Faculty Profiles - KOTANI, Ayumi

Shaping Subsurface Water Storage Dynamics: Climatic, Topographic, and Geologic Controls in Forested Headwater Catchments

Shodai Inokoshi, Takashi Gomi, Adam S. Wymore, Masanori Katsuyama, Tomoki Oda, Yuko Asano, Ayumi Kotani

2026.1

A report on the Fifth International Conference on Environmental Science and Technology (EST 2025) Open Access

JOURNAL OF JAPAN SOCIETY OF HYDROLOGY AND WATER RESOURCES Vol. 38 ( 4 ) page： 304 - 311 2025.11

Recent CO₂ and water vapor fluxes at Udleg forest research station, northern Mongolia Baseline data for climate–ecosystem studies Open Access

Ayumi Kotani, Mamoru Ishikawa, Tetsuya Hiyama, Shin Miyazaki, Baatarbileg Nachin, Dashtseren Avirmed, Temuujin Khurelbaatar

Mongolian Journal of Geography and Geoecology 2025.9

Recent CO₂ and water vapor fluxes at Udleg forest research station, northern Mongolia Baseline data for climate–ecosystem studies Reviewed International coauthorship

Kotani, A., Ishikawa, M., Hiyama, T., Miyazaki, S., Nachin, B., Avirmed, D., & Khurelbaatar, T

Mongolian Journal of Geography and Geoecology Vol. 62 ( 46 ) page： 182 - 188 2025.9

Authorship：Lead author Language：English

This study investigated seasonal and interannual patterns of net ecosystem exchange (NEE) and evapotranspiration (ET) obtained at a larch-dominated forest in northern Mongolia between 2010–2012 and 2022–2024. Seasonal and interannual variability in both fluxes has been observed; years with earlier leaf-out and higher early-season leaf area index (LAI) resulted in higher CO₂ uptake, while wetter summers promoted higher ET. Bayesian regression analysis revealed a shift in the relative influence of environmental drivers in the two periods. The soil water effect is remarkable in summer ET variation in previous relatively drier years. In contrast, surface soil temperature and solar radiation have become more influential than soil water in recent years. LAI emerged as a significant driver of NEE only in the latter period, suggesting improved photosynthetic responsiveness under favorable water conditions. These results indicate the sensitivity of larch ecosystems to decadal scale climate variability and suggest the importance of phenological dynamics and soil–plant–atmosphere interactions. Although these changes were likely within the natural variability range, they indicate the need for sustained monitoring. Long-term, interdisciplinary studies will be essential to understand the ecosystem's water–carbon coupling in the forest–steppe transition zone.

DOI： 10.5564/mjgg.v62i46.4135

The JapanFlux2024 dataset for eddy covariance observations covering Japan and East Asia from 1990 to 2023 Open Access

Ueyama, M; Takao, Y; Yazawa, H; Tanaka, M; Yabuki, H; Kumagai, T; Iwata, H; Awal, MA; Du, MY; Harazono, Y; Hata, Y; Hirano, T; Hiura, T; Ide, R; Ishida, S; Ishikawa, M; Kitamura, K; Kominami, Y; Komiya, S; Kotani, A; Inoue, Y; Machimura, T; Matsumoto, K; Matsuura, Y; Mizoguchi, Y; Murayama, S; Nagano, H; Nakai, T; Nakaji, T; Nakaya, K; Ohkubo, S; Ohta, T; Ono, K; Saitoh, T; Sakabe, A; Shimizu, T; Shimoda, S; Sugita, M; Takagi, K; Takahashi, Y; Takamura, N; Takanashi, S; Takimoto, T; Yasuda, Y; Wang, QX; Asanuma, J; Hasegawa, H; Hiyama, T; Iijima, Y; Ishidoya, S; Itoh, M; Kato, T; Kondo, H; Kosugi, Y; Kume, T; Maeda, T; Matsuura, S; Maximov, T; Miyama, T; Moriwaki, R; Muraoka, H; Petrov, R; Suzuki, J; Taniguchi, S; Ichii, K

EARTH SYSTEM SCIENCE DATA Vol. 17 ( 8 ) page： 3807 - 3833 2025.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Earth System Science Data

Eddy covariance observations play a pivotal role in understanding the land-Atmosphere exchange of energy, water, carbon dioxide (CO2), and other trace gases, as well as the global carbon cycle and earth system. To promote the networking of individual measurements and the sharing of data, FLUXNET links regional networks of researchers studying land-Atmosphere processes. JapanFlux was established in 2006 as a national branch of AsiaFlux. Despite the growing amount of shared data globally, the availability in Asia is currently limited. In this study, we developed an open dataset of the eddy covariance observations for Japan and East Asia, called JapanFlux2024, that was conducted by researchers affiliated with Japanese research institutions. The data were processed using selected standard methods from the FLUXNET community, with adaptations specific to the JapanFlux2024 dataset. Here, we present the data description and data processing and show the value of processed fluxes of sensible heat, latent heat, and CO2. The dataset will facilitate important studies for Japan and East Asia, such as land-Atmosphere interactions, improvement of process models, and upscaling fluxes using machine learning and remote sensing technology, as well as bridge collaborations between Asia and FLUXNET.

DOI： 10.5194/essd-17-3807-2025

Evaluating Forest Canopy Structures and Leaf Area Index Using a Five-Band Depth Image Sensor Open Access

Geilebagan, Takafumi Tanaka, Takashi Gomi, Ayumi Kotani, Genya Nakaoki, Xinwei Wang, Shodai Inokoshi

Forests Vol. 16 ( 8 ) 2025.8

The JapanFlux2024 dataset for eddy covariance observations covering Japan and East Asia from 1990 to 2023 Open Access

Masahito Ueyama, Yuta Takao, Hiromi Yazawa, Makiko Tanaka, Hironori Yabuki, Tomo’omi Kumagai, Hiroki Iwata, Md. Abdul Awal, Mingyuan Du, Yoshinobu Harazono, Yoshiaki Hata, Takashi Hirano, Tsutom Hiura, Reiko Ide, Sachinobu Ishida, Mamoru Ishikawa, Kenzo Kitamura, Yuji Kominami, Shujiro Komiya, Ayumi Kotani, Yuta Inoue, Takashi Machimura, Kazuho Matsumoto, Yojiro Matsuura, Yasuko Mizoguchi, Shohei Murayama, Hirohiko Nagano, Taro Nakai, Tatsuro Nakaji, Ko Nakaya, Shinjiro Ohkubo, Takeshi Ohta, Keisuke Ono, Taku M. Saitoh, Ayaka Sakabe, Takanori Shimizu, Seiji Shimoda, Michiaki Sugita, Kentaro Takagi, Yoshiyuki Takahashi, Naoya Takamura, Satoru Takanashi, Takahiro Takimoto, Yukio Yasuda, Qinxue Wang, Jun Asanuma, Hideo Hasegawa, Tetsuya Hiyama, Yoshihiro Iijima, Shigeyuki Ishidoya, Masayuki Itoh, Tomomichi Kato, Hiroaki Kondo, Yoshiko Kosugi, Tomonori Kume, Takahisa Maeda, Trofim Maximov, Ryo Moriwaki, Hiroyuki Muraoka, Roman Petrov, Jun Suzuki, Shingo Taniguchi, Kazuhito Ichii

2025.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Copernicus GmbH

Abstract. Eddy covariance observations play a pivotal role in understanding the land–atmosphere exchange of energy, water, carbon dioxide (CO2), and other trace gases, as well as the global carbon cycle and earth system. To promote the networking of individual measurements and the sharing of data, FLUXNET links regional networks of researchers studying land–atmosphere processes. JapanFlux was established in 2006 as a country branch of AsiaFlux. Despite the growing number of shared data globally, the availability in Asia is currently limited. In this study, we developed an open dataset of the eddy covariance observations for Japan and East Asia, called JapanFlux2024, that was conducted by researchers affiliated with Japanese research institutions. The dataset consists of data collected at 79 sites with 652 site-years from 1990 to 2023. The data format is fully compatible with the recent FLUXNET data product, FLUXNET2015. Here, we present the data description and data processing and show the value of processed fluxes of sensible heat, latent heat, and CO2. The dataset will facilitate important studies for Japan and East Asia, such as land-atmosphere interactions, improvement of process models, and upscaling fluxes using machine learning and remote sensing technology as well as bridge collaborations between Asia and FLUXNET.

DOI： 10.5194/essd-2024-615

Can Subdaily LST Be Constructed in High-Latitude Regions Using Polar Orbiting Satellites?

Zhiyan Liu, Kazuhito Ichii, Yuhei Yamamoto, Masahito Ueyama, Hideki Kobayashi, Tetsuya Hiyama, Ayumi Kotani, Trofim Maximov, Ryan C. Sullivan, Sébastien Biraud

IEEE Geoscience and Remote Sensing Letters Vol. 22 page： 1 - 5 2025

A Google Trends analysis of people's sense of seasons in Hokkaido Reviewed Open Access

Nagai Shin, Hiromi Nakagawa, Hiroshi Morimoto, Ayumi Kotani

Frontiers in Sustainable Tourism Vol. 3 2024.12

Decadal increases in carbon uptake offset by respiratory losses across northern permafrost ecosystems Open Access

Craig R. See, Anna-Maria Virkkala, Susan M. Natali, Brendan M. Rogers, Marguerite Mauritz, Christina Biasi, Stef Bokhorst, Julia Boike, M. Syndonia Bret-Harte, Gerardo Celis, Namyi Chae, Torben R. Christensen, Sara June Murner, Sigrid Dengel, Han Dolman, Colin W. Edgar, Bo Elberling, Craig A. Emmerton, Eugénie S. Euskirchen, Mathias Göckede, Achim Grelle, Liam Heffernan, Manuel Helbig, David Holl, Elyn Humphreys, Hiroki Iwata, Järvi Järveoja, Hideki Kobayashi, John Kochendorfer, Pasi Kolari, Ayumi Kotani, Lars Kutzbach, Min Jung Kwon, Emma R. Lathrop, Efrén López-Blanco, Ivan Mammarella, Maija E. Marushchak, Mikhail Mastepanov, Yojiro Matsuura, Lutz Merbold, Gesa Meyer, Christina Minions, Mats B. Nilsson, Julia Nojeim, Steven F. Oberbauer, David Olefeldt, Sang-Jong Park, Frans-Jan W. Parmentier, Matthias Peichl, Darcy Peter, Roman Petrov, Rafael Poyatos, Anatoly S. Prokushkin, William Quinton, Heidi Rodenhizer, Torsten Sachs, Kathleen Savage, Christopher Schulze, Sofie Sjögersten, Oliver Sonnentag, Vincent L. St. Louis, Margaret S. Torn, Eeva-Stiina Tuittila, Masahito Ueyama, Andrej Varlagin, Carolina Voigt, Jennifer D. Watts, Donatella Zona, Viacheslav I. Zyryanov, Edward A. G. Schuur

Nature Climate Change Vol. 14 ( 8 ) page： 853 - 862 2024.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Springer Science and Business Media LLC

Abstract

Tundra and boreal ecosystems encompass the northern circumpolar permafrost region and are experiencing rapid environmental change with important implications for the global carbon (C) budget. We analysed multi-decadal time series containing 302 annual estimates of carbon dioxide (CO2) flux across 70 permafrost and non-permafrost ecosystems, and 672 estimates of summer CO2 flux across 181 ecosystems. We find an increase in the annual CO2 sink across non-permafrost ecosystems but not permafrost ecosystems, despite similar increases in summer uptake. Thus, recent non-growing-season CO2 losses have substantially impacted the CO2 balance of permafrost ecosystems. Furthermore, analysis of interannual variability reveals warmer summers amplify the C cycle (increase productivity and respiration) at putatively nitrogen-limited sites and at sites less reliant on summer precipitation for water use. Our findings suggest that water and nutrient availability will be important predictors of the C-cycle response of these ecosystems to future warming.

DOI： 10.1038/s41558-024-02057-4

Mining plant phenology records from Kanazawa, Japan in the 1807–1838 Kakuson Diary Reviewed

Other Link： https://www.nature.com/articles/s41558-024-02057-4

Perspective and review: how to develop our understanding of temporal changes in the relationship between people and the landscape under societal and climate change in Northeast Asia? Reviewed Open Access

Nagai Shin, Taku M. Saitoh, Ayumi Kotani, Tomoaki Miura, Hiromi Nakagawa, Chifuyu Katsumata, Hiroshi Morimoto, Hideyuki Onishi

Frontiers in Environmental Science Vol. 12 page： 1236664 2024.2

Nagai Shin, Yoshikazu Sasai, Ayumi Kotani, Taku M Saitoh

International Journal of Biometeorology Vol. 68 ( 1 ) page： 125 - 131 2024.1

Comparison of ground temperature and permafrost conditions in the Arctic simulated by land surface process models of different complexity

Mori, J; Saito, K; Miyazaki, S; Machiya, H; Ise, T; Sueyoshi, T; Yamazaki, T; Iijima, Y; Ikawa, H; O'oishi, R; Ohta, T; Katata, G; Kotani, A; Sato, A; Sato, H; Sugimoto, A; Suzuki, R; Tanaka, K; Nitta, T; Hajima, T; Burke, E; Park, H

BULLETIN OF GLACIOLOGICAL RESEARCH Vol. 42 page： 69 - 94 2024

Stochastic representation of spatial variability in thaw depth in permafrost boreal forests Open Access

Taro Nakai, Tetsuya Hiyama, Ayumi Kotani, Yoshihiro Iijima, Takeshi Ohta, Trofim C. Maximov

PERMAFROST AND PERIGLACIAL PROCESSES 2023.8

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY

A simple stochastic representation of the spatial variability in thaw depth is proposed. Thaw depth distribution measured in the two larch-type forests in eastern Siberia, Spasskaya Pad and Elgeeii, showed different spatial, seasonal, and interannual variability, respectively. Year-to-year variation in active-layer thickness was minor in Spasskaya Pad compared to Elgeeii. A gamma distribution adequately represented both sites' thaw depth spatial variability as the cumulative probability. Thus, we developed a simple model using the gamma distribution that illustrates the spatial variability in thaw depth at any thawing stage as a function of a given mean thaw depth. A hierarchy of models was introduced that sequentially considered the constant state, linearity, and nonlinearity in the dependence of the rate parameter of the gamma distribution on the mean thaw depth. Although the requirements of the model levels differed between Spasskaya Pad and Elgeeii, the proposed model successfully represented the spatial variability in thaw depth at both sites during different thaw seasons.

DOI： 10.1002/ppp.2204

Winter temperature and growing season CO2 budgets of deciduous needle leaf forest in eastern Siberia Open Access

KOTANI Ayumi, NAKAI Taro, HIYAMA Tetsuya

Journal of Japanese Association of Hydrological Sciences Vol. 53 ( 0 ) page： 20 - 24 2023.3

Perspective: Improving the accuracy of plant phenology observations and land-cover and land-use detection by optical satellite remote-sensing in the Asian tropics Open Access

Nagai Shin, Chifuyu Katsumata, Tomoaki Miura, Narumasa Tsutsumida, Tomoaki Ichie, Ayumi Kotani, Michiko Nakagawa, Kho Lip Khoon, Hideki Kobayashi, Tomo’omi Kumagai, Shunsuke Tei, Runi anak Sylvester Pungga, Taizo Yamada, Akihiro Kameda, Masayuki Yanagisawa, Kenlo Nishida Nasahara, Hiroyuki Muraoka, Kazuhito Ichii, Yuji Tokumoto

Frontiers in Forests and Global Change Vol. 6 2023.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Frontiers Media SA

Recent advances in satellite-borne optical sensors led to important developments in the monitoring of tropical ecosystems in Asia, which have been strongly affected by recent anthropogenic activities and climate change. Based on our feasibility analyses conducted in Indonesia in Sumatra and Sarawak, Malaysia in Borneo, we discuss the current situation, problems, recent improvements, and future tasks regarding plant phenology observations and land-cover and land-use detection. We found that the Multispectral Instrument (MSI) on board the Sentinel-2A/2B satellites with a 10-m spatial resolution and 5-day observational intervals could be used to monitor phenology among tree species. For the Advanced Himawari Imager (AHI) on board the Himawari-8 geostationary satellite with a 1,000-m spatial resolution and 10-min observational intervals, we found that the time-series in vegetation indices without gaps due to cloud contamination may be used to accurately detect the timing and patterns of phenology among tree species, although the spatial resolution of the sensor requires further improvement. We also found and validated that text and pictures with geolocation information published on the Internet, and historical field notes could be used for ground-truthing land cover and land use in the past and present time. The future development of both high frequency (≤ 10 min) and high spatial resolution (≤ 10 m) optical sensors aboard satellites is expected to dramatically improve our understanding of ecosystems in the tropical Asia.

DOI： 10.3389/ffgc.2023.1106723

テレビ番組映像によりモンゴルの遊牧景観における人々と生態系の関わりの時間変化を紐解く Reviewed

小谷亜由美, 永井信

流域圏学会誌 Vol. 10 page： 31 - 40 2023

Record mining of cherry flowering phenology in Tokyo during the Meiji and Taisho eras from Atomi Kakei's diary Reviewed Open Access

Shin Nagai, Kotani Ayumi, Maruya Yasuyuki

JAPANESE JOURNAL OF BIOMETEOROLOGY Vol. 59 ( 3-4 ) page： 89 - 99 2022.11

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Japanese Society of Biometeorology

To evaluate the long-term relationship between climate change and plant phenology in spring, record mining of cherry flowering phenology before the Japan Meteorological Agency began recording phenological observations is an important task. We retrieved records of flowering phenology during the Meiji and Taisho eras from the diary of Atomi Kakei, a Japanese educator (1840−1926) and then evaluated the data quality and systematic errors. We were able to retrieve 22 years of flowering dates and 33 years of full-bloom dates across the period from 1873 to 1924. The flowering and full-bloom dates retrieved from this period were about 10 days later than those at present. The records of cherry flowering phenology in the diary may be considered to contain systematic errors of at least a few days caused by the differences of observation points and persons, discrete observation days, and differences of cherry species and individual trees but our findings indicated that diary records of the phenology of cherry flowering is useful for determining the phenological effects of climate change.

DOI： 10.11227/seikisho.59.89