Ground temperature regimes and geomorphological implications in a Mediterranean mountain (Serra da Estrela, Portugal)

Air and shallow ground temperatures from two monitoring sites at the Serra da Estrela (Portugal) are analysed. The Cântaro Gordo site is located at 1875 m ASL and the Fraga das Penas at 1640 m ASL. The climate of the study area is Mediterranean and very irregular, both on a yearly and monthly basis. This is particularly significant during winter, when differences in snow cover have direct influence on the ground thermal regimes and therefore on geocryological processes. To assess the significance of the ground thermal regimes for the geomorphological dynamics, bi-hourly records of temperature are studied at a daily basis. Eight types of daily regime were identified: isothermal unfrozen, non-isothermal unfrozen, surficial freeze–thaw, surficial freeze–thaw and subsurficial frost, surficial and subsurficial freeze–thaw, subsurficial frost, surficial and subsurficial frost and surficial frost but no daily rhythm. The occurrence of these regimes is analysed and their geomorphological significance is presented. Based on the altitudinal differences of the two monitoring sites, on the occurrence of the different regimes and on field observations, a conceptual model for the altitudinal and seasonal zoning of the daily thermal regimes of the ground is presented. This model was prepared for the Serra da Estrela, but it can be used in other Mediterranean or tropical areas if altitude and seasonal precipitation differences are taken in explanation.