Faculty Profiles - KOTANI, Ayumi

Papers - KOTANI, Ayumi

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

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

Agricultural and Forest Meteorology Vol. 188 page： 64-75 2014.1

Water, Energy and Carbon Cycle in the Larch Wood of East Siberia Open Access

OHTA Takeshi, KOTANI Ayumi

Water Science Vol. 58 ( 5 ) page： 43 - 73 2014

Primary factors in interannual variation of latent heat fluxes from overstory and understory in Siberian larch forest Open Access

Saito Atsushi, Kotani Ayumi, Ohta Takeshi, Iijima Yoshihiro

The Japanese Forest Society Congress Vol. 125 ( 0 ) page： 146 - 146 2014

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

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

IAHS Publication Vol. 360 page： 155 - 160 2013.1

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

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.

Scopus

Other Link： 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 Vol. 360 page： 155 - 160 2013

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

Hiyama T.

IAHS-AISH Proceedings and Reports Vol. 360 page： 155 - 160 2013

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 Vol. 26 ( 15 ) page： 2360 - 2368 2012.7

Seasonal variability of scalar turbulent transport above forest canopy Open Access

Kotani Ayumi, Hamazaki Shunki, Ohta Takeshi

Proceeding of Annual Conference Vol. 25 ( 0 ) page： 276 - 276 2012

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：THE JAPAN SOCIETY OF HYDROLOGY AND WATER RESOURCES

This study investigates seasonal variation in applicability of the turbulent similarity theory, and similarity or dissimilarity in the scalar transfer characteristics observed over forest canopy in the tropical monsoon, temperate, and boreal region. Deviation from the similarity theory and the small transfer efficiency was observed for CO2 variation at the boreal and temperature variation at the cool-temperate forest. Forests including deciduous trees showed clear seasonal variation in not only scalar flux itself but also its transfer characteristics especially in the case of CO2 variation, while the evergreen forest did not present such seasonal variation.

DOI： 10.11520/jshwr.25.0.276.0

Open Access

CiNii Research

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

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 ) page： 88-92 2011

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

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 ) page： 83-87 2011

Evapotranspiration over larch forest in southern area of eastern Siberia Open Access

Kotani Ayumi, Ohta Takeshi, Maximov Trofim

The Japanese Forest Society Congress Vol. 123 ( 0 ) page： Pb083 - Pb083 2011

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

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 Vol. 5 ( 5 ) page： 88 - 92 2011

Language：English Publishing type：Research paper (scientific journal) Publisher：Japan Society of Hydrology and Water Resources (JSHWR) / Japanese Association of Groundwater Hydrology (JAGH) / Japanese Association of Hydrological Sciences (JAHS) / Japanese Society of Physical Hydrology (JSPH)

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

Open Access

CiNii Research

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

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 Vol. 5 ( 5 ) page： 83 - 87 2011

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

Open Access

CiNii Research

Environmental factors controlling forest evapotranspiration and surface conductance on a multi-temporal scale in growing seasons of a Siberian larch forest

Yoshida Megumi, Ohta Takeshi, Kotani Ayumi, Maximov Trofim

JOURNAL OF HYDROLOGY Vol. 395 ( 3-4 ) page： 180 - 189 2010.12

Environmental factors controlling forest evapotranspiration and surface conductance on a multi-temporal scale in growing seasons of a Siberian larch forest Reviewed

Yoshida, M., Ohta, T., Kotani, A., and Maximov,T.

Journal of Hydrology 2010.1

Concise formulae for the atmospheric correction of hemisphericalthermal radiation measured near the ground surface Reviewed

A Kotani and M Sugita

Water Resourses Research Vol. 45 page： W07413 2009.8

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

This paper presents the analysis of the atmospheric effects on the measurement of the thermal radiation near the ground surface. The difference of the thermal radiation at surface and L at some height z was evaluated for various atmospheric conditions and for different sensor heights with the LOWTRAN 7 radiation transfer code. It was found that in many cases the effects of transmission of radiation primarily due to the presence of water vapor and secondarily to other minor gases and aerosols are not negligible for the upward component of thermal radiation, whereas they can be neglected for downward component. Based on the results of LOWTRAN 7 calculations, a simple regression equation of atmospheric path transmissivity ta in terms of the total water vapor w within the air layer between the surface and the sensor height and that of
emittance from the air layer between the ground and the sensor height La in terms of w and temperature were obtained; these will then allow the practical estimation of ta and La from measurements of air temperature and humidity near the ground for the atmospheric correction of the upward thermal radiation measured at a certain height. This procedure can be applied to derive net radiation at the ground surface from a four-component radiometer measurement above the ground and also to derive surface radiative temperature from pyrgeometer measurements of the upward long-wave radiation.

How universal is the C function in the bulk atmospheric boundary layer similarity approach for estimating surface sensible heat flux? Reviewed

M. Sugita, H. Kato, A. Kotani, M. Toda

Water resources research Vol. 45 page： W07418 2009.8

How universal is the C function in the bulk atmospheric boundary layer similarity approach for estimating surface sensible heat flux? Open Access

Sugita Michiaki, Kato Hidekazu, Kotani Ayumi, Toda Motomu

WATER RESOURCES RESEARCH Vol. 45 ( 7 ) 2009.7

Concise formulae for the atmospheric correction of hemispherical thermal radiation measured near the ground surface Open Access

Kotani Ayumi, Sugita Michiaki

WATER RESOURCES RESEARCH Vol. 45 ( 7 ) 2009.7

Response of gross ecosystem productivity, light use efficiency, and water use efficiency of Mongolian steppe to seasonal variations in soil moisture Open Access

Li Sheng-Gong, Eugster Werner, Asanuma Jun, Kotani Ayumi, Davaa Gombo, Oyunbaatar Dambaravjaa, Sugita Michiaki

JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES Vol. 113 ( G1 ) 2008.3

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Papers - KOTANI, Ayumi