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

粘土中的收缩膨胀在英国是一种主要的地质灾害，每年造成超过4亿GB的经济损失。到2050年，由于气候变化导致的极端天气，这一数字将上升到6亿GB以上。研究预测，到2040年，整个欧洲的收缩膨胀下沉将增加50%。英国的许多城镇和主要基础设施走廊都建立在粘土丰富的土壤上，特别是在英国东南部，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引起收缩膨胀的主要原因，并受矿物学、温度和降雨量的控制。因此，一些地区比其他地区更容易受到影响，这取决于其基础地质和地区气候。2022年1月至6月，英国经历了40多年来最干燥的天气，7月份达到顶峰，有记录以来最热的几天气温首次超过40摄氏度。这些前所未有的炎热干燥条件将导致粘土收缩程度，这在英国以前从未经历过，需要大量降雨才能恢复。气候变化预计将增加那些已经容易下沉的地区的收缩膨胀危险，并将扩展到以前从未发生过下沉的其他地区。但这些变化的速度尚不清楚。目前对收缩膨胀过程的理解建立在实验室研究和理论关系的基础上，但这些结果需要对现场地面条件(如水分随深度变化)的现场研究来验证。因此，最近迅速到来的极端高温和干旱是一个独特的机会--现在--来研究英国地下如何应对日益极端的天气条件。最重要的科学问题是：在英国日益极端的气候下，收缩-膨胀危险变化将如何发生？为了回答这个问题，我们将确定：a)2022年干旱和史无前例的7月热浪对易缩胀地区的下沉和土壤湿度的影响；b)在这些极端情况下，土壤湿度如何随深度变化，以及这种变化如何随着更潮湿条件的出现而演变；以及c)2022年经历的极端变化是否能够支持对气候变化对未来缩胀危险的更好理解？对刚刚经历的极端干燥和炎热条件的浅层地下反应是短暂的，并将随着更潮湿的秋冬天气而演变。目前，有一个独特的机会，可以在几十年来的最低点现场记录浅层地下水分和地面变形，并记录和监测地面对更潮湿条件开始的反应。为此，迫切需要资金建立三个缩胀观测站，以便定期进行实地观测，并在天气条件变化时对缩胀行为进行持续的地球物理测量。还将采集样品进行实验室分析，将测量的物理特性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.