Guangqian Wang

Tsinghua University, Peping, Beijing, China

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Publications (74)109.68 Total impact

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    ABSTRACT: With the increasing resolution of digital elevation models (DEMs), computational efficiency problems have been encountered when extracting the drainage network of a large river basin at billion-pixel scales. The efficiency of the most time-consuming depression-filling pretreatment has been improved by using the O(NlogN) complexity least-cost path search method, but the complete extraction steps following this method have not been proposed and tested. In this paper, an improved O(NlogN) algorithm was proposed by introducing a size-balanced binary search tree (BST) to improve the efficiency of the depression-filling pretreatment further. The following extraction steps, including the flow direction determination and the upslope area accumulation, were also redesigned to benefit from this improvement. Therefore, an efficient and comprehensive method was developed. The method was tested to extract drainage networks of 31 river basins with areas greater than 500,000 km2 from the 30-m-resolution ASTER GDEM and two sub-basins with areas of approximately 1000 km2 from the 1-m-resolution airborne LiDAR DEM. Complete drainage networks with both vector features and topographic parameters were obtained with time consumptions in O(NlogN) complexity. The results indicate that the developed method can be used to extract entire drainage networks from DEMs with billions of pixels with high efficiency.
    Geomorphology 06/2015; 238. DOI:10.1016/j.geomorph.2015.02.028 · 2.58 Impact Factor
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    Sha Zhou, Bofu Yu, Yuefei Huang, Guangqian Wang
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    ABSTRACT: The Budyko hypothesis states that the ratio of the actual evapotranspiration over precipitation (E/P) is fundamentally related to the ratio of the potential evapotranspiration over precipitation (E0/P). A number of Budyko functions have been proposed to describe such a relationship between E0/P and E/P. There is, however, no simple method to generate Budyko functions that meet the water and energy constraints. This study showed analytically that for any Budyko function, the sum of elasticity of evapotranspiration with respect to potential evapotranspiration and that with respect to precipitation equals to unity. This complementary relationship for sensitivity of evapotranspiration has important implications for evaluating hydrologic impact of change in climate and/or catchment characteristics. More importantly, this study found a function that is monotonically increasing with simple limiting properties. This function can be used to generate numerous valid Budyko functions, and can also be used to test the validity of the existing Budyko functions.
    02/2015; DOI:10.1002/2015GL063511
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    Haiyun Shi, Guangqian Wang
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    ABSTRACT: Due to climate change and its aggravation by human activities (e.g., hydraulic structures) over the past several decades, the hydrological conditions in the middle Yellow River have markedly changed, leading to a sharp decrease in runoff and sediment discharge. This paper focused on the impacts of climate change and hydraulic structures on runoff and sediment discharge, and the study area was located in the 3,246 km2 Huangfuchuan (HFC) River basin. Changes in annual runoff and sediment discharge were initially analysed by using the Mann-Kendall trend test and Pettitt change point test methods. Subsequently, periods of natural and disturbed states were defined. The results showed that both the annual runoff and sediment discharge presented statistically significant decreasing trends. However, compared with the less remarkable decline in annual rainfall, it was inferred that hydraulic structures might be another important cause for the sharp decrease in runoff and sediment discharge in this region. Consequently, sediment-trapping dams (STDs, a type of large-sized check dam used to prevent sediment from entering the Yellow River main stem) were considered in this study. Through evaluating the impacts of the variation in rainfall patterns (i.e., amount and intensity) and the STD construction, a positive correlation between rainfall intensity and current STD construction was found. This paper revealed that future soil and water conservation measures should focus on areas with higher average annual rainfall and more rainstorm hours.
    Hydrological Processes 01/2015; DOI:10.1002/hyp.10439 · 2.70 Impact Factor
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    Guangqian Wang, Xudong Fu, Haiyun Shi, Tiejian Li
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    ABSTRACT: Soil erosion is the root cause of environmental and ecological degradation in the Loess Plateau of the Yellow River. Watershed sediment dynamics was fully analyzed here, and a physically based, distributed, and continuous erosion model at the watershed scale, named the Digital Yellow River Integrated Model (DYRIM), was developed. The framework, the key supporting techniques, and the formulation for natural processes were described. The physical processes of sediment yield and transport in the Loess Plateau are divided into three subprocesses, including the water yield and soil erosion on hillslopes, gravitational erosion in gullies, and hyperconcentrated flow routing in channels. For each subprocess, a physically based simulation model was developed and embedded into the whole model system. The model system was applied to simulate the sediment yield and transport in several typical years in different watersheds of the Yellow River, and the simulation results indicated that this model system is capable of simulating the physical processes of sediment yield and transport in a large-scale watershed.
    Advances in Water Resources Engineering, Edited by Chih Ted Yang, Lawrence K. Wang, 01/2015: pages 1-40; Springer International Publishing., ISBN: 978-3-319-11022-6
  • Lubo Liu, Xudong Fu, Guangqian Wang
    Journal of Environmental Engineering 09/2014; 140(9):A5013001. DOI:10.1061/(ASCE)EE.1943-7870.0000745 · 1.22 Impact Factor
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    Haiyun Shi, Xudong Fu, Ji Chen, Guangqian Wang, Tiejian Li
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    ABSTRACT: This paper develops an algorithm for computing spatially distributed monthly potential evaporation (PE) over a mountainous region, the Lhasa River basin in China. To develop the algorithm, first, correlation analysis of different meteorological variables was conducted. It is observed that PE is significantly correlated with vapor pressure and temperature differences between the land surface and the atmosphere. Second, Dalton model, which was developed based on mass transfer mechanism, was modified by including the influences of the related meteorological variables. Third, the influences of elevation on monthly temperature, vapor pressure and wind velocity were analyzed, and the functions for extending these meteorological variables to any given altitude were developed. Fourth, the inverse distance weighting method was applied to integrate the extended meteorological variables from five stations adjacent to and within the Lhasa River basin. Finally, using the modified Dalton model and the integrated meteorological variables, we computed the spatially distributed monthly PE. This study indicated that spatially distributed PE can be obtained using data from sparse meteorological stations, even if only one station is available; the result showed that in the Lhasa River basin PE decreases when elevation increases. The new algorithm, including the modified model and the method for spatially extending meteorological variables, developed in this paper can provide the basic inputs for distributed hydrological models.
    Hydrological Sciences Journal/Journal des Sciences Hydrologiques 09/2014; 59(10):1856-1871. DOI:10.1080/02626667.2014.881486 · 1.25 Impact Factor
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    Sha Zhou, Bofu Yu, Yuefei Huang, Guangqian Wang
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    ABSTRACT: Water use efficiency is a critical index for describing carbon-water coupling in terrestrial ecosystems. However, the nonlinear effect of vapor pressure deficit (VPD) on carbon-water coupling has not been fully considered. To improve the relationship between gross primary production (GPP) and evapotranspiration (ET) at the sub-daily time scale, we propose a new underlying water use efficiency (uWUE = GPP · VPD0.5/ET) and a hysteresis model to minimize time lags among GPP, ET, and VPD. Half-hourly data were used to validate uWUE for 7 vegetation types from 42 AmeriFlux sites. Correlation analysis shows that the GPP · VPD0.5 and ET relationship (r = 0.844) is better than that between GPP · VPD and ET (r = 0.802). The hysteresis model supports the GPP · VPD0.5 and ET relationship. As uWUE is related to CO2 concentration, its use can improve estimates of GPP and ET, and help understand the effect of CO2 fertilization on carbon storage and water loss.
    07/2014; 41(14). DOI:10.1002/2014GL060741
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    Sha Zhou, Yuefei Huang, Bofu Yu, Guangqian Wang
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    ABSTRACT: With rapid socio-economic development over the past three decades in China, adverse effects of human activities on the natural ecosystem are particularly serious in arid regions where landscape ecology is fragile due to limited water resources and considerable interannual climate variability. Data on land use, surface and ground water, climate, gross domestic product (GDP) per capita from the middle Heihe River Basin were used to (i) examine changes in water consumption, land use composition, and vegetation cover; (ii) evaluate the effectiveness of short-term management strategies for environmental protection and improvement, and (iii) apply and extend the environmental Kuznets curve (EKC) framework to describe the relationship between economic development and environmental quality in terms of the normalized difference vegetation index (NDVI). The results showed that with rapid development of agriculture and economy, land use change for the period 1986–2000 was characterized by the expansion of constructed oases, considerable contraction of oasis-desert transitional zone and natural oases. This has led to a decrease in ecosystem stability. Since 2001, effective basin management has brought about improved environment conditions, with a more optimal hierarchical structure of vegetation cover. The original EKC model could not explain most of the observed variation in NDVI (R2 = 0.37). Including additional climate variables, the extended EKC model to explain the observed NDVI was much improved (R2 = 0.78), suggesting that inclusion of biophysical factors is a necessary additional dimension in the relationship between economic development and environmental quality for arid regions with great climate variability. The relationship between GDP per capita and NDVI, with the effect of precipitation and temperature taken into consideration, was adequately described by an N-shaped curve, suggesting that the relationship between society and the environment followed a process of promotion, contradiction, and coordination.
    Ecological Engineering 05/2014; DOI:10.1016/j.ecoleng.2014.04.020 · 3.04 Impact Factor
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    ABSTRACT: This paper develops a parallel dynamic programming algorithm to optimize the joint operation of a multi-reservoir system. First, a multi-dimensional dynamic programming (DP) model is formulated for a multi-reservoir system. Second, the DP algorithm is parallelized using a peer-to-peer parallel paradigm. The parallelization is based on the distributed memory architecture and the message passing interface (MPI) protocol. We consider both the distributed computing and distributed computer memory in the parallelization. The parallel paradigm aims at reducing the computation time as well as alleviating the computer memory requirement associated with running a multi-dimensional DP model. Next, we test the parallel DP algorithm on the classic, benchmark four-reservoir problem on a high-performance computing (HPC) system with up to 350 cores. Results indicate that the parallel DP algorithm exhibits good performance in parallel efficiency; the parallel DP algorithm is scalable and will not be restricted by the number of cores. Finally, the parallel DP algorithm is applied to a real-world, five-reservoir system in China. The results demonstrate the parallel efficiency and practical utility of the proposed methodology.
    Advances in Water Resources 05/2014; 67:1-15. DOI:10.1016/j.advwatres.2014.01.002 · 2.78 Impact Factor
  • Deyu Zhong, Guangqian Wang, Baosheng Wu
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    ABSTRACT: The drift velocity, at which sediment disperses relative to the motion of water-sediment mixtures, is a key variable in two-phase mixture equations. A constitutive relation for the drift velocity, expressed as a power series in the particle bulk Stokes number, was obtained by solving the momentum equation for sediment with the perturbation approach. It shows that gravity and turbulent diffusion are the primary dispersion effects on sediment, whereas flow inertia, particle-particle interactions, and other forces such as lift are the first-order particle inertial corrections that also play significant roles in sediment suspension. Analysis proves that studies based on turbulent diffusion theory are the zeroth-order approximations to the present formulation with respect to the particle inertia effect. The vertical concentration and velocity distributions of sediment in simple flows were investigated with the two-phase mixture equations closed by the drift velocity acquired in the research reported in this paper. The calculated concentration profiles agree well with measurements when the first-order particle inertial effect is considered. The calculated velocity of sediment coincides with available experiments that sediment lags behind water in open-channel flows as a result of turbulence-induced drag.
    Journal of Hydraulic Engineering 01/2014; 140(1):35-47. DOI:10.1061/(ASCE)HY.1943-7900.0000798 · 1.26 Impact Factor
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    ABSTRACT: This paper develops a methodology for optimizing the hydro unit commitment (HUC) for the Three Gorges Project (TGP) in China. The TGP is the world's largest and most complex hydropower system in operation. The objective is to minimize the total operational cost. The decision variables are the startup or shutdown of each of the available units in the system and the power releases from the online units. The mathematical formulation must take into account the head variation over the operation periods as the net head changes from hour to hour and affects power generation. Additionally, the formulation must consider the operation of 32 heterogeneous generating units and the nonlinear power generation function of each unit. A three-dimensional interpolation technique is used to accurately represent the nonlinear power generation function of each individual unit, taking into account the time-varying head as well as the non-smooth limitations for power output and power release. With the aid of integer variables that represent the on/off and operation partition statuses of a unit, the developed HUC model for the TGP conforms to a standard mixed integer linear programming (MILP) formulation. We demonstrate the performance and utility of the model by analyzing the results from several scenarios for the TGP.
    IEEE Transactions on Power Systems 11/2013; PP(99):1-10. DOI:10.1109/TPWRS.2013.2288933 · 3.53 Impact Factor
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    Hao Wang, Xudong Fu, Yuanjian Wang, Guangqian Wang
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    ABSTRACT: The distributed basin model (DBM) has become one of the most effective tools in river basin studies. In order to overcome the efficiency bottleneck of DBM, an effective parallel-computing method, named temporal-spatial discretization method (TSDM), is proposed. In space, TSDM adopts the sub-basin partitioning manner to the river basin. Compared to the existing sub-basin-based parallel methods, more computable units can be supplied, organized and dispatched using TSDM. Through the characteristic of the temporal-spatial dual discretization, TSDM is capable of exploiting the river-basin parallelization degree to the maximum extent and obtaining higher computing performance. A mathematical formula assessing the maximum speedup ratio (MSR) of TSDM is provided as well. TSDM is independent of the implementation of any physical models and is preliminarily tested in the Lhasa River basin with 1-year rainfall-runoff process simulated. The MSR acquired in the existing traditional way is 7.98. Comparatively, the MSR using TSDM equals to 15.04 under the present limited computing resources, which appears to still have potential to keep increasing. The final results demonstrate the effectiveness and applicability of TSDM.
    Computers & Geosciences 08/2013; 58:62–68. DOI:10.1016/j.cageo.2013.04.026 · 1.56 Impact Factor
  • QiHua Ran, DanYang Su, XuDong Fu, GuangQian Wang
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    ABSTRACT: To conduct a large-scale hydrologic-response and landform evolution simulation at high resolution, a complex physics-based numerical model, the Integrated Hydrology Model (InHM), was revised utilizing cluster parallel computing. The parallelized InHM (ParInHM) divides the simulated area into multiple catchments based on geomorphologic features, and generates boundary-value problems for each catchment to construct simulation tasks, which are then dispatched to different computers to start the simulation. Landform evolution is considered during simulating and implemention in one framework. The dynamical Longest-Processing-Time (LPT) first scheduling algorithm is applied to job management. In addition, a pause-integrate- divide-resume routine method is used to ensure the hydrologic validity during the simulation period. The routine repeats until the entire simulation period is finished. ParInHM has been tested in a computer cluster that uses 16 processors for the calculation, to simulate 100 years’ hydrologic-response and soil erosion for the 117-km2 Kaho’olawe Island in the Hawaiian Islands under two different mesh resolutions. The efficiency of ParInHM was evaluated by comparing the performance of the cluster system utilizing different numbers of processors, as well as the performance of non-parallelized system without domain decomposition. The results of this study show that it is feasible to conduct a regional-scale hydrologic-response and sediment transport simulation at high resolution without demanding significant computing resources.
    Science China Technological Sciences 08/2013; 56(8). DOI:10.1007/s11431-013-5276-4 · 1.11 Impact Factor
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    ABSTRACT: doi: 10.1061/(ASCE)WR.1943-5452.0000379
    Journal of Water Resources Planning and Management 05/2013; DOI:10.1061/(ASCE)WR.1943-5452.0000379 · 1.76 Impact Factor
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    Jie Qin, Deyu Zhong, Guangqian Wang, Sai Leung Ng
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    ABSTRACT: Static armored gravel surfaces composed of man-made and natural gravels have been analyzed using precise digital elevation models. The scaling behavior and spatial arrangement of the gravel surfaces were evaluated and discussed with respect to the successive formation of stable armor layers. The key results relate to structure functions and imbrication analysis of these surfaces: (1) man-made gravel surfaces show a similar scaling behavior and spatial correlation pattern to natural gravel surfaces; (2) man-made gravel surfaces have larger Hurst exponents than natural gravel surfaces; and (3) man-made gravels are poorly imbricated in comparison with natural gravels. Our results suggest that different morphological structures between man-made and natural gravels were attributed to shape features of individual grains.
    Geomorphology 05/2013; 190:16–26. DOI:10.1016/j.geomorph.2013.02.004 · 2.58 Impact Factor
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    ABSTRACT: Purpose ‐ Hydraulic instabilities are one of the most important reasons causing vibrations and fatigues in hydraulic turbines. The present paper aims to find the relationship between pressure pulsations and fatigues of key parts of a Kaplan turbine. Design/methodology/approach ‐ 3D unsteady numerical simulations were preformed for a number of operating conditions at high heads for a prototype Kaplan turbine, with the numerical results verified by online monitoring data. The contact method and the weak fluid-structure interaction method were used to calculate the stresses in the multi-body mechanism of the Kaplan turbine runner body based on the unsteady flow simulation result. Findings ‐ The results show that vortices in the vaneless space between the guide vanes and blades cause large pressure pulsations and vibrations for high heads with small guide vane openings. The dynamic stresses in the runner body parts are small for high heads with large guide vane openings, but are large for high heads with small guide vane openings. Originality/value ‐ A comprehensive numerical method including computational fluid dynamics analyses, finite element analyses and the contact method for multi-body dynamics has been used to identity the sources of unit vibrations and key part failures.
    Engineering Computations 03/2013; 30(3). DOI:10.1108/02644401311314376 · 1.21 Impact Factor
  • Hao Wang, Xudong Fu, Guangqian Wang
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    ABSTRACT: River coding method for drainage networks plays an very important role in the physical simulation of river basins. In this study we developed a new river coding method named Multi-tree Coding Method (MCM), which has the following features: (1) it is established on a topological pattern reflecting the dendriform structure of drainage networks; (2) the multi-tree code can be effectively managed by the database to perform convenient topological search toward drainage networks using Structured Query Language (SQL); (3) the multi-tree code does not exhibit digital overflow problems in the computer, thus any resolution and scale drainage networks can easily be coded; and (4) it supports high-efficient search process. A river reach can be directly positioned in a drainage network under MCM, without the complex search process from all river reaches. This feature has great potential to improve the computational performance of basin models. We demonstrate here the efficiency and practicality of MCM by testing it in the Yalu Tsangpo river basin, Tibet. A drainage network with 140,745 digital reaches was extracted from the digital elevation model (DEM), and the multi-tree codes of all river reaches were obtained.
    Computers & Geosciences 03/2013; 52:300–306. DOI:10.1016/j.cageo.2012.11.005 · 1.56 Impact Factor
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    Jie Qin, Deyu Zhong, Guangqian Wang
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    ABSTRACT: Morphological characteristics of ripples are analyzed considering bed surfaces as two dimensional random fields of bed elevations. Two equilibrium phases are analyzed with respect to successive development of ripples based on digital elevation models. The key findings relate to the shape of the two dimensional second-order structure functions and multiscaling behavior revealed by higher-order structure functions. Our results suggest that (1) the two dimensional second-order structure functions can be used to differentiate the two equilibrium phases of ripples; and (2) in contrast to the elevational time series of ripples that exhibit significant multiscaling behavior, the DEMs of ripples at both equilibri- um phases do not exhibit multiscaling behavior.
    Journal of Hydrology and Hydromechanics 01/2013; 61(4). DOI:10.2478/johh-2013-0037 · 1.23 Impact Factor
  • 12/2012; 4(23):531-539. DOI:10.4156/aiss.vol4.issue23.66
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    Jie Qin, Deyu Zhong, Guangqian Wang, Sai Leung Ng
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    ABSTRACT: Imbrication of static armor surfaces is investigated based on laser-scanned DEMs collected from both flume experiments and the field. Two approaches are employed to study the imbrication including inclination index and aspect and slope (AS) method. The inclination index is found to be a sensitive and valid method for indicating the existence of imbrication. Application of this method, however, requires high-resolution surfaces. A positive relationship is obtained between the inclination index and effective grain size, which can be used to deduce the historical armoring shear stress. The AS method based on the statistics of local gradients describes the imbrication in a more straightforward way. However, this method is based on the statistics of orientations of grids rather than individual grains. An improved AS method is proposed in this study based on orientations of grains with the help of automated grain segmentation method. The improved AS method makes this method more reasonable and increases the applicable range.
    Geomorphology 07/2012; s 159–160:116–124. DOI:10.1016/j.geomorph.2012.03.012 · 2.58 Impact Factor