Yutaka Ichikawa

Scenario-based Impact Assessment of Land Use/Cover and Climate Changes on Water Resources and Demand: A Case Study in the Srepok River Basin, Vietnam—Cambodia

This study investigates an interdisciplinary scenario analysis to assess the potential impacts of climate, land use/cover and population changes on future water availability and demand in the Srepok River basin, a trans-boundary basin. Based on the output from a high-resolution Regional Climate Model (ECHAM 4, Scenarios A2 and B2) developed by the Southeast Asia—System for Analysis, Research and Training (SEA-START) Regional Center, future rainfall was downscaled to the study area and bias correction was carried out to generate the daily rainfall series. Land use/cover change was quantified using a GIS-based logistic regression approach and future population was projected from the historical data. These changes, individually or in combination, were then input into the calibrated hydrological model (HEC-HMS) to project future hydrological variables. The results reveal that surface runoff will be increased with increased future rainfall. Land use/cover change is found to have the largest impact on increased water demand, and thus reduced future water availability. The combined scenario shows an increasing level of water stress at both the basin and sub-basin levels, especially in the dry season.

Evaluation of the state of water resources using Modified Water Poverty Index: a case study in the Srepok River basin, Vietnam – Cambodia

In order to evaluate clearly the state of water resources in the Srepok River basin – a typical rural area in South-East Asia, a Modified Water Poverty Index (MWPI) was developed. Indicators of five components of MWPI were evaluated using the benchmark approach. The cross-correlation among indicators of each component as well as among components were checked; and the high-correlated indicators were eliminated. The calculated MWPI and its components were then mapped and analysed to three different scales (basin, sub-basin and district). From the overall MWPI score, a general conclusion was drawn on the water poverty situation in the basin. The results reveal the variation of water poverty across the basin with the overall MWPI of 64.8, indicating that the basin is in a ‘medium-low’ water-poor situation. ‘Access’ and ‘Capacity’ components are observed to be the main causes of the water problem in the basin. There is a high disparity among the five components of MWPI when spatial and temporal variation of variables is taken into account. It is recommended that the state of water resources should be assessed based on the components rather than the composite index. The differences that scales make indicate the importance of selecting an appropriate scale for water resources assessment. By using the benchmark approach, the pertinence of MWPI results are improved and the potential for wider applicability can be extended. By examining the indicators in the five components, a policy for water development and management is proposed and specific interventions recommended. This result can provide useful information for decision-makers in prioritizing investments in the water sector.

Drought Impacts and Adaptation Strategies for Agriculture and Rural Livelihood in the Maharashtra State of India

Nearly one-sixth of India is defined as a Drought Prone Area, and as such recurring drought is one of the major challenges in the region. This article focuses on various drought impacts in an important state of India (i.e. Maharashtra State), which contributes about 15% of the country’s gross domestic product (GDP). Drought impacts vary from region to region, but the overall issues are similar and Maharashtra State is indicative of the rest of the Drought Prone Area of the country. This article briefly reviews the major impacts of the 2012 drought on Maharashtra State’s water resources, agriculture, food security, adopted adaptation and mitigation measures and also outlines scope for future research.

A spatial impact assessment of human-induced intervention on hydrological regimes: a case study in the upper Srepok River basin, Central Highlands of Vietnam

The objective of this study is to assess the impact of human activity on hydrological regimes in the upper Srepok River basin, Central Highlands of Vietnam. For this purpose, specific flow and water demand for each sub-basin were first estimated and then input into the calibrated river basin management model (MIKE Basin) to generate flow data. Future land use/cover was predicted using a geographic information system (GIS)-based logistic regression approach and the population projected from historical data. The hydrologic impact of human intervention was evaluated using the indicators of hydrologic alterations method and the range of variability approach under various developed scenarios. The results show that the overall hydrologic alteration (HA) values are classified as being moderate at all reaches; they generally increase from the upstream to the downstream reaches. Flow regimes have been altered along the river under the accumulated impacts of the operations of cascade dams. However, the impacts of land-use/cover change and population growth have been found to be greater at most of the reaches. The combined scenario shows that the HA of the Srepok 3 dam downstream reach is highest (75.7%), followed by the downstream reaches of Srepok 4 (65.8%) and Buon Koup dams (43.7%). Low flow, extreme flow, and frequency and rate of change are found to be the most alterative indicators. When environmental flow is considered, the HA of all reaches are reduced, and low and extreme flows are the most reductive indicators. It has been suggested that the trade-off between instream and offstream objectives should be considered in water allocation. The results of this study would be greatly important for future understanding of the human impact on hydrological regimes.

A FLOOD RISK CURVE DEVELOPMENT USING CONDITIONAL PROBABILITY DISTRIBUTION OF RAINFALL ON DURATION

To design integrated flood risk management, flood risk assessment based on the economic damage is essential. In previous studies, the authors have developed a method to estimate a flood risk curve considering spatio-temporal distribution of rainfall by applying the Synthesis Probability Method (SPM) that estimates probability function of annual maximum flood peak discharge (AMF). Recently, the SPM was improved by introducing the relation between total rainfall and the duration time, and the estimated probability distribution of AMF with the improved SPM showed a better agreement with the probability distribution of observed AMF. This study extended the improved SPM to flood risk curve development and estimated a flood risk curve of the Ayabe city in the Yura-gawa River basin.

Rural drinking water issues in India’s drought-prone area: a case of Maharashtra state

Obtaining sufficient drinking water with acceptable quality under circumstances of lack, such as droughts, is a challenge in drought-prone areas of India. This study examined rural drinking water availability issues during a recent drought (2012) through 22 focus group discussions (FGDs) in a drought-prone catchment of India. Also, a small chemical water quality study was undertaken to evaluate the suitability of water for drinking purpose based on Bureau of Indian Standards (BIS). The drought that began in 2011 and further deteriorated water supplies in 2012 caused a rapid decline in reservoir storages and groundwater levels that led, in turn, to the failure of the public water supply systems in the Upper Bhima Catchment. Dried up and low-yield dug wells and borewells, tanker water deliveries from remote sources, untimely water deliveries, and degraded water quality were the major problems identified in the FGDs. In addition to severe drinking water scarcity during drought, the quality of the drinking water was found to be a major problem, and it apparently was neglected by local governments and users. Severe contamination of the drinking water with nitrate-nitrogen, ammonium-nitrogen, and chlorides was found in the analyzed drinking water samples. Hence, in addition to the water scarcity, the results of this study point to an immediate need to investigate the problem of contaminated drinking water sources while designing relief measures for drought-prone areas of India.

COST-BENEFIT ANALYSIS OF LANDUSE REGULATION STRATEGY BASED ON FLOOD RISK ASSESSMENT USING A LOCATION EQUILIBRIUM MODEL INCORPORATING HOUSEHOLD INCOME DISTRIBUTION

流域管理的治水対策の費用便益評価を行う枠組みの中で，世帯の所得分布を考慮できるように立地均衡モデルを拡張し，これを用いて寝屋川流域における土地利用規制の費用便益評価を行うとともに，土地利用規制が世帯に与える影響を所得の違いに応じて分析した．その結果，土地利用規制の影響は各所得層で異なることが明らかになった．所得に対する費用の割合は所得が低いほど大きく，低所得層の負担が大きくなることがわかった．また，再現期間で5年（時間45mm程度）相当の弱いレベルの土地利用規制で総便益が最大となり，再現期間で25年以上の強い土地利用規制を実施した場合は，費用が便益を上回る結果となった．以上より，本流域では，比較的高い頻度で浸水する地区の住宅地としての利用は避けた方がよい可能性のあることが明らかとなった．

COST-BENEFIT ANALYSIS OF BUILDING REGULATION BASED ON FLOOD RISK ASSESSMENT AND ITS COMPARISON TO LAND USE REGULATION

本研究では，大阪地域と東京地域を対象として，水災害危険度に基づいて建築規制を実施した場合に生じる費用と便益を比較することで，建築規制の利害得失や適用性について検討した．その結果，いずれの地域においても，今回検討した範囲では建築規制の総便益は正となり，建築規制は水防災対策として一定程度の適用性を有していること，大阪地域のほうが東京地域より建築規制の総便益が大きくなり，比較的少ない負担で効果的に水災害被害額を減少させうることが明らかとなった．さらに，同じ地区を規制対象とする建築規制と土地利用規制を比較したところ，建築規制のほうが土地利用規制より総便益が若干大きいか同程度となることがわかった．このことから，建築規制は床下浸水を許容する土地利用規制とほぼ同程度の適用性を有していると考えられる．

A REAL TIME DAM INFLOW PREDICTION SYSTEM BASED ON DISTRIBUTED RAINFALL-RUNOFF MODEL

Today, we can get high quality information about spatial distribution of rainfall observed by radar on real time. In order to make effective use of such a spatial rainfall information, and to improve the flood forecasting accuracy for dam operation, we developed a real time dam inflow prediction system based on distributed rainfall-runoff model. In our system, channel flow is calculated by using the integrated kinematic wave model for channel networks, and the state of channel flow is updated with Kalman filter. Simulations are carried out with dam inflow data and precipitation data observed by rain gauges, and it was confirmed thatthe prediction system performs well.

Scale-up of a Distributed Runoff Model

To consider the interaction between runoff process and meteorological one, a methodology to scale up a distributed runoff model is developed.In our methodology, the stream network is regarded as a set of sub-networks devided by grids whose size is so large as to be compatible with meteorological scale. The model of flow within these sub-networks and its numerical solution algorithm are given.