http://hdl.handle.net/2117/3856 2013-05-22T20:29:23Z http://hdl.handle.net/2117/19180 Title: Blending of radar and gauge rainfall measurements: a preliminary analysis of the impact of radar errors Authors: Sempere Torres, Daniel; Berenguer Ferrer, Marc; Velasco Forero, Carles Abstract: Several methodologies have been proposed to combine radar and raingauge measurements with the aim of generating improved quantitative precipitation estimates (QPEs). These methods are based on interpolating point raingauge measurements (implicitly assumed to be “the truth”) and benefiting from the structure of the rainfall field as depicted by the radar. The use of a non-parametric approach based on radar measurements has been recently demonstrated, showing the benefits in the interpolation of raingauge measurements under the hypotheses of the Kriging approach. Several experiments have been carried out over a large number of cases and a variety of regions, Kriging with an external drift (i.e. the radar description of the rainfall field) being the approach showing more robust and (overall) better performance. Here, the impact of the discrepancies between two almost-collocated radars on the blended QPE fields was investigated. 2013-05-13T13:09:06Z http://hdl.handle.net/2117/18644 Title: Ensemble radar precipitation estimation for nowcasting and hydrology in the Alps Authors: Germann, Urs; Hering, Alessandro; Berenguer Ferrer, Marc; Sempere Torres, Daniel; Salvadè, Georges Abstract: This paper explores the novel idea of generating ensables of radar precipitation estimates. 2013-04-05T11:35:36Z http://hdl.handle.net/2117/16962 Title: Predictability assessment of nowcasts in high-impact heavy precipitation events Authors: Bech, Joan; Berenguer Ferrer, Marc 2012-11-19T18:55:18Z http://hdl.handle.net/2117/16960 Title: Adding value to the measurements of an X-band radar on Catalonian coast Authors: Berenguer Ferrer, Marc; Sempere Torres, Daniel Abstract: Rainscanner@Barcelona is an experiment assessing the hydrological value of a small X-band radar in urban areas. 2012-11-19T18:40:07Z http://hdl.handle.net/2117/16959 Title: The diurnal cycle of precipitation from continental radar mosaics and numerical weather prediction models. Part II: intercomparison among numerical models and with nowcasting Authors: Berenguer Ferrer, Marc; Surcel, Madalina; Zawadzki, Isztar; Xue, Ming; Kong, Fanyou Abstract: This second part of a two-paper series compares deterministic precipitation forecasts from the Storm-Scale Ensemble Forecast System (4-km grid) run during the 2008 NOAA Hazardous Weather Testbed (HWT) Spring Experiment, and from the Canadian Global Environmental Multiscale (GEM) model (15 km), in terms of their ability to reproduce the average diurnal cycle of precipitation during spring 2008. Moreover, radar-based nowcasts generated with the McGill Algorithm for Precipitation Nowcasting Using Semi-Lagrangian Extrapolation (MAPLE) are analyzed to quantify the portion of the diurnal cycle explained by the motion of precipitation systems, and to evaluate the potential of the NWP models for very short-term forecasting. The observed diurnal cycle of precipitation during spring 2008 is characterized by the dominance of the 24-h harmonic,which shifts with longitude, consistent with precipitation traveling across the continent. Time–longitude diagrams show that the analyzed NWP models partially reproduce this signal, but show more variability in the timing of initiation in the zonal motion of the precipitation systems than observed from radar. Traditional skill scores show that the radar data assimilation is the main reason for differences in model performance, while the analyzed models that do not assimilate radar observations have very similar skill. The analysis of MAPLE forecasts confirms that the motion of precipitation systems is responsible for the dominance of the 24-h harmonic in the longitudinal range 1038–858W, where 8-h MAPLE forecasts initialized at 0100, 0900, and 1700UTC successfully reproduce the eastward motion of rainfall systems. Also, on average, MAPLE outperforms radar data assimilating models for the 3–4 h after initialization, and nonradar data assimilating models for up to 5 h after initialization. 2012-11-19T18:26:28Z http://hdl.handle.net/2117/16481 Title: A scenario-incorporating analysis of the propagation of uncertainty to flash flood simulations Authors: Quintero Duque, Felipe; Sempere Torres, Daniel; Berenguer Ferrer, Marc; Baltas, Evangelos Abstract: This study proposes a methodology to analyze the propagation of uncertainty arising from radar rainfall and model parameter estimation to the flow simulations obtained from flash flood modeling. For this purpose an ensemble approach that describes the error from radar rainfall estimation and a novel approach that considers the seasonality and variability of catchment conditions in the estimation of model parameters have been implemented. The methodology analyzes the separate effect of each sourceof uncertainty and their interaction on runoff simulations. The methodology has been applied in the Besòs river basin, Catalonia (Spain) with a drainage area of 1020 km2. The results show that the effect of parameter estimation uncertainty produces a smaller spread in the model realizations than the effect caused by the uncertainty in rainfall estimation. 2012-09-13T12:21:28Z http://hdl.handle.net/2117/16400 Title: Blending of radar and gauge rainfall measurements: a preliminary analysis of the impact of radar errors Authors: Sempere Torres, Daniel; Berenguer Ferrer, Marc; Velasco Forero, Carlos Alfonso Abstract: Several methodologies have been proposed to combine radar and raingauge measurements with the aim of generating improved quantitative precipitation estimates (QPEs). These methods are based on interpolating point raingauge measurements (implicitly assumed to be “the truth”) and benefiting from the structure of the rainfall field as depicted by the radar. The use of a non-parametric approach based on radar measurements has been recently demonstrated, showing the benefits in the interpolation of raingauge measurements under the hypotheses of the Kriging approach. Several experiments have been carried out over a large number of cases and a variety of regions, Kriging with an external drift (i.e. the radar description of the rainfall field) being the approach showing more robust and (overall) better performance. Here, the impact of the discrepancies between two almost-collocated radars on the blended QPE fields was investigated. 2012-08-29T10:52:45Z http://hdl.handle.net/2117/15903 Title: Improving risk management for flash floods and debris flow events Authors: Uijlenhoet, Remko; Sempere Torres, Daniel; Velasco Montes, David; Berenguer Ferrer, Marc; Bateman Pinzón, Allen; Germann, Urs; Thielen, Jutta; Beven, K.; Zappa, Massimiliano; Demarchi, M.; Bertoli, M.; Gaechter, M.; Velasco, E.; Wittwer, C.; Sánchez-Diezma Guijarro, Rafael; Vilaclara, E.; Pegram, Geoffrey; Papa, M.; Escaler, I.; Lombardi, G.; Santiago, A.; Zawadzki, Isztar 2012-05-21T15:36:58Z http://hdl.handle.net/2117/15630 Title: Flow structure and resistance in flexible vegetated channels Authors: Velasco Montes, David; Bateman Pinzón, Allen; Redondo Apraiz, José Manuel Abstract: The present paper helps to understand the behaviour of the flow through plants, as a first approximation to the environmental interactions happening in natural rivers. 2012-03-21T10:34:48Z http://hdl.handle.net/2117/13456 Title: A variational approach to retrieve 3D radar reflectivity composites Authors: Roca Sancho, Jordi; Berenguer Ferrer, Marc; Sempere Torres, Daniel Abstract: This study proposes an alternative methodology to obtain high-resolution radar reflectivity composites based on a variational approach considering different error sources in an explicit manner. The methodology retrieves the 3-dimensional precipitation field most compatible with the observations from the different radars of the network. With this aim, the methodology uses a model that simulates the radar sampling of the atmosphere. The model settings are different for each radar and include features such as the radar location, hardware parameters (beam width, pulse length…) and the scan strategy. The methodology follows the concept of an inverse method based on the minimization of a cost function that penalizes discrepancies between the simulated and actual observations for each radar. The simulation model is able to reproduce the effect of beam broadening with the distance and attenuation by intense precipitation. The methodology has been applied on two radars close to Barcelona (Spain). 2011-10-07T12:07:28Z http://hdl.handle.net/2117/13455 Title: A radar-based flash flood forecasting for the Llobregat river basin in the Catalonia region (Spain) Authors: Quintero Duque, Felipe; Versini, Pierre Antonie; Baltas, Evangelos; Berenguer Ferrer, Marc; Sempere Torres, Daniel Abstract: In this research paper, a flash flood modeling system implemented in a Mediterranean river basin is presented. Radar precipitation estimation along with hydrological modeling techniques are implemented within the system for simulating the runoff generation and routing processes occurring in the catchment. However, there exists an uncertainty related with the estimation of radar precipitation (Zawadzki, 1984) and from model calibration (Beven, 2006). Such uncertainty is propagated to the resulting discharge simulations. The aim of this research paper is to propose a methodology to analyze the propagation of uncertainty occurring at the different processes of the modeling system. For this purpose, a Monte Carlo simulation approach is used to consider the uncertainty arising from rainfall and model parameter estimation. 2011-10-07T11:52:20Z http://hdl.handle.net/2117/13416 Title: Geostatistical radar-raingauge combination with nonparametric correlograms: methodological considerations and application in Switzerland Authors: Schiemann, Reinhard; Erdin, Rebecca; Willi, Marco; Frei, Christoph; Berenguer Ferrer, Marc; Sempere Torres, Daniel Abstract: Modelling spatial covariance is an essential part of all geostatistical methods. Traditionally, parametric semivariogram models are fit from available data. More recently, it has been suggested to use nonparametric correlograms obtained from spatially complete data fields. Here, both estimation techniques are compared. Nonparametric correlograms are shown to have a substantial negative bias. Nonetheless, when combined with the sample variance of the spatial field under consideration, they yield an estimate of the semivariogram that is unbiased for small lag distances. This justifies the use of this estimation technique in geostatistical applications. Various formulations of geostatistical combination (Kriging) methods are used here for the construction of hourly precipitation grids for Switzerland based on data from a sparse realtime network of raingauges and from a spatially complete radar composite. Two variants of Ordinary Kriging (OK) are used to interpolate the sparse gauge observations. In both OK variants, the radar data are only used to determine the semivariogram model. One variant relies on a traditional parametric semivariogram estimate, whereas the other variant uses the nonparametric correlogram. The variants are tested for three cases and the impact of the semivariogram model on the Kriging prediction is illustrated. For the three test cases, the method using nonparametric correlograms performs equally well or better than the traditional method, and at the same time offers great practical advantages. Furthermore, two variants of Kriging with external drift (KED) are tested, both of which use the radar data to estimate nonparametric correlograms, and as the external drift variable. The first KED variant has been used previously for geostatistical radar-raingauge merging in Catalonia (Spain). The second variant is newly proposed here and is an extension of the first. Both variants are evaluated for the three test cases as well as an extended evaluation period. It is found that both methods yield merged fields of better quality than the original radar field or fields obtained by OK of gauge data. The newly suggested KED formulation is shown to be beneficial, in particular in mountainous regions where the quality of the Swiss radar composite is comparatively low. An analysis of the Kriging variances shows that none of the methods tested here provides a satisfactory uncertainty estimate. A suitable variable transformation is expected to improve this. 2011-10-04T10:21:55Z http://hdl.handle.net/2117/13095 Title: SBMcast - An ensemble nowcasting technique to assess the uncertainty in rainfall forecasts by Lagrangian extrapolation Authors: Berenguer Ferrer, Marc; Sempere Torres, Daniel; Pegram, Geoffrey Abstract: Deterministic nowcasting based on Lagrangian extrapolation of recent radar observations is a technique used in many operational and research centers and has proven to be useful at extending the anticipation with which flows can be forecasted with a rainfall–runoff model. However, the improvement in flow forecasts is not known a priory and case-dependent, mostly depending on the predictability of the rainfall field. In this work a probabilistic technique has been developed to automatically quantify the uncertainty in radar-based nowcasts obtained by Lagrangian extrapolation to be used in hydrology. The technique follows the ensemble approach: it generates a number of realizations of rainfall forecasts compatible with observations and that reserve the space and time structure of the rainfall field according to the String of Beads model. The results show that the technique reasonably reproduces the evolution of the rainfall field, but that, overall, the errors are underestimated in part due to the fact that the uncertainty in rainfall forecasts due to errors in the motion field is neglected in this current version of the method. 2011-08-23T10:40:36Z http://hdl.handle.net/2117/13090 Title: Radar rainfall: separating signal and noise fields to generate meaningful ensembles Authors: Pegram, Geoffrey; Llort Pavon, Xavier; Sempere Torres, Daniel Abstract: For the purpose of generating meaningful stochastic ensembles of radar estimates of rainfall, a relatively simple and objective method of separating a radar rainfall image into signal and noise is described. An alternative noise field, with the same spectrum as the original noise, can then be simulated and combined with the signal field of each successive image, to generate an ensemble member for performing sensitivity studies. The method is based on identifying the appropriate wavelength in the power spectrum which defines the variance threshold used to separate noise from signal. The algorithm is explained and figures illustrate the efficacy of the procedure. 2011-08-23T08:47:03Z http://hdl.handle.net/2117/12742 Title: Assessment of the susceptibility of roads to flooding based on geographical information – test in a flash flood prone area (the Gard region , France) Authors: Versini, Pierre Antonie; Gaume, Eric; Andrieu, Herve Abstract: In flash flood prone areas, roads are often the first assets affected by inundations which make rescue operations difficult and represent a major threat to lives: almost half of the victims are car passengers trapped by floods. In the past years, the Gard region (France) road management services have realized an extensive inventory of the known road submersions that occurred during the last 40 years. This inventory provided an unique opportunity to analyse the causes of road flooding in an area frequently affected by severe flash floods. It will be used to develop a road submersion susceptibility rating method, representing the first element of a road warning system. This paper presents the results of the analysis of this data set. A companion paper will show how the proposed road susceptibility rating method can be combined with distributed rainfall-runoff simulations to provide accurate road submersion risk maps. The very low correlation between the various possible explanatory factors and the susceptibility to flooding measured by the number of past observed submersions implied the use of particular statistical analysis methods based on the general principals of the discriminant analysis. The analysis led to the definition of four susceptibility classes for river crossing road sections. Validation tests confirmed that this classification is robust, at least in the considered area. One major outcome of the analysis is that the susceptibility to flooding is rather linked to the location of the road sections than to the size of the river crossing structure (bridge or culvert). 2011-06-09T09:42:46Z