Air temperatures (Ta) are rising in a changing climate, increasing temperature-associated extreme events. The way these increases are influencing extreme temperatures at the soil surface and belowground in the soil profile has received little attention. We validated surface and soil temperature (Ts: 0-100 cm depth) simulations in the SOILWAT2 model for 29 locations comprising 5 broad ecosystem types in the central and western United States. We determined the temperature characteristics of these locations from 1980-2015, and explored simulations of Ta and Ts change over 2030-2065 and 2065-2100 time periods using General Circulation Model (GCM) projections and the RCP 8.5 emissions scenario. Our primary objective was to contrast the magnitude (°C) and occurrence (events per decade, based on 1980-2015 variation) of the top 50% and top 5% of Ta and Ts extreme threshold values (i.e. the boundary temperature designating extreme events) from April-October between 20th and 21st century time periods.
Results/Conclusions
All GCMs projected substantial temperature increases in the 21st century. On average, the top 5% of Ts extreme thresholds will increase by 3.4 °C in 2030-2065 and by 5.3 °C in 2065-2100. These increases will often approach +10 °C at 0-20 cm by the end of the century, and increases from 0-100 cm will commonly exceed 5.0 standard deviations above 1980-2015 values. The top 5% of Ts extreme thresholds will increase from 0.9 events per decade in 1980-2015 to 23 events in 2030-2065 and 38 events in 2065-2100. Additionally, by 2065-2100 the majority of months will experience co-occurring top 50% extreme thresholds at most soil depths (0-100 cm), which did not occur in 1980-2015. These projections of Ta and Ts extreme thresholds illustrate the non-analog temperature increases that ecosystems of the central and western US will experience in the 21st century as a result of climate change.