Journal Article

Hydroclimatic Constraints on Tree Transpiration‐Induced Cooling Across Global Biomes

Xu, Xianli, Liu, Ran, Hayat, Muhammad

2025

Overview

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 (SWCcrit) 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. Plain Language Summary The fact that trees play an important role in mitigating global warming, yet we still don't completely understand their transpiration cooling (TC) under changing climate using ground data. This study used the first global sap flow database to find out the trees' TC and their hydroclimatic controlling mechanisms across different biomes. We found the highest TC in tropical rainforests and the lowest in temperate grassland deserts. Among the selected site variables, air temperature, and vapor pressure deficit were important drivers of TC in warm‐wet biomes, while precipitation and soil water content in hot‐dry biomes. The amount of soil water restricted TC in different ways across biomes, with higher threshold values in warm‐wet and lower values in hot‐dry biomes. These findings are likely to develop more integrated and effective climate mitigation and adaptation strategies and improve the model's representation of hydroclimatic constraints. Key Points Transpiration‐induced cooling is highest in tropical rainforests, moderate in temperate forests, and lowest in temperate grassland deserts The transpiration‐induced cooling is mainly driven by available energy in warm‐wet biomes, while water availability in hot‐dry biomes Globally, we found an average critical soil water content threshold (SWCcrit), with higher values in warm‐wet biomes and lower values in hot‐dry biomes

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Air temperature / biomes / Climate / Climate change / Climate change mitigation / Constraints / Cooling / critical soil water content threshold / Deserts / Ecosystems / Global warming / Grasslands / hydroclimatic variables / Moisture content / Precipitation / Rainforests / Sap / SAPFLUXNET data set / Soil / Soil water / Sweat cooling / Transpiration / transpiration‐induced cooling / Trees / Tropical cyclone rainfall / Vapor pressure / Vapors / Vapour pressure / Water content