Global climate change, rice productivity and methane emissions: comparison of simulated and experimental results

Abstract

Irrigated rice production is a major food source for a large portion of the world’s population, and a major anthropogenic source of the greenhouse gas methane (CH 4). Potential impacts of global climate change [elevated carbon dioxide (CO 2) and/or elevated temperature] on rice can be predicted with simulation models, but experiments are necessary to determine how well these models mimic the responses of the field crop. This paper compares grain yield, biomass, and methane emissions from experiments at the International Rice Research Institute (IRRI) at Los Baños, the Philippines, with potential responses based on simulations using the ORYZA1 process model and the climate data from those experiments. Yield and biomass were compared for the 1995 and 1996 dry seasons (DS) and the 1994 wet season (WS). Emissions of CH 4 from rice fields were evaluated for the 1995 WS and 1996 DS. Simulated and experimental responses (adjusted for effects of the open-top chambers on plant growth) differed with climate change scenario, response parameter, and season. Under current climate conditions (ambient CO 2 and ambient temperature), simulated grain yield was 14% lower than the adjusted experimental grain yield in the 1996 DS, but was 17 and 37% higher than experimental grain yield in the 1995 DS and 1994 WS, respectively. With current climate, simulations underestimated experimental aboveground, belowground, and total biomass. The simulated CH 4 emissions were the same as the experimental emissions, assuming CH 4 emissions were 2.9% of the simulated total biomass carbon. With elevated CO 2 and ambient temperature, simulations predicted greater increases (compared with current climate) in grain yield, aboveground biomass, and total biomass, but generally smaller increases in belowground biomass and CH 4 emissions than the significant (at p < 0.05) increases that were found experimentally. With ambient CO 2 and elevated temperature, both simulations and experiments generally showed either no change or a decrease in grain yield and biomass, but none of the responses in the experiments were statistically significant. Simulated ambient CO 2 and elevated temperature resulted in a smaller decrease in CH 4 emissions than the significant decrease found in the experiments. For both elevated CO 2 and elevated temperature, simulated grain yield increased in all three seasons, whereas there were no significant effects on experimental grain yield. The simulations predicted smaller increases in belowground biomass and CH 4 emissions with elevated CO 2 and elevated temperature than the significant increases in the experiments. To better correspond to experimental results, this study suggested that current simulation models could be improved in terms of effects of temperature on grain yield and use of belowground biomass to estimate CH 4 emissions.