Abstract Earth's arid and semi‐arid regions have been hypothesized to contribute significantly to interannual variability of the global terrestrial carbon sink. Arid and semi‐arid regions such as the Western U.S. also show high vulnerability to climate extremes in the form of droughts, heatwaves, and large forest fires, compelling a need to quantify their climate‐carbon responses. We quantify the net ecosystem exchange of (NEE) using a high‐resolution regional inverse model with constraints from both in situ and space‐based observations during 2015–2016. Posterior fluxes are evaluated against withheld aircraft observations across the North American observation network. Observationally constrained fluxes suggest moisture‐driven seasonal compensation in NEE across the 2 years, evidenced by a decrease in NEE of 244–262 Tg C during the early carbon uptake period and an increase in NEE of 281–389 Tg C later during the carbon uptake period, relative to 2016. Atmospheric constraints on NEE, combined with remote sensing and machine learning‐based upscaled gross primary productivity (GPP) products, allow for benchmarking of net and gross fluxes as estimated by a suite of terrestrial biosphere models. These benchmarks allow us to link changes in NEE and GPP constrained by atmospheric and space‐based observations to changes in stomatal conductance and water use efficiency. High‐precision in situ observations, such as those from the Global Greenhouse Gas Reference Network, are key constraints for bias‐free carbon flux estimates.
Rastogi et al. (Mon,) studied this question.