Hydrological Research Letters
Online ISSN : 1882-3416
ISSN-L : 1882-3416
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  • Kenji Tsuruta, Yoshiko Kosugi, Masanori Katsuyama, Ken’ichirou Kosugi, ...
    2020 Volume 14 Issue 1 Pages 1-8
    Published: 2020
    Released: January 18, 2020
    JOURNALS OPEN ACCESS

    We quantified long-term trends in evapotranspiration, runoff, and deep percolation using 40 years of hydrological data, examining the effects of evapotranspiration on runoff during forest development in a coniferous species. Using the flow duration curve, we evaluated the effects of evapotranspiration on the entire range of flow stages (high to low flows). During the 40-year forest development, deep percolation ranged from 97 mm to 105 mm. Annual evapotranspiration increased by 623–766 mm, which appeared to be caused by increased air temperature as well as forest development. Annual runoff consequently decreased by 937–777 mm. In particular, pronounced decreases in daily flow were found with an exceedance probability of >11% in the flow duration curve. Long-term effects of evapotranspiration on runoff during forest development continued for a longer period than predicted by previous catchment studies of ~20 years duration. Our results suggest that the long-term patterns of evapotranspiration and runoff during forest development would differ from those reported by previous catchment studies under climate warming conditions and highlight the need for further research into separating the effects of forest development and increasing air temperature on evapotranspiration in long-term hydrological data.

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  • Hiroshi Matsuyama, Jiei Flores, Kosuke Oikawa, Kengo Miyaoka
    2020 Volume 14 Issue 1 Pages 9-16
    Published: 2020
    Released: January 18, 2020
    JOURNALS OPEN ACCESS

    This study compared precipitable water vapor (PWV) of JRA-55 and GPS in Japan by considering different elevations in JRA-55 (geopotential height) and GPS (antenna height) because JRA-55’s PWV is pointed out to be underestimated as a result of dry bias in the middle and upper troposphere in the forecast model. We selected 26 grid points of JRA-55 over Japanese islands and the respective nearest 26 GPS stations operated by the Geospatial Information Authority of Japan. First, we linearly converted the geopotential height of 26 grid points to air pressure at the antenna height, assuming the sea surface and 1500-m height corresponding to 1013.25 hPa and 850 hPa, respectively. We then calculated JRA-55’s PWV by vertically integrating specific humidity in the pressure coordinate system using the antenna height from July 2010 through December 2012 (designated as “corrected PWV”). At 22 grid points among the 26, the geopotential height is higher than the antenna height, where the majority of the data of PWV provided by the JRA project was smaller than that retrieved from GPS. The underestimation of the corrected PWV decreased, although 65% of them remained underestimated. The underestimation of the corrected PWV increased in winter and decreased in summer.

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  • Guesh Zeru, Tena Alamirew, Haile A. Shishaye, Megersa Olmana, Nata Tad ...
    2020 Volume 14 Issue 1 Pages 17-22
    Published: 2020
    Released: January 22, 2020
    JOURNALS OPEN ACCESS

    In this study, the Hydrograph Analysis: Rainfall and Time-Trends (HARTT) model was used to determine the contribution of climatic and non-climatic stresses on groundwater levels in the Lake Haramaya well-field, Ethiopia. Monthly precipitation and monitored water-level data were used as explanatory variables of the method. Variability in rainfall explained 81.3% of groundwater levels using 2-month average time-delay. The coefficient of the impact of rainfall on groundwater level (K1) was found to be 0.00562 ± 0.0007 mm. This K1 value indicates that a 1 mm increase in rainfall from the annual average rainfall raises the groundwater-level by 0.00562 ± 0.0007 mm, while 1 mm decrease in rainfall causes a 0.00562 ± 0.0007 mm drop in groundwater-level in the area. However, the average falling trend of the groundwater level (K2) was 1.51 ± 0.133 m/year, even with rainfall causing water-levels to rise between 1.01 to 3.29 m/year. With decreased rainfall, rainfall accounted for about 19.5% of the total-drawdown, while 80.5% was due to cumulative effects of non-climatic variables. This shows that rainfall inputs are negated by cumulative non-climatic stresses leading to the long-term net decline in groundwater level. Projected water-level results show that groundwater levels will be below pumping positions in <24 years which may have dire consequences for local landowners.

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  • Fenglan Wang, Keigo Noda, Issaku Azechi, Masateru Senge
    2020 Volume 14 Issue 1 Pages 23-28
    Published: 2020
    Released: January 28, 2020
    JOURNALS OPEN ACCESS

    In this research, power generation potential is estimated using overflow discharge for eight headworks (Inuyama, Meiji-yousui, Muromatsubara, Kansakawa, Furikusa, Onyu, Hosokawa and Okajima) located in Aichi and Gifu Prefectures, and the characteristics of their power generation are clarified in order to evaluate the feasibility of small hydropower plants. The results are as follows. Firstly, overflow discharge is more stable than the discharge of intake water at the headworks, which suggests that power generation using overflow discharge is more suitable for actual power generation. Secondly, maximum power outputs of 43 kW to 2,002 kW, under a discharge utilization factor of 60%, show great potential for power generation at these eight headworks. Finally, fluctuations in monthly power generation are higher than that of annual power generation due to the influences of irrigation and seasonal changes in precipitation on water intake.

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  • Hiroyuki Deguchi, Daisuke Sasaki, Mikiyasu Nakayama
    2020 Volume 14 Issue 1 Pages 29-33
    Published: 2020
    Released: January 30, 2020
    JOURNALS OPEN ACCESS

    The Central Asian countries have abundant but unevenly distributed natural resources including water. The Central Asia Power System (CAPS) project initiated by the Asian Development Bank and the Central Asia-South Asia Electricity Transmission and Trade Project (CASA-1000) initiated by the World Bank are planned to catalyze trade of electricity in this region. However, the existing surplus of the hydropower generation capacity of Tajikistan in summer may only meet the anticipated power demand by one project. The CAPS project (to be completed in 2023) may monopolize the surplus in Tajikistan and the CASA-1000 project (to be completed later) may suffer from the shortage of electricity. It stems from the failure of aid coordination between the Asian Development Bank and the World Bank. This study reveals (a) how the assumptions made for the CAPS and CASA-1000 projects differ, and (b) possible causes of the failed aid coordination. It turned out that (a) the officer in a development bank who is in charge of project development has little motivation to submit his or her project to aid coordination, (b) only “geographic demarcation” between two projects was discussed and agreed upon in the aid coordination, and (c) no technical detail of these projects was discussed in the aid coordination.

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