start-ver=1.4
cd-journal=joma
no-vol=19
cd-vols=
no-issue=4
article-no=
start-page=223
end-page=230
dt-received=
dt-revised=
dt-accepted=
dt-pub-year=2025
dt-pub=2025
dt-online=
en-article=
kn-article=
en-subject=
kn-subject=
en-title=
kn-title=Unique drought tendency of an understudied region in the Mekong Delta, Vietnam
en-subtitle=
kn-subtitle=
en-abstract=
kn-abstract=Water resource vulnerability due to uneven precipitation and water allocations is a significant issue in many regions of the world, including the Mekong Delta. Although numerous studies have already evaluated drought tendencies in many parts of the Mekong Delta, some areas have been excluded. This study targeted these excluded areas, including one inland, one coastal area, and two islands, which are defined as “understudied regions.” The meteorological drought intensity, frequency, and duration in the study areas in the Mekong Delta were evaluated using different time scales of the Standardized Precipitation Index (SPI) between 1994–2020. Unique contrasts in drought features were found between the study areas, indicating that severe drought events occupied the highest percentages inland from 2011 onward, while the most extreme drought events occurred in the coastal areas. Furthermore, trends in drought intensity, tendency, frequency, and duration were identified within the same delta region, demonstrating that combining SPI with other indicators can detect drought patterns in the Mekong Delta. These findings emphasize the importance of comprehensive evaluation of drought tendencies, including in understudied regions, for a better understanding of the features and future of water resources management.
en-copyright=
kn-copyright=

en-aut-name=TsuhaYu
en-aut-sei=Tsuha
en-aut-mei=Yu
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=1
ORCID=

en-aut-name=SomuraHiroaki
en-aut-sei=Somura
en-aut-mei=Hiroaki
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=2
ORCID=

en-aut-name=TramVo Ngoc Quynh
en-aut-sei=Tram
en-aut-mei=Vo Ngoc Quynh
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=3
ORCID=

en-aut-name=MoroizumiToshitsugu
en-aut-sei=Moroizumi
en-aut-mei=Toshitsugu
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=4
ORCID=

affil-num=1
en-affil=Graduate School of Environmental and Life Science, Okayama University
kn-affil=

affil-num=2
en-affil=Graduate School of Environmental and Life Science, Okayama University
kn-affil=

affil-num=3
en-affil=Research Center for Climate Change, Nong Lam University
kn-affil=

affil-num=4
en-affil=Graduate School of Environmental and Life Science, Okayama University
kn-affil=
en-keyword=drought index
kn-keyword=drought index
en-keyword=drought trend
kn-keyword=drought trend
en-keyword=water resource variability
kn-keyword=water resource variability
en-keyword=inland area
kn-keyword=inland area
en-keyword=island area
kn-keyword=island area
END

start-ver=1.4
cd-journal=joma
no-vol=19
cd-vols=
no-issue=2
article-no=
start-page=94
end-page=100
dt-received=
dt-revised=
dt-accepted=
dt-pub-year=2025
dt-pub=2025
dt-online=
en-article=
kn-article=
en-subject=
kn-subject=
en-title=
kn-title=Effects of different management approaches on unmet water demand in coffee-producing areas during wet and dry years: a case study of the Srepok River Watershed, Vietnam
en-subtitle=
kn-subtitle=
en-abstract=
kn-abstract=The primary cause of conflicts over water allocation is growing demand and limited supply, which has become an increasingly serious issue in many watersheds. To alleviate water disputes, effective management strategies can be employed, particularly in the context of intensifying agricultural production and unpredictable changes in weather. In this study, two models, SWAT and WEAP, and the modified surface water supply index (MSWSI) were utilized to evaluate water allocation in the Srepok River Watershed (SRW), considering the prioritization of demand and various irrigation methods, during both wet and dry years. The crop irrigation was chosen to be the main focus in relation to the unmet water demand (UWD). The results indicated that coffee was the primary cause of UWD in the middle of the watershed during the second half of the dry season, and annual crops (AC) were the secondary cause. This research further elucidated that while prioritizing demand had an insignificant impact, transitioning from hose irrigation to sprinkler irrigation could be remarkably effective in mitigating the issues of UWD in coffee crops during both wet and dry years.
en-copyright=
kn-copyright=

en-aut-name=SamTruong Thao
en-aut-sei=Sam
en-aut-mei=Truong Thao
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=1
ORCID=

en-aut-name=SomuraHiroaki
en-aut-sei=Somura
en-aut-mei=Hiroaki
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=2
ORCID=

en-aut-name=MoroizumiToshitsugu
en-aut-sei=Moroizumi
en-aut-mei=Toshitsugu
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=3
ORCID=

affil-num=1
en-affil=Graduate School of Environmental and Life Science, Okayama University
kn-affil=

affil-num=2
en-affil=Graduate School of Environmental and Life Science, Okayama University
kn-affil=

affil-num=3
en-affil=Graduate School of Environmental and Life Science, Okayama University
kn-affil=
en-keyword=hydrological model
kn-keyword=hydrological model
en-keyword=drought
kn-keyword=drought
en-keyword=coffee irrigation
kn-keyword=coffee irrigation
en-keyword=water-saving technique
kn-keyword=water-saving technique
en-keyword=water allocation
kn-keyword=water allocation
END

start-ver=1.4
cd-journal=joma
no-vol=19
cd-vols=
no-issue=1
article-no=
start-page=36
end-page=43
dt-received=
dt-revised=
dt-accepted=
dt-pub-year=2025
dt-pub=2025
dt-online=
en-article=
kn-article=
en-subject=
kn-subject=
en-title=
kn-title=Evaluation of the temporal behavior of fulvic acid iron in Asahi River, Okayama, Japan
en-subtitle=
kn-subtitle=
en-abstract=
kn-abstract=Iron is essential for biogeochemical processes in aquatic ecosystems, but its riverine concentration can be affected by environmental conditions. This study assessed weekly fulvic acid iron (FAFe) concentration at a single sampling site in Asahi River from 2022–2023 to explore the differences in the temporal scales. The objectives of this study were to evaluate the effects of physicochemical properties of the river on the concentration of FAFe, analyze the concentration of FAFe in spring, summer, autumn and winter, and assess the relationship between FAFe concentration and land use types of the watershed. The results indicated that physicochemical parameters, such as pH and surface water temperature (SWT) seemed to influence FAFe concentration (p < 0.05). Hydrological dynamics influenced FAFe concentration and transport, revealing an increasing trend during spring (p < 0.001) and summer (p = 0.05), with non-significant trends during autumn and winter (p > 0.05). FAFe exhibited a strong positive correlation with total organic carbon (TOC) (p < 0.001). Upland fields significantly influenced FAFe concentration (p < 0.01) through runoff with abundant NO3– and PO43– into the river. Thus, FAFe concentration in Asahi River was influenced by pH, SWT, TOC, hydrological regime, and agricultural runoff.
en-copyright=
kn-copyright=

en-aut-name=YengehRohdof Lactem
en-aut-sei=Yengeh
en-aut-mei=Rohdof Lactem
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=1
ORCID=

en-aut-name=SomuraHiroaki
en-aut-sei=Somura
en-aut-mei=Hiroaki
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=2
ORCID=

en-aut-name=MoroizumiToshitsugu
en-aut-sei=Moroizumi
en-aut-mei=Toshitsugu
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=3
ORCID=

en-aut-name=MoriYasushi
en-aut-sei=Mori
en-aut-mei=Yasushi
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=4
ORCID=

en-aut-name=MaedaMorihiro
en-aut-sei=Maeda
en-aut-mei=Morihiro
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=5
ORCID=

affil-num=1
en-affil=Graduate School of Environmental and Life Science, Okayama University
kn-affil=

affil-num=2
en-affil=Graduate School of Environmental and Life Science, Okayama University
kn-affil=

affil-num=3
en-affil=Graduate School of Environmental and Life Science, Okayama University
kn-affil=

affil-num=4
en-affil=Graduate School of Environmental and Life Science, Okayama University
kn-affil=

affil-num=5
en-affil=Graduate School of Environmental and Life Science, Okayama University
kn-affil=
en-keyword=dissolved iron
kn-keyword=dissolved iron
en-keyword=seasonal variation
kn-keyword=seasonal variation
en-keyword=dissolved organic matter
kn-keyword=dissolved organic matter
en-keyword=fulvic acid iron
kn-keyword=fulvic acid iron
END

start-ver=1.4
cd-journal=joma
no-vol=15
cd-vols=
no-issue=3
article-no=
start-page=77
end-page=83
dt-received=
dt-revised=
dt-accepted=
dt-pub-year=2021
dt-pub=2021
dt-online=
en-article=
kn-article=
en-subject=
kn-subject=
en-title=
kn-title=Evaluation of drought features in the Dakbla watershed, Central Highlands of Vietnam
en-subtitle=
kn-subtitle=
en-abstract=
kn-abstract=The drought impacts in the Dakbla watershed were assessed based on a combination of hydrological modeling and drought indices. Three drought indices, the Standardized Precipitation Index (SPI), Standardized Soil Moisture Index (SSI), and Streamflow Drought Index (SDI) were utilized to evaluate the drought features of meteo-hydrology and agriculture. The results indicated that these indices are well adapted to the local conditions, especially the 12-month time scale. Evaluations of drought features on the watershed scale could provide more specific information regarding drought risk than regional-scale/district-level assessments, because a watershed is a hydrologically fundamental unit to consider water resources management. Additionally, evaluations of drought impacts using the SSI showed longer and higher trends than those using the SPI and SDI in terms of drought duration and frequency. Considering the spatial distribution of drought frequency, the areas predominated by agricultural land in the target watershed had higher drought risk. Thus, assessment of agricultural droughts along with meteo-hydrological droughts is extremely important to support realistic local drought management strategies by considering water availability, water balance, and soil characteristics, especially in specific agricultural areas.
en-copyright=
kn-copyright=

en-aut-name=Ngoc Quynh TramVo
en-aut-sei=Ngoc Quynh Tram
en-aut-mei=Vo
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=1
ORCID=

en-aut-name=SomuraHiroaki
en-aut-sei=Somura
en-aut-mei=Hiroaki
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=2
ORCID=

en-aut-name=MoroizumiToshitsugu
en-aut-sei=Moroizumi
en-aut-mei=Toshitsugu
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=3
ORCID=

affil-num=1
en-affil=Graduate School of Environmental and Life Science, Okayama University
kn-affil=

affil-num=2
en-affil=Graduate School of Environmental and Life Science, Okayama University
kn-affil=

affil-num=3
en-affil=Graduate School of Environmental and Life Science, Okayama University
kn-affil=
en-keyword=hydrological modeling
kn-keyword=hydrological modeling
en-keyword=drought indices
kn-keyword=drought indices
en-keyword=drought features
kn-keyword=drought features
en-keyword=watershed scale assessment
kn-keyword=watershed scale assessment
en-keyword=agricultural activities
kn-keyword=agricultural activities
en-keyword=mountainous region
kn-keyword=mountainous region
END

start-ver=1.4
cd-journal=joma
no-vol=18
cd-vols=
no-issue=4
article-no=
start-page=87
end-page=94
dt-received=
dt-revised=
dt-accepted=
dt-pub-year=2024
dt-pub=2024
dt-online=
en-article=
kn-article=
en-subject=
kn-subject=
en-title=
kn-title=Evaluation and selection of a set of CMIP6 GCMs for water resource modeling in the poorly gauged complex terrain of the Tana River basin in Kenya
en-subtitle=
kn-subtitle=
en-abstract=
kn-abstract=The Tana River basin is among the least monitored in terms of meteorological data in Kenya. The Kenya Meteorological Department (KMD) provided data on a ten-day timescale, which is not adequate for water resource evaluation. To bridge this data gap, there is a growing need to leverage General Circulation Models (GCMs) and global datasets to assess current and future water resources in this basin. This study focused on evaluating the performance of 19 CMIP6 GCMs concerning precipitation (pr), maximum temperature (tasmax), and minimum temperature (tasmin) for the complex terrain of the Tana River basin. This involved a rigorous process of disaggregating the data provided by the KMD into a daily timescale for downscaling. The GCMs’ historical output was prepared using the Climate Data Operator (CDO) in Cygwin. The Kling Gupta Efficiency (KGE) was computed for each variable at three stations: Nyeri (upstream), Kitui (midstream), and Bura (downstream). The KGE results were validated using Taylor statistics. Five GCMs, CMCC-ESM2, MPI-ESM1-2-HR, ACCESS-CM2, NorESM2-MM, and GFDL-ESM4, performed best with a multivariable Multi-station KGE statistic of 0.455–0.511. The outputs from these selected GCMs were subsequently downscaled for later use in assessing the water resources and crop water demand in the basin.
en-copyright=
kn-copyright=

en-aut-name=Mwendwa WambuaDaniel
en-aut-sei=Mwendwa Wambua
en-aut-mei=Daniel
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=1
ORCID=

en-aut-name=SomuraHiroaki
en-aut-sei=Somura
en-aut-mei=Hiroaki
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=2
ORCID=

en-aut-name=MoroizumiToshitsugu
en-aut-sei=Moroizumi
en-aut-mei=Toshitsugu
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=3
ORCID=

affil-num=1
en-affil=Graduate School of Environmental and Life Science, Okayama University
kn-affil=

affil-num=2
en-affil=Graduate School of Environmental and Life Science, Okayama University
kn-affil=

affil-num=3
en-affil=Graduate School of Environmental and Life Science, Okayama University
kn-affil=
en-keyword=climate change
kn-keyword=climate change
en-keyword=adaptation
kn-keyword=adaptation
en-keyword=scenarios
kn-keyword=scenarios
en-keyword=downscaling
kn-keyword=downscaling
en-keyword=disaggregation
kn-keyword=disaggregation
en-keyword=temporal
kn-keyword=temporal
END

start-ver=1.4
cd-journal=joma
no-vol=14
cd-vols=
no-issue=4
article-no=
start-page=143
end-page=149
dt-received=
dt-revised=
dt-accepted=
dt-pub-year=2020
dt-pub=2020
dt-online=
en-article=
kn-article=
en-subject=
kn-subject=
en-title=
kn-title=Estimation of long-term external nutrient loading from watersheds to Lake Biwa by a combined rainfall-runoff model and loading-discharge curve approach
en-subtitle=
kn-subtitle=
en-abstract=
kn-abstract=External nutrient loadings to Lake Biwa were estimated using a combined tank model and loading-discharge curve approach. The model was applied to collective drainage basins of the lake’s Imazu (northwest), Hikone (northeast), and Otsu (south) areas. The hourly model was conducted using particular discharges from Kita (Ado) river, Takatoki (Ane) river, and Yasu River to obtain loading curves for phosphate (PO4) and silica (SiO2) by assimilating measured concentrations (2002–2003). The tank model was updated by adding an evapotranspiration routine and direct paths of groundwater discharges to the lake floor. The daily model was calibrated through analysis of water budget among the basin, inflow, lake and outflow, and then validated. The model was established and combined into a loading-discharge curve to determine the long-term external nutrient loadings entering the lake (1980–2017). Seasonal variation in nutrient loadings increased during spring and summer and decreased during winter. Annual phosphate-phosphorus (PO4-P) loading ranged from 217 to 296 tons yr–1 in the North Basin and 45 to 76 tons yr–1 in the South Basin, while SiO2 loading fluctuated from 16,027 to 32,655 tons yr–1 and 2,518 to 5,490 tons yr–1 in the North and South Basins, respectively.
en-copyright=
kn-copyright=

en-aut-name=Le TienHuu
en-aut-sei=Le Tien
en-aut-mei=Huu
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=1
ORCID=

en-aut-name=OkuboKenji
en-aut-sei=Okubo
en-aut-mei=Kenji
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=2
ORCID=

en-aut-name=Ho ThiPhuong
en-aut-sei=Ho Thi
en-aut-mei=Phuong
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=3
ORCID=

en-aut-name=SaitoMitsuyo
en-aut-sei=Saito
en-aut-mei=Mitsuyo
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=4
ORCID=

affil-num=1
en-affil=Graduate School of Environmental and Life Science, Okayama University
kn-affil=

affil-num=2
en-affil=Graduate School of Environmental and Life Science, Okayama University
kn-affil=

affil-num=3
en-affil=School of Chemical, Biological and Environmental Technologies, Vinh University
kn-affil=

affil-num=4
en-affil=Graduate School of Environmental and Life Science, Okayama University
kn-affil=
END