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Taichung, Taiwan

Chang F.-J.,National Taiwan University | Chiang Y.-M.,Zhejiang University | Tsai M.-J.,National Taiwan University | Shieh M.-C.,Water Resources Agency | And 2 more authors.
Journal of Hydrology | Year: 2014

The complex temporal heterogeneity of rainfall coupled with mountainous physiographic context makes a great challenge in the development of accurate short-term rainfall forecasts. This study aims to explore the effectiveness of multiple rainfall sources (gauge measurement, and radar and satellite products) for assimilation-based multi-sensor precipitation estimates and make multi-step-ahead rainfall forecasts based on the assimilated precipitation. Bias correction procedures for both radar and satellite precipitation products were first built, and the radar and satellite precipitation products were generated through the Quantitative Precipitation Estimation and Segregation Using Multiple Sensors (QPESUMS) and the Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks-Cloud Classification System (PERSIANN-CCS), respectively. Next, the synthesized assimilated precipitation was obtained by merging three precipitation sources (gauges, radars and satellites) according to their individual weighting factors optimized by nonlinear search methods. Finally, the multi-step-ahead rainfall forecasting was carried out by using the adaptive network-based fuzzy inference system (ANFIS). The Shihmen Reservoir watershed in northern Taiwan was the study area, where 641 hourly data sets of thirteen historical typhoon events were collected. Results revealed that the bias adjustments in QPESUMS and PERSIANN-CCS products did improve the accuracy of these precipitation products (in particular, 30-60% improvement rates for the QPESUMS, in terms of RMSE), and the adjusted PERSIANN-CCS and QPESUMS individually provided about 10% and 24% contribution accordingly to the assimilated precipitation. As far as rainfall forecasting is concerned, the results demonstrated that the ANFIS fed with the assimilated precipitation provided reliable and stable forecasts with the correlation coefficients higher than 0.85 and 0.72 for one- and two-hour-ahead rainfall forecasting, respectively. The obtained forecasting results are very valuable information for the flood warning in the study watershed during typhoon periods. © 2013 Elsevier B.V.

Cheng S.-J.,Diwan University | Lee C.-F.,Diwan University | Lee J.-H.,Water Resources Agency
Water Resources Management | Year: 2010

This study mainly explores effects of urbanization factors on hydrograph parameters. Urbanization impacts of the developing watershed are evaluated based on rainfall-runoff simulations. A total of 51 rainfall-runoff events occurred from 1966 to 2002. Forty of these were calibrated, and effects of urbanization factors on runoff hydrographs resulting from a simple hydrological model were assessed. The block Kriging method was used to estimate the mean rainfall of the Wu-Tu watershed, and its hourly excesses were calculated by using the non-linear programming method. The remaining 11 cases were used to test the established relationships. The calibration and verification results confirm that the integral methods used in this study effectively illustrate the hydrological and geomorphic conditions in complex urbanization processes. Parameter n responds more sensitively than parameter k to increasing impervious areas and population densities. Additionally, parameter n responds more strongly to imperviousness than to population. Therefore, an impervious area is an important reference for analyzing hydrological changes of urbanization in the Wu-Tu watershed. © Springer Science+Business Media B.V. 2009.

Chang L.-C.,Tamkang University | Shen H.-Y.,Tamkang University | Wang Y.-F.,Water Resources Agency | Huang J.-Y.,Tamkang University | Lin Y.-T.,Tamkang University
Journal of Hydrology | Year: 2010

Estimation of flood depths and extents may provide disaster information for dealing with contingency and alleviating risk and loss of life and property. We present a two-stage procedure underlying CHIM (clustering-based hybrid inundation model), which is composed of linear regression models and ANNs (artificial neural networks) to build the regional flood inundation forecasting model. The two-stage procedure mainly includes data preprocessing and model building stages. In the data preprocessing stage, K-means clustering is used to categorize the data points of the different flooding characteristics in the study area and to identify the control point(s) from individual flooding cluster(s). In the model building stage, three classes of flood depth forecasting models are built in each cluster: the back-propagation neural network (BPNN) for each control point, the linear regression models for the grids that have highly linear correlation with the control point, and a multi-grid BPNN for the grids that do not have highly linear correlation with the control point. The practicability and effectiveness of the proposed approach is tested in the Dacun Township, Changhua County in Central Taiwan. The results show that the proposed CHIM can continuously and adequately provide 1-h-ahead flood inundation maps that well match the simulation flood inundation results and very effectively reduce 99% CPU time. © 2010 Elsevier B.V. All rights reserved.

Hovius N.,University of Cambridge | Meunier P.,CNRS ENS Geology Laboratory | Lin C.-W.,National Cheng Kung University | Chen H.,National Taiwan University | And 4 more authors.
Earth and Planetary Science Letters | Year: 2011

Large earthquakes deform the Earth's surface and drive topographic growth in the frontal zones of mountain belts. They also induce widespread mass wasting, reducing relief. The sum of these two opposing effects is unknown. Using a time series of landslide maps and suspended sediment transport data, we show that the MW7.6 Chi-Chi earthquake in Taiwan was followed by a period of enhanced mass wasting and fluvial sediment evacuation, peaking at more than five times the background rate and returning progressively to pre-earthquake levels in about six years. Therefore it is now possible to calculate the mass balance and topographic effect of the earthquake. The Choshui River has removed sediment representing more than 30% of the added rock mass from the epicentral area. This has resulted in a reduction of surface uplift by up to 0.25m, or 35% of local elevation change, and a reduction of the area where the Chi-Chi earthquake has built topography. For other large earthquakes, erosion may evolve in similar, predictable ways, reducing the efficiency of mountain building in fold-and-thrust belts and the topographic expression of seismogenic faults, prolonging the risk of triggered processes, and impeding economic regeneration of epicentral areas. © 2011 Elsevier B.V.

Hilton R.G.,CNRS Paris Institute of Global Physics | Hilton R.G.,Durham University | Galy A.,University of Cambridge | Hovius N.,University of Cambridge | And 2 more authors.
Geology | Year: 2011

Mountain building exposes fossil organic carbon (OCfossil) in exhumed sedimentary rocks. Oxidation of this material releases carbon dioxide from long-term geological storage to the atmosphere. OCfossil is mobilized on hillslopes by mass wasting and transferred to the particulate load of rivers. In large fluvial systems, it is thought to be oxidised in transit, but in short, steep rivers that drain mountain islands, OCfossil may escape oxidation and re-enter geological storage due to rapid fluvial transfer to the ocean. In these settings, the rates of OCfossil transfer and their controls remain poorly constrained. Here we quantify the erosion of OCfossil from the Taiwan mountain belt, combining discharge statistics with measurements of particulate organic carbon load and source in 11 rivers. Annual OCfossil yields in Taiwan vary from 12 ± 1 to 246 ± 22 tC km-2 yr-1, controlled by the high physical erosion rates that accompany rapid crustal shortening and frequent typhoon impacts. Efficient transfer of this material ensures that 1.3 ± 0.1 × 106 tC yr-1 of OCfossil exhumed in Taiwan is delivered to the ocean, with <15% loss due to weathering in transit. Our findings suggest that erosion of coastal mountain ranges can force efficient transfer and long-term re-accumulation of OCfossil in marine sediments, further enhancing the role of mountain building in the long-term storage of carbon in the lithosphere. © 2011 Geological Society of America.

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