Simulation of the methane emission in rice fields in China during the past 40 years by DNDC model and GIS technical

Emissions of the greenhouse gases N₂O, CO₂, and CH₄ have increased in the past years. CH₄ has a distinct contribution to global warming and climate change. Rice production plays an important role in CH₄ emission. Thus, the rice fields in China should be considered in assessing CH₄ emission. This study simulated CH₄ emission in rice fields in China during the past 40 years (1971 to 2010) using the denitrification-decomposition (DNDC) model, a process-based biogeochemistry model. This study focused on the relationship between climate data and CH₄ emission. For regional scale, a GIS database at 10×10 km cover the entire land of China was employed. We compare this database and the land use map to create a new GIS database which includes all rice plant area in China. This new database contains daily climate data (minimum and maximum air temperature and precipitation) from over 700 meteorological stations nationwide (Chinese Meteorological Data Center), soil data (texture, clay fraction, porosity, saturated hydraulic conductivity, field capacity, and wilting point) that were obtained from The Harmonized World Soil Database, and field management data (sowing date, harvest date, fertilizing rate, and cultivated area). The management data contain both observation and simulation data. These data are necessary to establish the DNDC model. A total of 4244 points in China were simulated. Results showed that almost 90% CH₄ emission between 50 and 300 kg/ha, which is similar with the observed result from experiment. And the higher methane emission is Jiangsu, Zhejiang, Guangdong, Guangxi, Jiangxi, Hunan and Hainan. Northeast China demonstrated low CH₄ emission. With the temperature change, the 70% points of this simulation is decreasing CH₄ emission whereas other points is increasing. About %91 of points are changing in -60% to 60%. So the warming weath- r may decrease CH₄ emission. According to the sensitively analysis, the temperature increase will lead to the CH₄ emission decrease. Another reason is that climate change will lead to the extreme weather which will reduce the rice yield so that the CH₄ emission will be decreasing. The simulation and observation results show considerable differences. These differences can be attributed to the variation of each region and the uncertainty of many parameters during the simulation. Thus, the simulation results must be carefully analyzed to prove the impact of climate change on CH₄ emission. Further studies may use the DNDC model to simulate CH₄ emission in future climate situation in China and to find effective measures for reducing CH₄ emission and increasing rice production.