The numerous lakes found throughout the Tibetan Plateau have a large effect on evaporation from the plateau. We analyzed variation in the water cycle in Yamdrok Yumtso Lake basin under the temperature increase of 1.13°C during the 45 years from 1961-2005. Both vapor pressure and relative humidity increased by approximately 17%, resulting in a 13.7% increase in longwave radiation flux and a smaller daily range of surface air temperature. A 5.7% decrease in sunshine duration caused solar radiation flux to decrease by 3%. Heat and water balances were simulated over land and the lake. The lake covers 10% of the total basin area. Evaporation from the lake was larger than that from land, with lake evaporation making up 26% of the basin total. Evaporation from the lake decreased 7% (May-September) over the study period, and observed small pan evaporation also decreased. This trend was not found in the evaporation from land and from precipitation. With water vapor in the air increasing and evaporation from the ground surface (lake and land) decreasing, the water vapor may have come from areas outside the basin and possibly even beyond the plateau.

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Flooding is one of the major risks anticipated to increase in association with anthropogenically induced climate change which is likely to intensify the global water cycle. Currently, 20 to 300 million people per year are affected by floods that threaten both social security and sustainable development. This study presents the first estimate of future populations at risk of flooding. Results indicate that in the case of 3°C warming from the average of 1980-1999, approximately 300 million people could be at risk even in years of relatively low flooding; this number corresponds to the number of people affected in a devastating flood year at present. If the temperature increase is greater than 3°C, the flood-affected population would likely be even larger. We suggest that approximately 2°C warming, rather than 3°C warming, should be considered the critical level of temperature increase.

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Measurements of CO₂ flux (FCO₂) and H₂O flux (FH₂O) were carried out on paddy fields of Thailand and Japan during the 2004, 2005 and 2006 growing seasons using the Bowen ratio technique. The objective was to determine the water resource requirement to achieve a certain amount of CO₂ assimilation per land area and analyze the ratio between FCO₂ and FH₂O (CWFR = FCO₂/FH₂O). The relationship between FCO₂ and FH₂O was investigated using regression analysis in 4 growing stages. Relatively high correlations (r² = 0.56-0.96, p < 0.01) between FCO₂ and FH₂O were found when data were grouped by growing stage. Using daytime average data, there was high correlation (r² = 0.61-0.94, p < 0.01) between daytime average CWFR (CWFR_d) and daytime average vapor pressure deficit (VPD_d) in paddy fields of Japan and Thailand for each growing stage. Pooled data from Thailand and Japan showed high correlations (r² = 0.61-0.94, p < 0.01) between CWFR_d and VPD_d for each growing stage. The developed regression equation was tested using an independent published dataset, and it was found that the estimation error was only 2.7%. The regression equations will be useful for estimating CWFR_d by only VPD_d and accordingly for assessing the water resource requirement.

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The recent population increase and economic development have increased the energy demand in many countries. As global fossil fuel reserves are limited, it is highly likely that the supply of fossil fuels will come under increased pressure and the development of alternative energies throughout the world will become essential. Assuming a Japanese population of 64 million in 2100 with a 20% increase of the power demand per capita from the present level, we studied the electric power supply and demand situation in 2100 by conducting the trial calculation of the maximum development potential of hydroelectric energy, a renewable energy produced in Japan. The findings indicate that the hydroelectric generation capacity can reach approximately 190 billion kWh/year, which is 1.97 times that of 2005 levels. This would be achieved by raising the height of existing dams and flexibly operating dams for power generation in harmony with the flood control and water supply for agricultural and other usage. Presupposing the completion as planned of the nuclear power plants currently under construction and a fivefold increase of the total output of wind power and other alternative power generation sources, it is concluded that a stable power supply will be possible in 2100 without dependence on fossil fuels.

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To understand the inter-annual and spatial variation of altitudinal increase in rainfall amount, duration and intensity over Doi (Mount) Inthanon and Mae Chaem Watershed, Northern Thailand, we have conducted rainfall observations in this area since 1997. Ten years of continuous data for 18 rain gauge stations were accumulated. Altitudinal increases in rainfall were observed for all nine years. Annual rainfall hours also had an altitudinal increase, whereas mean rainfall intensity had no clear altitudinal increase for the nine year period. Not only altitudinal rainfall increase but also inter-annual rainfall fluctuation was determined from the variations of rainfall hours. There was no difference in the intensity of altitudinal increases in rainfall between the western and eastern slopes of Doi Inthanon.

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In this study, the amount of domestic water use was quantified by estimating the usage rates of various water-related appliances. Tokyo Metropolis was selected as a case study because it was relatively easy to obtain detailed data from Tokyo Waterworks Bureau. In the analysis, the calculations for domestic water use reproduced actual usage figures from 1998 to 2006. From the maximum domestic water use per capita in 1997 the projected reduction was estimated to be 9% by 2025 and 10% by 2050. In addition, our results indicate that water use for both bath and toilet is expected to remain high in the future. We performed a simulation assuming that a 6 L-type toilet is installed by all consumers, with the results suggesting that domestic water use per capita per day could reduce to around 200 L. It was therefore concluded that the replacement of a conventional toilet with a water-saving-type toilet is one of the most effective solutions for reducing domestic water use.

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The objective of the study is to develop a GIS-based water infrastructure inventory (WII) for water resources assessment in the upper Srepok basin, Vietnam. The water availability and demand were estimated using common methods. Different water scarcity indicators were estimated to examine the water situation at district level under present and future conditions and future water development needs are assessed. Results reveal that the aggregated information on the basin scale misleads the issue of water situation, especially the scarcity at local level due to high spatio-temporal variations of water resources availability and demands. Most districts in the study basin will experience severe water scarcity in 2010 and 2020 in both physical and economic terms. Generated data from the WII shows very low percentage of water withdrawals in several districts with respect to available resources. Therefore, to meet future demand, significant investment in water infrastructure is needed.

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Stemflow was measured in a planted young stand of Japanese cypress for four years from ages 9 to 12. Canopy cover increased with growth from 55% to 94% during the measurement period. The ratio of stemflow SF to rainfall R, SF/R (the funneling ratio FR that represents the efficiency in collecting stemflow), was 5.9% (81.3) at age 9 on an annual basis; however, it abruptly fell to 2.8% (30.0) at age 10. Following the drop, SF/R recovered gradually with growth, reaching 3.8% at age 11 and 4.3% at 12, while FR remained almost constant at values of around 30. The relation between R and SF/R analyzed quarterly on a rain event basis revealed that changes in canopy structure and/or tree architecture caused the drop in SF/R in the April-June period at age 10. Saplings of the species must compete for light and water until canopy closure because their growth rate is slower than that of competitors. As stemflow effectively supplies rainwater into the soil around the root system, it can be hypothesized that large SF/R and FR at age 9, and probably younger ages, are a strategy to acquire water for juvenile unclosed stands in dry summers.

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Soil loss plots on open and under canopy sites were installed to study the effect of the canopy on interrill erosion. The erosion rate under the canopy was smaller than that on an open site, and it was highly correlated with the maximum rainfall intensity for 3 hour and total rainfall, independent of the slope angle. The throughfall rate showed a relatively continuous value under high rainfall intensity conditions, although varied with rainfall intensity. When the throughfall rate was initiated at a relatively continuous value, the rainfall intensity was very similar to the threshold of rainfall intensity for erosion under a canopy. These results imply that the canopy storage had been changed due to the rainfall intensity, and this change affected the interrill erosion under the canopy. These results will contribute to the development of an erosion prediction model under a forest canopy.

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A reliable, practical method for estimating the evapotranspiration associated with rice cultivation is vital for proper water management in Thailand. We investigated the possibility of estimating rice-related evapotranspiration using only daily air temperature and wind speed, as a practical method for local application in Thailand. By applying regression analysis to a theoretical investigation, we developed a set of daily based equations that estimated evapotranspiration of rice cultivation for a typical Thai plains environment during the rainy season. The estimation error of the developed equations was approximately 20% on a daily scale, and 10% on a weekly scale. Although additional validation of the derived equations is needed for application at other location and at other times of the year, the developed equations show potential for use in water management of cultivation in Thailand.

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The plains on the lowlands surrounding Lake Biwa, Japan, have long been used for rice (Oriza sativa L.) cultivation. In this study, we investigate the fate of herbicides commonly used in this agroecosystem. During the spring, the highest concentrations of simetryn, mefenacet, bromobutide and dymron were detected on the lake’s surface and at the mid-depth (20 m), indicating that agricultural runoff enters the lake and directly affects its water quality. Our findings also suggest that these contaminants might serve as an indicator of the transport pathways of some agricultural pollutants into the lake.

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Changes in future weather extremes are projected using a global atmospheric general circulation model and a non-hydrostatic regional climate model under the global warming environment in the near future (2030s) and at the end of the 21st century. The global 20-km mesh model can simulate tropical cyclones more realistically in their strength, structure and geographical distribution together with associated heavy rainfall and strong surface winds as compared with lower resolution models. According to the SRES A1B scenario, it is projected that at the end of the 21st century there will be a 40%∼60% increase in precipitation and a 15%∼20% increase in surface wind speeds within a 100 km radius of the tropical cyclone center. Ensemble simulations using the global 60-km model version are performed to obtain information on the uncertainty of projections. Downscaling with the 5-km mesh non-hydrostatic regional climate model is also performed for the Japanese summer rainy season. It is found that the frequency of heavy precipitation will increase in the future for the hourly as well as daily precipitation. In particular, the strong hourly precipitation will increase even in near future: 99.9%-ile value of hourly precipitation increases 7% in the near future and 21% at the end of the 21st century.

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