UK shrink-swell hazard under climate-change-driven weather extremes

粘土的收缩膨胀是英国的主要地质灾害，每年给经济造成的损失超过4亿英镑。到2050年，由于气候变化导致的极端天气，这一数字将超过6亿英镑。研究预测，到2040年，整个欧洲的收缩膨胀沉降将增加50%。英国的许多城镇、城市和主要基础设施走廊都建立在富含粘土的土壤上，尤其是在英国东南部，那里是伦敦大部分地区的基础。这些土壤中粘土矿物的体积变化是收缩膨胀的主要原因，并受矿物学、温度和降雨的控制。因此，一些地区比其他地区更容易受到影响，这取决于其潜在的地质和区域气候。2022年1月至6月期间，英国经历了40多年来最干燥的天气，7月达到顶峰，气温首次超过40摄氏度，是有记录以来最热的日子。这些前所未有的炎热、干燥的条件将导致粘土的收缩程度，这在英国是前所未有的，而大量的降雨将是恢复粘土的必要条件。预计气候变化将增加那些已经容易下沉的地区的收缩膨胀危险，并将扩大到以前没有发生下沉的其他地区。但是这些变化的速率是未知的。目前，对收缩膨胀过程的理解是基于实验室研究和理论关系的，但这些结果需要通过实地研究来验证，如水分随深度的变化。因此，最近快速发生的极端高温和干旱是一个独特的机会，可以研究英国地下如何应对日益极端的天气条件。首要的科学问题是：在英国日益极端的气候下，收缩膨胀风险将如何变化？为了回答这个问题，我们将确定：a) 2022年的干旱和前所未有的7月热浪对收缩膨胀易感地区的沉降和土壤湿度的影响；B)在这些极端情况下，土壤湿度如何随深度变化，以及随着更湿润条件的出现，土壤湿度如何演变；c) 2022年经历的极端变化是否可以加强对气候变化对未来收缩膨胀危害的影响的理解？浅层地下对刚刚经历的极端干热条件的响应是短暂的，并将随着秋冬天气的湿润而演变。现在，有一个独特的机会来记录几十年来最低点的浅层地下水分和地面变形，并记录和监测地面对潮湿条件的反应。为此，需要紧急资金来建立三个收缩膨胀观测站，以便在天气条件变化时进行定期的实地观测和连续的收缩膨胀行为的地球物理测量。还将采集样品进行实验室分析，将测量的物理性质与现场实验联系起来。

Shrink-swell in clay soils is a major geohazard in the UK and costs the economy over £400 million a year. By 2050 this will rise to over £600 million due to climate-change-driven weather extremes. Research predicts a 50% increase in shrink-swell subsidence across Europe by 2040. Many towns, cities and major infrastructure corridors in the UK are founded on clay-rich soils, especially in the south-east UK, where they underlie most of London. Volume change of clay minerals within these soils is the primary cause of shrink-swell, and is controlled by mineralogy, temperature and rainfall. So, some areas are more susceptible than others depending on their underlying geology and regional climate. Between January and June 2022, the UK experienced the driest weather in over 40 years, culminating in July, with the hottest days on record when temperatures exceeded 40 degrees Celsius for the first time ever. These unprecedented hot, dry conditions will have resulted in levels of clay shrinkage never previously experienced in the UK, and significant rainfall will be necessary for their recovery. Climate change is expected to increase shrink-swell hazard in those areas already susceptible to subsidence and will expand into other areas where subsidence has not occurred before. But the rates of these changes are unknown. Understanding of shrink-swell processes at present is based on laboratory-based research and theoretical relationships, but these results require validation from field research on in situ ground conditions such as moisture changes with depth. The recent rapid onset heat extremes and drought, therefore, is a unique opportunity-right now-to investigate how the UK subsurface responds to increasingly extreme weather conditions. The overarching science question is: How will shrink-swell hazard change under an increasingly extreme UK climate? To answer this we will determine: a) the impact of the 2022 drought and unprecedented July heatwave on subsidence and soil moisture in shrink-swell-susceptible regions; b) how soil moisture varies with depth during these extremes, and how this evolves with the onset of wetter conditions; and c) whether the extreme changes experienced in 2022 can underpin improved understanding of climate change impact on future shrink-swell hazard?The shallow subsurface response to the extreme dry and hot conditions just experienced, is short-lived and will evolve with wetter Autumn-Winter weather. Right now, there is a unique opportunity to record in situ shallow subsurface moisture and ground deformation at its lowest ebb for decades, and to record and monitor the ground response to the onset of wetter conditions. For this, urgency funding is necessary to establish three shrink-swell observatories for regular field observations and continuous geophysical measurements of shrink-swell behaviour as weather conditions change. Samples will also be acquired for laboratory analysis that will link measured physical properties to the field experiments.