Community Land Model version 5 (CLM5) simulations of canopy water amount

We utilized the simulation results of the Community Land Model version 5 (CLM5), which serves as the land component of the Community Earth System Model Version 2 (CESM2) (Lawrence et al., 2019), to develop CWAI under historical and future climates. CLM5 incorporates advanced plant hydraulic configurations, enabling effective simulation of water movement and storage across various plant tissues. This facilitates a more accurate representation of numerous ecosystem biogeophysical and biogeochemical processes(Kennedy et al., 2019; Wu et al., 2020). Our simulations examined two periods: the historical period (2001–2015) and the future period (2086–2100). These simulations were differentiated by specific climatic forcing datasets, while keeping other settings and parameters like land cover and CO2 concentrations (default value of 367 ppm) consistent.For the historical period (2001–2015), we employed the default CRUNCEP7 data, which integrates Climatic Research Unit Time Series (CRUTS) version 3.24 and National Centers for Environmental Prediction (NCEP) reanalysis, providing comprehensive climatic input. Notably, CRUNCEP7 is also the default air forcing data in the Global Carbon Project TRENDY simulations (Friedlingstein et al., 2019). For the future scenario (2086–2100), we employed climatic forcing data from the Coupled Model Intercomparison Project Phase 6 (CIMP6) database, specifically using CEMS2 outputs under the SSP5-8.5 scenarios. By driving CLM5 with meteorological outputs from CESM2, we aimed to closely replicate conditions anticipated in a fully-coupled model environment, enhancing the robustness and relevance of our simulations. These historical and future simulations provide crucial intermediate variables for our study, such as canopy water potential, nitrogen supply for photosynthesis, and stomatal conductance, which are not available in the CMIP6 datasets.In this study, the CLM5 was run in the offline mode. To achieve steady states of carbon, water, and energy at the start of the simulations, CLM5 was run for 400 years in the “spin‐up” mode with accelerated decomposition rates of soil organic matters, followed by an additional 800 years’ run in the “normal mode” without accelerated decomposition. By the end of the spin‐up, the total ecosystem C was drifting by less than 0.02 Pg C year–1 at global scale, much lower than the 0.1 Pg C yr-1 threshold recommended for the C4MIP by Jones et al. (2016). The simulation results for tropical forests within the latitudinal band of 23.5°N to 23.5°S were extracted in this study.