As a first step in estimating the impact on nature when heavy rainfall control is implemented , we will construct heavy rainfall control scenarios and evaluate their flood flow control effects. Consider the risk of rain areas shifting due to the control of heavy rains and causing floods or droughts in other basins. Estimate the impact on water resources and society, and evaluate how a water-based society will change, by considering the behavioral changes of the residents.
Additionally, construct a conceptual model, “weather commons,” that captures the mechanism of cooperation by local residents to live with heavy rains reduced using new regulatory technologies, and clarify the conditions for its establishment (Fig. 1). Construct social and institutional response scenarios for ELSI/RRI topics based on this conceptualization.
The awareness of “living in the bosom of nature,” where people revere and co-exist with nature, will permeate, and the scope of application of heavy rain regulation techniques will be decided within the scope of “people living their lives by borrowing the bosom of nature.”

① Estimation of changes in runoff and water resources due to heavy rainfall control

Based on the results of heavy rainfall control experiments conducted using the numerical weather model developed in Research and Development Item 1, we investigated how rainfall hyetographs change under rainfall control. We evaluated the impact on runoff for the heavy rainfall event that occurred in 2012 in the Kurokawa River basin in the Kyushu region, assuming that rainfall control had been implemented. As a result, it was found that the assumed rainfall control reduced the total basin precipitation by approximately 12% and decreased peak river discharge by about 13%. Furthermore, flood inundation simulations indicated that the area with inundation depths exceeding 1 m was reduced by approximately 14%.

② Strategic examination for solving ELSI

ELSI refers to ethical, legal, and social issues, and factors such as the uncertainty of nature, environmental impact, and the effects on residents' disaster prevention awareness system are important to consider. The implementation of weather control was examined, and a framework for identifying and addressing specific ELSI issues was developed. Additionally, planning and regional collaboration considerations for future small-scale outdoor experiments were organized, as shown in Figure 3.

③ Theoretical study of the weather commons

Through a questionnaire survey of citizens, we empirically clarified public acceptance of weather modification and the conditions under which it is accepted. Based on the concept of the weather commons, we proposed the idea of a ‘weather identity’ as a form of coexistence with weather, and analyzed its relationship with acceptance of weather modification. The results indicated that everyday engagement with weather and views of nature are related to the level of acceptance of weather modification (Figure 4).

We have developed multiple scenarios that vary in the extent of heavy rainfall control to evaluate the effectiveness of flood flow management. Moreover, we will propose concrete autonomous and symbiotic control technologies aimed at the formation of a meteorological commons.　Additionally, we are designing social and institutional response scenarios to address ELSI topics.