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.

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.

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.

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.

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.

A Snow Model (SM) using a temperature-index method was used to optimize the degree-day factor (DDF) and precipitation gradient (PG) for the different elevation zones of the Panjshir sub-basin for snowmelt runoff modelling. The values derived for DDF and PG were calibrated and validated by comparing observed snow cover area and snow cover area simulated by SM. The Snowmelt Runoff Model (SRM) was used to simulate daily runoff over the hydrological years 2009–2014 using the optimized values for SRM accuracy. The optimized DDF values were 0.3 to 0.9 (cm °C^–1 d^–1) for elevations from 1593 m to 5694 m. Meanwhile the PG was +0.002 m^–1 for elevations 1593–4000 m and 0 m^–1 above 4000 m. The simulated runoff by SRM during the entire data period correlated very well with a Nash-Sutcliffe coefficient NS = 0.93 utilizing both observed and simulated snow cover area. This method not only evaluates the characteristics of snowfall and snowmelt in different elevation zones to obtain the DDF and PG, but can also estimate the snowmelt runoff.

Numerous leak detection methods have been developed for pipeline systems because of the shortage of water resources, increased water demand, and leak accidents. These methods have their advantages and disadvantages in terms of cost, labor, and accuracy; therefore, it is important to narrow down the location of a leak as easily, rapidly, and accurately as possible. This study applies the technologies based on the execution of a transient event (transient test-based technologies (TTBTs)), and a model is presented for representing the relation between the leak location and the damping of the pressure transient due to the leakage. The model is verified with laboratory experiments in which the leak location can be narrowed down to be less than 10% to 30% of the total pipe length. The model is found to be more effective if the leak location is nearer to the upstream end. In addition, the leak location found by the damping model varies with an approximate absolute error of 2% to 5% of the pipe length. It is suggested that the damping model is suitable for narrowing down and not for finding the leak location, and should be used in combination with other leak detection methods.

Nowadays, a deterioration of floodplain water quality in the Lower Mekong River Basin in Cambodia is expected because of urbanization/industrialization by landfilling. This study aimed to evaluate the impact of floodplain landfilling on basin water quality. Field observations of total phosphorus (TP), chemical oxygen demand and heavy metals were conducted in the Mekong River Basin in Cambodia and the Chao Phraya River Basin in Thailand. In the Mekong River Basin, TP was 2.05 mg/L in the floodplain where large-scale landfill was carried out using waste, with iron (Fe) at the factory site 6.54 mg/L. In comparison, in the Chao Phraya River Basin, TP and Fe concentrations were low. A degree of floodplain water quality management commensurate to the level of economic development was confirmed from water quality conservation efforts, among others, in Thailand.

The objectives of this study were to improve the yield estimation of paddy rice based on the unmanned aerial vehicle remote sensing (UAV-RS) and solar radiation data sets. The study used the UAV-RS-based normalized difference vegetation index (NDVI) at the heading stage, the solar radiation data of geostationary satellite Himawari-8 and the solar radiation data of polar orbiting satellite Aqua/MODIS. A comparison of two satellite-based solar radiation data sets (Himawari-8 and MODIS PAR) showed that the coefficient of determination (R²) of estimated yield based on Himawari-8 solar radiation was 0.7606 while the R² of estimated yield based on the MODIS PAR was 0.4749. Additionally, the root mean square error (RMSE) of Himawari-8 solar radiation was 26.5 g/m² while the RMSE of estimated yield based on the MODIS PAR was 39.2 g/m² (The average observed yield was 489.3 g/m²). The Estimated yield based on Himawari-8 solar radiation, therefore, outperformed the MODIS PAR-based estimated yield. The improvement of the temporal resolution of the satellite-based dataset allowed by using the Himawari-8 data set contributed to the improvement of estimation accuracy. Satellite-based solar radiation data allow yield estimation based on remote sensing in regions where there are no ground observation data of solar radiation.

This study investigated runoff to clarify the effect of bedrock groundwater dynamics on runoff generation processes in granodiorite headwater catchments (NA and NB) located in the western Tanzawa Mountains, Central Japan. The rainfall–runoff response and water balance calculated using the hydrological cycle (HYCY) model with outflow were also analyzed based on the observed precipitation, runoff, and bedrock groundwater level (at a depth of 50 m). In 2013, the annual runoff rate was 398 mm (21% of the rainfall) in NA and 1209 mm (63% of the rainfall) in NB, respectively. The bedrock groundwater level varied for approximately 3 m, and responded to 30-mm rainfall events. The significant relationship between the base flow and bedrock groundwater level indicated that the bedrock groundwater markedly influenced base flow generation. The calculated annual bedrock infiltration values of 656 mm (34% of the rainfall) in NA and 52 mm (3% of the rainfall) in NB significantly influenced the runoff rate. Our results demonstrated that significant and negligible amounts of bedrock groundwater infiltration were observed, even in neighboring catchments. Those bedrock groundwater dynamics significantly influenced the observed differences in the runoff rate and base flow generation.