Abstract
The average global temperature in 2023 is certain to be the hottest in recorded observation history. It has been scientifically clarified in the IPCC report that changes in the global environment, typified by global warming, are the result of long-term effects of human activities on the global environment. This suggests that global environmental changes are the accumulation of human activities, each on a small scale, affecting the entire planet. These global environmental changes are linked to many global issues in our society, such as energy, natural disasters, and food. The Earth can be considered a system. The components of the Earth system are huge, and the relations among them are diverse. Furthermore, it exhibits complex system behavior that is both nonlinear and nonequilibrium. We need to consider from the standpoint of systems science what actions we should take to realize a society that maintains balances with nature to build the earth system as a sustainable system. The world’s water problems have become more serious in recent years. We focus on water circulation system, which is one of the most important systems of the Earth system. We have been able to perform large-scale/small-scale water circulations to clarify where water comes from, what it carries, how it changes phases, and how it behaves and circulates over time and space scales. Our simulations have explored what kind of actions we can take to create a sustainable water environment. In my presentation, I will introduce the water general circulation model that we have been developed, including an overview of atmospheric general circulation model which can explicitly express the process of cloud formation and disappearance, ocean model, and land surface and groundwater system model, and coupled method that interchanges the physical quantities among those models. Furthermore, we will introduce the method for artificial use of water or artificial environmental changes due to human actions into this water general circulation model. Case studies will be presented to illustrate how states of the environment can be changed by altering anthropogenic actions. Based on these results, I would like to introduce future perspectives on Earth system science.

Biography
Keiko Takahashi received Ph.D in engineering from Tokyo Institute of Technology in 1991. She joined Kao Corporation in Tokyo until 1993. She was an invited research scientist in Computer Laboratory of University of Cambridge UK during 1993-1994 and in Tokyo Institute of Technology during 1994-1998. She worked as a scientist and Director-General of Center for Earth Information Science and Technology in Japan Agency for Marine-Earth Science and Technology until 2021. Since April 2021, she has been a research professor of Waseda University. She had been a member of Science Council of Japan during 2014-2020. Her current research interests are climate/weather prediction and understanding response mechanisms to the global climate change with multi-scale multi-physics simulations.