够在季节性到次季节性的基础上预测这些破坏性极端事件可能发生的时间，将使保险公司和地方政府能够实施计划和战略，帮助在这些事件发生之前做好准备，从而提高抵御能力，减轻由此产生的洪水对社会经济的负面影响

NERC:Anna Whitford:NE/S007512/1Extreme rainfall events are recognised as causing significant socioeconomic damage and loss of life as the intense rainfall can generate dangerous floods, particularly in small steep catchments and urban areas. These extreme rainfall events are driven by a combination of thermodynamic (linked to temperature) and dynamic (linked to atmospheric circulation) forces on both local and regional scales. While research in recent years has revealed much about the thermodynamic drivers of extreme rainfall, there is still much we do not know about the dynamical drivers (Westra et al., 2014). These dynamic drivers range from very large, planetary scale atmospheric waves (Rossby waves) down to very localised small-scale convective currents. In this project we are focussing on the large-scale atmospheric drivers, in particular the relationships between Rossby waves and extreme rainfall events. These large-scale atmospheric waves have been shown in previous studies to be drivers of extreme heatwave events and also of 5 to 7-day extreme rainfall events. These connections occur for both anonymously high amplitude waves and also for very slow-moving (quasi-stationary) waves (Petoukhov et al., 2013; Wolf et al., 2018; Kornhuber et al., 2019). We therefore aim to confirm whether these connections also occur for shorter multi-day (3 days and less) extreme rainfall events and then investigate whether there are also connections to daily and sub-daily extreme events. Midlatitude waveguides are narrow bands of high altitude wind (jets) which occur in the atmosphere and can effectively trap the Rossby waves within the latitude band of the waveguide. Midlatitude waveguides have been found to occur in conjunction with anomalously high quasi-stationary wave activity and extreme heat events (Petoukhov et al., 2013; White, 2019), suggesting they have an influence on the development of conditions conducive to anomalous Rossby wave development. This project aims to identify whether the same waveguide - Rossby wave associations are present for extreme rainfall events. Once any connections between the Rossby waves and extreme rainfall have been identified, we will use output from seasonal to subseasonal climate forecast models and Rossby wave indices to investigate whether it is possible to produce forecasts of extreme rainfall event occurrence on seasonal timescales based on the Rossby wave activity.It has been shown that, due to climate change, the conditions which support the development of anomalous RWs have increased in frequency (Petoukhov et al., 2013; Kornhuber et al., 2019). At the same time, the evidence for increases in the intensity and frequency of extreme rainfall due to global warming (Trenberth et al., 2003) indicates we urgently need to understand the drivers behind these damaging events. Therefore, improving our understanding of how anomalous RWs effect extreme rainfall is vital to enhance our ability to forecast and prepare for these events and any associated flooding. This project would ultimately provide a key piece of research towards this understanding and the results will help improve our ability to project future extreme event frequency. The outcomes of this project could have large positive impacts for the insurance industry and for local and national government agencies e.g. the UK Environment Agency. Being able to forecast on a seasonal to sub-seasonal basis, when these damaging extreme events may occur would allow insurers and local governments to implement plans and strategies to help prepare before these events occurred, thereby increasing resilience and mitigating the negative socioeconomic impacts of any resulting flooding