EFFECTS OF SHIFTING RICE TRANSPLANTATION DATE ON AGRICULTURAL WATER USE UNDER CLIMATE CHANGE IN JAPAN

Abstract

 Agriculture is one of the industries most vulnerable to climate change. Moreover, the yields and appearance quality of rice are predicted to deteriorate under climate change as a result of higher summer temperatures. To reduce the negative impacts on rice cultivation, various adaptation measures, ranging from incremental to transformative, have been proposed. Among these adaptation measures, shifting the transplantation date is relatively inexpensive and easy to implement. Thus, it has been implemented widely by farmers. However, farmers’ requests to shift the transplantation date may be constrained by river administrators because river water in Japan is currently being used to nearly its maximum extent. In this study, we developed a framework to evaluate the effects of shifting the transplantation date of rice under climate change on the rice yield and water supply–demand balance of agricultural water. The framework consisted of two process-based models of crop science and hydrology. The rice yield and water balance were calculated by shifting the current transplantation date at increments of one week to five weeks before and after the current date. To evaluate the effects in different regions of Japan, we selected 77 areas based on reference gauging stations for river water uses and associated rice cultivation areas. The results showed that the transplantation date with higher yield improved the water balance (harmonious relationship) at 38 areas, but it worsened the water balance (tradeoff relationship) at 37 areas. The results imply that transplantation dates that increase the yield may be easily selected from the perspective of river administrators in the areas with harmonious relationships but may be hampered by deterioration in the water supply–demand balance in areas with tradeoff relationships.