Amplification of ENSO-driven vegetation variability at decadal and longer timescales

Abstract. The El Niño-Southern Oscillation (ENSO) is recognized as the dominant driver of global vegetation variability on interannual timescales. Here, we examine how ENSO affects decadal to multi-decadal vegetation variability. We address this with partial spectral and mediation analysis applied to multi-centennial pre-industrial control simulations from 11 CMIP6 models with dynamic leaf area index (LAI). We find a spectral reddening of ENSO-driven vegetation variability, with a 20–25 % amplification of the LAI signal at multi-decadal timescales and a 25–65 % reduction at interannual timescales. The coherence between ENSO and LAI on multi-decadal timescales is governed by a direct causal impact of ENSO on LAI (88 %), while the Pacific Decadal Oscillation (PDO) acts as a weak mediator (12 %). Mechanistically, persistence in vegetation originates from ENSO-induced changes in near-surface soil moisture, which is subsequently amplified by vegetation dynamics. This ENSO-related memory also manifests in Gross Primary Production (GPP), but it is suppressed in Net Primary Production (NPP) by a compensatory increase in autotrophic respiration. Our results illustrate how terrestrial persistence acts as a predictable, non-oceanic source of decadal variability, which could help extend the skill of climate predictions and improve hydrological risk management.