On what scales can GOSAT flux inversions constrain anomalies in terrestrial ecosystems?

Brendan Byrne,Dylan B A Jones,Saroja M Polavarapu,Shamil Maksyutov,David F Baker,Kimberly Strong,Anna B Harper

doi:10.5194/acp-19-13017-2019

Abstract

Abstract. Interannual variations in temperature and precipitation impact the carbon balance of terrestrial ecosystems, leaving an imprint in atmospheric CO2. Quantifying the impact of climate anomalies on the net ecosystem exchange (NEE) of terrestrial ecosystems can provide a constraint to evaluate terrestrial biosphere models against and may provide an emergent constraint on the response of terrestrial ecosystems to climate change. We investigate the spatial scales over which interannual variability in NEE can be constrained using atmospheric CO2 observations from the Greenhouse Gases Observing Satellite (GOSAT). NEE anomalies are calculated by performing a series of inversion analyses using the GEOS-Chem adjoint model to assimilate GOSAT observations. Monthly NEE anomalies are compared to “proxies”, variables that are associated with anomalies in the terrestrial carbon cycle, and to upscaled NEE estimates from FLUXCOM. Statistically significant correlations (P<0.05) are obtained between posterior NEE anomalies and anomalies in soil temperature and FLUXCOM NEE on continental and larger scales in the tropics, as well as in the northern extratropics on subcontinental scales during the summer (R2≥0.49), suggesting that GOSAT measurements provide a constraint on NEE interannual variability (IAV) on these spatial scales. Furthermore, we show that GOSAT flux inversions are generally better correlated with the environmental proxies and FLUXCOM NEE than NEE anomalies produced by a set of terrestrial biosphere models (TBMs), suggesting that GOSAT flux inversions could be used to evaluate TBM NEE fluxes.

Highlights

Organisms within terrestrial ecosystems have evolved to fit their climatic environment
We present a series of observing system simulation experiments (OSSEs) to examine the smallest spatial scales for which net ecosystem exchange (NEE) anomalies can be recovered from Gases Observing Satellite (GOSAT) observations
We consistently find that Tsoil and FLUXCOM NEE show the strongest agreement with the flux inversions, whereas self-calibrated Palmer Drought Severity Index (scPDSI) and solar-induced chlorophyll fluorescence (SIF) show weaker agreement

Summary

Introduction

Organisms within terrestrial ecosystems have evolved to fit their climatic environment. Interannual variability (IAV) in the atmospheric growth rate of CO2 is largely explained by changes in the carbon balance of terrestrial ecosystems in response to climate variability (Keeling et al, 1976a, b; Conway et al, 1994; Keeling et al, 1995; Battle et al, 2000). Many studies have examined extreme heat waves or droughts in the extratropics, such as the 2003 European heat wave (Ciais et al, 2005) and the 2010 Russian heat wave and wildfires (Guerlet et al, 2013; Ishizawa et al, 2016) In these cases, positive temperature anomalies and drought conditions result in an anomalous release of CO2 from terrestrial ecosystems to the atmosphere

Results

Discussion

Conclusion