Landslide behaviour and climate change: predictable consequences for the Ventnor Undercliff, Isle of Wight

The Ventnor Undercliff, located on the south coast of the Isle of Wight, is an ancient landslide complex of marginal stability that is prone to ground movement and occasional landslide events. The impact of ground movement on property and services in the town has been significant in the past. Since 1995, the local authority has made a significant investment in continuous monitoring and analysis of weather and ground movement data at key sites amongst other landslide management initiatives. These data reveal strong relationships between antecedent rainfall, groundwater and ground movement rates, confirming that prolonged periods of heavy winter rainfall and excess groundwater levels are a fundamental control on landslide behaviour. Climate change projections over the next 100 years point to significant increases in sea level and winter rainfall which are expected to result in accelerated ground movement rates and more frequent landslide events in the Undercliff. There are concerns that hitherto marginally stable areas of the Undercliff may become unstable due to reactivation of ground movement and the occurrence of new landslides. In areas previously affected by ground movement or landslides, the frequency and rate of ground movement and landsliding is expected to increase. The paper presents historical and new data to demonstrate the relationships between rainfall and ground movement and uses these to predict the likely impacts of climate change on future landslide behaviour. The paper concludes that climate change poses a very real threat and significant challenge to the future management and mitigation of the ground instability risks in the Ventnor Undercliff, which may be echoed for other similarly marginally stable ancient landslides in the UK.