Moisture, thermal inertia, and the spatial distributions of near-surface soil and air temperatures: Understanding factors that promote microrefugia

• Published in: Agricultural and forest meteorology 2013-07, Vol.176, p.77-89
• Main Authors: Ashcroft, Michael B., Gollan, John R.
• Format: Article
• Language: English
• Subjects: Agricultural and forest climatology and meteorology. Irrigation. Drainage; Agronomy. Soil science and plant productions; air; air temperature; biodiversity; Biological and medical sciences; Canopies; canopy; Climate change; cold; Diurnal range; drying; Elevation; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; Humidity; latitude; Mathematical models; Moisture; Physical properties; Physics, chemistry, biochemistry and biology of agricultural and forest soils; refuge habitats; Refugia; Soil (material); Soil moisture; Soil science; Soil temperature; Spatial distribution; Temperature variability; Topoclimate; vapor pressure; Water and solute dynamics
• ISSN: 0168-1923; 1873-2240
• DOI: 10.1016/j.agrformet.2013.03.008

•Moisture reduces exposure to temperature extremes, facilitating climate refugia.•Variability of air temperatures related to humidity, but soil temperatures to VPD.•Moisture differentially affects spatial distribution of soil and air temperatures.•Microrefugia will be more apparent under dry conditions. Climate change poses significant threats to biodiversity, but some species may be able to escape its effects in small locations with unusual and stable climates (microrefugia). However, there are still great uncertainties about where microrefugia are located, and the exact role that moisture plays in buffering extreme temperatures. In this study we quantified the effects of moisture on the distribution and variability of near-surface soil and air temperatures. We collected hourly 1cm soil and 5cm air temperatures and humidities at 111 sites from May 2011 to March 2012. Sites were diverse in terms of elevation (2–1428m), distance from coast (180m–403km), canopy cover (0–100%), topographic exposure, and susceptibility to cold air drainage. We found that variability (diurnal range) of both soil and air temperatures decreased under moister conditions. While air temperatures were related more strongly to humidity, soil temperatures were related more to vapour pressure deficit (VPD). That is, both high temperature and low humidity were required before the VPD was sufficient to dry out the soil and allow soil temperatures to vary. We then used a regional regression approach to model the spatial distribution of minimum and maximum air and soil temperatures for each day over the 10 months in terms of latitude, elevation, canopy cover, distance to coast, cold air drainage potential, and topographic exposure to the south and northwest. We found that elevation was the dominant factor explaining the distribution of soil and air temperatures under moist conditions. Other factors, such as canopy cover and topographic exposure, had a stronger influence on air temperatures whenever humidity was low. However, these factors only affected soil temperatures at times when higher temperatures combined with low humidity to produce higher VPD. Our results provide new insights into how moisture influences the spatial distribution of near-surface soil and air temperatures. Microrefugia will be more apparent under drier conditions, but climate change may affect refugia for soil and air temperatures differently. Higher temperatures will cause VPD to increase more than would be expected