Tropical Forest Canopy Thermoregulation Observed from Space

Canopy temperature (T_c) is a key regulator of plant physiological processes, growth, and productivity, and serves as an indicator of surface energy partitioning and plant water status. Despite its importance, many dynamic vegetation models implicitly assume T_c to be equal to air temperature (T_air); while land surface models calculate an effective surface temperature based on energy balance, but typically have not evaluated this calculation against data. Using satellite-derived land surface temperature as a proxy for T_c, in combination with ERA5-Land T_air, we assessed whether tropical rainforests actively thermoregulate T_c relative to T_air. We find that ΔT (T_c – T_air) follows a consistent diurnal cycle, which is primarily controlled by diurnal variations in net radiation. Forest canopies are cooler than air at night, warm early in the morning and cool again below T_air in late afternoon. During the hottest part of the day, the slope (β) of the canopy-air relationship indicates strong megathermy in dry forests, while humid forests show responses ranging from limited homeothermy to megathermy depending on their capacity to dissipate heat. Humid forests with sufficient water availability show buffering of T_c against T_air variability through evaporative cooling, whereas dry forests frequently experience canopy warming as aridity constrains evaporative cooling. In humid forests, this evaporative cooling persists through the wet season but weakens—or reverses to canopy warming—during the dry season as water stress intensifies. Together, these findings provide an observational benchmark for improving the representation of canopy temperature, evaporative cooling, and vegetation–atmosphere energy and water exchanges in land-surface models.