Landslides and climate change.

Climate change refers to a statistically significant variation in either the mean state of the climate or in its variability, persisting for an extended period, typically decades or longer. Climate change on Earth may be due to natural internal processes or external forcing, or to persistent anthropogenic perturbation of the composition of the atmosphere or of land use. The Fourth Assessment Report of the Intergovernmental Panel on Climate Change states that the warming of the climate system is unequivocal. Moreover, there is a high level of confidence that this warming is a result of human activities releasing greenhouse gases to the atmosphere from the burning of fossil fuels, deforestation and agricultural activities. A range of future greenhouse gas emission scenarios are also presented, based on estimates of economic growth, technological development and international cooperation. In all scenarios temperatures continue to rise worldwide, with global mean temperatures averaging plus 2 to 4 °C by the end of the century, accompanied by changes in the amounts and patterns of precipitation. The predicted rate of warming seems to be faster than ever recorded and in particular over the last 2000 years, and also since the Earth was exiting the Little Ice Age. There will also be an increase in the frequency and intensity of extreme temperature and precipitation events at any time of the year, regardless of the season. If the evidence of climate change is unequivocal, is climate change triggering more landslides, or will it in the future? Intuitively, yes: climate changes have the potential to modify the stability of slopes, both natural and constructed. This issue is important and urgent, no matter what are the actual causes of climate changes. It has been proved that most landslides are caused by saturated soil moisture conditions and by loss in soil strength, triggered by climatically-controlled processes, such as intense and/or prolonged precipitation events, rapid snowmelt, glacier thinning, permafrost degradation or river migration, depending on geomorphological settings. If climate change leads to increased frequency and/or magnitude of these events and processes, the frequency and/or magnitude of landslides in a region will be similarly influenced. Thus, we can expect more instability, as a consequence of the increasing number of short but intense events, as well as by increasing cumulative rainfall etc. Although the frequency and/or magnitude of landslides may increase with the anticipated climate change, the regional distribution of landslides is not expected to change significantly, as many of the primary factors controlling landslide susceptibility, such as geology, physiography and slope, are remaining relatively constant. Potentially unstable areas, however, could for example include slopes presently underlain by degrading permafrost. A sort of domino effect may also be expected: increased landslide activity may lead to increased sediment loads and channel instability in rivers. Currently, where the best practice in landslide risk mitigation is established, the design and management of infrastructure and urban assets affected by natural slope instability is carried out on the basis of specified standards and guidelines that assume static environmental conditions. However, the rate of dominant input parameters (i.e., precipitation and temperature) is now clearly changing. Hence, a review of this approach is demanded, as the assumption of a steady climate state can be misleading. However, such impacts are currently speculative and will be difficult to unravel from “pure” anthropogenic effects, in some case driven by climate changes themselves. Accordingly, compound effects of climate change and other human actions (where humans are both co-triggers and element at risk) must be accounted for. In this sense, some studies seem to highlight the fact that climate change is important, but land use change is even mor...