Influencia de la orografía y de la inestabilidad convectiva en la distribución espacial de lluvias extremas en Cataluña

All the flash flood events in Catalonia in the last half century have been methodically studied, with special emphasis on the Novernber 1982 event. The relationship between the space distribution of the rainfall and the orography has been analysed. On the basis of the Palma de Mallorca radiosonde ascents, the convective instability has been ascertained and the minimum necessary ascent for the instabilization has been obtained. Streamlines in the lower troposphere have been drawn, which has enabled us to ascertain the dominant flow direction. Some hydrological information has also been included

Effect of radar rainfall time resolution on the predictive capability of a distributed hydrologic model

The performance of distributed hydrological models depends on the resolution, both spatial and temporal, of the rainfall surface data introduced. The estimation of quantitative precipitation from meteorological radar or satellite can improve hydrological model results, thanks to an indirect estimation at higher spatial and temporal resolution. In this work, composed radar data from a network of three C-band radars, with 6-minutal temporal and 2 × 2 km2 spatial resolution, provided by the Catalan Meteorological Service, is used to feed the RIBS distributed hydrological model. A Window Probability Matching Method (gage-adjustment method) is applied to four cases of heavy rainfall to improve the observed rainfall sub-estimation in both convective and stratiform Z/R relations used over Catalonia. Once the rainfall field has been adequately obtained, an advection correction, based on cross-correlation between two consecutive images, was introduced to get several time resolutions from 1 min to 30 min. Each different resolution is treated as an independent event, resulting in a probable range of input rainfall data. This ensemble of rainfall data is used, together with other sources of uncertainty, such as the initial basin state or the accuracy of discharge measurements, to calibrate the RIBS model using probabilistic methodology. A sensitivity analysis of time resolutions was implemented by comparing the various results with real values from stream-flow measurement stations

Improving QPF by blending techniques at the Meteorological Service of Catalonia

The current operational very short-term and short-term quantitative precipitation forecast (QPF) at the Meteorological Service of Catalonia (SMC) is made by three different methodologies: Advection of the radar reflectivity field (ADV), Identification, tracking and forecasting of convective structures (CST) and numerical weather prediction (NWP) models using observational data assimilation (radar, satellite, etc.). These precipitation forecasts have different characteristics, lead time and spatial resolutions. The objective of this study is to combine these methods in order to obtain a single and optimized QPF at each lead time. This combination (blending) of the radar forecast (ADV and CST) and precipitation forecast from NWP model is carried out by means of different methodologies according to the prediction horizon. Firstly, in order to take advantage of the rainfall location and intensity from radar observations, a phase correction technique is applied to the NWP output to derive an additional corrected forecast (MCO). To select the best precipitation estimation in the first and second hour (t+1 h and t+2 h), the information from radar advection (ADV) and the corrected outputs from the model (MCO) are mixed by using different weights, which vary dynamically, according to indexes that quantify the quality of these predictions. This procedure has the ability to integrate the skill of rainfall location and patterns that are given by the advection of radar reflectivity field with the capacity of generating new precipitation areas from the NWP models. From the third hour (t+3 h), as radar-based forecasting has generally low skills, only the quantitative precipitation forecast from model is used. This blending of different sources of prediction is verified for different types of episodes (convective, moderately convective and stratiform) to obtain a robust methodology for implementing it in an operational and dynamic wa

Une approximation de la prévision saisonnière des étiages et sécheresses en Catalogne

Les étiages et les sécheresses sont une caractéristique hydro-climatique en Espagne. La dernière sécheresse qui a affecté l’Espagne a été extraordinairement grave en Catalogne, où elle s’est prolongée entre l’année 2004 et le printemps de 2008. L’objectif de cette contribution est de montrer l’évolution de cette dernière sécheresse dans le cadre de la caractérisation des sécheresses en Espagne, ainsi qu’une approximation pour faire une prévision saisonnière du débit des rivières qui nourrissent les principaux barrages des Bassins Internes de la Catalogne et la ville de Barcelone. Etant donné que les principales rivières naissent dans les Pyrénées et Pré-Pyrénées, nous avons centré l’analyse pluviométrique sur cette région. En premier lieu, nous avons caractérisé les situations météorologiques associées au déficit de précipitation en la région d’étude. Ensuite, nous avons créé des séries de précipitation mensuelle représentatives des trois bassins d’étude, en utilisant 127 stations pour la période 1940-2008 et nous avons obtenu la distribution par centiles, valeurs qui seront utilisées pour calibrer le modèle hydrologique et obtenir le rang des débits prévus. Nous avons analysé toutes les prévisions disponibles sur des sites Internet et, après une validation pour la période 1998-2008 nous avons sélectionné les prévisions du modèle ECM4. Alors, nous avons créé un index de prévision saisonnière comme combinaison linéaire des valeurs climatiques et la prédiction de ECM4, qui a aussi été validée. Cette information a été introduite dans un modèle hydrologique et nous avons recréé l’évolution prévue de la dernière sécheresse, en considérant les demandes potentielles de la population. Nous avons trouvé une considérable amélioration sur la prévision du volume d’eau retenu aux barrages, amélioration qui pourra être appliquée dans le futur. L’avantage de cette méthode est qu’on peut l’appliquer sur la base de prévisions saisonnières de libre diffusion. Ce travail a été développé dans le contexte du projet SOSTAQUA

Systèmes d'analyses météorologiques dans le Nord-Est de l'Espagne : Validation de SAFRAN et SPAN

International audienceWe present an application and validation of the SAFRAN meteorological analysis system for north-east Spain. SAFRAN is also compared to the SPAN analysis system and the meteorological model HIRLAM-HNR, both operational at AEMET. This application of SAFRAN is intended for hydrological studies. This is the first study that shows an application of SAFRAN outside of France and that compares it with SPAN. This is also the first article validating SPAN's rainfall values. Using one year of observational data, the results show that both SAFRAN and SPAN have a similar performance, which is also similar to SAFRAN's performance in France. Thus, SAFRAN and SPAN are both good tools to force land surface models at high resolution in the area of SAFRAN works under the assumption of the existence of climatically homogeneous zones. Two different sets of zones were tested, one based on the AEMET meteorological warning zones and another one based on hydrological catchments. Better results were obtained when using meteorological warning zones. However, the difference is small. In north-east Spain, SAFRAN has the same limitations that were previously shown in France: the spatial structure of the fields is not realistic enough and wind speed is underestimated. As expected, both SAFRAN and SPAN work better in flat areas than over areas of steep relief. This can be a problem in hydrological studies, especially for the Ebro river basin, where most of the runoff is generated in the Pyrenees