研究者詳細 - 小谷　亜由美

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

PubMed

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 42 巻頁： 69 - 94 2024年

源頭部湧水湿地における炭素貯蔵量とCO2フラックスの評価 Open Access

青木翔太, 小谷亜由美, 五味高志, 水内佑輔

水文・水資源学会研究発表会要旨集 37 巻 ( 0 ) 頁： 185 2024年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：水文・水資源学会

この研究は、湧水湿地におけるCO2収支の計測例がないことに着目し、そのCO2フラックスと炭素貯留量を調査しました。湧水湿地は他の湿地と異なる空間的特性を持ち、CO2フラックスや土壌炭素量に影響を与える可能性があります。研究の目的は、湧水湿地におけるCO2フラックスの評価とその季節変動や環境要因の検討です。これにより、地球規模のCO2収支に関する基礎データが提供され、地球温暖化緩和適応策の構築に寄与することが期待されます。本研究は、東京大学生態水文学研究所穴の宮試験流域内の湧水湿地を調査しました。調査地は年平均降雨量1644mm、年平均気温15.2℃で、面積は約40㎡でした。上流部、中流部、下流部でCO2計測チャンバーを使用し、湿地土壌表面のCO２濃度を10分間隔で計測し、濃度変化からフラックスを求めました。また、リターや植生の有無を調査し、土壌サンプルを収集して炭素量を計測しました。気温、地温、土壌水分量、日射、湿度は10分間隔で自動測定し、降水量は研究所のデータを使用しました。フラックスの計測は2023年8月から2024年1月まで合計9回、バイオマスと土壌サンプルの採取は期間内に1回行われました。上流ではコナラやアカマツの枯れ葉が一年中堆積し、その量には地域差がありました。夏と秋のCO2フラックスは似ており、これはリターと気温の関係であると考えられます。冬には枯れ葉の量が少なくなり、フラックスも低下します。下流では植生があり、夏と秋には負の値が見られますが、冬にはそれがなくなります。この研究のCO2フラックスは他の研究と比較して正の値であり、炭素貯留量も干潟に比べて低いことがわかりました。この研究はCO2フラックスの理解と湧水湿地に関する知見を提供しました。

DOI： 10.11520/jshwr.37.0_185

Open Access

東シベリアの落葉針葉樹林における冬季温度と植物成長期のCO2収支

小谷亜由美, 中井太郎, 檜山哲哉

日本水文科学会誌 53 巻 ( 0 ) 頁： 20 - 24 2023年3月

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査読有り

小谷亜由美

流域圏学会誌 10 巻頁： 31 - 40 2023年

Carbon Cycles in Forests

Maximov, TC; Maksimov, AP; Kononov, AV; Kotani, A; Dolman, J

WATER-CARBON DYNAMICS IN EASTERN SIBERIA 236 巻頁： 69 - 100 2019年

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

Liu Z., Ichii K., Yamamoto Y., Ueyama M., Kobayashi H., Hiyama T., Kotani A., Maximov T., Sullivan R.C., Biraud S.

IEEE Geoscience and Remote Sensing Letters 22 巻頁： 1 - 5 2025年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IEEE Geoscience and Remote Sensing Letters

This study introduces a new method for constructing subdaily land surface temperatures (LSTs) in northern high-latitude areas. The method is based on 1) an integration of observations from multiple satellites-sensors, including Moderate Resolution Imaging Spectroradiometer (MODIS) and Visible Infrared Imaging Radiometer Suite (VIIRS); and 2) the use of swath data to more comprehensively utilize the information content available from overlapping events from each platform within a day. The initial validation phase demonstrated a comparably high performance for LSTs among different products with a root mean square error (RMSE) at approximately 3~^{\circ } C. Subsequently, the results confirmed that more than 23 observations per day at 70°N could be achieved, almost quadrupling the observation frequency achieved with twice-daily LST products combining MODIS and VIIRS. At one of the sample sites, the subdaily LST was clearly identified as a near-hourly temporal variation, and the gaps in the early morning and late afternoon were effectively filled.

DOI： 10.1109/lgrs.2025.3546797

その他リンク： http://xplorestaging.ieee.org/ielx8/8859/10764750/10908397.pdf?arnumber=10908397

A Google Trends analysis of people's sense of seasons in Hokkaido 査読有り Open Access

Nagai Shin, Hiromi Nakagawa, Hiroshi Morimoto, Ayumi Kotani

Frontiers in Sustainable Tourism 3 巻 2024年12月

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

See, CR; Virkkala, AM; Natali, SM; Rogers, BM; Mauritz, M; Biasi, C; Bokhorst, S; Boike, J; Bret-Harte, MS; Celis, G; Chae, N; Christensen, TR; Murner, SJ; Dengel, S; Dolman, H; Edgar, CW; Elberling, B; Emmerton, CA; Euskirchen, ES; Goeckede, M; Grelle, A; Heffernan, L; Helbig, M; Holl, D; Humphreys, E; Iwata, H; Jaerveoja, J; Kobayashi, H; Kochendorfer, J; Kolari, P; Kotani, A; Kutzbach, L; Kwon, MJ; Lathrop, ER; Lopez-Blanco, E; Mammarella, I; Marushchak, ME; Mastepanov, M; Matsuura, Y; Merbold, L; Meyer, G; Minions, C; Nilsson, MB; Nojeim, J; Oberbauer, SF; Olefeldt, D; Park, SJ; Parmentier, FJW; Peichl, M; Peter, D; Petrov, R; Poyatos, R; Prokushkin, AS; Quinton, W; Rodenhizer, H; Sachs, T; Savage, K; Schulze, C; Sjoegersten, S; Sonnentag, O; Louis, VLS; Torn, MS; Tuittila, ES; Ueyama, M; Varlagin, A; Voigt, C; Watts, JD; Zona, D; Zyryanov, VI; Schuur, EAG

NATURE CLIMATE CHANGE 14 巻 ( 8 ) 頁： 853 - 862 2024年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Nature Climate Change

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

Open Access

その他リンク： 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? 査読有り Open Access

Shin, N; Saitoh, TM; Kotani, A; Miura, T; Nakagawa, H; Katsumata, C; Morimoto, H; Onishi, H

FRONTIERS IN ENVIRONMENTAL SCIENCE 12 巻頁： 1236664 2024年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Frontiers in Environmental Science

The relationship between people and the landscape consists of multi-layer components such as the atmosphere, water, living things, nutrients, livelihood, society, and information. To clarify temporal changes in this relationship, previous studies have used conventional approaches based on field work and satellite observation. However, interpretations based on these conventional two approaches are subject to temporal, spatial, representative, and interpretability gaps. In this perspective and review paper, we propose three approaches to bridge these gaps: (1) text mining of historical documents and data (mining for handwritten or printed old documents, books, diaries, field notes, and statistics), (2) video mining (mining for descriptions, interviews, narrations, and background of photos/video), and (3) social sensing (observing real-world events by using digital communication tools such as social networking services, YouTube, and Google Trends). We discuss the utility, limitation, and perspective of each of these proposed approaches by presenting case examples of their application from Northeast Asia. We found that (1) the text mining approach can be useful to remove the temporal, representative, and interpretability gaps but requires immense amounts of time and labor; (2) the video mining approach can be useful to remove the temporal, representative, and interpretability gaps, but uncertainties remain and there are usage limitations with video materials; and (3) the social sensing approach can be useful to reduce the spatial, representative, and interpretability gaps, but it requires careful consideration in terms of data quality and ethical issues. To deepen our understanding of the relationship between people and the landscape during periods of social and climate change on a scale of seasons to centuries from the viewpoint of personal attributes and traits, we conclude that an integrated analysis that combines the conventional approaches such as field work and satellite observation and the proposed approaches should be further developed. Through the development of our proposed integrated analytical approaches, we expect to establish a new transdisciplinary study that integrates anthropology, sociology, informatics, history, and natural sciences.

DOI： 10.3389/fenvs.2024.1236664

Open Access

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

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

PERMAFROST AND PERIGLACIAL PROCESSES 2023年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Permafrost and Periglacial Processes

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

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

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

FRONTIERS IN FORESTS AND GLOBAL CHANGE 6 巻 2023年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Frontiers in Forests and Global Change

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

跡見花蹊日記を用いた明治・大正期における東京のサクラの開花季節記録のマイニング査読有り

永井信, 小谷亜由美, 丸谷靖幸

日本生気象学会雑誌 59 巻 ( 3-4 ) 頁： 89 - 99 2022年11月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：日本生気象学会

春の気候変動と植物季節の対応関係を長期的に評価するためには，気象庁による生物季節観測が行われていない過去におけるサクラの開花季節の記録の発掘（マイニング）は重要な課題である．本研究は，明治から大正期を対象に，教育者である跡見花蹊（あとみかけい：天保11年 [1840年]〜大正15年・昭和元年 [1926年]）の日記からサクラの開花季節の記録をマイニングし，その品質と系統的な誤差を調査した．明治6年（1873年）から大正13年（1924年）の間に，開花日を22年，満開日を33年，それぞれマイニングできた．この期間における開花日や満開日は，現在と比べて10日程度遅かった．日記の記録は，観察場所や観察者の違い・不連続な観察日・サクラの種や個体差を要因とした系統的な誤差を少なくとも数日程度含むと考えられる一方，植物季節に対する気候変動の影響を明らかにするための有用性が示された．

DOI： 10.11227/seikisho.59.89

Can Yandex statistics and google trends be used to detect people?s interests in berries in the Russian Far East? 国際共著

Shin Nagai, Kotani Ayumi, Maruya Yasuyuki, Gavrilyeva Tuyara

POLAR SCIENCE 33 巻頁： 100871 - 100871 2022年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Polar Science

Ripening berries are one of nature's important contributions to people in the Russian Far East. We examined the spatiotemporal variability of people's interests in 12 types of berries and their attributes by accessing Yandex statistics (Yandex) and Google Trends (GT) about these topics in the Russian Far East. On Yandex, time-series data for people's interests in many berries for all target regions showed clear seasonal changes, with an annual peak that occurs at the time of ripening. Interest in berries was observed in many cities and regions in the far east of Russia, where indigenous peoples and Sakha traditionally utilize berries for subsistence. The attributes of accessed terms were closely related to terms about berry varieties and edible berries, berry purchases, photographs, and recipes. These results supported the usability of Yandex and GT data to evaluate the spatiotemporal variability of people's interests in berries. Despite systematic biases, such as in the Internet environment and user characteristics as well as limitations of spatial resolution and access period, the integrated use of Yandex and GT should be developed to evaluate the spatiotemporal variability of people's interests in berries, especially in areas that are difficult to access.

DOI： 10.1016/j.polar.2022.100871

Monitoring of cherry flowering phenology with Google Trends 査読有り

Shin Nagai, Kotani Ayumi, Tei Shunsuke, Tsutsumida Narumasa

PLOS ONE 17 巻 ( 7 ) 2022年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PLoS ONE

Google Trends (GT) is an online tool designed for searching for changes over time. We assessed its use for evaluating changes in the timing of cherry flowering phenology, which is of intense interest to Japanese people. We examined the relationship between time-series of relative search volume (RSV: relative change in search requests over time obtained from the GT access engine) and cherry flowering information published on websites (as ground truth) in relation to three famous ancient cherry trees. The time-series of RSV showed an annual bell-shaped seasonal variability, and the dates of the maximum RSV tended to correspond to the dates of full bloom. Our results suggest that GT allows monitoring of multiple famous cherry flowering sites where we cannot obtain long-term flowering data to evaluate the spatiotemporal variability of cherry flowering phenology.

DOI： 10.1371/journal.pone.0271648

Contrasting 20-year trends in NDVI at two Siberian larch forests with and without multiyear waterlogging-induced disturbances 査読有り

タンクモデルパラメータ値によるわが国寡雪地域の流域条件と長期流出特性の関係

堀田裕貴, 田中隆文, 小谷亜由美

日本水文科学会誌 52 巻 ( 1 ) 頁： 1 - 22 2022年4月

Nagano Hirohiko, Kotani Ayumi, Mizuochi Hiroki, Ichii Kazuhito, Kanamori Hironari, Hiyama Tetsuya

ENVIRONMENTAL RESEARCH LETTERS 17 巻 ( 2 ) 2022年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Environmental Research Letters

The fate of a boreal forest may depend on the trend in its normalized difference vegetation index (NDVI), such as whether the NDVI has been increasing significantly over the past few decades. In this study, we analyzed the responses of two Siberian larch forests at Spasskaya Pad and Elgeeii in eastern Siberia to various waterlogging-induced disturbances, using satellite-based NDVI and meteorological data for the 2000-2019 period. The forest at Spasskaya Pad experienced waterlogging (i.e. flooding events caused by abnormal precipitation) during 2005-2008 that damaged canopy-forming larch trees and increased the abundance of water-resistant understory vegetation. By contrast, the forest at Elgeeii did not experience any remarkable disturbance, such as tree dieback or changes in the vegetation community. Significant increasing NDVI trends were found in May and June-August at Elgeeii (p < 0.05), whereas no significant trends were found at Spasskaya Pad (p > 0.05). NDVI anomalies in May and June-August at Elgeeii were significantly associated with precipitation or temperature depending on the season (p < 0.05), whereas no significant relationships were found at Spasskaya Pad (p > 0.05). Thus, the 20 year NDVI trend and NDVIerature-precipitation relationship differed between the two larch forests, although no significant trends in temperature or precipitation were observed. These findings indicate that nonsignificant NDVI trends for Siberian larch forests may reflect waterlogging-induced dieback of larch trees, with a concomitant increase in water-resistant understory vegetation.

DOI： 10.1088/1748-9326/ac4884

Dynamic Mapping of Subarctic Surface Water by Fusion of Microwave and Optical Satellite Data Using Conditional Adversarial Networks

The ABCflux database: Arctic-boreal CO2 flux observations and ancillary information aggregated to monthly time steps across terrestrial ecosystems

Virkkala Anna-Maria, Natali Susan M., Rogers Brendan M., Watts Jennifer D., Savage Kathleen, Connon Sara June, Mauritz Marguerite, Schuur Edward A. G., Peter Darcy, Minions Christina, Nojeim Julia, Commane Roisin, Emmerton Craig A., Goeckede Mathias, Helbig Manuel, Holl David, Iwata Hiroki, Kobayashi Hideki, Kolari Pasi, Lopez-Blanco Efren, Marushchak Maija E., Mastepanov Mikhail, Merbold Lutz, Parmentier Frans-Jan W., Peichl Matthias, Sachs Torsten, Sonnentag Oliver, Ueyama Masahito, Voigt Carolina, Aurela Mika, Boike Julia, Celis Gerardo, Chae Namyi, Christensen Torben R., Bret-Harte M. Syndonia, Dengel Sigrid, Dolman Han, Edgar Colin W., Elberling Bo, Euskirchen Eugenie, Grelle Achim, Hatakka Juha, Humphreys Elyn, Jarveoja Jarvi, Kotani Ayumi, Kutzbach Lars, Laurila Tuomas, Lohila Annalea, Mammarella Ivan, Matsuura Yojiro, Meyer Gesa, Nilsson Mats B., Oberbauer Steven F., Park Sang-Jong, Petrov Roman, Prokushkin Anatoly S., Schulze Christopher, St Louis Vincent L., Tuittila Eeva-Stiina, Tuovinen Juha-Pekka, Quinton William, Varlagin Andrej, Zona Donatella, Zyryanov Viacheslav I.

EARTH SYSTEM SCIENCE DATA 14 巻 ( 1 ) 頁： 179 - 208 2022年1月

Seasonality in Human Interest in Berry Plants Detection by Google Trends 査読有り

Ayumi Kotani, Nagai Shin, Shunsuke Tei, Andrey Makarov, Tuyara Gavrilyeva

Frontiers in Forest Global Change 4 巻頁： 688835 2021年9月

Geographical, Climatological, and Biological Characteristics of Tree Radial Growth Response to Autumn Climate Change 査読有り

Shunsuke Tei, Ayumi Kotani, Atsuko Sugimoto, Nagai Shin

Frontiers in Forest Global Change 4 巻頁： 687749 2021年8月

Mizuochi Hiroki, Iijima Yoshihiro, Nagano Hirohiko, Kotani Ayumi, Hiyama Tetsuya

REMOTE SENSING 13 巻 ( 2 ) 頁： 1 - 19 2021年1月

Author Correction: The FLUXNET2015 dataset and the ONEFlux processing pipeline for eddy covariance data (Scientific Data, (2020), 7, 1, (225), 10.1038/s41597-020-0534-3)

Pastorello G.

Scientific Data 8 巻 ( 1 ) 2021年

Seasonal variations in carbon dioxide exchange fluxes at a taiga–tundra boundary ecosystem in Northeastern Siberia

Shunsuke Tei, Tomoki Morozumi, Ayumi Kotani, Shinya Takano, Atsuko Sugimoto, Shin Miyazaki, Ryo Shingubara, Rong Fan, Roman Petrov, Egor Starostin, Ruslan Shakhmatov, Aleksandr Nogovitcyn, Trofim Maximov

Polar Science 2021年

Lessons learned from more than a decade of greenhouse gas flux measurements at boreal forests in eastern Siberia and interior Alaska

Hiyama T.

Polar Science 2021年

Detection of year-to-year spring and autumn bio-meteorological variations in siberian ecosystems

Nagai Shin, Kotani Ayumi, Morozumi Tomoki, Kononov Alexander V, Petrov Roman E, Shakhmatov Ruslan, Ohta Takeshi, Sugimoto Atsuko, Maximov Trofim C, Suzuki Rikie, Tei Shunsuke

POLAR SCIENCE 25 巻 2020年9月

Direct measurement of leaf area index in a deciduous needle-leaf forest, eastern Siberia

Shin Nagai, Kotani Ayumi, Sato Tomonori, Sugimoto Atsuko, Maximov Trofim C, Nogovitcyn Aleksandr, Miyamoto Yumiko, Kobayashi Hideki, Tei Shunsuke

POLAR SCIENCE 25 巻 2020年9月

The FLUXNET2015 dataset and the ONEFlux processing pipeline for eddy covariance data

Pastorello G.

Scientific data 7 巻 ( 1 ) 2020年7月

Assessment of drought condition using remotely sensed drought severity index and its correlations with soil moisture product in Inner Mongolia

Wang L.

Theoretical and Applied Climatology 141 巻 ( 1-2 ) 頁： 715 - 728 2020年7月

Application of an open-path eddy covariance methane flux measurement system to a larch forest in eastern Siberia

Nakai T.

Agricultural and Forest Meteorology 282-283 巻 2020年3月

Application of Improved Remotely Sensed Drought Severity Index Based on Soil Moisture Product in Inner Mongolia

Wang Lusha, Kotani Ayumi, Tanaka Takafumi, Ohta Takeshi

SOLA 16 巻 ( 0 ) 頁： 259 - 264 2020年

掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人日本気象学会

Based on the drought severity index (DSI), which is derived from the ratio of evapotranspiration (ET) to potential evapotranspiration (PET) and normalized difference vegetation index (NDVI), as measured by remote sensing, we replaced the ET/PET ratio with soil moisture (0-10 cm) to establish an improved index (IDSI) and evaluated the drought situation in Inner Mongolia. The two components in IDSI are independently derived; however, the effects of evapotranspiration are contained in the soil moisture, and even precipitation changes could be reflected. We used monthly IDSI data for Inner Mongolia to evaluate drought throughout the growing season (May–September) during 2001-2010. The IDSI showed that 2001, 2007, and 2009 were years with significant drought. Areas that experienced extreme drought were less extensive than those found by the DSI because we removed the ET/PET component, which already contains the effects of the NDVI. IDSI results not only contained the degree of precipitation change for a given month through soil moisture, but also reflected the influence of water and heat in the previous month through the NDVI. Moreover, IDSI results were generally consistent with agricultural drought disaster records.

DOI： 10.2151/sola.2020-043

Effects of extreme drought and wet events for tree mortality: Insights from tree-ring width and carbon isotope ratio in a Siberian larch forest

Tei S.

Ecohydrology 12 巻 ( 8 ) 2019年12月

Strong and stable relationships between tree-ring parameters and forest-level carbon fluxes in a Siberian larch forest

Tei S.

Polar Science 21 巻頁： 146 - 157 2019年9月

Impact of unusually wet permafrost soil on understory vegetation and CO2 exchange in a larch forest in eastern Siberia 査読有り

Kotani Ayumi, Saito Atsushi, Kononov Alexander V, Petrov Roman E, Maximov Trofim C, Iijima Yoshihiro, Ohta Takeshi

AGRICULTURAL AND FOREST METEOROLOGY 265 巻頁： 295 - 309 2019年2月

北極陸域モデル相互比較GTMIPの熱・水収支解析査読有り

斉藤和之, 森淳子, 町屋広和, 宮崎真, 伊勢武史, 末吉哲雄, 山崎剛, 飯島慈裕, 伊川浩樹, 市井和仁, 伊藤昭彦, 大石龍太, 太田岳史, 堅田元喜, 小谷亜由美, 佐々井崇博, 佐藤篤司, 佐藤永, 杉本敦子, 鈴木力英, 田中克典, 新田友子, 庭野匡思, Burke Eleanor, 朴昊澤, 山口悟

雪氷 80 巻 ( 2 ) 頁： 159 - 174 2018年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人日本雪氷学会

北極陸域モデル相互比較（GTMIP）は観測-モデル研究連携の構築，現行の陸域過程モデルの不確実性把握，次世代モデル構築のための課題抽出を目的とし，物理系から生態系にまたがる国内外の21モデルと6観測サイトが参加して行われた．評価項目は熱・水収支，積雪・凍土，炭素循環にわたるが，本稿では4サイト（フェアバンクス，ケヴォ，ティクシ，ヤクーツク）の観測値をもとに構築した共通駆動データを使用した34年間（1980-2013）の比較（stage 1）での熱・水収支について，その結果を報告する．
大気との熱・水収支に関して，物理系と生態系モデルの間では系統的な差異は見られず，個々のモデルの特徴のほうが大きかった．サイト間でも挙動の違いがあるものの，モデルの種類や複雑さとは必ずしも連動せず，背景（植生や凍土状況）に起因する違いのほうが大きかった．全体的に，モデル中央値は観測値をよく代表する推定値であったが，特に地下部との熱・水収支に関わる積雪や土壌水分・地温については，既定値設定や実装過程の有無によるモデル性能の差異もしくは系統的誤差が生じており，今後のモデル改良・高度化における重要性が示唆された．

DOI： 10.5331/seppyo.80.2_159

Reconciliation of top-down and bottom-up CO2 fluxes in Siberian larch forest

Takata Kumiko, Patra Prabir K., Kotani Ayumi, Mori Junko, Belikov Dmitry, Ichii Kazuhito, Saeki Tazu, Ohta Takeshi, Saito Kazuyuki, Ueyama Masahito, Ito Akihiko, Maksyutov Shamil, Miyazaki Shin, Burke Eleanor J., Ganshin Alexander, Iijima Yoshihiro, Ise Takeshi, Machiya Hirokazu, Maximov Trofim C., Niwa Yosuke, O'ishi Ryo'ta, Park Hotaek, Sasai Takahiro, Sato Hisashi, Tei Shunsuke, Zhuravlev Ruslan, Machida Toshinobu, Sugimoto Atsuko, Aoki Shuji

ENVIRONMENTAL RESEARCH LETTERS 12 巻 ( 12 ) 2017年12月

New data-driven estimation of terrestrial CO2 fluxes in Asia using a standardized database of eddy covariance measurements, remote sensing data, and support vector regression

Ichii Kazuhito, Ueyama Masahito, Kondo Masayuki, Saigusa Nobuko, Kim Joon, Carmelita Alberto Ma., Ardoe Jonas, Euskirchen Eugenie S., Kang Minseok, Hirano Takashi, Joiner Joanna, Kobayashi Hideki, Marchesini Luca Belelli, Merbold Lutz, Miyata Akira, Saitoh Taku M., Takagi Kentaro, Varlagin Andrej, Bret-Harte M. Syndonia, Kitamura Kenzo, Kosugi Yoshiko, Kotani Ayumi, Kumar Kireet, Li Sheng-Gong, Machimura Takashi, Matsuura Yojiro, Mizoguchi Yasuko, Ohta Takeshi, Mukherjee Sandipan, Yanagi Yuji, Yasuda Yukio, Zhang Yiping, Zhao Fenghua

JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES 122 巻 ( 4 ) 頁： 767 - 795 2017年4月

Analysing the origin of rain- and subsurface water in seasonal wetlands of north-central Namibia

Hiyama Tetsuya, Kanamori Hironari, Kambatuku Jack R., Kotani Ayumi, Asai Kazuyoshi, Mizuochi Hiroki, Fujioka Yuichiro, Iijima Morio

ENVIRONMENTAL RESEARCH LETTERS 12 巻 ( 3 ) 2017年3月

Impact of rice cultivation on evapotranspiration in small seasonal wetlands of north-central Namibia

Kotani Ayumi, Hiyama Tetsuya, Ohta Takeshi, Hanamura Miho, Kambatuku Jack R., Awala Simon K., Iijima Morio

HYDROLOGICAL RESEARCH LETTERS 11 巻 ( 2 ) 頁： 134 - 140 2017年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：水文・水資源学会／日本地下水学会／日本水文科学会／陸水物理研究会

This paper aims to evaluate the effect of mixed-cropping of rice and upland crops on evapotranspiration (ET) in a small seasonal wetland in the north-central Namibia. Meteorological observations were conducted in the experimental sloped field, which simulated the cultivation of both rice in a wetland environment and upland crops in the surrounding rain-fed area, and included a reference wetland with natural vegetation. During cultivation, ET from the rice field was similar to that from the wetland. However, during the dry period ET was remarkably reduced in the post-harvest field, while continuous ET occurred in the natural wetland even after surface water had dried up. The response of surface conductance to meteorological variables was investigated by means of the Jarvis–Stewart conductance model. During cultivation, surface conductance of the rice field and the wetland had a distinct stress response compared with that of the rain–fed crop field. During the dry period, surface conductance of the wetland site, in which the surface water dried–up, still responded to the meteorological conditions in contrast to those of the post-harvest field with plowed bare soil.

DOI： 10.3178/hrl.11.134

Factors contributing to soil nitrogen mineralization and nitrification rates of forest soils in the Japanese archipelago

Urakawa Rieko, Ohte Nobuhito, Shibata Hideaki, Isobe Kazuo, Tateno Ryunosuke, Oda Tomoki, Hishi Takuo, Fukushima Keitaro, Inagaki Yoshiyuki, Hirai Keizo, Oyanagi Nobuhiro, Nakata Makoto, Toda Hiroto, Kenta Tanaka, Kuroiwa Megumi, Watanabe Tsunehiro, Fukuzawa Karibu, Tokuchi Naoko, Ugawa Shin, Enoki Tsutomu, Nakanishi Asami, Saigusa Nobuko, Yamao Yukio, Kotani Ayumi

FOREST ECOLOGY AND MANAGEMENT 361 巻頁： 382 - 396 2016年2月

Persistence and memory timescales in root-zone soil moisture dynamics

Ghannam Khaled, Nakai Taro, Paschalis Athanasios, Oishi Christopher A., Kotani Ayumi, Igarashi Yasunori, Kumagai Tomo'omi, Katul Gabriel G.

WATER RESOURCES RESEARCH 52 巻 ( 2 ) 頁： 1427 - 1445 2016年2月

The GRENE-TEA model intercomparison project (GTMIP) Stage 1 forcing data set

Sueyoshi T.

Earth System Science Data 8 巻 ( 1 ) 頁： 1 - 14 2016年1月

The effect of assimilating satellite-derived soil moisture data in SiBCASA on simulated carbon fluxes in Boreal Eurasia

van der Molen M. K., de Jeu R. A. M., Wagner W., van der Velde I. R., Kolari P., Kurbatova J., Varlagin A., Maximov T. C., Kononov A. V., Ohta T., Kotani A., Krol M. C., Peters W.

HYDROLOGY AND EARTH SYSTEM SCIENCES 20 巻 ( 2 ) 頁： 605 - 624 2016年

The GRENE-TEA model intercomparison project (GTMIP) Stage 1 forcing data set

Sueyoshi T., Saito K., Miyazaki S., Mori J., Ise T., Arakida H., Suzuki R., Sato A., Iijima Y., Yabuki H., Ikawa H., Ohta T., Kotani A., Hajima T., Sato H., Yamazaki T., Sugimoto A.

EARTH SYSTEM SCIENCE DATA 8 巻 ( 1 ) 頁： 1-14 2016年

The effect of assimilating satellite derived soil moisture in SiBCASA on simulated carbon fluxes in Boreal Eurasia

Van Der Molen M.

Hydrology and Earth System Sciences Discussions 12 巻 ( 9 ) 頁： 9003 - 9054 2015年9月

Biogeochemical nitrogen properties of forest soils in the Japanese archipelago

Urakawa R.

Ecological Research 30 巻 ( 1 ) 頁： 1-2 2015年1月

The GRENE-TEA model intercomparison project (GTMIP): overview and experiment protocol for Stage 1

Miyazaki S., Saito K., Mori J., Yamazaki T., Ise T., Arakida H., Hajima T., Iijima Y., Machiya H., Sueyoshi T., Yabuki H., Burke E. J., Hosaka M., Ichii K., Ikawa H., Ito A., Kotani A., Matsuura Y., Niwano M., Nitta T., O'ishi R., Ohta T., Park H., Sasai T., Sato A., Sato H., Sugimoto A., Suzuki R., Tanaka K., Yamaguchi S., Yoshimura K.

GEOSCIENTIFIC MODEL DEVELOPMENT 8 巻 ( 9 ) 頁： 2841 - 2856 2015年

Radiative and precipitation controls on root zone soil moisture spectra

Nakai Taro, Katul Gabriel G, Kotani Ayumi, Igarashi Yasunori, Ohta Takeshi, Suzuki Masakazu, Kumagai Tomo'omi

GEOPHYSICAL RESEARCH LETTERS 41 巻 ( 21 ) 頁： 7546 - 7554 2014年11月

Radiative and precipitation controls on root zone soil moisture spectra 査読有り

Nakai, T., Katul, G.G., Kotani, A., Igarashi, Y., Ohta, T., Suzuki, M., Kumagai, T.

Geophysical Research Letters 41 巻頁： 7546-7554 2014年11月

Effects of waterlogging on water and carbon dioxide fluxes and environmental variables in a Siberian larch forest, 1998-2011

Ohta Takeshi, Kotani Ayumi, Iijima Yoshihiro, Maximov Trofim C., Ito Syogo, Hanamura Miho, Kononov Alexander V., Maximov Ayal P.

AGRICULTURAL AND FOREST METEOROLOGY 188 巻頁： 64 - 75 2014年5月

Sap flow changes in relation to permafrost degradation under increasing precipitation in an eastern Siberian larch forest

Iijima Yoshihiro, Ohta Takeshi, Kotani Ayumi, Fedorov Alexander N., Kodama Yuji, Maximov Trofim C.

ECOHYDROLOGY 7 巻 ( 2 ) 頁： 177 - 187 2014年4月

Temporal variations in the linkage between the net ecosystem exchange of water vapour and CO2 over boreal forests in eastern Siberia

Kotani Ayumi, Kononov Alexander V., Ohta Takeshi, Maximov Trofim C.

ECOHYDROLOGY 7 巻 ( 2 ) 頁： 209 - 225 2014年4月

International Joint Conference of 11th AsiaFlux International Workshop, 3rd HESSS and 14th Annual Meeting of KSAFM “Communicating Science to Society: Coping with Climate Extremes for Resilient Ecological-Societal Systems”の報告

丸山篤志, 宮崎真, 小谷亜由美, 栗林正俊, 斎藤琢, 小野圭介

生物と気象 14 巻頁： D1-7 2014年1月

Effects of waterlogging on water and carbon dioxide fluxes and environmental variables in a Siberian larch forest 査読有り

Ohta, T., Kotani, A., Iijima, Y., Maximov, T., Ito, S., Hanamura, M., Kononov, A., Maximov, A.

Agricultural and Forest Meteorology 188 巻頁： 64-75 2014年1月

東シベリア・カラマツ林における水・エネルギー・炭素循環

太田岳史, 小谷亜由美

水利科学 58 巻 ( 5 ) 頁： 43 - 73 2014年

東シベリアカラマツ林における、上層植生と下層植生から生じる潜熱フラックスの変動要因

斉藤淳志, 小谷亜由美, 太田岳史, 飯島慈裕

日本森林学会大会発表データベース 125 巻 ( 0 ) 頁： 146 - 146 2014年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：日本森林学会

東シベリア地域カラマツ林での2005～2012年のタワー観測データを用いて、カラマツ林上層部(3.3m以上)と下層部(3.3m以下) の潜熱フラックスを区別して解析を行った。本研究ではペンマン・モンティース式を用いて、各潜熱の年々変動に対する環境要素の寄与率を計算し、上・下層潜熱それぞれの増加・減少傾向の要因について明らかにした。 上層潜熱には減少傾向が見られ、下層潜熱には増加傾向が見られた。その原因としては、以下のように考えられる。上層潜熱の年々変動に対して最も高い寄与を示した要素は、上層表面コンダクタンスであった。観測地域で発生した長期湿害の影響により2007年頃から上層カラマツの活性が低下し、上層表面コンダクタンスが減少したことが上層潜熱減少の要因であると考えられる。下層潜熱の年々変動に対して高い寄与率を示した要素は、下層表面コンダクタンス、大気飽差、有効エネルギー量の3つであった。下層表面コンダクタンスには減少傾向が見られたが、下層表面コンダクタンスの減少以上に大気飽差と有効エネルギー量の増加の影響が大きかったため、結果的に下層潜熱は増加したと考えられる。

DOI： 10.11519/jfsc.125.0_146

Changes in eco-hydrological systems under recent climate change in eastern Siberia 査読有り

Hiyama TETSUYA, Ohta TAKESHI, Sugimoto ATSUKO, Yamazaki TAKESHI, Oshima KAZUHIRO, Yonenobu HITOSHI, Yamamoto KAZUKIYO, Kotani AYUMI, Park HOTAEK, Kodama Yuji, ther

IAHS Publication 360 巻頁： 155 - 160 2013年1月

記述言語：英語掲載種別：研究論文（学術雑誌）

Global warming is likely to transform Siberian environments. Recent eco-hydrological evidence indicates that water and carbon cycles have been changing rapidly, with potentially serious effects on the Siberian flora and fauna. We have comprehensively analysed dendrochronological, hydrological, and meteorological data and satellite remote sensing data to track changes in vegetation and the water and carbon cycles in the Lena River Basin, eastern Siberia. The basin is largely covered with larch forest and receives little precipitation. However, from 2005 to 2008 the central part of the basin experienced an extraordinarily high level of precipitation in late summer and winter. This resulted in the degradation of permafrost, forest, and hydrological elements in the region. Dendrochronological data implied that this event was the only incidence of such conditions in the previous 150 years. Based on data collected before and after the event, we developed a permafrost-ecosystem model, including surface soil freeze-thawing processes, to better represent the heat, water, and carbon fluxes in the region. We focused on the surface soil layer, in which an increased thawing depth is now apparent, surface soil moisture, and net primary production. An analysis of observed and model-simulated data indicated that the annual maximum thawing depth (AMTD) had increased gradually on a decadal scale and deepened abruptly after 2005. Climatological analyses of atmospheric water circulation over the region indicated that the recent increases in precipitation over the central Lena River Basin were partly related to cyclone activity. Consequently, the increased precipitation from late-summer to winter resulted in increases in soil moisture, soil temperature, and AMTD in the region. © 2013 IAHS Press.

Changes in eco-hydrological systems under recent climate change in eastern Siberia

その他リンク： http://orcid.org/0000-0002-1596-7543

Changes in eco-hydrological systems under recent climate change in eastern Siberia

Hiyama Tetsuya, Ohta Takeshi, Sugimoto Atsuko, Yamazaki Takeshi, Oshima Kazuhiro, Yonenobu Hitoshi, Yamamoto Kazukiyo, Kotani Ayumi, Park Hotaek, Kodama Yuji, Hatta Shigemi, Fedorov Alexander N., Maximov Trofim C.

COLD AND MOUNTAIN REGION HYDROLOGICAL SYSTEMS UNDER CLIMATE CHANGE: TOWARDS IMPROVED PROJECTIONS 360 巻頁： 155 - 160 2013年

Hiyama T.

IAHS-AISH Proceedings and Reports 360 巻頁： 155 - 160 2013年

Interannual variation of evapotranspiration in an eastern Siberian larch forest

Xue Bao-Lin, Komatsu Hikaru, Kumagai Tomo'omi, Kotani Ayumi, Otsuki Kyoichi, Ohta Takeshi

HYDROLOGICAL PROCESSES 26 巻 ( 15 ) 頁： 2360 - 2368 2012年7月

森林群落上でのスカラー乱流輸送特性の季節変化

小谷亜由美, 浜崎俊貴, 太田岳史

水文・水資源学会研究発表会要旨集 25 巻 ( 0 ) 頁： 276 - 276 2012年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：水文・水資源学会

森林-大気間における熱・水蒸気・CO2（以下ではスカラーと称する）交換の乱流輸送特性に，森林群落が与える影響として，樹冠や樹体分布などによる空気力学的乱流特性への影響と樹木生理に伴うスカラーの放出・吸収源の時間変動特性への影響が考えられる．本研究では，熱帯モンスーン落葉林，熱帯モンスーン常緑林，暖温帯混交林，冷温帯落葉林，冷温帯混交林，寒帯落葉林，寒帯常緑林の７つの森林群落上で測定された各スカラーと風速データを用いて，①接地層乱流相似則の適用可否と乱流相似則からの乖離の発生条件，②相関係数を指標としたスカラー間の変動相似性とスカラー輸送効率について，複数の森林での観測結果の特徴を比較することで共通点と相違点を抽出し，その原因を考察した．主な結果として，乱流輸送特性のうち運動量輸送特性はサイトや季節によらず共通であったが，スカラー輸送特性はスカラー種類，サイト，季節により，共通点と相違点が明らかになった．フラックス絶対値が小さく30分内での変動も小さくなる寒帯林でのCO2密度変動や冬季の冷温帯林での温度変動では，接地境界層乱流相似則から乖離する傾向がみられ，輸送効率が小さくなった．落葉樹を含む森林ではとくにCO2密度変動について相似則からの乖離や輸送効率に季節変化がみられたが，熱帯常緑林での季節変化は小さかった．

DOI： 10.11520/jshwr.25.0.276.0

Spatial variations in evapotranspiration over East Asian forest sites. I. Evapotranspiration and decoupling coefficient

Spatial variations in evapotranspiration over East Asian forest sites. II Surface conductance and aerodynamic conductance 査読有り

Khatun R, Ohta T, Kotani A, Asanuma J, Gamo M, Han S, Hirano T, Nakai Y, Saigusa N, Takagi K, Wang H, Yoshifuji N

Hydorological Rearch Letters ( 5 ) 頁： 88-92 2011年

Spatial variations in evapotranspiration over East Asian forest sites. I. Evapotranspiration and decoupling coefficient 査読有り

Khatun R, Ohta T, Kotani A, Asanuma J, Gamo M, Han S, Hirano T, Nakai Y, Saigusa N, Takagi K, Wang H, Yoshifuji N

Hydorological Rearch Letters ( 5 ) 頁： 83-87 2011年

Khatun Rehana, Ohta Takeshi, Kotani Ayumi, Asanuma Jun, Gamo Minoru, Han Shijie, Hirano Takashi, Nakai Yuichiro, Saigusa Nobuko, Takagi Kentaro, Wang Huimin, Yoshifuji Natsuko

Hydrological Research Letters 5 巻 ( 5 ) 頁： 83 - 87 2011年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：水文・水資源学会／日本地下水学会／日本水文科学会／陸水物理研究会

Evapotranspiration (ET) is not only a vital component of water budget, but also plays an important role in the energy budget of the earth-atmospheric system, ultimately driving many regional and global scale climatological processes. This paper describes the ET characteristics and factors controlling ET across the 17 forest sites in East Asia (2°S to 64°N latitude). ET was measured using the eddy covariance technique at each site. Daytime dry-canopy data for the growing season were used in this study. Growing season mean ET gradually decreased as latitude increased, with a range of 4.4 to 1.2 mm d−1. The growing season mean decoupling coefficient (Ω) ranged from 0.42 to 0.11 across the studied sites. At low-latitude forest sites, Ω was close to 0.50, indicating that the bulk surface was partially decoupled from the atmosphere and ET was strongly controlled by net radiation and vapour pressure deficit. At high-latitude forest sites, Ω was low (∼0.12), indicating that the bulk surface was well coupled to the atmosphere and ET was mainly controlled by surface conductance. The value of Ω was determined mainly by the ratio of aerodynamic conductance to surface conductance across the studied forests of East Asia.

DOI： 10.3178/hrl.5.83

Spatial variations in evapotranspiration over East Asian forest sites. II. Surface conductance and aerodynamic conductance

東シベリア南部のカラマツ林における群落蒸発散

小谷亜由美, 太田岳史, マキシモフトロフィーム

日本森林学会大会発表データベース 123 巻 ( 0 ) 頁： Pb083 - Pb083 2011年

Khatun Rehana, Ohta Takeshi, Kotani Ayumi, Asanuma Jun, Gamo Minoru, Han Shijie, Hirano Takashi, Nakai Yuichiro, Saigusa Nobuko, Takagi Kentaro, Wang Huimin, Yoshifuji Natsuko

Hydrological Research Letters 5 巻 ( 5 ) 頁： 88 - 92 2011年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：水文・水資源学会／日本地下水学会／日本水文科学会／陸水物理研究会

Evapotranspiration over forest surfaces is mainly constrained by environmental and forest structural components through their influence on surface conductance (Gs) and aerodynamic conductance (Ga). Tower based eddy covariance data from 16 forest sites in East Asia (2°S to 64°N) were used to examine the sensitivity of Matsumoto and Nakai models for predicting Gs and Ga, respectively. Daytime dry-canopy data for the growing season were used in this study. Comparisons between model predictions and observed Gs and Ga showed good agreement, suggesting that the models were suitable for predicting Gs and Ga with reasonable accuracy. However, the model for Gs was unable to predict Gs accurately when soil water content was low (∼10%). In this circumstance, effective soil water content and a more comprehensive method for modelling the soil water content function must be used. Gs in East Asia was largely depended on vapour pressure deficit and secondarily on soil water content. Ga was largely affected by leaf area index compared with stand density.

DOI： 10.3178/hrl.5.88