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

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-21^st century and to assess the risk in rice production fluctuations on a regional scale as affected by climate change.

• (1) In the development of experimental station-sized models, paddy ecosystem response models will be developed to predict changes in rice growth and crop yields in response to climate change, incorporating factors including water, soil, rice variety and cultivation conditions. In this way, we will propose new rice production techniques that will allow rice growers to respond and adjust to climate change.
• (2) In the development of regional scale models, we will use three distinct patterns of rice cultivation: (a) Japan, where a good irrigation system is in place, (b) Southeast Asia (Mekong Delta) where paddies are dominantly dependent on rainfall, therefore the water resource constraints and crop yields fluctuations are considerably large, and (c) big river basins in China characterized by a rather high rate of irrigation but heavily dependent on water sources that stretch out over huge areas. We will sort out, for each of these patterns, the factors that determine the fluctuations in harvested area and crop yields per unit area. We will construct models that will permit easy estimation of regional-level fluctuations in crop yields, based on the results of these analyses, and will develop methodologies for wide-area assessment of risks in regional-level rice yields against 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).

(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).