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1. Introduction
In the event of an eruption, the water environment may be contaminated with released volcanic ash. Therefore, quantitatively grasping to what extent the volcanic ejecta discharged by the eruption is affecting the water environment is supposed to occur in the future in the event of an eruption disaster that is considered to occur Connect. Based on this, I started studying how the eruption that occurred in Owakudani in Hakone on June 29, 2015 influences the surrounding water environment.
2. Results and Discussion
1. Muddy of a river
Owakasawa, which became turbid by the eruption, caused the mainstream HayaRiver to become cloudy, and the turbidity of Hayakawa continued to the downstream. As time passes since the eruption the turbidity of Hayakawa is almost gone.
2. EC ・ pH of river
In Oowakusawa, high EC ・ low pH of 6,780 μS / cm, pH 2.4 was observed in the investigation immediately after eruption. In the long term, EC of Oowakusawa is declining, and higher values are observed for pH as compared with immediately after the eruption. In main line HayaRiver, influence of Oowakusawa appears in EC slightly at the point after Oowakusawa merger.
3. Major dissolved components
In Oowakusawa, cations contained a lot of Ca²⁺ at the time of survey in July 2015, and the anion occupied most of Cl^- and SO₄^2-. However, there is a tendency that Cl^- decreases with the passage of time from the eruption. Regarding the influence on the main stream Hayakawa, in the July 2015 survey, the Cl^-/TAni at the point after the Ohakakazawa merger is high, and the influence on the mainstream is seen.
4. Rainwater
High EC, low pH is observed at the point near Owakudani, and influence of volcanic gas is considered.

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In order to clarify the water balance in the forest area, the annual amount of canopy interception in the Sugi plantation forest was estimated. It was found that the estimation formula in consideration of the rainfall intensity and the evaporation intensity is better in the reproducibility than the regression expression using only the simple rainfall amount. Furturemore, the evaporation coefficient during the rainfall for each rainfall event was roughly agrees with the value of LAI and was proportional to the rainfall intensities.

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As a method of estimating effective rainfall, Yamada et al have proposed a method considering distribution characteristics of water holding capacity in the basin.But the theory of water retention capacity is based on a deterministic viewpoint and the uncertainty of loss rainfall curve is not taken into account.
Therefore, in this study, Cheng, derived Fokker-Planck equation using effect rainfall derived from water holding capacity theory on the basis of Yoshimi and Yamada, Cheng s study.The validity of the theory was verified by comparing this with the Ensemble calculation result using effective rainfall to the input rainfall of the probability differential equation of rainfall runoff.From the obtained results, validity of the proposed theory in this paper was demonstrated.

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Vu Gia and Thu Bon (VGTB) river basin is one of the most important river basin in the central Vietnam as it sustains local economy. In recent decades, the socioeconomy in the region has been rapidly expanding along with the ongoing growth of GDP in the country. In order to support the socioeconomic expansion, several major projects of constructing dams for producing hydroelectric power have been pushed forward in the VGTB. While construction of such infrastructures has brought substantial profits to the region, the region has started to face serious issues in flood risk management because socioeconomic expansion resuted in increase in economic value within VGTB and therefore the region became more vulnerable to flood hazard. As there are no flood control dams in the basin, use of existing dams for water resources is the one of possible options to improve the flood risk management. Considering this background, the present study aims to investigate the effectiveness of hypothetical dam pre-release for reducing the flood damage in downstream.

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Flood awareness and response may differ across many regions based on cultural context and availability of resources. To capture this, we designed a questionnaire and conducted survey interview in the Marikina River Basin, Philippines. We used the available flood hazard map and selected four (4) communities in Rodriguez, San Mateo, Marikina and Pasig within the Marikina River basin catchment that have experienced the catastrophic event in 2009. The total of number of individuals (N=205) were interviewed face-to-face to know how these communities were able to remember and responded to that event. Results revealed that 94% of the entire sample were able to remember the date and year. But interesting results on their actions taken at that time differed from each community. In Rodriguez there were only 50% of the residents who evacuated and 39% stayed home. Some survey results will be applied in socio-hydrological model particularly the social memory equation.

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This research aims to determine the effect of climate and societal changes in water availability of two watersheds in PPC, quantifying the effects on the annual as well as the seasonal availability of water. Soils and Water Assessment Tool (SWAT) was used to assess the potential of two sources. Climate data were acquired from PAG-ASA (baseline) and ISIMIP-FT framework (climate change) available at the NIES server. Water demand is base from the historical and projected population and tourist arrival. Initial analyses showed an over-extraction of water on the current source in the early months each year (2012-2016). In addition, a decrease in river flow from February-October is evident in all RCP scenarios while the demand continues to increase because of the increase in population as well as in tourist arrival. Further analyses will determine when are the over-abstractions occur to contribute to better water resource management decision.

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Even though both of generation and expansion of forest fire depends on soil moisture and wind, mechanisms of how soil moisture affects fire is not clarified. Therefore, stem bark char height of burnt trees were broadly investigated in this study.

Target are of this investigation is Kamaishi where large scale fire event occurred. The burnt area was 430ha which is larger than total burnt area in Japan in 2016. Since the degree of fire was shown in tree stems as stem bark char, totally 1125 points of stem bark char height were measured.

As a results, stem bark char height shown clear difference of degree of burnt, specially near Aodashihama. As for the direction of scars, they showed wind direction and movement of fire expansion. However, when slope is steep, the direction tends to slope direction.

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For Toyama prefecture, snow is a precious water resource that must be indispensable. However, snow melting water is very susceptible to weather conditions, and there are concerns about the influence on the hydrological and water resources associated with recent precipitation patterns due to global warming and changes in melting snow.Long-term water cycle analysis using IFAS was carried out and the accuracy was evaluated taking snowmelt into consideration.

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Recent years heavy rainfall was analyzed to consider an adaotation plan of disaster mitigation. A relathionship between antecedent precipitation index rain and hourly rainfall was examined in Tohoku-district heavy rainfall events. As result, it was possible to set the standard heavy rainfall value of disaster.

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This research aims to analyse the risk characteristics of all prefectures in Japan, focusing on (1) return period and severity of disaster which is main factor of the risk, and (2) relation between the risk value and the total asset of each prefecture. From the analyses of risk curves, we clarified that there are prefectures whose main risk factor is rare big damage with return period of 50-100 years (group-A), and those whose main risk factor is frequent small damage with return period of less than 10 years (group-D). Prefectures in group-A tend to have large total asset values, and the risk values are relatively small compared with them. In contrast, prefectures in group-D tend to have small total asset values, and the risk values are relatively big compared with them. This difference of risk characteristics and possible budget amount should be considered in the future strategies of risk management.

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River flooding causes billions of USD every year, its risks are expected to increase due to climate change, subsidence and socio-economic development. However, previous studies on global flood risks have estimated direct flood damage alone, they have not estimated indirect flood losses. To quantify global flood loss and damage, this study develops downscaling method of flood depth deriving from a global river and inundation model to flood depth, flooded area fraction, and flooded period at 1 km horizontal resolution. We compared downscaled flooded period with that estimated by a satellite observation in the case of Thailand in 2011, the model showed good estimation when considering flood protection level and river mask.

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Sediment disasters tend to take place at steep slope. Therefore, Japan where mountains occupy almost 70% of area is inherently vulnerable against sediment disasters. Rain is one of the triggers to generate sediment disaster and rainfall amount is widely used for a index of occurrence of sediment disaster. However, rain fall amount as an index gives alert to wider area than actual. Moreover, steepness of slope, soil depth and shear strength in soil affect occurrence of sediment disaster.
In the present study, we propose a system to give probability of occurrence of sediment disaster with 100m mesh scale by taking the following three indices, radar rainfall information, artificial structure and fragility of soil. Then, the system gives region specific risk of sediment disaster. Moreover, the system shows the probability of sediment disaster on GIS with colored map.

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This study was conducted to ascertain educational effects of water quality surveys for students to be nursing teachers. The discussion parts of the students’ reports were analized by a method of text mining to grasp their understanding level on the importance of the surveys. Results show that frequently appearing words were "water", "river", "beautiful", "dirty", "tap water", "many", "thinking", "in water", "high" in decending order, and these words were included in numerous descriptions. Many descriptions were related to "grasping the importance of water quality survey", "being able to check the water quality by changing the color of transparent water by reagent", "water safety", and "chlorine disinfection". It is indicated that the students have deepened their recognition on the water quality and its safety through the survey exercise. It is confirmed that incorporating the water quality survey into the curriculum increases educational effects and enhances the understanding of the water quality.

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