James White (United Kingdom) 1; David Entwisle (United Kingdom) 1; Anna Harrison (United Kingdom) 1; Hughes Andrew (United Kingdom) 1; Hulbert Andrew (United Kingdom) 1; Jones Lee (United Kingdom) 1; Majdi Mansour (United Kingdom) 1; Wang Lei (United Kingdom) 1; Kathryn Lee (United Kingdom) 1
1 - British Geological Survey, Keyworth, UK
The effects of clay shrinkage due to drought, commonly referred to as subsidence, are estimated to have cost the United Kingdom (UK) economy £3 billion over the past decade. Predictions from global climate models suggest the UK will experience increases in average temperature and changes in rainfall patterns, with longer dryer summers and wetter winters, as a consequence of human-induced climate change. These changes will alter the behaviour of the ground in the near surface, with potentially detrimental consequences for infrastructure and housing. We present hazard maps at 1:50,000 scale, indicating local susceptibility to increased clay shrinkage within a medium-emissions future climate scenario.
Geological formations in the UK have varying propensities to shrink and swell with changes in water content with clay rich units being most prone. From the interpretation of geological maps, produced by the British Geological Survey, the south eastern part of the UK contains most of the units that are likely to shrink and swell.
Soil moisture deficit was used to identify near surface changes in water content. Soil moisture deficit is a consequence of the variability in rainfall, evapotranspiration, soil type, run-off potential, and downward water infiltration, and is a quantitative measure of dryness in the topsoil and near surface geology, relative to a full saturation (field capacity). It was calculated from the 1950s to present day across Great Britain using a high resolution national recharge model, ZOODRM and observed historical data sets. A link was then established between past climate, using soil moisture deficit values, and gross subsidence insurance claims. A threshold value of soil moisture deficit, with an associated length of time above that threshold, was identified as a common trigger for subsidence claims.
UKCP09 provides projections of climate change in the UK into the 21st Century. A selected subset of the UKCP09 climate projections were used to derive a range of physically plausible regional climate models under a medium-emissions scenario. This subset is processed to generate precipitation and evapotranspiration grids across Great Britain, which feed into ZOODRM’s soil moisture deficit calculations, extending them to 2080. These soil moisture deficit values are combined with the geotechnical information about the underlying geology, and provide a projection for future increases in susceptibility to subsidence. Based on our assessment, south-eastern England, will be more susceptible to clay shrinkage related subsidence, whereas the north and west of England, Scotland and Wales are unlikely to see increased risk.