In volume-sensitive clays the annual cycle of wetting and drying causes shrink and swell displacements. These movements cause damage to many infrastructure types, including railway and highway embankments and cut slopes, earth dams and flood embankments. At present there is little information on the impacts of expected climate change on the stability and serviceability of infrastructure embankments and slopes constructed of clay in the UK. In this paper, a water balance model is used to calculate daily changes in soil moisture content in the surface layers of a clay slope. Summer soil moisture deficit and winter runoff are calculated over a baseline period (1960–1991) for four locations in the UK. The calculations are repeated using synthetically generated time series of weather data representative of UKCIP climate change scenarios for the 21st century. Results indicate that recent summers considered to be exceptionally dry are likely to become the average condition later in the 21st century. Although total annual runoff is predicted to decrease, extreme wet events are still likely to occur. This will increase the magnitude of the cycles of winter soil wetting and summer drying. The implications for the design and maintenance of clay slopes and embankments are discussed.