ALBERT

Description: We describe interplays of water and food production over the 70 years (1950-2020) of Japanese watersheds. Here, we focus the changes on the rice transplanting period because it is critical for rice cultivation and requires considerable water for puddling. The transplanting periods have shifted from mid-June in the 1950s to early May in the 2000s. We propose a framework for assessing how the shifts of the transplanting period affected rice production and drought risks based on two process-based models. We conducted the simulation with shifted transplanting dates (or starting date of irrigation) from the current date by one week up to five weeks earlier and later. We then integrate the results of mean crop yield and drought risk for each transplanting date to examine the interrelated nature of crop production and drought risk. We applied the method to two watersheds, contrasting in terms of hydrological regimes. The earlier transplanting periods compared to those in the 1950s generally increased the yield, whereas the changes in the drought risk differed. In the Shinano river, the earlier transplanting date resulted in lower drought risk and the current transplanting period corresponds to the day that minimizes drought risk and maximizes yields. In the Kinu river, the earlier transplanting date resulted in a higher drought risk. Thus, the shift in the transplanting period would have conflicted with the water management agencies. We highlight the importance of the socio-economic (i.e., increase food production) can be a driver of changes in water cycles.

Description: The impacts of climate change and increased water use for irrigation make it difficult to manage sustainable water use and food production. Sufficient research has not been conducted on how humans adapt to water risks due to climate change. One of the difficulties in considering adaptation measures is that adaptation actions in one sector conflict with the interests of other stakeholders and trade-off relationships emerge among various sectors. Here, we examined how an effective adaptation in one sector (agriculture) influences the other (water resources) by calculating the “benefits of agricultural production” and “drought risk” under current and future climate scenarios. We built a framework consisting of two process-based models of hydrology and crop science and evaluated shifting of the transplantation date as a promising measure to avoid the degradation of rice quality in Japan. Shifting the transplantation date had opposing effects on the total yield and quality of rice, with an earlier date increasing the total yield and a later date increasing the quality. Furthermore, an earlier transplantation date reduced the drought risk. Thus, in terms of the preferred adaptation options, total yield and drought were harmonious, whereas rice quality and drought were trade-offs. Our results imply that the current transplantation date has resulted from the farmers’ selection to maximize total yield, but this selection may change to other factors, possibly rice quality, due to climate change. This study highlights the importance of coupled models to describe the interaction between hydrology and society because farmers’ selections depend on socio-economic conditions.