Using the sediment rating curve (SRC) model, the regression-based regionalization approach was evaluated in 16 catchments. It is relied upon multiple regression equation in which the fitted model parameters are the dependent variables and catchment descriptors are the independent variables. Based on the jack-knife validation, the overall predictive accuracy is reasonably good and satisfactory result was obtained in large majority of the catchments. The validated model parameter-catchment descriptor relationship was then applied to parameterize SRC in the upper Sre Pok river basin (Vietnam) facing development of cascade dam-reservoirs, for subsequent sediment yield prediction. This ungauged basin has potential to release suspended sediment about 2.09 Mt/yr to downstream. This amount could be reduced to 0.31 Mt/yr if the development does not provide appropriate sediment flushing facilities.
Sedimentation is a global environmental problem that has been placing critical impacts of irrigation, agriculture, navigation, fisheries and aquatic ecosystem. The Mekong River Basin (MRB) has recently been suffering from environmental degradation despite its global significance of biodiversity. In this study, the Revised Universal Soil Loss Equation (RUSLE) model was adopted in a GIS framework to assess soil erosion and coupled with a sediment accumulation and routing scheme to simulate suspended sediment load at monthly scale in the MRB. Suspended sediment load (SSL) measurements at nine gauging stations in the MRB, from 1987-2000, were compared with the sediment yield values simulated from the model. The average Nash-Sutcliffe efficiency was 0.64, ranging from 0.14 to 0.94, resulting in a mean coefficient of determination, R2 = 0.62. Subsequently, reasonable soil erosion distribution in the basin and longitudinal profile and temporal changes of SSL at the monitored sites were assessed. Thus, the results confirmed the derived spatial soil erosion map explicitly in estimates of soil erosion and suspended sediment load in the relatively large river such as the Mekong River.
Generally, the methods of predicting landslides can be divided into two types - statistical model and numerical model. Compared with the statistical model, the numerical model can provide more detail and precise result, but is difficult to employ on basin-scale because of time-consuming calculation. This paper proposed a novel method, which was based on numerical model and multiple regressions as well as using the slope unit as the slope-stability analysis target, to predict the landslides on a basin scale. This method used a new warning indicator, critical water content (Wcr), which is derived from numerical model and had a clear physical meaning. The new method also had great performance on calculation to predict the occurring time and the locations of landslides. The heavy rainfall disaster occurring in the Shizugawa basin in 2012, located in Uji, Kyoto, was simulated by the new method. The results showed that the new method can not only predict the landslides but also estimate the runoff of the slopes on a basin scale.
Sediment flushing is one of the proposed methods for preserving the storage capacity of dam reservoirs. In flushing with water level drawdown, the incoming flood erodes a flushing channel in the deposited sediment. Flow pattern as well as flushing channel formation procedure in shallow reservoirs is complex phenomenon due to the dynamic interaction between flow field and bed changes. In the present study, the flow field and flushing channel formation procedure were investigated in various shallow reservoir geometries using physical experiments and numerical simulation. A fully 3D numerical model which applies Finite Volume Method (FVM) was utilized. Reasonable agreement was found between the numerical and experimental outcomes. The results would be useful to understand the influence of geometry on flow pattern and flushing process to conduct more efficient sediment management strategies.
Substantial experiments on community-based rural piped water supply model have been carried out at different locations in Bangladesh by Rural Development Academy (RDA), Bogra since 1999. Mainly to assess the performance of the social experiments, 30% samples have been selected out of 98 piped water supply systems. The study reveals water supply system is technically sound and water quality lies within the range of Bangladesh drinking water standard; per capita water use and tap connection have been increased from 29.51lit. to 99.96 lit and 59.95 to 118.45 respectively; and water borne diseases reduced from 60.28% to 20.40%. Communities are capable enough for operation and maintenance and cost sharing of the project. Some measures have to be taken and also subsidy needed water supply system for better outcome of the project. GO and NGO may come forward to replicate this model massively.
This study aims to evaluate longitudinal trends of flow regime and the degrees of its alteration by dams and weirs in Sagami River focusing on the major confluence. We simulated river flow and then evaluated flow regimes statistically under three scenarios. As a result, significant alterations by dams and weirs on the natural flow were detected particularly on the median flows, minimum flow, low pulse duration as increments, and high pulse count as decrement. The magnitudes of discharge, the numbers of high and low pulses, and the rate of change were amplified strongly at the confluence in the scenarios assuming natural tributary, indicating that tributaries have potentials to mitigate the altered flow regime. The release from a dam on the tributary mitigated the alteration on the mainstream more positively than the natural tributary in several aspects, though the tributary streamflow was distorted. Overall, our results contribute to shape an integrated operation scheme of dams within a stream network for the conservation of flow regime in rivers.
Spatial distribution and temporal variation of salinity and suspended sediment concentration (SSC) in the Chikugo river estuary, Japan, were measured for two weeks and investigated the effect of salinity mixing on the movement of the estuarine turbidity maximum (ETM). Vertically homogeneous salinity distribution and high SSC occurred during spring tide, and conversely, vertical stratification and clear water occurred during neap tide. Mixing, salinity intrusion, magnitude and location of ETM zone changed according to the semilunar tidal cycle. The flow ratio was determined using river discharge and the tidal prism, and a uniformly linear relationship was found between flow ratio and SSC. The relationship between salinity and SSC showed that SSC attained a peak in the region where salinity was 10 psu in lower estuary and region of 0.5 psu in the upper estuary. These indicate that the dominant factor determining SSC occurrence is the spring neap transition process and flow ratio.
An earthquake with a magnitude of 9.0 occurred off the Pacific Coast of Miyagi Prefecture, Japan on March 11th, 2011, accompanied by a devastating tsunami that caused severe damage to people and infrastructures. There have been many studies on the effects of coastal embankment, breakwater, as well as non-structural solutions such as pine trees, mangrove forest, and coastal dunes for reducing tsunami energy when it spreads to coastal areas. However, researches on sensitivity of coastal embankment structure in relation with tsunami disaster based on tsunami Shields number have not been widely carried out. Thus, the main objectives of this research are to investigate the sensitivity of coastal embankment structure in relation with tsunami disaster. In this study, a NEWFLUME model based on Reynolds Averaged Navier-Stokes (RANS) equations is applied to simulate the recent Great East Japan Earthquake and Tsunami 2011 along the coast of Suzaki. Results of numerical simulation have shown the reduction of tsunami Shields number in front of coastal embankment and landward area approximately 400 meter far from the backside of the embankment. In addition, estimated time of tsunami arrival was delayed due to the effect of various height of coastal embankment.
This paper investigates the interaction between flow patterns and geometry of in-ground stilling basin (ISB) and its influence on flushing efficiency from ISB. The main governing parameters in our study were the normalized ISB length, drop number, normalized end-sill geometry (height and width), and Froude number. Using large scale particle velcocimetry, we classified the flow patterns into four groups of B-jump, U-jump, Periodic and Steady submerged jump. We found the favorable flow pattern has a positive correlation with drop number, while a negative correlation with relative ISB length. Moreover, the lateral free spaces of the end-sill do not increase the chances for sediment to be flushed out from ISB.
Shallow water models, which assume the incompressibility of water and hydrostatic pressure distribution, serve as effective mathematical tools to describe dynamics of surface water flows. The 2-D shallow water equations (2-D SWEs) are among the most effective one. Solutions to the 2-D SWEs are sensitive to the choice of the friction slopes, the terms for turbulence and friction forces on side-walls. This paper carries out comparative numerical analysis on two Manning's friction slope formulae, a conventional water depth-based one and a hydraulic radius-based one, in order to see their influences on the solutions to the 2-D SWEs. Computational results of the hydraulic bores reveal relatively high accuracy of the hydraulic radius-based formula compared to the water depth-based counterpart.
Linear stability analysis of flows in open-channels with vegetation at one of their sides is performed. The lateral gradient of the streamwise velocity induced by the drag difference between the vegetated zone and the adjacent non-vegetated zone may result in flow instability in the shear layer around the edge of the vegetated zone, causing the generation of discrete horizontal vortices. We assume that the base state flow field before the occurrence of instability is characterized by a sub-depth-scale turbulence which is mainly generated by bottom friction. By introducing perturbations to the flow depth as well as the streamwise and transverse velocities in the base state, the conditions re-quired for perturbations grow in time were studied over a wide range of hydraulic parameters. The theory is validated by means of its application to experimental data.
In this paper a comparison between two commonly mesh-free Lagrangian particles methods which have the ability to deal with problems with large free surface deformations i.e., weakly compressible smoothed Particle Hydrodynamic (SPH), and the original version of Moving Particle Semi-implicit (MPS) were done. Two benchmark tests, a collapse of a water column with a rigid obstacle, and dam break on a wet bed, are taken into consideration to examine the two methods. The results show that the particles from MPS are scattered and the water surface shape is scratchy, on the contrary the profile of water by SPH is commonly smooth and gentle. One of the advantages of SPH method is found that it yields rather smoother results even if the particles density becomes smaller. The CPU time for the presented cases with SPH is smaller than MPS, even though SPH requires smaller Δt.
Principal Component Analysis (PCA) is proposed on long-beam velocities of Horizontal Acoustic Doppler Current Profiler (HADCP) to extract flow dynamics in near-bank regions and check simulation results, particularly Regional Ocean Modeling System (ROMS) performed for the Hudson River estuary (New York, USA). We here analyzed data measured by Horizontal Acoustic Doppler Current Profiler (HADCP) at West Point, on the inner bank downstream of a bend. Results show an agreement between HADCP and ROMS in the first mode, which capture more than 97% energy of the turbulent flow measured along three HADCP beams. In addition, there appears an asymmetry between ebb and flood in the second temporal coefficient. Low-order PCA coefficients of HADCP and ROMS have fluctuation in ebb tide which may be associated with topographically-generated eddies. Tidal effect is found in lower order temporal coefficients and their spectra.
A computational study is conducted to investigate the effect of side-by-side arrangement of cylindrical piers on river bed morphodynamics and the local scour holes. This phenomenon is simulated by a sophisticated 3D model in which the flow is simulated by large-eddy simulation and the sediment is simulated in a Lagrangian framework as rigid spheres transported by the water. The bed morphodynamics is the result of pick-up and deposition of the solitary sediment particles. Through comparison for scour of a single cylinder with experimental data, the model shows a reasonable agreement of scour patterns and evolution of local scouring. For the side-by-side arrangement of cylinders, the bed scouring at the nose of both cylinders is mostly identical and the bed morphological changes are nearly symmetric along the center plane in streamwise direction. Maximum scour depth exhibits a growing trend with decrease in distance of cylinders, which agrees well with the experimental data from previously published literature.
The present study is about flow structure and bed deformation around a group of double spur dike with the main purpose of how to reduce the local scour in the neighborhood of a conventional-type spur dike. Four types of submerged pile group, with different densities were installed in the same area at the upstream adjacent of the first spur-dike. The corresponding effects of each new model on flow and bed deformation mechanism were compared with those of the conventional spur-dike group. Flow velocity was reduced at the neighborhood of the first spur dike in the cases with a pile group. Local scour was also reduced both in depth and volume. With a decrease of the pile density flow patterns became more similar to the conventional case, local scour depth and bed erosion in the spur-dike field were increased. The promotion of sediment deposition in the spur-dike field was observed in the cases with medium and lower pile density, respectively.
Field measurements and numerical modeling were used to investigate the causes of the Laturharhari embankment breach during the January 2013 Jakarta floods. A forensic analysis shows the immediate cause of the breach was overtopping followed by scour of the landward side of the earthen berm atop the embankment, with the overtopping possibly accelerated by piping of floodwaters along the soil-concrete interface of an improperly designed structure built into the embankment. Numerical modeling shows the underlying reason for floodwaters rising to such a precarious level was trash observed to be clogging 3 of the 4 sluices of Karet gate downstream.
Urban inundation has particularly been reported to lead to extensive property damage and casualties due to the concentration of people and properties in highly urbanized areas. The sewer system is one of the most important components of urban inundation analysis. The numerical simulation model developed for this study consists of a 1D slot model of sewer pipe flow, and estimates head loss between manhole and sewer pipes based on the rigid column theory. In order to obtain validation data, the fundamental laboratory experiments were conducted so as to estimate the effects of head loss depending on different manhole shapes with no benching and no invert. First, straight case experiments were conducted to evaluate the head loss with circular and square type manhole shapes under the steady state condition. Next, unsteady state experiments were conducted. Finally, a numerical simulation model was tested and validated to confirm the model갢s applicability in using head loss coefficients obtained from laboratory experiments. Simulation results demonstrated high agreement with experimental data, so the newly developed model can be used to analyze urban sewerage systems.
Densely populated megadelta regions such as the Mekong Delta are exposed to great risk due to flooding from the sea under climate change. However, many previous flood simulation studies have not explicitly considered sea level rise. Here, we aimed to assess the impact of sea level rise to the damage due to extreme floods in the Mekong Basin using a global river routing model and risk assessment approach. Using the flood event in 2000 as a case study, we estimated that the amount of damage would increase by 4 to 21 % for sea level rises of 0.5 m and 2.0 m, respectively. This increase would mainly affect the socioeconomic aspect of the Mekong Delta due to high concentration of assets and large increase of inundation depth.
This paper applies a hydrological model, the Hydrological Predictions for the Environment (HYPE) model to a data sparse basin named KAMO River basin (KRB), in order to estimate the hydrological variations under climate and land-use changes. The goodness of fit of the model to observed discharge data indicates the value of Nash-Sutcliffe efficiency of calibration and validation was 0.72 and 0.69, respectively. The trend analysis indicated that with the impact of climate change, the annual precipitation and stream flow seemed to decrease. But there was no evidence to prove the flood risk decreasing. Land use changes had great impact on stream flow. The urbanization and deforestation led to high peak flow. Furthermore, they tended to present a greater effect on runoff in summer. This study shows that the HYPE model was capable of simulating and predicting hydrological variations in the basin as the results close to the ones found through studies in other basins experiencing similar climate and land-use changes.
A distributed flow routing model with kinematic wave flow approximation (1K-FRM) was applied to project river discharge in the Indochina Peninsula region. The input data for flow routing model 1K-FRM were the generated-runoff data at 3-hourly time step from the latest versions of the Meteorological Research Institute atmospheric general circulation model (MRI-AGCM3.2S, MRI-AGCM3.2H) and the Model for Interdisciplinary Research on Climate (MIROC5) for three 25-year periods: 1979-2003 (present climate), 2015-2039 (near future climate), and 2075-2099 (future climate). Simulated discharge data for the near future climate and the future climate were compared with those for the present climate to evaluate the changes in flow in the region under a changing climate. The statistical significance of river discharge changes in the Indochina Peninsula region was also analyzed.
In present study, physical based Water and Energy Budget - based Distributed Hydrological Model (WEB-DHM) was applied to investigate the intra-basin river runoff and to elucidate the potential impacts of climate change on hydrology in the Soan River Basin, Pakistan, a semi-arid and poorly gauged basin (PGB). The model performance was evaluated in terms of river discharge and soil moisture. WEB-DHM simulated surface soil moisture was validated by soil moisture assimilated by Land Data Assimilation System developed by the University of Tokyo (LDAS-UT). WEB-DHM was derived with bias corrected precipitation and other parameters from four Atmosphere-Ocean General Circulation Models (AOGCMs). The analysis of twenty years simulated daily discharge for the past (1981-2000) and future (2046-2065) showed that it is likely that flooding trend will increase in the future. However, it is about as likely as not that the drought will intensify in the future. The study demonstrate an example for climate change impact assesnhydrological processes in a PGB.
This study assesses the future effects of land use and climate (rainfall) changes on river flow regime and subsequent impacts on the water quality in Gin river, Sri Lanka. Future land use in the Gin catchment was predicted using a GIS based statistical regression approach. HadRM3P Regional Climate Modelling system generated the future rainfall for the SRES A2 and SRES A1B emission scenarios. Yamanashi distributed hydrological model (YHyM/BTOPMC) was used to simulate the future hydrological conditions in the basin. Year 2020 total iron load was modeled using a rating curve constructed with the observed relationship between total iron concentration and stream flow. Results indicate that future total iron load would be peaked in June following more pronounced peak flows under SRES A2 scenario compared to the current peak load in October. Due to the future extreme rainfall events, peak total iron load occurrence in Gin river could be increased by about 40%.
Terrestrial water storage (TWS) at high spatial and temporal resolution is deemed necessary for many hydrological and water resource management applications. Since its launch, Gravity Recovery and Climate Experiment (GRACE) satellite has been providing terrestrial water storage change data at global and regional scales. However, the application of GRACE data for local-scale water resources management has been limited because of its coarse resolution. The purpose of this work is to investigate the feasibility of downscaling GRACE with a statistical method. In this work, empirical regression methods based on the relationship between GRACE and other hydrological fluxes were applied to downscale a 1 degree gridded GRACE product to 0.25 degree. Observed groundwater level data were used to validate the downscaling performance. Results indicated that GRACE TWS had good relationship with storage change obtained by water balance equation. Statistical regression downscaling method can improve GRACE data resolution effectively.
Seasonal climate forecasting information can be utilized by water resource managers for planning activities to reduce uncertainty with the additional predictive information. The aim of this study was to determine the predictability of extremely dry and wet conditions by looking into past extreme events and simulating at the basin-scale how well these events can be reconstructed in the Pampanga river basin, Philippines. Three-month seasonal climate forecast (SCF) model ensembles derived from the MIROC-5 Atmosphere Ocean Global Circulation Models (MIROC 5.0 AOGCM) were used to drive the Water and Energy Budget-based Distributed Hydrological Model (WEB-DHM). Extremely dry and wet years in 1982-2000 were integrated into WEB-DHM. Some outputs were incorporated into the crop model ORYZA2000 to quantify crop production on selected ENSO years 1983, 1987, 1991 and 1999-2000 (coinciding with SPAM forecasts). Crop production, drying and flooding trends were well simulated.
With design hyetographs, created by different ranking methods for the duration (24 h or 72 h) and a 100-year-return-period rainfall depth, a hydrological model simulated the peaks of discharge for extreme rainfalls in a southern Taiwan watershed under climate change. The discharge peak with the conventional ranking method can be overestimated by an enhanced effect of the temporal distribution's shapes of lower-intensity rainfalls. To reduce the overestimation, the peak-weighted and cumulative-rainfall-depth-weighted ranking (cumulative-depth ranking) methods determined by the shape characteristics of rainfalls are introduced into this study. For the peak-ranking method, the discharge peaks did not change those of the conventional method even in longer duration (72 h) of design hyetograph. The cumulative-depth ranking method resulted in at most 15% reduction of the peak from the conventional one. Under the effect of climate change, the cumulative-depth ranking method reduced the discharge peaks by approximately 4% for 24-h duration and approximately 15% for 72-h one, respectively.
The use of meteorological ensembles to produce sets of hydrological predictions has increased the ability to issue flood warnings. However, the spatial scale of a hydrological domain is still much finer than that of a meteorological model, and Numerical Weather Prediction (NWP) models have challenges with misplacement. This study assesses the pre-processing methods with consideration of appropriate ensemble members and a spatial shift of ensemble NWP rainfall fields, in order to improve the accuracy improvement of the ensemble flood forecasting. The analysis shows that appropriate ensemble members of NWP rainfall improves the accuracy of the mean value when ensemble forecasting a flood, whereas the transposition of NWP rainfall fields has a more suitable impact on the accuracy of the best values.
CASC2D model is a widely used event-based hydrologic model to simulate rainfall-runoff and sediment transports, but it is challenge for this Hortonian overland flow based model to simulate hydrologic processes in forested catchments. In this study, CASC2D model was improved for continuous simulation in forested catchments by considering evapotranspiration, subsurface flow, groundwater storage, and modifying infiltration and interception methods. The model was applied to the Kuchibuto River catchment, Fukushima Prefecture. Four storm events in 2011 and seven events in 2012 were selected for model calibration and verification, respectively. Simulated hydrographs showed a good agreement with those of observed. Comparing with original CASC2D model, modified model significantly improved accuracy of simulation due to the inclusion of subsurface flow and groundwater storage processes and modified infiltration constraint condition.
Based on the sensitivity analysis at annual, monthly and daily scales, parameters of the Xinanjiang model could be divided into three groups and optimized independly without considering the effects from other groups. This paper focuses on the optimization of data adjustment parameters, Cp and Cep, which are sensitive at annual scale. The concept of aridity index is introduced into the optimization process, and proposed a relationship describing Cp and Cep as a function of annual runoff coefficient and pan aridity index. Three different methods are developed to estimate the value of Cp and Cep in ideal condition and actual practice respectively. The results show that, compared with optimizing Cp and Cep independly, the method considering the relationship of runoff coefficient and pan aridity index will narrow the parameter space, and keep the same accuracy. The effectivity of method using the simple linear relationship will depend on the length of data series and correlation between annual runoff coefficient and pan aridity index.
One of the main objectives of research in hydrology is to improve the accuracy of catchment storage estimation for water resources management and flood prediction purposes. Rain water falling to the ground surface will either run off along the surface or infiltrate into the soil. The infiltrated water which is defined as loss rainfall can be used to estimate the potential catchment storage. Total rainfall-total loss rainfall relationship has been developed to estimate catchment storage by using tanh function fitting curve for 47 catchments located in 16 prefectures in Japan between 2002 and 2011 (June to October). The obtained results indicate that runoff parameters in the tanh function represented by a and b parameters can be utilized to estimate the potential water storage for catchments having stabilized tanh curve type. Among 47 catchments, only 23.4% of the overall catchments have stabilized tanh curve types which are located in Honshu Island.
Numerical weather prediction models have been improved to adequately represent the growing influence of urban areas to surrounding weather. Recently, updated LES-derived empirical equations on the aero-dynamic urban surface parameters displacement height d, and roughness length for momentum z0m, have been introduced. Using a high spatial resolution d, z0m, and anthropogenic heat emission distribution, dry case simulation was conducted using Weather Research and Forecasting Model with domains covering Tokyo, Nagoya, and Osaka. It was found that default WRF generally underestimate roughness. Results were also compared with actual observations of 2 m air temperature and surface wind speed, and were found to be well represented in the model when detailed parameters were used.
In this study, we first time test the feasibility of partitioning evapotranspiration using high frequency in-situ measurements of water vapor isotopes in a paddy field, Mase, Japan. By combining isotope measurements with Keeling plot method and Craig-Gordon model, transpiration is found representing more than 90% of the total evapotranspiration flux at the daily scale. However, the errors in this method could not be neglected. The primary cause of these errors is demonstrated to be the underestimate of water evaporation estimated by Craig-Gordon model. The variation of measured water vapor d-excess is significantly affected by the dominant components of evapotranspiration on diurnal time scale, it is suggested that the vegetation play a significant role in land surface water exchange process.
Dynamical downscaling is a promising tool to assess the future fate of water in a catchment. To overcome strong biases in Coupled Ocean-Atmosphere General Circulation Models (CGCMs), the Pseudo Global Warming Downscaling (PGW-DS), which combines climatology differences (future-past) of CGCM ensembles and Reanalysis Dataset (RD) was proposed as a reliable and efficient method, but downscaling of RD at a basin scale was not assessed. Hence, this study evaluated the results from a long-term, high-resolution Downscaled Precipitation (DP) derived from a RD over the Tone river basin. DP showed strong bias over mountainous regions owing to resolution enhancement. DP and CGCM precipitations were merged with Statistical Bias Correction methods (SBC) to obtain a comprehensive outlook on biases and the most appropriate SBC. Characteristics of biases were quite different in DP and CGCM, which performed very poor for extreme rainfall intensities and thus required an explicit treatment. Seasonal inconsistency in extreme events of CGCMs affected the corrected rainfall and discharges significantly. Conversely, a simple cumulative gamma method was successful for DP to represent climatology, extreme statistics of rainfall and discharges owing to the use of RD, which generated lesser bias compared to CGCMs. The proposed method will be applied to PGW-DS to obtain reliable information of future changes of water in the basin.
Considering still high uncertainty within results of climate projections by General Circulation Models (GCMs) with various emission scenarios, a multi-model approach after bias corrections and downscaling is very important for climate change impact assessment on water resources at a river basin scale. In addition to the methodologies for selecting GCMs which express regional climate characteristics reasonably, this paper aims to reduce the GCM bias of extreme rainfall where most of GCMs underestimate and improve the poor seasonal variation of GCM bias too. In the Yoshino River, where heavy rainfall events are mainly characterized by the Baiu in June and July and typhoon in August and September, we recognized big bias in extremely heavy rainfalls from June to September. Investigating the tendency of GCMs, seasonal bias corrections were introduced additionally. The results of holistic bias correction and downscaling provide reliable, quantitative and qualitative information to the policy makers for planning for integrated water management in the Yoshino River.
Areal Mean Precipitation (AMP) uncertainties have been a long concerning issue. It is necessary to quantify the AMP error and assess its impacts on Rainfall Runoff (RR) simulation, which is one of the guidance for improving the accuracy and robustness of RR models. In this paper, AMP uncertainties were quantified by both published and proposed indices in five variety sized catchments in Asia. Moreover, AMP errors were also computed using both in-situ observations and remote sensing data. Satellite based precipitation product (GsMAP-MVK) was used with the effort to mitigate the problem of sparse data, especially severe in poorly gauged river basins. The declining trends in the relation of model performances and AMP error have been observed. The AMP error estimation was improved when accounting for the spatial variability of precipitation and the gauge locations along with the gauge density. The daily basis GsMAP-MVK grasps the precipitation variability in space better than the annual basis and it can reliably use to estimate the AMP error based on “Sample Design method” (Esdd).
Due to the global climate changes, the scale and frequency of natural disasters are more difficult to predict and measure. Extreme rainfall often brings astonishing amount of water and causes very serious damage in the mountain areas. For instances, during typhoon Morakot in 2009, many roadways and bridges were destroyed by the rainfall in south Taiwan; furthermore, the typhoon Megi brought amazing hourly rainfall to damage the Highway No.9 in I-lan County at 2010. Facing the challenges from the extreme weather conditions, the development of an early warning system has become a critical issue. Therefore, in the proposed study, the authors collected the field data of landslides and debris flows in No.18 Highway of middle Taiwan. And the authors collected the rainfall records of typhoons and storms from 2008 to 2012. Pattern recognition analysis was conducted to identify typical precipitation patterns that would cause slope failures and related debris flows. Threshold rainfall intensities and rainfall amounts that would possibly trigger the failures were chosen as two indices and their applicability based on different theoretical or empirical approaches from the selected precipitation patterns. Correlation between triggering rainfall indices and occurrences of landslides is to be established through this analysis.
With long coastline (3,200 km) and many large deltas, Vietnam is particularly susceptible with climate change. In the recent decade, Northern Vietnam has been facing terrible weather regime disturbances with increasing frequency and intensity of extreme weather events. As the earth temperature is projected growing higher, many scientists have indicated the warmer condition in the South-East Asia associated with increasing trend in precipitation; however, there is still a limited understanding about the future climate condition in Northern Vietnam. This study uses the observation climatological data and the updated dataset of 5th phase of Climate Model Intercomparison Project (CMIP5) to investigate the future variation in climate condition as well as water resources in the North of Vietnam. Despite of the decline in rainfall and the increase in evaporation during the recent decades, future rainfall and evapotranspiration are expected to increase. Thus, future water budget might increases, mostly in summer and autumn.
Water shortages have been periodically affecting the social and economic development of many regions in the world. Such effects could be mitigated by using techniques that considers the uncertainty of hydrologic variables. This paper aims at developing a model based on implicit stochastic optimization (ISO) and genetic algorithms (GA) for deriving monthly reservoir hedging rules. The ISO-GA procedure consists of optimizing the reservoir system operation under a set of possible inflow scenarios and using the acquired optimal dataset in order to construct discrete hedging rules based on GA. The proposed methodology was applied to the reservoir that supplies water to the city of Matsuyama, Japan. Based on the results, it is concluded that the devised rules are less vulnerable than the standard rules of operations during water shortage periods.
A distributed biosphere hydrological model with three layered energy balance snow melt module (WEB-DHM-S) and the Moderate Resolution Imaging Spectroradiometer (MODIS) derived snow cover data have been implemented to optimize the snowfall correction factor (SCF) for the correction of radar based snowfall within the framework of Shuffled Complex Evolution, University of Arizona optimization scheme. The optimal value of SCF is obtained for the minimum error between the simulated and observed runoff and between the simulated and MODIS derived snow cover area. The system is applied at Yagisawa dam basin of Japan to correct Radar-AMeDAS precipitation. The SCF is optimized at 3.27 in year 2003. This optimized SCF is validated in 2002, producing improved simulations of discharge and SCA. This approach can be applied to correct radar precipitation where satellite derived SCA are available.
Glaciers are important water reservoirs for the Andean basins. Due to their tropical latitudes, their energy balance is very sensitive to climate change. The present study analyzed the ablation in the tropical Andean glacier Condoriri by applying an energy balance of the hydrologic year 2011-2012. The total ablation was separated into sublimation and melting. Sublimation accounts for 54.4% of total ablation, which is similar to results from other tropical glaciers. It was found that ablation changes with elevation; melting decreases with elevation. The water from melting glacier accounts for 8.5% of the total water input. The glacier balance shows that the equilibrium line altitude (ELA) is located at 5080 m above sea level, similar to ELA estimation of other studies. Analyzing the temperature trends shows that global warming not only will increase the ablation, but also will modify the melting-ablation relation. Higher temperatures will increase the energy used for melting and decrease the energy used for sublimation.
In semi arid Maharashtra State of India, the availability of groundwater is extremely uneven both in space and time. It is due to the uneven distribution of rainfall and variations in geology. In this background, understanding ground water situation and its uses is very important for its better management. Therefore, the study aims to assess the groundwater resource through the use of indicators. Dhubdhubhi watershed in drought prone southern Maharashtra state is selected as the study area. Seven different groundwater indicators are calculated under three aspects: renewable groundwater resource for utilization, importance of groundwater for use and contemporary state of groundwater development. Indicators obtained under these aspects reveal current renewable water resources, uses and development in the watershed. The results show that the groundwater development in the watershed as a whole is sustainable. However, in two mini- watersheds abstraction exceeds recharge questioning the sustainability at local scale.
The groundwater in the Pleistocene confined aquifer (PCA) of the Red River Delta (RRD) was examined using self-organizing map (SOM) and Gibbs diagrams to determine, for the first time, its spatial classifications in terms of its hydrogeochemical characteristics. In this study, the groundwater chemistry dataset used in the analysis is composed of 8 major dissolved ions (i.e. Ca2+, Mg2+, Na+, K+, HCO3-, Cl-, SO42- and CO32-) that are consistently found in 52 groundwater monitoring wells within the study area. Based on the results, the groundwater in the PCA monitoring wells of the delta can be classified into 2 major water types: high and low salinity. Each water type is composed of cluster-types that have similar hydrogeochemical characteristics. The high salinity water type has 2 clusters (or sub-types), while the low salinity (or fresh water) has 4. From the Gibbs diagrams, results indicate that the high salinity in the groundwater is mostly influenced by either (or both) anthropogenic activities and salt water intrusion.
The objective of this study was to solve the Richards equation by constrained interpolation profile (CIP) method for unsaturated homogenous soil. The Richards equation was divided into advection and non-advection phases. Advection phase was approximated by CIP method while, the non-advection phase was approximated by explicit method. For the computational purpose, MATLAB platform (version 7.12.0) was used. The CIP method was applied for 12 soil types. However, this paper analyzed the results of four major soil types; sand, loam, silt and clay. The CIP outputs for all soil types displayed common pattern and agreement with the available literatures. The simulated results were compared with those of well-known Hydrus-1D model. The CIP outputs showed well agreement with Hydrus-1D. The proposed method could be a useful tool for predicting the infiltration as well as water movement in the vadoze zone.
The terrestrial water cycle is being altered by human activity such as water diversion and withdrawal for agricultural use. In this study, a global water resource model was enhanced to perform a simulation considering nonlocal water resources which is diverted from remote places. In this study irrigation water requirement was met by major four major sources: river, reservoirs, nonlocal water sources and nonlocal water source. We created geographical data of water diversion systems for five regions of major irrigated cropland. The simulated result showed that annual irrigation water requirement for nonlocal water resources were 62km3 and that account large part of total irrigation water requirement in our subject areas.
This study was conducted to improve a global crop calendar product using satellite-sensed vegetation indexes. In this study, we newly used EVI and SAVI, in addition to NDVI, to define crop calendar by phenological analysis. Using a global cropping map, parameters to define planting and harvesting dates are determined to three vegetation indexes. Estimated crop calendars using three vegetation indexes agree with a statistical crop calendar at approximately same level. Improvements of global crop calendar using EVI and SAVI are not captured. On the other hand, determining cropping parameters brings about improvement of the crop calendar, which causes an improvement of analyzed agricultural water usage.
Rice yields at the Sangker river basin in western Cambodia are simulated by a coupled model of the distributed hydrological model WEB-DHM and the rice growth model SIMRIW-rainfed. The results are validated by in-situ statistical data and FAOSTAT. Then, future rice yields are also simulated by using GCMs outputs. In addition, a simple irrigation model is introduced into the coupled model. By using this model, rice yields in consideration of climate change and irrigation are assessed. In this study, effectiveness of irrigation in this river basin is shown for both of the present and future climates. The results showed that, by constructing irrigation facilities, a stable rice yield can be obtained even if no yield is obtained at rain-fed paddy fields. Also, this study showed that a variation of future rainfall pattern will affect a variation of rice yield.
The effects of irrigation process on reed colony of Shuangtai Estuarine Wetland in Liaoning Provence, China, are discussed with the field investigation (salinity distribution, reed growth of shoot height, density, and above biomass) and hydrological measurement (water levels inside and outside the reed colony). Reed production proves to have an optimum at 5 salinity. The salinity will decrease below 5 in growing season due to irrigation, and after drainage the salinity level will rise. The observation on water levels suggests that the ratio of interception to rainfall by reed body in the growing period is about 0.4. Evapotranspiration rate is estimated by surface water balance equation without inflow and outflow. The calculation result also indicates that the irrigation is required for keeping water balance before raining season in middle July.
In Mekong river basin, productivity of rice is unstable because more than 70 % of paddy fields were classified as rain-fed paddy. In addition, future global climate change and land use change will make negative impact on rice production in this region. In order to analyze the stability of rice production quantitatively, it is important to consider the rice farming management such as strategy of rain-fed rice yield stabilization. In this study, rice production model was developed combined with distributed type water circulation model. Developed rice production model was applied to Mekong river basin, and verified with the statistic data of Northeast Thailand from 1986 to 1995. As a result, rice planted area, yield, production was good agreement with statistic data, especially errors in rice yield was improved by considering the strategy of rain-fed rice yield stabilization.
This paper first focused on the influence of the Water User Association through a case study of the Aichi Irrigation Scheme using field surveys and census data for Aichi prefecture. In the authors' opinion, the most serious influence is now appearing as the start-up condition of an irrigation project based on an agreement of more than 66% of cultivators as representative condition based on Land Improvement Act. The representative condition assumes that the percentage of agreed cultivators is nearly equal to that of the farmland area. The expansion of large cultivators negated the assumption. The percentage of agreed area estimated by percentage of agreed cultivators is called the EI (Equality Index). The authors developed the Lorenz curve of cultivated area of Aichi prefecture. By using this, EI of area is 0.38 in 1960 and 0.2 in 2010. In 2010, the value shows conflict of agreement of cultivators and that of area.
We have evaluated evapotranspiration from different types of cropland and its water sources under future climate conditions when the current cultivation and irrigation practices will be kept in the future. A future increase in evapotranspiration from irrigated croplands will be larger than that from rain-fed croplands. To compensate increasing water loss from irrigated croplands through evapotranspiration, a larger amount of water will be supplied from non-river water sources than today: cultivation of the second crops in a double-cropping system in India is a typical example. Additional adaptation measures will be necessary to prevent future water shortage where the capacity of currently existing reservoirs or groundwater will be insufficient for future irrigation requirement.
Indochina Peninsula (especially central and southern part) is known as the region which experiences the earliest onset of the Asian Summer Monsoon (ASM). In this study, we analyzed the cloud activity, atmospheric heating, and moisture advection for the years of wet (2009) and dry (2013). The ASM onset was earlier in the wet year followed by the active cloud activity and atmospheric heating over all around the Indochina Peninsula from the middle of March. In the dry year, cloud activity in the middle of March was limited to the area over the Tonle Sap Lake in Cambodia. Atmospheric heating for this year was not clear and the ASM onset was later. The result implies the importance of the role of the soil wetness over the Indochina Peninsula. Thus, observing the post-monsoon rainfall, there is a possibility to forecast the timing of the ASM onset and the relative amount of the pre-monsoon rainfall in the Indochina Peninsula.