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Presentation Mode : All
Conference Day : 05/08/2021
Time Slot : AM2 11:00 - 13:00
Sections : HS - Hydrological Sciences










Hydrological Sciences | Thu-05 Aug




HS19-A013
Evaluating the Pluvial Flood Using Monitoring and Modelling in a Lowland Urban Area with the Drainage System Composed of Sewer and Open Channel Networks

Aung Khaing MIN1+, Takashi TASHIRO2#
1Water Supply and Sanitation Division, Building Department, Ministry of Construction, Myanmar, 2Disaster Mitigation Research Center, Nagoya University, Japan


Pluvial flooding is an inevitable problem in an urban area, particularly in cities situated in lowland areas. The causes of pluvial flooding are difficult to identify because there are many complex factors that influence this phenomenon, such as extreme rainfall, urbanization, inadequate drainage system, improper solid waste management, and variations in the water level of receiving water bodies. Conventional studies employed only numerical methods to analyze the pluvial flood problem, which could not clearly reflect the causes and severity of pluvial flooding.  In the present study, the InfoWorks ICM and multiple water level loggers were used, respectively for modelling and monitoring to investigate the occurrence of pluvial flooding in the city with the drainage system composed of sewer and open channel networks. The monitoring results showed that the water levels of receiving water bodies, and garbage blockages in the drains and trash screens affected the severity of pluvial flooding in addition to extreme rainfall. It was conventionally reported that the numerical model taken into account of sewer network could not reflect the severest time and distribution of practical inundations in such locations. However, our simulation results could spatiotemporally reflect most of the inundation situations in the investigated area. Consequently, the proposed approach using monitoring and modelling proved to be useful for identifying the occurrence of pluvial flooding and providing quantitative data for flood risk management.

HS19-A015
Relationship Between Location of Ancient Shrines and Hazard Map for Flooding in Chikuma-gawa River

Tetsuya YAMAGUCHI#+, Toshiyuki MORIYAMA, Kei ARAMAKI
Fukuoka Institute of Technology, Japan


The Chikuma-gawa River in Nagano Prefecture is one of the most frequent flood disasters river in Japan. In the past 400 years, 27 times floods have been recorded in the Chikuma-gawa River of the Nagano Valley. In particular, the 1742 floods recorded the largest area with flooding, resulting in more than 2,800 deaths. Records before 1742 were few, and there were no detailed records of flooded areas or water levels. However, the 2019 floods was the second largest after the 1742 floods, and there are concerns that flood damage caused by global warming will increase in the future. On the other hand, the River Bureau of the Ministry of Land, Infrastructure, Transport and Tourism has created a flood prediction hazard map for Chikuma-gawa River and warned . However, compared to past floods, we were not sure if the predicted hazard area with flooding is appropriate. In the future, it will be necessary to refer to the maximum area with flooding of the past 1,000 years.There are many old shrines in the Nagano Valley. About 1,100 years ago, an official lists of shrines were created in Japan, and the shrines listed on that lists were called "Shikinaisya". In addition, the old shrine which was not described was called "Shikigesya". When the location of these shrines were compared to the predicted hazard area with flooding in the Chikuma-gawa River, it was found that many shrines were outside from the predicted hazard area except for some shrines. It also found that all shrines in the predicted hazard area have been swept away by flooding in the past and after that they have been rebuilt. This fact indicates that hazard map for flooding which is obtained from predicted precipitation with statistic method and terrain analysis are likely to match historical flood records.

HS19-A018
Extreme Precipitation Analysis Using d4PDF - An Examination of the Frequency of Rainfall Once in 100 Years in Japan -

Hajime YANAGISAWA#+, So KAZAMA, Yoshiya TOUGE
Tohoku University, Japan


Due to the effects of global warming, extreme precipitation, which causes enormous damage, is increasing in Japan. The aim of this study was to determine how often annual extreme daily precipitation (AEDP) events, referred to as once-in-100-year events, occur in Japan. Hence, the frequency of spatial occurrence of AEDP events in the country was analyzed using database for policy decision-making for future climate change as the precipitation data. The analysis included a large ensemble analysis that cannot be obtained from point precipitation and radar rainfall data, such as AMeDAS. Using the best-fit generalized extreme value distribution according to standard least-squares criterion, we calculated the probability precipitation for every 20 km mesh and derived the frequency of spatial occurrence of once-in-100-year-AEDP events in Japan. The results indicate that a once-in-100-year AEDP occurs once in about 1.65 years in the country. Moreover, we predicted that this frequency may increase to up to once in approximately 1.1 years with representative concentration pathway (RCP) 8.5. The mean area of occurrence of AEDP events with a 100-year return period was 10 meshes (about 4,000 km2), and the median area was 2 meshes (about 800 km2). The difference between the median area and the mean area represents the variation in the area of extreme precipitation from year to year. We also evaluated the frequency of extreme precipitation by comparing the return period and the return area.

HS19-A021
Modelling Water Loss Control Interventions in Urban Water System from a Water-energy-environment Nexus Perspective

Seo Hyung CHOI, Eunher SHIN#+
UNESCO International Centre for Water Security & Sustainable Management, Korea, South


Nexus has been highly postulated by researchers and decision-makers because it represents the interlinkages and interdependencies between sectors such as water, energy, food, land use, climate, and environment. Also, Nexus makes the decision-making process more sustainable by identifying potential synergies and minimizing trade-offs between sectors.The urban water systems generally consist of intake-conveyance-water treatment-transmission-distribution-end use-wastewater collection-wastewater treatment-water reuse process. When municipalities or water authorities establish strategies and interventions for water loss control in the urban water systems, they only consider outputs in the water sector. This study developed the urban water system model using system dynamics to derive the urban water loss management plan from the Water-Energy-Environment Nexus perspective. To quantify the consumption and transfer of resources between sectors, water footprint, total energy use, and carbon footprint are applied as indicators of water, energy, and environment, respectively.The developed model was analyzed by applying 12 scenarios considering three urban energy intensity levels (low, medium, high) and four water loss levels (good condition, high NRW&low AL, high NRW&medium AL, high NRW&high AL). Reducing apparent losses was prioritized in the conventional economic-oriented water loss control program. However, handling real losses takes a top priority from the Nexus perspective. Besides, it was proved that the energy intensity for unit urban water supply had a significant impact on resource consumption and transfer. Therefore, it should be considered an essential factor to be analyzed in advance. A sustainable, systematic, and feasible water loss management is expected to be possible through this generalized and holistic urban water-energy-environmental Nexus model.

HS19-A006
Assessment of Effects of Effluent Patterns on the Hypoxia Development Due to Climate Change in the Ariake Sea, Japan

Hao LIN+, Shinichiro YANO#, Sato YUYA, Haraguchi NANAKO, Yasuyuki MARUYA
Kyushu University, Japan


A lot of studies have shown that changes in precipitation patterns, as one of consequent of climate change, are driving the change of river and marine system. The Ariake Sea is considered as an estuary or inner bay-type region of freshwater influence (ROFI) located in Kyushu Island, western Japan, which is one of the most important shallow sea for fisheries and seaweed production. In recent years, extreme flooding events occurred frequently in Japan. Very large river discharge will cause decrease of salinity and density stratification, which may generally prevent vertical supply of dissolved oxygen (DO) from surface layer to bottom one and can promote the development of hypoxia near the sea bottom. The degradation of water quality may cause serious damage to the fisheries. For proposing the adaptation, this study conducted different scenarios of flood patterns to evaluate the development of hypoxia by coupling the three-dimensional hydrodynamic model (Delft3D-FLOW) and the ecosystem model (Delft3D-WAQ) in the bay. By comparing with the magnitude, duration and the number of peak flows in each flood pattern at the central area of the bay (Sta.B3, monitoring site by MAFF, JAPAN), the internal of branch of the bay: Isahaya Bay (Sta.B6, i.q.), and the northern head of the bay (Sta.A), it could be shown that the duration and peak discharge of effluent can significantly affect the development of hypoxia in the bottom layer. Meanwhile, the enhancement of peak river discharge and duration of flood due to the climate change can affect marine benthic ecosystem through variation of tempo-spatial scale of hypoxia. Especially, at Sta.B3 and Sta.A, the development of hypoxia is more vulnerable to the effects of effluent patterns.

HS19-A001
Modelling of pCO2 dynamics in a shallow coastal water considering effects of stratification

Bing XIONG1+, Naoki SAITO1, Hiroto KOMORI1, Shinichiro YANO1#, Keisuke NAKAYAMA2, Katsuaki KOMAI3
1Kyushu University, Japan, 2Kobe University, Japan, 3Kitami Institute of Technology, Japan


Shallow coastal waters with vegetations such as seagrass, mangroves, salt marshes, have recently attracted extensive scientific attention, due to their high efficiency in the storage and sequestration of atmospheric carbon dioxide (CO2). And the carbon stored and sequestered by marine organisms is called “blue carbon”. However, due to the complexity of the tempo-spatial distribution of CO2 in the shallow coastal waters, it is difficult for us to accurately assess the amount of CO2 absorption of them. In addition, some studies reported that the partial pressure of CO2 (pCO2) fluctuates with the development of density stratification due to riverine freshwater effluents. But the effect of stratification on CO2 absorption in shallow coastal waters has been unclear due to the scarce related researches. Field measurement is generally considered to be one of the most effective methods to determine the biogeochemical distribution and dynamics in the seawater. However, in the case of study on the dynamic characteristics of coastal water quality in shallow seas, a particularly small temporal and spatial scale and a particularly large amount of data are usually required, which is difficult to achieve through normal field measurements. For this situation, 3-dimensional (3D) numerical simulation can be one of effective measures that complement field measurement data and enable further analysis. In this study, we developed a hydrodynamic-ecological coupled 3D numerical model that could accurately describe the distribution and dynamics of pCO2 under different mixing conditions in the Yatsushiro Sea, Japan. Also, we evaluated the effect of stratification on the flux of CO2 through the air-sea interface by applying this model.

HS19-A005 | Invited
Influence of Hydrological Conditions on the Water Contamination of Rural Canals in Agro-urban Environments

Daniele MASSERONI#+, Ludovica BELTRAME , Andrea GALLI, Cosimo PERUZZI, Claudio GANDOLFI , Marina TESAURO , Michela CONSONNI , Elisabetta TANZI
University of Milan, Italy


In many parts of the world, rural canals in agro-urban environments represent the water bodies destined to receive stormwater runoff from urban, industrial and agrarian surfaces. The risk of acute and chronic contamination of riparian vegetation and sediments, and the deterioration of water quality, make it problematic to use these canals to convey water for irrigation purposes and, more generally, to maintain environmental and ecological equilibriums of peri-urban areas. This study aims to investigate the influence of hydrological conditions on the chemical, physical and microbiological quality of water along a rural canal in a watershed located in the metropolitan area of Milan, Italy, one of the most anthropized areas in Europe. Water samples were collected periodically over one year at 9 points along the canal, both upstream and downstream of urban, industrial and agricultural effluents located along the canal path. Nineteen chemical-physical water characteristics such as biological and chemical oxygen demands, suspended soils, nutrients and heavy metals, were evaluated for all samples, and the presence of Enterobacters was investigated in-depth for a comprehensive characterization of water contamination levels with respect to environmental quality standards. Preliminary results show that the frequency and magnitude of rainfall events, as well as the shifts from dry to wet periods, have significant impacts on the water quality in the canal, with increased levels of chemical pollutants and Enterobacters found during the wet periods and immediately after rainfall events. At the same time, how the watershed is organized and managed (e.g. presence of cultivations, interconnections between urban, industrial and agricultural areas) is shown to play a key role. These preliminary findings provide useful information for assessing the anthropic impact on the water quality of rural canals in agro-urban settings and confirm that it is urgent to understand the fate of pollutants in the water cycle.

HS19-A012 | Invited
Watershed Governance for Sustainable Water Resource Use in Subtropical Islands

Jun YASUMOTO1#+, Ryuichi SHINJO1, Bam RAZAFINDRABE1, Takahiro HOSONO2, Ko YASUMOTO3, Nanami MIZUSAWA3, Shinji NAKAYA4, Kei NAKAGAWA5, Makoto KAGABU5, Yasuhiro TAWARA6, Mina HIROSE7, Tomohiro TOKI1
1University of the Ryukyus, Japan, 2Kumamoto University, Japan, 3Kitasato University, Japan, 4Shinshu University, Japan, 5Nagasaki University, Japan, 6Geosphere Environmental Technology Corporation, Japan, 7General Incorporated Association, Tropical Technology Plus, Japan


Water resources on subtropical islands are highly vulnerable to various stresses such as changes in industrial structure and climate change. Therefore, in recent years, depletion and pollution of water resources, namely groundwater has become major social issues. Pollution of groundwater degrades coral reef ecosystems through the water cycle and causes a decline in ecosystem services.Two reasons appear to lead to this issue: [i] insufficient understanding and visualization of groundwater flow and transport processes of pollutants, and [ii] lack of watershed governance for communicating and utilizing the scientific information in an easy-to-understand manner to the society.The target area of this research is Yaese Town located in Southern Okinawa, where urban and rural areas coexist. The main water resource in Yaese Town is groundwater, which is stored in the highly heterogeneous Ryukyu limestone. In Yaese Town, groundwater has been used as a valuable source of drinking water and water for irrigation. However, in recent years, groundwater pollution by nitrate nitrogen has become apparent, making related countermeasures an urgent issue.For sustainable use of water resources in subtropical islands, it is necessary to quantitatively understand the flow of groundwater and the generation and transport processes of pollutants, as proposed in this technology seed. Furthermore, if we can visualize such scientific information, it will be possible to communicate the current status of water resources to local residents in an easy-to-understand manner. In addition, the sharing of such data will facilitate the planning and implementation of effective pollutant load reduction measures based on consensus building among stakeholders.In this paper, we will briefly introduce the results of our research on [i] the understanding and visualization of groundwater flow and transport processes of pollutants.

HS33-A012
Role of Water Vapor in the Recent Tibetan Plateau Warming Based on Analysis of Era5 Reanalysis

Xinzheng TANG#+, Ji CHEN
The University of Hong Kong, Hong Kong SAR


Water vapor is an important atmospheric element of the earth’s climate system by affecting the downward longwave radiation mainly. Also, participating in the hydrological cycle, water vapor is a direct source of recharge of surface water and groundwater resources by precipitation. As the head source of several major rivers in Asia feeding over 30% world population, Tibetan Plateau (TP) has experienced a significant warming with a larger rate than the global average, which indicates that TP is one of the most sensitive regions to climate change. It is of great significance to investigate the features of water vapor change over TP for exploring the impact of water vapor on regional warming and forecasting extreme weather and climate events. In this study, observation and ECMWF ERA5 reanalysis data were used to analyze the regional temperature and water vapor change over TP during the period 1979-2019. A process-based radiative method is utilized to quantify the contribution of water vapor to the TP warming. The study can provide a scientific understanding of the regional climate change and its mechanism in TP.

HS33-A024
Post-processing of Short-term Precipitation Forecasts by Convolutional Neural Network

Wentao LI#+
Hohai University, China


Precipitation forecasts are important to applications such as hydrological forecasting. Raw precipitation forecasts from numerical weather prediction (NWP) models suffer from systematic bias. Statistical post-processing methods can be used to correct these biases. However, traditional post-processing methods are usually based on forecasts at a single location or lead time, which cannot take full advantage of the multiple spatial scale information in raw forecasts. In this research, we apply convolutional neural networks in post-processing to make full use of multiple spatial scale information in raw weather forecasts. Moreover, multiple meteorological variables such as geopotential height are also used as predictors in the model to improve the forecast accuracy. The post-processed forecasts are evaluated in metrics such as continuous ranked probability skill score (CRPSS), probability integral transform (PIT) histogram and relative operating characteristic (ROC) curve. The benefits of using multiple scale predictors in convolutional neural network are discussed.

HS33-A028
Evaluation of Drought Forecast Using Downscaled NMME Seasonal Predictions on Korea Peninsular

Jaepil CHO1#+, Hyewon JEON1, Junhyuk LEE2, Soon-Kun CHOI3
1Integrated Watershed Management Institute, Korea, South, 2NoteSquare Inc, Korea, South, 3National Institute of Agricultural Sciences, Korea, South


For proactive drought management and prepardness, forecasting information with several months of lead time that can be operationally used for monthly forecast shold be provided. In this study, North American Multi-Model Ensemble (NMME) forecasts with 1 degree resolution and 9-month lead time was used as prediction information. Spatial downscaling was conducted by adding forecasted anomaly values ​​to the monthly average observations for 1982-2010 hindcast period at each grid with 1 km resolution. For the temporal downscaling, specific year and month with the most similar spatial patterns to the forecasted precipitation and temperature were decided from the historical database and daily data were extracted form the year and month and bias-corrected for each grid. Finally, the Effective Drought Index (EDI) was calculated by linking the downscaled forecast data to the updated observation data up to the issuing month. Predictability of the forecasted EDI index was evaluated by comparing the spatial distribution of forecasted EDI to observational one.
※ This research was conducted with the support of the Rural Development Administration (Project number: PJ014932).

HS16-A009
Low Flow Projection Considering Actual Evapotranspiration Under Climate Change Scinarios

Eunji KIM+, Boosik KANG#
Dankook University, Korea, South


The low flow is used to evaluate the water supply reliability which is reference flow regime for dam operation and river management. The lower 3% of the cumulative probability distribution of annual flow is defined as low flow. The purpose of this study is to project low flow incorporating the actual evapotranspiration estimated through the GCM scenarios of the CMIP5. In order to reflect the specific monsoon climate characteristics of South Korea, the GCMs precipitation was bias-corrected individually for flood (June to September) and non-flood season (October to May). The actual evapotranspiration of GCMs has limitation in regional bias-correction due to lack of the observed data. The actual evapotranspiration can be estimated indirectly by complementary relationship hypothesis between potential and areal evapotranspiration. For potential and wet evapotranspiration, the FAO Penman-Monteith equation and the Priestley-Taylor equation are used, respectively. The long-term streamflow considering the actual evapotranspiration was simulated by IHACRES model. The CMD (catchment moisture deficit) module of IHACRES model hiring the effective rainfall using precipitation, temperature, and potential evapotranspiration as input data, was improved in this study so that the actual evapotranspiration could be directly used instead of potential evapotranspiration. The low flow can be estimated through the annual probability distribution of the flow regime derived from the IHACRES model. The projection shows 4.95 MCM/year (RCP4.5) and 1.36MCM/year (RCP8.5) decrease in low flow regime during near-term future (2011-2040), despite 0.52mm/year (RCP4.5) and 1.36mm/year (RCP8.5) increase in precipitation.

HS16-A019
Analysis of the Potential Elements to Improve the Popularity of the Rivers

Miho WAKAARI1#+, Haruki OGUMA1, Hayata YANAGIHARA2
1MIYAGI PREFECTURAL SENDAI NIKA SENIOR HIGH SCHOOL, Japan, 2Tohoku University, Japan


In order to raise people’s interest in rivers, this study aims to consider factors related to the popularity of rivers by analyzing the correlation between river water quality and popularity, and that between waterfall’s elements and popularity.  This study shows the popularity of rivers, using the article area published in the travel information magazine. Firstly, among the rivers published in the travel information magazine “Rurubu”; which suggests tourists where to visit when traveling in Japan, this study conducted a correlation analysis between water quality and popularity of rivers whose articles are classified as the “leisure.” Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) were used for river water quality information. No correlation was found with the popularity of rivers for both BOD and COD. In rivers with large BOD and COD values, most of the events were held at night and the scenery around the river is able to be viewed from the boat. The result shows the water quality tends to be poor at events which people do not come into contact with rivers, regardless of their popularity. Secondly, for the waterfalls listed in the magazine, this study performed a correlation analysis between distance from neighboring cities and popularity of waterfalls, and that between popularity of waterfalls and their heights. There was a positive correlation between distance from neighboring cities and popularity as well as height and popularity. In conclusion, its popularity was influenced by the distance from neighboring cities rather than the height. Judging from results, people find the time required to reach the waterfall more unusual and attractive than the height peculiar to the waterfall, finding it interesting. In other words, even if some waterfalls have harder access than others, maintaining each environmental condition could be the efficient way to capture people’s attention to the rivers.