Journal Article

Airborne observations of methane emissions from rice cultivation in the Sacramento Valley of California

Trainer, M., Blake, D. R., Atlas, E. L., Andrews, A. E., Wofsy, S. C., Daube, B. C., Guha, A., Misztal, P. K., Holloway, J. S., Santoni, G. W., Peischl, J., Perring, A. E., Kofler, J., Pollack, I. B., Spackman, J. R., Ryerson, T. B., Goldstein, A. H., Dlugokencky, E. J., Fischer, M. L., Schwarz, J. P., Karl, T., Kosciuch, E., Parrish, D. D.

2012

Overview

Airborne measurements of methane (CH4) and carbon dioxide (CO2) were taken over the rice growing region of California's Sacramento Valley in the late spring of 2010 and 2011. From these and ancillary measurements, we show that CH4 mixing ratios were higher in the planetary boundary layer above the Sacramento Valley during the rice growing season than they were before it, which we attribute to emissions from rice paddies. We derive daytime emission fluxes of CH4 between 0.6 and 2.0% of the CO2 taken up by photosynthesis on a per carbon, or mole to mole, basis. We also use a mixing model to determine an average CH4/CO2 flux ratio of −0.6% for one day early in the growing season of 2010. We conclude the CH4/CO2 flux ratio estimates from a single rice field in a previous study are representative of rice fields in the Sacramento Valley. If generally true, the California Air Resources Board (CARB) greenhouse gas inventory emission rate of 2.7 × 1010 g CH4/yr is approximately three times lower than the range of probable CH4 emissions (7.8–9.3 × 1010 g CH4/yr) from rice cultivation derived in this study. We attribute this difference to decreased burning of the residual rice crop since 1991, which leads to an increase in CH4 emissions from rice paddies in succeeding years, but which is not accounted for in the CARB inventory. Key Points CH4 levels in Sacramento Valley higher during rice growing season than before Rice CH4 fluxes between 0.6 and 2.0% of CO2 taken up by photosynthesis Inventoried emission rate is a factor of three lower than probably CH4 emissions

• Publisher: Blackwell Publishing Ltd,American Geophysical Union
• Subject: Agriculture / Atmospheric sciences / Biosphere / Boundary layers / California / Carbon dioxide / Carbon footprint / Cereal crops / Climatology. Bioclimatology. Climate change / Cultivation / Earth, ocean, space / Emission inventories / Exact sciences and technology / External geophysics / Geobiology / Geophysics / Grain cultivation / Greenhouse gases / Growing season / Meteorology / Methane / methane emissions / Photosynthesis / rice / Rice fields / Sacramento Valley / Systems science / Troposphere