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Rainfall pulses generate rapid increases and subsequent declines in soil moisture (SM), yet global ecosystem responses during SM dry-downs remain poorly quantified. Using 6502 soil dry-down events identified from global eddy-covariance observations, we compared carbon fluxes during dry-downs (treatment) to fluxes during the same periods without dry-downs in other years (control). During early dry-downs days, gross primary production (GPP) and respiration both exceeded controls, with stronger GPP gains enhancing net carbon uptake. This enhancement persisted for several days before diminishing as SM decreased and atmospheric dryness intensified. Latent and sensible heat fluxes also rose initially, but latent heat enhancement weakened over time, accompanied by enhanced sensible heat. Machine-learning analyses show that photosynthetic capacity and radiation drive positive GPP anomalies, while water limitations induce negative ones. Satellite data supported these patterns, whereas Earth system models underestimate their magnitude. These findings highlight transient pulse responses and support the broader applicability of the pulse-reserve paradigm. Ecosystems accumulate carbon for several days after moisture pulses, but this benefit fades as soil dries and heat stress intensifies, according to an analysis that uses carbon flux-tower observations, Earth system models, machine learning, and satellite images.
Bai et al. (Wed,) studied this question.