Alpine Summer Surface Temperature Amplification Is Spatially Heterogeneous and Intensified by Wind and Sun

Recent studies suggest that alpine microtopography may buffer against climate warming by creating more diverse climates over small spatial extents. Here, we examined with thermocouples how daytime summer surface temperatures differed from free-air temperatures and how much summer diel temperatures varied across small areas (8 × 8 m) for eight paired (open and krummholz) alpine plots at Cardinal Divide, Alberta, Canada. We found summer daytime surface temperature amplifications with open plots averaging 26.7°C ± 0.2 SE on the ground relative to 21.1°C ± 0.1 SE at a 2-m free-air height (5.6°C ± 0.1 SE amplification). Krummholz plots decreased surface amplifications, compared to those observed in the open alpine, averaging 27.3°C ± 0.2 SE on the ground relative to 22.9°C ± 0.1 SE at 2 m (4.4°C ± 0.1 SE amplification). Wind and solar radiation altered temporal patterns in surface temperatures, resulting in increased amplification and decoupling from free-air temperatures. At wind speeds of 3 m/s and solar radiation of 900 W/m², surface temperatures in open alpine plots were up to 21°C higher than free-air temperatures. Surface temperature variability over diel periods within 8 × 8 m plots differed by up to 9.9°C, illustrating high local variation in microclimates at a similar magnitude as the dry-air adiabatic lapse rate for a 1-km change in altitude. Individual locations with krummholz cover had diel ranges 11.3°C less than locations with no tree cover. Given the surface amplification and local spatial variability that we found, the use of standard 2-m free-air temperature data in climate models for alpine plants represents a mismatch in scales. More work is needed to develop climate surface models for alpine environments to assess risk from climate warming and determine opportunities for local refugia.