Long-term soil temperature dynamics in the Sierra Nevada, Spain Marc Oliva a, ⁎, Antonio Gómez Ortiz b , Ferran Salvador b , Montserrat Salvà b , Paulo Pereira c , Miguel Geraldes a a Institute of Geography and Spatial Planning, University of Lisbon, Alameda da Universidade, 1600-214 Lisbon, Portugal b Department for Physical and Regional Geography, University of Barcelona, Montalegre 6, 8, 08001 Barcelona, Catalonia, Spain c Environmental Management Center, Mykolas Romeris University, Ateities st. Vilnius, Lithuania abstract article info Article history: Received 27 September 2013 Received in revised form 10 July 2014 Accepted 11 July 2014 Available online xxxx Keywords: Sierra Nevada Periglacial environment Solifluction processes Soil temperatures Seasonal frost Snow cover Soil temperatures play a key role on the dynamics of geomorphological processes in periglacial environments. However, little is known about soil thermal dynamics in periglacial environments of semiarid mid-latitude mountains, where seasonal frost is dominant. From September 2006 to August 2012 we have monitored soil temperatures at different depths (2, 10, 20, 50 and 100 cm) in a solifluction landform located at 3005 m.a.s.l. in the summit area of the Sierra Nevada (South Spain). Mean annual temperatures in the first meter of the soil ranged from 3.6 to 3.9 °C while the mean annual air tem- perature at the nearby Veleta peak was 0.08 °C. Therefore, these data point out the inexistence of widespread permafrost conditions today in this massif. Seasonal frost controls the geomorphodynamics even in the highest lands. Climate conditions have shown a large interannual variability, as it is characteristic in a high mountainous Mediterranean environment. These variations are reflected in the patterns of soil thermal dynamics. The depth and duration of the frozen layer are strongly conditioned by the thickness of the snow cover. The date of the first significant snowfalls conditioned the beginning and rhythm of freezing of the soil. Wet years resulted in a thick snow cover which insulated the ground from external climate oscillations and favored a shallow frost layer (2008–2009, 2009–2010 and 2010–2011). On the other hand, years with low precipitations promoted deeper freezing of the soil down to 60–70 cm extending until late May or early June (2006–2007, 2007–2008 and 2011–2012). When snow melted a high increase of temperatures of 10–12 °C in few weeks was recorded at all depths. At this time of the year, periglacial activity is enhanced due to higher water availability and the ex- istence of freeze–thaw cycles. These were recorded mostly in spring and autumn in the first 50 cm depth of the soil, ranging from 9.8 days (at 2 cm) to 3.7 days (at 50 cm). However, the inactivity of solifluction landforms suggests that the combination of present-day soil temperatures together with moisture conditions is not favorable to promote solifluction activity in the periglacial belt of the Sierra Nevada. Future climate scenarios point to a temperature increase and precipitation decrease in the area, which would entail deeper but shorter frozen soil layers. These conditions would not be favorable for active periglacial slope processes in the Sierra Nevada. © 2014 Elsevier B.V. All rights reserved. 1. Introduction The research on soil thermal regime in periglacial environments has developed substantially over the last decades. In many periglacial regions the air temperature increase recorded since the late 70s has impacted, to a greater or lesser extent, the soil temperatures (e.g. Romanovsky et al., 2010a). In the current context of future climate un- certainty, an accurate knowledge of present-day soil thermal dynamics is essential for understanding how ecosystems in periglacial environ- ments may react to shifting climate scenarios. Thus, the areas where permafrost is present, albeit in slightly negative values, are those most likely to be affected by soil thawing. A change of the state in soil condi- tions can affect the network of infrastructures, equipments and human settlements spread over permafrost areas, as well as the dynamics of geomorphological processes (Nelson et al., 2002). Since the International Polar Year 2007–2008, research focused on soil thermal regimes in permafrost environments has been channeled through international initiatives which aim to monitor its thermal state and active layer dynamics (i.e. Global Terrestrial Network for Permafrost, Circumpolar Active Layer Monitoring). The most significant studies have been carried out in wide parts of the Arctic, where the Geoderma 235–236 (2014) 170–181 ⁎ Corresponding author at: Centro de Estudos Geográficos/IGOT, Universidade de Lisboa, Edifício FLUL, Alameda da Universidade, 1600-214 Lisboa, Portugal. E-mail address: oliva_marc@yahoo.com (M. Oliva). http://dx.doi.org/10.1016/j.geoderma.2014.07.012 0016-7061/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Geoderma journal homepage: www.elsevier.com/locate/geoderma