El Niño‐Southern Oscillation‐Induced Variability of Terrestrial Gross Primary Production During the Satellite Era

Abstract

Terrestrial gross primary production (GPP) is the largest carbon flux entering the biosphere from the atmosphere, which serves as a key driver of global carbon cycle and provides essential matter and energy for life on land. However, terrestrial GPP variability is still poorly understood and difficult to predict, especially at the annual scale. As a major internal climate oscillation, El Niño-Southern Oscillation (ENSO) influences global climate patterns and thus may strongly alter interannual terrestrial GPP variation. Using a remote sensing-driven ecosystem model with long-term satellite and climate data, we comprehensively examined the impacts of ENSO on global GPP dynamics from 1982 to 2016, focusing on lag effects of ENSO and their spatial heterogeneity. We found a clear seasonal lag effect of previous-year ENSO indices on current-year global GPP variability. The composite Oceanic Niño Index in the previous-year's August-October showed the strongest correlation with global annual GPP (R = −0.51, p < 0.01). Spatially, 20.1% and 11.7% of vegetated land area showed significant negative and positive correlations with the ENSO cycle, respectively. ENSO effects on annual GPP exhibited diverse seasonal evolutions, and the timings of peak ENSO influences were heterogeneous across the globe. Annual GPP from TRENDY land surface model ensemble did not capture the major lag effects of ENSO identified in the satellite-derived GPP and top-down-based land sink. Despite the complexity of the climate system, our efforts linking ENSO with global GPP dynamics provide a simple framework to understand and project climatic influences on the terrestrial carbon cycle.

Effects of Anthropogenic Activity on Global Terrestrial Gross Primary Production

“…Variations in shortwave radiation and volcanic activity are natural forcings that drive ENSO events through their effects on SST anomalies (Liu et al, ). Although the coupling of shortwave radiation with ENSO to drive GPP variations is currently the subject of active research (Zhang et al, ), the underlying mechanism of this coupling has yet to be determined. Our model results suggest that two factors, CO 2 fertilization and shortwave radiation, explain nearly all of the GPP variation during 1952–2010.…”

Large‐Scale Reductions in Terrestrial Carbon Uptake Following Central Pacific El Niño

“…We obtained monthly 1982–2016 GPP from two light‐use efficiency (LUE) models: The MODIS primary production model (MOD17) (Smith et al., 2016) and the Coupled Carbon and Water (CCW) model (Zhang et al., 2016; Zhang, Song, et al., 2019). Both models were driven by fraction of absorbed photosynthetically active radiation from the third generation GIMMS AVHRR normalized difference vegetation index (Pinzon & Tucker, 2014; Zhu et al., 2013) and by temperature, shortwave radiation, and vapor pressure deficit (VPD) from the CRU‐NCEP reanalysis, with model parameters calibrated using global eddy covariance flux towers.…”

“…(1) July (of year t−1) through June (of year t), roughly coinciding with initiation through decay of ENSO events and with the southern hemisphere growing season (2) January through December of year t (the calendar year), coinciding with the northern hemisphere growing season and reflecting known lags between ENSO and ecosystem productivity (e.g., Zhang, Dannenberg, et al, 2019) Analyses were conducted over two temporal intervals: (1) the full period of record for each individual data set, and (2) the period common to all datasets . The former facilitates best estimates of ENSO effects on terrestrial carbon cycling from each individual data set, while the latter enables comparison across models.…”

Examining the sensitivity of the terrestrial carbon cycle to the expression of El Niño

“…Lastly, a comparison with satellitederived observations might help to estimate whether LPJ-GUESS or indeed an alternative DGVM captures the correct sensitivity in the response of vegetation dynamics to ENSO events. Nevertheless, as direct global measurements of carbon fluxes do not exist, and those that do are often based on models themselves, future work might restrict comparison to less direct proxies of variability, such as leaf area index (Zhu et al, 2013) and/or GRACE terrestrial water storage (Rodell et al, 2004).…”