Canopy temperature dynamics are closely aligned with ecosystem water availability across a water- to energy-limited gradient

Canopy temperature (T_c) plays an important role in regulating the rates of mass and energy fluxes at the leaf surface. Better understanding of the relationship between T_c and water availability may enable more accurate monitoring of ecosystem functioning in a changing climate. Here, we used high spatiotemporal resolution thermal infrared cameras deployed at three eddy covariance flux tower sites along a water- to energy-limited gradient – including a predominately water-limited grassland/shrubland site, a seasonally water-limited evergreen needleleaf forest, and a predominantly energy-limited deciduous broadleaf forest – to determine T_c seasonality and its relationship with gross primary productivity (GPP) and environmental drivers. We found midday T_c was generally warmer than air temperature (T_air) during the growing season (T_c:T_air slope: 1.14–1.27) for all sites. Water-limited sites exhibited higher positive T_c deviations from T_air (2.30 ± 0.06 °C) compared to the energy-limited site (1.29 ± 0.09 °C) partly due to their reduced latent heat fluxes during water-limited periods. We further found that the T_c:T_air slope increased with site aridity, namely for 1.14 slope for the grassland, 1.15 for the evergreen forest, and 1.27 for the broadleaf forest. Peak GPP occurred when T_c was higher than T_air across all sites, with peak GPP at the grassland site occurring at +1.1 °C (T_c-T_air) and peak GPP at the broadleaf evergreen site occurring at +2.2 °C (T_c-T_air). T_c-T_air dynamics were mostly associated with soil water content at water-limited sites where canopies undergo a substantial cooling during the transition from dormancy to the peak GPP, while net radiation played a crucial role at the energy-limited site where the canopy heats up compared to T_air over the same phenological transition. Our findings provide novel insights into T_c-ecosystem water availability links, highlighting the drivers of T_c-T_air across diverse ecosystems in various phenological stages, which has implications for ecosystem management in a changing climate.