New research published this week by the British Geological Survey (BGS) suggests that the low rainfall in the last two years could still create an increased risk of subsidence from clay shrinkage and swelling despite the heavy rainfall recorded so far this year.
The research, published in the Proceedings of the Geologists’ Association, has highlighted the importance of rainfall and temperature on the incidence of clay shrink-swell.
The model presented in the research suggested moderate potential for clay shrink-swell for the same period last year (2011) and a few years before that. However, the last two years have been have been exceptionally dry, and are comparable to a similar dry period between 1998 and 1999 when insurance claims for subsidence damage reached values of £200m in the UK.
BGS head of science for land use, planning and development Helen Reeves said: “We estimate that one in five homes in the UK is at risk from damage caused by shrinking and swelling processes because they are built on clay.”
The Association of British Insurers (ABI) predicts that by 2050 the annual average cost of subsidence claims could increase from £300M to £600M with an extreme or ‘event’ year costing £1.2Bn.
The details of the research show that if summer temperatures reach a monthly average above 22C, there will be the additional effect of increasing the potential for clay minerals to shrink and swell. According to the BGS, the last time this occurred was in 2010 and if the weather this summer does improve and there is a prolonged warm spell, there could be increased potential for subsidence. Nonetheless, the BGS has predicted that even if the weather remains wet this summer, due to the effect of the low rainfall over the last two years, it is still likely that the number of subsidence claims will rise.