HOW HOT IS IT ANYWAY? DAILY SKIN-SURFACE SOIL TEMPERATURE IN EAST AFRICA

Detailed soil temperature measurements with depth allow an estimate of soil diffusivity. We conducted a multi-year measurement campaign in East Africa to characterize environments ranging from closed canopy forest to desert to montane settings. We use inverse and forward modeling of standard heat flow equations to estimate hourly temperatures at the soil-air interface for multiple stations in East Africa. At 25 cm and deeper the daily signal is highly attenuated (less than 1 °C daily variation); open environments (e.g., grasslands) have average annual soil temperatures up to 7 °C higher than mean annual air temperatures whereas forest soils have long term mean temperatures very similar to mean annual air temperature. Daily surface soil temperatures in open environments in the desert regions of Kenya can regularly reach > 65°C. Combining seasonal daily soil surface temperatures into a composite day provides constraints on animal behavior in different environments through the daily cycle. This has implications for early hominin behavior in their avoidance of daily high temperatures by moving to more shaded environments where surface temperatures are much cooler, and for modeling hominin energy budgets in the daily cycle.