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991.
A framework for testing the ability of models to project climate change and its impacts 总被引:1,自引:0,他引:1
J. C. Refsgaard H. Madsen V. Andréassian K. Arnbjerg-Nielsen T. A. Davidson M. Drews D. P. Hamilton E. Jeppesen E. Kjellström J. E. Olesen T. O. Sonnenborg D. Trolle P. Willems J. H. Christensen 《Climatic change》2014,122(1-2):271-282
Models used for climate change impact projections are typically not tested for simulation beyond current climate conditions. Since we have no data truly reflecting future conditions, a key challenge in this respect is to rigorously test models using proxies of future conditions. This paper presents a validation framework and guiding principles applicable across earth science disciplines for testing the capability of models to project future climate change and its impacts. Model test schemes comprising split-sample tests, differential split-sample tests and proxy site tests are discussed in relation to their application for projections by use of single models, ensemble modelling and space-time-substitution and in relation to use of different data from historical time series, paleo data and controlled experiments. We recommend that differential-split sample tests should be performed with best available proxy data in order to build further confidence in model projections. 相似文献
992.
Oliver Montenbruck André Hauschild Yago Andres Axel von Engeln Christian Marquardt 《GPS Solutions》2013,17(2):199-209
The processing of GPS radio occultation measurements for use in numerical weather predictions requires a precise orbit determination (POD) of the host satellite in near-real-time. Making use of data from the GRAS instrument on Metop-A, the performance of different GPS ephemeris products and processing concepts for near-real-time and real-time POD is compared. While previous analyses have focused on the achievable along-track velocity accuracy, this study contributes a systematic comparison of the resulting estimated bending angles. This enables a more rigorous trade-off of different orbit determination methodologies in relation to the end-user needs for atmospheric science products. It is demonstrated that near-real-time GPS orbit and clock products have reached a sufficient quality to determine the Metop-A along-track velocity with an accuracy of better than 0.05 mm/s that was formerly only accessible in post-processing. The resulting bending angles are shown to exhibit standard deviation and bias differences of less than 0.3 % compared with post-processed products up to altitudes of at least 40 km, which is notably better than 1 % accuracy typically assumed for numerical weather predictions in this height regime. Complementary to the analysis of ground-based processing schemes, the potential of autonomous on-board orbit determination is investigated for the first time. Using actual GRAS flight data, it is shown that a 0.5 m 3D rms position accuracy and a 0.2 mm/s along-track velocity accuracy can in fact be obtained in real-time with the currently available GPS broadcast ephemeris quality. Bending angles derived from the simulated real-time processing exhibit a minor performance degradation above tangent point heights of 40 km but negligible differences with respect to ground-based products below this altitude. Onboard orbit determination and, if desired, bending angle computation, can thus enable a further simplification of the ground segment in future radio occultation missions and contribute to reduced product latencies for radio occultation data assimilation in numerical weather predictions. 相似文献
993.
994.
Pedro H. A. Medeiros Andreas Güntner Till Francke George L. Mamede José Carlos de Araújo 《水文科学杂志》2013,58(4):636-648
Abstract Rainfall–runoff induced soil erosion causes important environmental degradation by reducing soil fertility and impacting on water availability as a consequence of sediment deposition in surface reservoirs used for water supply, particularly in semi-arid areas. However, erosion models developed on experimental plots cannot be directly applied to estimate sediment yield at the catchment scale, since sediment redistribution is also controlled by the transport conditions along the landscape. In particular, representation of landscape connectivity relating to sediment transfer from upslope areas to the river network is required. In this study, the WASA-SED model is used to assess the spatial and temporal patterns of water and sediment connectivity for a semi-arid meso-scale catchment (933 km2) in Brazil. It is shown how spatial and temporal patterns of sediment connectivity within the catchment change as a function of landscape and event characteristics. This explains the nonlinear catchment response in terms of sediment yield at the outlet. Citation Medeiros, P. H. A., Güntner, A., Francke, T., Mamede, G. L. & de Araújo, J. C. (2010) Modelling spatio-temporal patterns of sediment yield and connectivity in a semi-arid catchment with the WASA-SED model. Hydrol. Sci. J. 55(4), 636–648. 相似文献
995.
Louise Crochemore Charles Perrin Vazken Andréassian Uwe Ehret Simon P. Seibert Salvatore Grimaldi 《水文科学杂志》2013,58(3):402-423
AbstractThis paper investigates the relationship between expert judgement and numerical criteria when evaluating hydrological model performance by comparing simulated and observed hydrographs. Using a web-based survey, we collected the visual evaluations of 150 experts on a set of high- and low-flow hydrographs. We then compared these answers with results from 60 numerical criteria. Agreement between experts was found to be more frequent in absolute terms (when rating models) than in relative terms (when comparing models), and better for high flows than for low flows. When comparing the set of 150 expert judgements with numerical criteria, we found that most expert judgements were loosely correlated with a numerical criterion, and that the criterion that best reflects expert judgement varies from expert to expert. Overall, we identified two groups of 10 criteria yielding an equivalent match with the expertise of the 150 participants in low and high flows, respectively. A single criterion common to both groups (the Hydrograph Matching Algorithm with mean absolute error) may represent a good indicator for the overall evaluation of models based on hydrographs. We conclude that none of the numerical criteria examined here can fully replace expert judgement when rating hydrographs, and that both relative and absolute evaluations should be based on the judgement of multiple experts.
Editor D. Koutsoyiannis 相似文献
996.
Manuel Carbajal-Romero Esteban Flores-Mendez Norberto Flores-Guzmán Jaime Núñez-Farfán Enrique Olivera-Villaseñor Francisco José Sánchez-Sesma 《Geofísica Internacional》2013,52(1):21-30
The present work shows the propagation of Scholte interface waves at the boundary of a fluid in contact with an elastic solid, for a broad range of solid materials. It has been demonstrated that by an analysis of diffracted waves in a fluid it is possible to infer the mechanical properties of the elastic solid medium, specifically, its propagation velocities. For this purpose, the diffracted wave field of pressures and displacements, due to an initial wave of pressure in the fluid, are expressed using boundary integral representations, which satisfy the equation of motion. The source in the fluid is represented by a Hankel’s function of second kind and zero order. The solution to this wave propagation problem is obtained by means of the Indirect Boundary Element Method, which is equivalent to the well-known Somigliana representation theorem. The validation of the results is carried out by using the Discrete Wave Number Method and the Spectral Element Method. Firstly, we show spectra of pressures that illustrate the behavior of the fluid for each solid material considered, then, we apply the Fast Fourier Transform to show results in time domain. Snapshots to exemplify the emergence of Scholte’s waves are also included. 相似文献
997.
María Teresa Ramírez-Herrera José Antonio Navarrete-Pacheco 《Pure and Applied Geophysics》2013,170(6-8):1067-1080
The M w = 9.0 earthquake that occurred off the coast of Japan’s Tohoku region produced a great tsunami causing catastrophic damage and loss of life. Within hours of the tsunami event, satellite data were readily available and massive media coverage immediately circulated thousands of photographs and videos of the tsunami. Satellite data allow a rapid assessment of inundated areas where access can be difficult either as a result of damaged infrastructure (e.g., roads, bridges, ports, airports) or because of safety issues (e.g., the hazard at Nuclear Power Plant at Fukushima). In this study, we assessed in a day tsunami inundation distances and runup heights using satellite data (very high-resolution satellite images from the GeoEye1 satellite and from the DigitalGlobe worldview, SRTM and ASTER GDEM) of the Tohoku region, Northeast Japan. Field survey data by Japanese and other international scientists validated our results. This study focused on three different locations. Site selection was based on coastal morphologies and the distance to the tsunami source (epicenter). Study sites are Rikuzentakata, Oyagawahama, and Yagawahama in the Oshika Peninsula, and the Sendai coastal plain (Sendai City to Yamamoto City). Maximum inundation distance (6 km along the river) and maximum runup (39 m) at Rikuzentakata estimated from satellite data agree closely with the 39.7 m inundation reported in the field. Here the ria coastal morphology and horn shaped bay enhanced the tsunami runup and effects. The Sendai coastal plain shows large inundation distances (6 km) and lower runup heights. Natori City and Wakabayashi Ward, on the Sendai plain, have similar runup values (12 and 16 m, respectively) obtained from SRTM data; these are comparable to those obtained from field surveys (12 and 9.5 m). However, at Yagawahama and Oyagawahama, Miyagi Prefecture, both SRTM and ASTER data provided maximum runup heights (41 to 45 m and 33 to 34 m, respectively), which are higher than those measured in the field (about 27 m). This difference in DEM and field data is associated with ASTER and SRTM DEM’s pixel size and vertical accuracy, the latter being dependent on ground coverage, slope, aspect and elevation. Countries with less access to technology and infrastructure can benefit from the use of satellite imagery and freely available DEMs for an initial, pre-field surveys, rapid estimate of inundated areas, distances and runup, and for assisting in hazard management and mitigation after a natural disaster. 相似文献
998.
The aim of this work is to compare macroturbulent coherent structures (MCS) geometry and organization between ice covered and open channel flow conditions. Velocity profiles were obtained using a Pulse‐Coherent Acoustic Doppler Profiler in both open channel and ice‐covered conditions. The friction imposed by the ice cover results in parabolic shaped velocity profiles. Reynolds stresses in the streamwise (u) and vertical (v) components of the flow show positive values near the channel bed and negative values near the ice cover, with two distinctive boundary layers with specific turbulent signatures. Vertically aligned stripes of coherent flow motions were revealed from statistics applied to space‐time matrices of flow velocities. In open channel conditions, the macroturbulent structures extended over the entire depth of the flow whereas they were discontinued and nested close to the boundary walls in ice‐covered conditions. The size of MCS is consequently reduced in scale under an ice cover. The average streamwise length scale is reduced from 2.5 to 0.4Y (u) and from 1.5 to 0.4Y (v) where Y is the flow depth. In open channel conditions, the vertical extent of MCS covers the entire flow depth, whereas the vertical extent was in the range 0.58Y–1Y (u) and 0.81Y–1Y (v) in ice‐covered conditions. Under an ice cover, each boundary wall generates its own set of MCS that compete with each other in the outer region of the flow, enhancing mixing and promoting the dissipation of coherent structures. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
999.
ABSTRACTThe clustering of catchments is important for prediction in ungauged basins, model parameterization and watershed development and management. The aim of this study is to explore a new measure of similarity among catchments, using a data depth function and comparing it with catchment clustering indices based on flow and physical characteristics. A cluster analysis was performed for each similarity measure using the affinity propagation clustering algorithm. We evaluated the similarity measure based on depth–depth plots (DD-plots) as a basis for transferring parameter sets of a hydrological model between catchments. A case study was developed with 21 catchments in a diverse New Zealand region. Results show that clustering based on the depth–depth measure is dissimilar to clustering on catchment characteristics, flow, or flow indices. A hydrological model was calibrated for the 21 catchments and the transferability of model parameters among similar catchments was tested within and between clusters defined by each clustering method. The mean model performance for parameters transferred within a group always outperformed those from outside the group. The DD-plot based method was found to produce the best in-group performance and second-highest difference between in-group and out-group performance.
EDITOR D. Koutsoyiannis; ASSOCIATE EDITOR A. Viglione 相似文献
1000.
André Gustavo da Silva Melo Honorato Gustavo Barbosa Lima da Silva Celso Augusto Guimarães Santos 《水文科学杂志》2013,58(15-16):2060-2075
ABSTRACTCombinations of low-frequency components (also known as approximations) resulting from the wavelet decomposition are tested as inputs to an artificial neural network (ANN) in a hybrid approach, and compared to classical ANN models for flow forecasting for 1, 3, 6 and 12 months ahead. In addition, the inputs are rewritten in terms of the flow, revealing what type of information was being provided to the network, in order to understand the effect of the approximations on the forecasting performance. The results show that the hybrid approach improved the accuracy of all tested models, especially for 1, 3 and 6 months ahead. The input analyses show that high-frequency components are more important for shorter forecast horizons, while for longer horizons, they may worsen the model accuracy. 相似文献