Changes in land cover and shallow landslide activity: A case study in the Spanish Pyrenees

Abstract

The Pyrenees, like many other mountain areas in Europe, have experienced depopulation and land abandonment during the 20th Century. This has encouraged vegetation recovery in formerly occupied areas, including reforestation to promote woodland. The objective of this study is to analyse the effects of these changes on shallow landsliding, a process responsible for erosion and land degradation in many mountain areas. A sequence of aerial images reveals a slight decrease in the landslide occurrence rate in the last half of the 20th Century and a parallel increase in the landslide extinction rate, i.e. the rate at which evidence of landslide activity is removed by vegetation colonisation. A logistic regression routine was used to assess the influence of land use and vegetation recovery in the occurrence of shallow landslides.The result shows that the former arable fields on the valley slopes still facilitate landsliding, even after land abandonment and revegetation by shrubs or trees. A shift in the topographic location of landslides was also detected, pointing to an increased importance of water redistribution in the slopes after prolonged rainfall periods.

Which data for quantitative landslide susceptibility mapping at operational scale? Case study of the Pays d'Auge plateau hillslopes (Normandy, France)

“…In the Pays d'Auge, the land use has strongly changed during the last 70 years, which constitutes an important limitation in mapping the landslide susceptibility. It should be considered to assess and map the landuse evolution which can be integrated into the susceptibility analysis (Beguería, 2006b;Guns et al, 2012). The introduction of the time variability of the land use necessitates the availability of multi-temporal landslide inventories, as only with these can the landslide occurrence conditions (landuse change) be assessed.…”

Shallow landslide initiation on terraced slopes: inferences from a physically based approach

“…Different studies have been performed to evaluate the role of land use in shallow-landsliding, mainly through the use of statistical methods (e.g. Baeza and Corominas 2001;Beguerıa 2006;Piacentini et al 2012;Galve et al 2015;Trigila et al 2015;Persichillo et al 2016). These methods are based on conceptual models that describe the functional relationships between instability factors and the past and present distribution of slope failures (Carrara 1983).…”

Fire-related debris flows in the Iberian Range, Spain

“…The absence of plant cover in the months following a wildfire, and associated changes in soil characteristics, can lead to the occurrence of very high erosion rates until the vegetation recovers 6-24 months later (Cerdà, 1998;Prosser and Williams, 1998), with sheet wash and rilling being the dominant erosion processes. The vulnerability of wildfire-affected steeplands to debris flows has frequently been cited in recent decades as the most important form of post-fire erosion, and such flows are capable of delivering tons of sediment in response to individual rainstorms (Swanson, 1981;Wells, 1987;Cannon et al, 1997;Cannon and Reneau, 2000;Cannon et al, 2001aCannon et al, , 2001bGabet, 2003;Beguería, 2006;Shakesby and Doerr, 2006;Gabet and Bookter, 2008;Gartner et al, 2008;Nyman et al, 2011). Debris flows have commonly been related to shallow landslides triggered on sparsely vegetated hillslopes during intense rainstorms, which increase pore pressure and destabilise a portion of the slope (Blijenberg, 1998).…”

“…Materials cleared by landslides become the main sediment source for debris flows (Johnson and Rodine, 1984;Blijenberg, 1998;Lorente et al, 2002Lorente et al, , 2003Beguería, 2006;Bathurst et al, 2007). However, recent reports have attributed the triggering of fire-related debris flows to increased rates of runoff eroding the uppermost areas of hillslopes (Cannon et al, 2001a;Gabet and Bookter, 2008;Cannon et al, 2011;Parise and Cannon, 2011).…”

“…Fire-related debris flows are commonly reported in Spanish mountains, particularly the Pyrenees (Lorente et al, , 2003Beguería 2006;García-Ruiz et al, 2010) and the Iberian Range (García-Ruiz et al, 1988). In most cases, the triggering of these debris flows has been attributed to periodical fires ignited by humans to convert shrublands to grasslands.…”