This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Japan has been experiencing increasingly severe damage from torrential rainfall triggered by typhoons and stationary linear rain bands. In response, an ambitious and unconventional idea is taking shape: artificially inducing heavy rainfall over the ocean to reduce extreme downpours on land.
This pioneering project was selected for the Cabinet Office's Moonshot Research and Development Program and is led by Professor Shunji Kotsuki of the Institute for Advanced Academic Research/Center for Environmental Remote Sensing, who serves as project manager. While Kotsuki runs his laboratory and discussions with rigorous logic, he is guided by a clear belief: "When you aim to accomplish something meaningful, it ultimately comes down to passion and energy." In this Q&A, he speaks about the current state of weather control and AI-based weather forecasting research, as well as the mindset that underpins his pursuit of challenging, future-oriented science. As part of Moonshot Goal 8, titled "Realization of a society safe from the threat of extreme winds and rains by controlling and modifying the weather by 2050," I am leading a project called "Artificial generation of upstream maritime heavy rains to govern intense-rain-induced disasters over land (AMAGOI)." In Japan, flood damage can exceed 1 trillion yen in severe years, and such disasters can even result in loss of life, making them a major social challenge.
At the same time, there are clear limits to conventional hardware-based countermeasures, such as flood-control dams and levees. The torrential rains that have caused the most serious damage in Japan have been driven primarily by significant inflows of water vapor from the ocean. Based on this understanding, our approach is to artificially induce cumulonimbus cloud formation over the sea, triggering heavy rainfall in advance.
By doing so, we aim to reduce the amount of water vapor reaching land and ultimately mitigate the risk of extreme rainfall disasters over populated areas. Weather is inherently chaotic—even the slightest change can dramatically alter what happens next. Once torrential rain has already begun, it is almost impossible to intervene artificially.
However, we believe that intervening early with minimal yet well-targeted actions can yield significant effects. I refer to this approach as "identifying the key control points" in the weather system. From a data science perspective, determining where these control points lie—and how to intervene effectively—is central to weather control and represents a fascinating scientific challenge.
Numerical simulations conducted so far suggest that it may be possible to reduce torrential rainfall by 10%–20%. Based on these simulation results, I am planning to conduct an experimental artificial rainfall trial over the ocean in fiscal 2025. In this experiment, dry ice will be dispersed from an aircraft, serving as a nucleus for water vapor and thereby inducing precipitation.
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