The climate and its consequences on the activity of the landslides in Spain

Abstract

The climate is the most influencing factor on the stability of the slopes and existing landslides in Spain. Landslides are concentrated in the main mountain ranges, especially in the Pyrenees, and the Cantabrian and Betic ranges. However, the banks of the rivers draining the large Tertiary basins are also unstable. Relief, together with the lithological component, account for the geographic distribution of the slope failures. In coastal areas, failures are concentrated on rocky cliffs exposed to marine erosion. The relationship between climate and slope instability is complex due to the great variety of failure mechanisms. High-intensity, short-lasting rainfall episodes (over 100 mm in the Cantabrian range and over 180 mm in the Pyrenees) generally cause shallow landslides, debris flow and rockfalls. Prolonged low or moderate-intensity rainfall lasting for several days or weeks reactivate landslides and mudslides. The behaviour of large landslides is very dependent on the geological-geomorphological context, but their reactivation is frequently associated with abnormally rainy seasonal periods. In any case, anthropic modifications (logging, leaks, overloading) are a decisive cause of new, apparently spontaneous, slope failures. Two rainy periods with associated landsliding activity were detected in the last century, in 1905-1930 and 1958-1987, and a relatively calm period from the 30s to the 50s. This apparent cyclicity has also been observed in other European regions, although not simultaneously. With reference to the consequences of the climate change, the uncertainty related to the increased frequency of torrential rainfall and abnormally rainy episodes in the future prevent from any conclusive statement. Increased torrentiality will cause a greater number of shallow landslides and debris flows, the effects of which could be exacerbated by changes in land use and reduced plant cover in the mediterranean region. The increase of winter precipitation in the Cantabrian Range and northern Neogene Basins will reactivate large landslides more often.