The environment for permafrost in Japan is pr

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image: Permafrost exists because the surface air temperature is low throughout the year.
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Credit: Yokohata et al. 2022, Advances in Earth and Planetary Sciences

Areas where the ground temperature is below 0°C for more than two years are called permafrost. Permafrost is widely distributed mainly in tundra and taiga areas at high latitudes of the northern hemisphere. The existence of permafrost has only been confirmed in very limited places with high altitudes and high latitudes in today’s Japan, due to its location at the southern limit of the global distribution of permafrost. Previous studies have assessed the current state of permafrost and predicted the future in Europe and the Tibetan Plateau, but little research has been done in the East Asian region, including Japan. In our previous research, we assessed the current situation and predicted the future in the Daisetsu Mountains (https://www.eurekalert.org/news-releases/923643). In this study, a similar analysis was performed across Japan. We used a 1 km resolution climate projection in Japan to estimate areas within a temperature environment that maintains permafrost. By calculating the number of days when the temperature falls below and above 0°C in a year and using an empirical formula obtained from observing the distribution of permafrost, we estimated the area of ​​permafrost at Japan with a resolution of 1 km.

Figure 1 shows the results of our estimated map of the permafrost area in Japan. Observation points where permafrost has been locally confirmed are shown in red. Our estimation results are consistent with the observation shown in Figure 1. As mentioned above, in Japan today, the existence of permanents has only been confirmed at very limited points in the Daisetsu Mountains , the Northern Alps and Mount Fuji. Our research revealed that permafrost may exist in other places, such as the Hidaka Mountains, Mount Shiretokodake, Mount Sharidake, Southern Alps, Mount Akan, and Mount Yotei.

Figure 2 shows the evolution of the area with the surface air temperature conditions necessary to maintain permafrost in Japan. The difference in results due to the difference in the climate models used for the estimation is shown in grey. The area of ​​permafrost is expected to decrease from around the year 2000. This is because the surface air temperature in Japan is increasing due to global warming, as shown in our previous study of the Daisetsu Mountains.

Although permafrost has only been identified in very limited areas in Japan today, our research suggests that there may be unidentified permafrost in various regions. Permafrost itself, which exists in Japan, is extremely rare, so it may be a place of interest to people as a freezing place where permafrost exists. Additionally, as mentioned above, Japan’s permafrost is located at the southern limit of the global distribution of permafrost, so it is considered extremely sensitive to global warming. For this reason, Japan’s permafrost is an important observation target as an indicator of climate change impacts, and the area shown in Figure 1 is an important candidate for future permafrost study points. For example, Shiretoko is designated a UNESCO World Heritage Site, but it is extremely vulnerable to global warming, so it is recommended by the World Heritage Committee to strengthen monitoring of the natural environment. Understanding the impact of climate change that is already happening by monitoring Japan’s permafrost is a very important task.


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