NIAES > Priority Research Areas (2006-2008) > Modeling of Paddy Ecosystem Responses to Climate Change and Development of Wide Area Assessment Methodology for Rice Production

Modeling of Paddy Ecosystem Responses to Climate Change and Development of Wide Area Assessment Methodology for Rice Production

Background and Objectives

The world populations is projected to reach 8.4 billion by 2030, of which over 5 billion will live on rice. Meanwhile, it is feared that the increasing trend toward global warming and frequent outbreaks of extreme weather will be a serious blow to rice production. We seek to contribute in the effort toward a stable production (supply) of rice by assessing the risk in rice production due to climate changes, and by proposing new cultivation techniques that would allow farmers to respond and adjust to climate changes.

Project Outline

Factors affecting fluctuations in growth

Fig. 1   Factors affecting fluctuations in growth and crop yields of rice in paddy ecosystems

Experimental station-size models will be developed to represent fluctuations in the growth and crop yields of rice as the paddy ecosystemfs response to a rise in carbon dioxide concentration, global warming, frequent occurrence of abnormal temperatures, wider fluctuations of precipitation, and other climate change phenomena. Also, simplified wide-area models will be developed for the risk assessment of rice production on a regional scale. These models will be used to forecast fluctuations in rice production in Japan and Asia in the mid-21st century and to assess the risk in rice production fluctuations on a regional scale as affected by climate change.

Relevant Outcomes to Date

(1) For the first time in the world, we have made clear at the plant community level that, while a higher CO2 concentration in the atmosphere increases the photosynthesis activity of rice but at a slower rate of increase, along with the growth of rice, the rate of photorespiration is raised by the increase in CO2 concentration through all the rice growth stages (Fig. 2). On a separate matter, our Free-Air Carbon Dioxide Enrichment (FACE) experiment, the worldfs first ever of its kind applied to rice, has shown that a rise in atmospheric CO2 concentration of approximately 200 ppm forces the stoma to be semi-closed, and the overall water consumption of the rice community from seedling planting to harvesting is reduced by approximately 8%. These findings are important for future forecasting of rice crop yields and estimation of water requirements in rice paddies (a major outcome of fiscal 2007). (1) For the first time in the world, we have made clear at the plant community level that, while a higher CO2 concentration in the atmosphere increases the photosynthesis activity of rice but at a slower rate of increase, along with the growth of rice, the rate of photorespiration is raised by the increase in CO2 concentration through all the rice growth stages (Fig. 2). On a separate matter, our Free-Air Carbon Dioxide Enrichment (FACE) experiment, the worldfs first ever of its kind applied to rice, has shown that a rise in atmospheric CO2 concentration of approximately 200 ppm forces the stoma to be semi-closed, and the overall water consumption of the rice community from seedling planting to harvesting is reduced by approximately 8%. These findings are important for future forecasting of rice crop yields and estimation of water requirements in rice paddies (a major outcome of fiscal 2007).

Growth stage figure

Fig. 2   Growth stage-wise changes in community photosynthesis and rate of photorespiration in relation to the rise in CO2 concentration

(2) With respect to the Asian Region, we applied the continental-scale agricultural water circulation model to estimate the ratio of irrigation water requirement for farmland (the degree of water deficit expected in the event of no irrigation) against the amount of water resources available for use (the water amount available for use in irrigation). A zone whose ratio exceeds 1 is unable to procure from the water resources of its own the minimum amount of water needed for the growth of crops. These findings are helpful in making predictions regarding fluctuations of crop production as affected by water resource constraints (a major outcome of fiscal 2006).

Picture

Fig. 3   Distribution of ratios between water requirement for irrigation in farmland and amount of water resou‚’ce available (cumulative yearly average 1961-1990)