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Wang G.,Beijing Normal University | Hapuarachchi H.A.P.,International Center for Water Hazard and Risk Management | Takeuchi K.,International Center for Water Hazard and Risk Management | Ishidaira H.,Yamanashi University
Hydrological Processes | Year: 2010

Grid-based modelling is an effective approach for handling the spatial heterogeneity of basin characteristics, such as land use, soil, rainfall and topographical information. In this study, the grid-based block-wise use of TOPMODEL together with the Muskingum-Cunge (BTOPMC) model (block-wise use of TOPMODEL together with the Muskingum-Cunge) was improved by using an erosion module to estimate soil erosion and sediment outflow during storm events. Instead of representing a grid using a single erosion type, the model accounts for the erosion caused by both raindrop detachment in the sheet area as well as concentrated flow detachment in the channel area. The sediment transport process is simulated at the assumed river channel networks, which avoids the problems that are caused by the difference between the channel widths in the upstream and downstream areas. This also enables the model to be applicable in simulating soil erosion and sediment outflow from a large river basin. Geographic information system (GIS) techniques have been utilized in the model to delineate the river network and extract the basin information from the digital elevation model (DEM) data. Through a case study in China's Lushi basin, the improved BTOPMC model got an average Nash-Sutcliffe (NS) efficiency of about 86.1% in discharge simulations and an average NS efficiency of about 75% in sediment outflow simulations. Overall, the results show a satisfactory accuracy for all of the selected events. Moreover, by analysing the spatial distribution of soil erosion or deposition, the erosion-prone areas can be identified and prioritized. Copyright © 2009 John Wiley & Sons, Ltd.

Taylor R.G.,University College London | Scanlon B.,University of Texas at Austin | Doll P.,Goethe University Frankfurt | Rodell M.,NASA | And 22 more authors.
Nature Climate Change | Year: 2013

As the world's largest distributed store of fresh water, ground water plays a central part in sustaining ecosystems and enabling human adaptation to climate variability and change. The strategic importance of ground water for global water and food security will probably intensify under climate change as more frequent and intense climate extremes (droughts and floods) increase variability in precipitation, soil moisture and surface water. Here we critically review recent research assessing the impacts of climate on ground water through natural and human-induced processes as well as through groundwater-driven feedbacks on the climate system. Furthermore, we examine the possible opportunities and challenges of using and sustaining groundwater resources in climate adaptation strategies, and highlight the lack of groundwater observations, which, at present, limits our understanding of the dynamic relationship between ground water and climate. © 2013 Macmillan Publishers Limited. All rights reserved.

Pokhrel Y.N.,Rutgers University | Fan Y.,Rutgers University | Miguez-Macho G.,University of Santiago de Compostela | Yeh P.J.-F.,International Center for Water Hazard and Risk Management | Han S.-C.,NASA
Journal of Geophysical Research: Atmospheres | Year: 2013

We explore the mechanisms whereby groundwater influences terrestrial water storage (TWS) in the Amazon using GRACE observations and two contrasting versions of the LEAF-Hydro-Flood hydrological model: one with and the other without an interactive groundwater. We find that, first, where the water table is shallow as in northwestern Amazonia and floodplains elsewhere, subsurface stores (vadose zone and groundwater) are nearly saturated year-round, hence river and flooding dominate TWS variation; where the water table is deep as in southeastern Amazonia, the large subsurface storage capacity holds the infiltrated water longer before releasing it to streams, hence the subsurface storage dominates TWS variation. Second, over the whole Amazon, the subsurface water contribution far exceeds surface water contribution to total TWS variations. Based on LEAF-Hydro-Flood simulations, 71% of TWS change is from subsurface water, 24% from flood water, and 5% from water in river channels. Third, the subsurface store includes two competing terms, soil water in the vadose zone and groundwater below the water table. As the water table rises, the length of vadose zone is shortened and hence the change in groundwater store is accompanied by an opposite change in soil water store resulting in their opposite phase and contributions to total TWS. We conclude that the inclusion of a prognostic groundwater store and its interactions with the vadose zone, rivers, and floodplains in hydrological simulations enhances seasonal amplitudes and delays seasonal peaks of TWS anomaly, leading to an improved agreement with GRACE observations. ©2013. American Geophysical Union. All Rights Reserved.

Masood M.,Design Circle 1 | Takeuchi K.,International Center for Water Hazard and Risk Management
Natural Hazards | Year: 2012

Floods are regular feature in rapidly urbanizing Dhaka, the capital city of Bangladesh. It is observed that about 60% of the eastern Dhaka regularly goes under water every year in monsoon due to lack of flood protection. Experience gathered from past devastating floods shows that, besides structural approach, non-structural approach such as flood hazard map and risk map is effective tools for reducing flood damages. In this paper, assessment of flood hazard by developing a flood hazard map for mid-eastern Dhaka (37.16 km 2) was carried out by 1D hydrodynamic simulation on the basis of digital elevation model (DEM) data from Shuttle Radar Topography Mission and the hydrologic field-observed data for 32 years (1972-2004). As the topography of the area has been considerably changed due to rapid land-filling by land developers which was observed in recent satellite image (DigitalGlobe image; Date of imagery: 7th March 2007), the acquired DEM data were modified to represent the current topography. The inundation simulation was conducted using hydrodynamic program HEC-RAS for flood of 100-year return period. The simulation has revealed that the maximum depth is 7.55 m at the southeastern part of that area and affected area is more than 50%. A flood hazard map was prepared according to the simulation result using the software ArcGIS. Finally, to assess the flood risk of that area, a risk map was prepared where risk was defined as the product of hazard (i. e., depth of inundation) and vulnerability (i. e., the exposure of people or assets to flood). These two maps should be helpful in raising awareness of inhabitants and in assigning priority for land development and for emergency preparedness including aid and relief operations in high-risk areas in the future. © 2011 Springer Science+Business Media B.V.

Kwak Y.,International Center for Water Hazard and Risk Management | Iwami Y.,International Center for Water Hazard and Risk Management
ASPRS 2014 Annual Conference: Geospatial Power in Our Pockets, Co-Located with Joint Agency Commercial Imagery Evaluation Workshop, JACIE 2014 | Year: 2014

Near-real-time flood flood mapping is one of the most important parts of emergency response efforts. This paper aims to estimate extreme flood inundation area over the entire Bangladesh, where monsoon river floods are dominant and frequent, affecting over 80% of the total population. The authors improved a water-extent extraction method for a better discrimination capacity to discern flood areas from cloud and mixed areas by using a modified land surface water index (MLSWI) based on the Moderate Resolution Imaging Spectrometer (MODIS) 8-day composites (approx. 500m resolution) data. Flood areas in the Brahmaputra River were verified by comparing them with ALOS AVNIR2 (approx. 10m resolution) data. The results showed the superiority of the developed method in providing instant and accurate nationwide mapping of floodwater extent in the three main rivers for the 2007 extreme event in the Bangladesh.

Syamsidik,University of Syiah Kuala | Istiyanto D.C.,International Center for Water Hazard and Risk Management
Journal of Earthquake and Tsunami | Year: 2013

The challenge of protecting communities in tsunami-prone populated small islands is difficult to meet. Likewise, the islands are often found with a lack of disaster mitigation infrastructure. A tsunami that occurred around the Mentawai Islands of Indonesia on October 25, 2010, causing around 500 dead, is the inspiration for this paper. This study was aimed at elaborating practices in protecting communities of small islands from tsunamis by incorporating information about the estimated time of arrival of a tsunami into the islands mitigation measures. A field survey to obtain the impacts of the tsunami on the number of casualties and damages was conducted in February 2011 around the Mentawai Islands. In the survey, a set of questionnaires were distributed in the Mentawai Islands to investigate the small island residents' responses just after the shock from the tsunami waves. This study was also followed by numerical simulations to obtain tsunami wave Estimated Time of Arrival (ETA) for the Mentawai islands. Numerical simulations were conducted using Delft3D software coupled with Tsunami toolkit. This research found that the ETAs for the Mentawai Islands range between 9-20 min. With the existing tsunami early warning system in Indonesia, the ETAs are quite short. Comparing the Simulated ETAs to the findings from the Mentawai Islands tsunami survey led to the recommendation that the best way to increase the community's preparedness for a tsunami would be by managing village-based spatial planning. Such spatial planning may include relocating the residents far away from the coastal area. This would enable the community to have more time to evacuate should a tsunami threat occur. © 2013 World Scientific Publishing Company.

Vink K.,National Graduate Institute for Policy Studies | Vink K.,International Center for Water Hazard and Risk Management
Water International | Year: 2014

Vulnerable people require additional measures to ensure their water capabilities, as they have certain characteristics making them more vulnerable than others. As pointed out by recent studies, transboundary water access laws and policies do not sufficiently address the needs of vulnerable people. The prevailing legal arrangements often only address extrinsic vulnerability and forgo focusing on intrinsic vulnerability, which creates the need for different transboundary water legislation. This paper shows how international treaties can address the right to certain water capabilities by considering not merely the current but also future global populations into the creation of their transboundary agreements. © 2014 International Water Resources Association.

Vink K.,National Graduate Institute for Policy Studies | Takeuchi K.,International Center for Water Hazard and Risk Management
International Journal of Disaster Risk Reduction | Year: 2013

This paper focuses on measures taken for vulnerable people in Disaster Risk Management (DRM) laws in Japan, the Netherlands and the United States. As DRM laws were found to lack a definition of vulnerable people, an original working definition of vulnerable people in a community was defined.DRM laws and policies with a focus on flood disasters in Japan and the USA cover some groups of potentially vulnerable people who are supported during various phases of disaster management, such as elderly, children and people with disabilities. The basic disaster law in the Netherlands mentions 'not self-reliant people' during the response phase, and leaves further details to the regional safety plans. All countries lack clearly defined characteristics in the laws themselves as to who may be categorized among the various groups of potentially vulnerable people. Furthermore, there is little to no anticipation of expected increases in the amounts of vulnerable people.The support for vulnerable people in DRM laws has not been quantified on a global scale, even though the Hyogo Framework for Action called for the development of measurement tools in 2005. Further research should aim at developing tools with which to quantify the support of vulnerable people in DRM laws. © 2013 Elsevier Ltd.

Park J.G.,Tokyo University of Information Sciences | Harada I.,Tokyo University of Information Sciences | Kwak Y.,International Center for Water Hazard and Risk Management
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences - ISPRS Archives | Year: 2016

Topography and geology are factors to characterize the distribution of natural vegetation. Topographic contour is particularly influential on the living conditions of plants such as soil moisture, sunlight, and windiness. Vegetation associations having similar characteristics are present in locations having similar topographic conditions unless natural disturbances such as landslides and forest fires or artificial disturbances such as deforestation and man-made plantation bring about changes in such conditions. We developed a vegetation map of Japan using an object-based segmentation approach with topographic information (elevation, slope, slope direction) that is closely related to the distribution of vegetation. The results found that the object-based classification is more effective to produce a vegetation map than the pixel-based classification.

Masood M.,International Center for Water Hazard and Risk Management | Masood M.,National Graduate Institute for Policy Studies | Hanasaki N.,Japan National Institute of Environmental Studies | Takeuchi K.,International Center for Water Hazard and Risk Management
Hydrology and Earth System Sciences | Year: 2015

The intensity, duration, and geographic extent of floods in Bangladesh mostly depend on the combined influences of three river systems, the Ganges, Brahmaputra and Meghna (GBM). In addition, climate change is likely to have significant effects on the hydrology and water resources of the GBM basin and may ultimately lead to more serious floods in Bangladesh. However, the assessment of climate change impacts on the basin-scale hydrology by using well-calibrated hydrologic modeling has seldom been conducted in the GBM basin due to the lack of observed data for calibration and validation. In this study, a macroscale hydrologic model H08 has been applied over the basin at a relatively fine grid resolution (10 km) by integrating the fine-resolution DEM (digital elevation model) data for accurate river networks delineation. The model has been calibrated via the analysis of model parameter sensitivity and validated based on long-term observed daily streamflow data. The impacts of climate change (considering a high-emissions path) on runoff, evapotranspiration, and soil moisture are assessed by using five CMIP5 (Coupled Model Intercomparison Project Phase 5) GCMs (global circulation models) through three time-slice experiments; the present-day (1979-2003), the near-future (2015-2039), and the far-future (2075-2099) periods. Results show that, by the end of 21st century, (a) the entire GBM basin is projected to be warmed by ~ 4.3 °C; (b) the changes of mean precipitation (runoff) are projected to be +16.3% (+16.2%), +19.8% (+33.1%), and +29.6% (+39.7%) in the Brahmaputra, Ganges, and Meghna, respectively; and (c) evapotranspiration is projected to increase for the entire GBM (Brahmaputra: +16.4%, Ganges: +13.6%, Meghna: +12.9%) due to increased net radiation as well as warmer temperature. Future changes of hydrologic variables are larger in the dry season (November-April) than in the wet season (May-October). Amongst the three basins, the Meghna shows the highest increase in runoff, indicating higher possibility of flood occurrence. The uncertainty due to the specification of key model parameters in model predictions is found to be low for estimated runoff, evapotranspiration and net radiation. However, the uncertainty in estimated soil moisture is rather large with the coefficient of variation ranging from 14.4 to 31% among the three basins. © Author(s) 2015.

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