Debris flow, rainfall and climate change in Scotland

In August 2004 a series of landslides in the form of debris flows occurred in Scotland. Critically, the A83, A9 and A85 routes, which form important parts of the major road network, were all affected by these events. Although debris flows occur with some frequency in Scotland, they affect the major road network only relatively rarely. However, when they do affect roads the degree of damage, in terms of the infrastructure and the loss of utility to road users, can have a major detrimental effect on both economic and social aspects of the use of the asset. Following these events work was put in place to assess and rank the hazards and to develop a management and mitigation strategy. The management strategy is largely based upon the reduction of the exposure of road users to risks from debris flow. It operates upon the principle of Detection, Notification and Action (DNA). A crucial element of this work is the continuing development of a rainfall threshold to indicate conditions likely to produce debris-flow activity, and the development of a tentative threshold is described herein. Clearly, any change in rainfall patterns as a result of recent climate trends and future climate change has the potential to affect the frequency and intensity of debris flow and thus the effectiveness of the associated management strategy for such events, and the potential effects of such phenomena are considered in this paper.