Hydroclimatic Constraints on Tree Transpiration-Induced Cooling Across Global Biomes

Abstract

Despite trees' critical role in regulating global warming, their direct transpiration-induced cooling (TIC) effects in response to background climate at the global scale are currently not well understood by ground observations. We used the global observation-based SAPFLUXNET data set to quantify the trees' TIC and investigate how hydroclimatic variables affect TIC across biomes. Results show that TIC (i.e., air temperature reduction (ΔT)) was highest in tropical rainforests (3.24°C m⁻² d⁻¹) and lowest in temperate grassland deserts (0.06°C m⁻² d⁻¹). ΔT was mainly driven by air temperature and vapor pressure deficit in warm-wet biomes, while precipitation and soil water content (SWC) in hot-dry biomes. Globally, we found an average critical SWC threshold (SWC_crit) for ΔT (0.37 m³ m⁻³), with higher values in warm-wet and lower values in hot-dry biomes. These findings provide novel insights into the role of trees in mitigating global warming and improving the hydroclimatic constraints in models.