Publications

Ichii, K; Ueyama, M; Kondo, M; Saigusa, N; Kim, J; Alberto, MC; Ardo, J; Euskirchen, ES; Kang, M; Hirano, T; Joiner, J; Kobayashi, H; Marchesini, LB; Merbold, L; Miyata, A; Saitoh, TM; Takagi, K; Varlagin, A; Bret-Harte, MS; Kitamura, K; Kosugi, Y; Kotani, A; Kumar, K; Li, SG; Machimura, T; Matsuura, Y; Mizoguchi, Y; Ohta, T; Mukherjee, S; Yanagi, Y; Yasuda, Y; Zhang, YP; Zhao, FH (2017). New data-driven estimation of terrestrial CO2 fluxes in Asia using a standardized database of eddy covariance measurements, remote sensing data, and support vector regression. JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES, 122(4), 767-795.

Abstract
The lack of a standardized database of eddy covariance observations has been an obstacle for data-driven estimation of terrestrial CO2 fluxes in Asia. In this study, we developed such a standardized database using 54 sites from various databases by applying consistent postprocessing for data-driven estimation of gross primary productivity (GPP) and net ecosystem CO2 exchange (NEE). Data-driven estimation was conducted by using a machine learning algorithm: support vector regression (SVR), with remote sensing data for 2000 to 2015 period. Site-level evaluation of the estimated CO2 fluxes shows that although performance varies in different vegetation and climate classifications, GPP and NEE at 8days are reproduced (e.g., r(2)=0.73 and 0.42 for 8day GPP and NEE). Evaluation of spatially estimated GPP with Global Ozone Monitoring Experiment 2 sensor-based Sun-induced chlorophyll fluorescence shows that monthly GPP variations at subcontinental scale were reproduced by SVR (r(2)=1.00, 0.94, 0.91, and 0.89 for Siberia, East Asia, South Asia, and Southeast Asia, respectively). Evaluation of spatially estimated NEE with net atmosphere-land CO2 fluxes of Greenhouse Gases Observing Satellite (GOSAT) Level 4A product shows that monthly variations of these data were consistent in Siberia and East Asia; meanwhile, inconsistency was found in South Asia and Southeast Asia. Furthermore, differences in the land CO2 fluxes from SVR-NEE and GOSAT Level 4A were partially explained by accounting for the differences in the definition of land CO2 fluxes. These data-driven estimates can provide a new opportunity to assess CO2 fluxes in Asia and evaluate and constrain terrestrial ecosystem models.

DOI:
10.1002/2016JG003640

ISSN:
2169-8953