National-scale estimation of methane emission from paddy fields in Japan: Database construction and upscaling using a process-based biogeochemistry model

Abstract

We have estimated methane (CH₄) emission from total rice (Oryza sativa L.) paddies in Japan by means of a process-based biogeochemistry model, DeNitrification-DeComposition(DNDC)-Rice, combined with a geographic information system (GIS) database of climate, soil and farming practices. In the GIS database, 2 million ha of rice paddies were divided into 17,408 units according to 136 climate areas, 16 soil types, four classes of drainage rate and two classes of groundwater level, to simulate CH₄ flux from each of the units applying the DNDC-Rice model. As a result, the national-scale CH₄ emission in 1990 was estimated to be 216 Gg carbon (C), 13% lower than a previous inventory estimated by the Tier 2 method. By our Tier 3 approach, a relatively higher CH₄ flux was estimated from eastern regions than from western regions of Japan, presumably due to the differences in climate and water management. Sensitivity analysis and uncertainty assessment indicated that it is important to account for the heterogeneity in soil properties such as field water capacity, iron (Fe) concentration and drainage rate, in order to reduce the uncertainty in regional estimates.

Key words:

• methane emission
• DNDC-Rice model
• regional estimation.

SUPPLEMENTARY MATERIAL

Supplementary material for this article is available online from http://dx.doi.org/10.1080/00380768.2013.836943

ACKNOWLEDGMENTS

We thank Professer C. Li (University of New Hampshire) for his advice regarding the original DNDC model. We also thank Dr. Y. Shiratori (Niigata Agricultural Research Institute) and Y. Saito (Yamagata Integrated Agricultural Research Center) for their kind suggestions on drainage conditions and farming management data for simulation. We thank Dr. H. Obara (National Institute for Agro-Environmental Sciences, NIAES) for his help collecting farming management data from Agricultural Research Centers in some prefectures. We also thank Dr. Y. Takata (NIAES) for providing the digital soil map overlaid on drainage index.