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Upscaling terrestrial carbon dioxide fluxes in Alaska with satellite remote sensing and support vector regression
Author(s) -
Ueyama Masahito,
Ichii Kazuhito,
Iwata Hiroki,
Euskirchen Eugénie S.,
Zona Donatella,
Rocha Adrian V.,
Harazono Yoshinobu,
Iwama Chie,
Nakai Taro,
Oechel Walter C.
Publication year - 2013
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1002/jgrg.20095
Subject(s) - environmental science , eddy covariance , carbon sink , ecosystem respiration , primary production , atmospheric sciences , flux (metallurgy) , carbon cycle , carbon flux , carbon dioxide , ecosystem , soil respiration , climatology , ecology , soil water , geology , soil science , chemistry , biology , organic chemistry
Carbon dioxide (CO 2 ) fluxes from a network of 21 eddy covariance towers were upscaled to estimate the Alaskan CO 2 budget from 2000 to 2011 by combining satellite remote sensing data, disturbance information, and a support vector regression model. Data were compared with the CO 2 budget from an inverse model (CarbonTracker). Observed gross primary productivity (GPP), ecosystem respiration (RE), and net ecosystem exchange (NEE) were each well reproduced by the model on the site scale; root‐mean‐square errors (RMSEs) for GPP, RE, and NEE were 0.52, 0.23, and 0.48 g C m −2 d −1 , respectively. Landcover classification was the most important input for predicting GPP, whereas visible reflectance index of green ratio was the most important input for predicting RE. During the period of 2000–2011, predicted GPP and RE were 369 ± 22 and 362 ± 12 Tg C yr −1 (mean ± interannual variability) for Alaska, respectively, indicating an approximately neutral CO 2 budget for the decade. CarbonTracker also showed an approximately neutral CO 2 budget during 2000–2011 (growing season RMSE = 14 g C m −2 season −1 ; annual RMSE = 13 g C m −2 yr −1 ). Interannual CO 2 flux variability was positively correlated with air temperature anomalies from June to August, with Alaska acting as a greater CO 2 sink in warmer years. CO 2 flux trends for the decade were clear in disturbed ecosystems; positive trends in GPP and CO 2 sink were observed in areas where vegetation recovered for about 20 years after fire.