Informe sobre l’estada de recerca a la Universitat d’Edimburg; agost, octubre – desembre 2006

Estudi realitzat a partir d’una estada al laboratori del Dr. Maurizio Mencuccini a la School of GeoSciences de la University of Edinburgh, entre els mesos d’agost i desembre del 2006. El treball realitzat s’ha centrat en tres projectes. Primerament, s’ha desenvolupat un sensor per mesurar el flux de saba al xilema i al floema, basat en la utilització de polsos de calor per tal d’estimar la velocitat del flux de massa en un medi porós. A diferència del mètode que es fa servir normalment per estimar el flux al xilema, s’ha aconseguit un nou mètode que assoleix l’escalfament fent servir un làser, la qual cosa fa que el mètode sigui no intrusiu. Per altra banda, s’ha estudiat la variabilitat de l’anatomia del floema en funció de l’edat de l’arbre en poblacions de tres espècies diferents (Pinus sylvestris, Fraxinus excelsior i Acer pseudoplatanus). L’objectiu de l’estudi és veure si l’edat/mida dels arbres afecta la mida dels elements conductors al floema, la superfície de floema funcional, o la relació entre superfície de floema funcional i superfície de fulles. Finalment, s’ha estudiat l’intercanvi de gasos a nivell de branca en funció de l’edat de l’arbre i la posició a la capçada en un bosc de Pinus sylvestris.

Isotermes d'adsorpció d'alquilfenols en sediments i altres materials

Projecte de recerca elaborat a partir d’una estada al Center of Applied Geosciences de la Eberhard Karls Universität entre abril i octubre del 2007. Durant l'estada es va adquirir la tècnica per a la realització d'isotermes d'adsorció aplicant-la posteriorment a l'estudi de dos compostos del grup dels alquilfenols (nonilfenol i octilfenol). Aquestes isotermes es van realitzar en diversos sediments provinents de la conca hidrogràfica del riu Ebre i en altres dos materials (lignit i torba), tots ells amb diferent contingut de carboni orgànic total (que varia entre 0,4% per a un dels sediments i 47,8% per a la torba), per a estudiar la influència d'aquest paràmetre en els comportament del nonilfenol pel que fa a l'adsorció. Per altra banda es va afegir l’octilfenol a l’estudi, tant per separat com en combinació amb el nonilfenol, i es va extendre la isoterma per al nonilfenol a concentracions més baixes, properes a les concentracions que es poden trobar d’aquest compost al medi. Aquestes últimes isotermes es van realitzar utilitzant en tots els casos un dels sediments del riu Ebre, amb un contingut de carboni orgànic del 5,8 %, per a poder comparar els resultats sense la influència d’aquest paràmetre. Totes les mostres es van analitzar utilitzant un cromatogràf de gasos acoblat a un espectròmetre de masses.

Integración de Hadoop con planificadores batch

Cada vez es mayor el número de aplicaciones desarrolladas en el ámbito científico, como en la Bioinformática o en las Geociencias, escritas bajo el modelo MapReduce, empleando herramientas de código abierto como Apache Hadoop. De la necesidad de integrar Hadoop en entornos HPC, para posibilitar la ejecutar aplicaciones desarrolladas bajo el paradigma MapReduce, nace el presente proyecto. Se analizan dos frameworks diseñados para facilitar dicha integración a los desarrolladores: HoD y myHadoop. En este proyecto se analiza, tanto las posibilidades en cuanto a entornos que ofrecen dichos frameworks para la ejecución de aplicaciones MapReduce, como el rendimiento de los clúster Hadoop generados con HoD o myHadoop respecto a un clúster Hadoop físico.

Social perceptions of floods and flood management in a Mediterranean area (Costa Brava, Spain)

Taking as an example three study cases in the Costa Brava area, this paper examines the social perceptionof floods through surveys, interviews and Focus Group sessions. Perception is then related to vulnerability, flood management, and citizen’s preferences regarding alternatives to curb flood losses in the future. The study concludes that flood awareness and the willingness to take actions regarding this hazard are clearly related to the degree of social involvement with the affairs of the local community. Furthermore, participatory settings such as Focus Group sessions appear to enable a better environment for assessing and implementing flood management options that attempt to modify human activities rather than modify natural processes as has been frequently the case in the past

Stationarity analysis of historical flood series in France and Spain (14th-20th centuries)

Interdisciplinary frameworks for studying natural hazards and their temporal trends have an important potential in data generation for risk assessment, land use planning, and therefore the sustainable management of resources. This paper focuses on the adjustments required because of the wide variety of scientific fields involved in the reconstruction and characterisation of flood events for the past 1000 years. The aim of this paper is to describe various methodological aspects of the study of flood events in their historical dimension, including the critical evaluation of old documentary and instrumental sources, flood-event classification and hydraulic modelling, and homogeneity and quality control tests. Standardized criteria for flood classification have been defined and applied to the Isère and Drac floods in France, from 1600 to 1950, and to the Ter, the Llobregat and the Segre floods, in Spain, from 1300 to 1980. The analysis on the Drac and Isère data series from 1600 to the present day showed that extraordinary and catastrophic floods were not distributed uniformly in time. However, the largest floods (general catastrophic floods) were homogeneously distributed in time within the period 1600¿1900. No major flood occurred during the 20th century in these rivers. From 1300 to the present day, no homogeneous behaviour was observed for extraordinary floods in the Spanish rivers. The largest floods were uniformly distributed in time within the period 1300-1900, for the Segre and Ter rivers.

A methodology for the classification of convective structures using meteorological radar: Application to heavy rainfall events on the Mediterranean coast of the Iberian Peninsula

During the period 1996-2000, forty-three heavy rainfall events have been detected in the Internal Basins of Catalonia (Northeastern of Spain). Most of these events caused floods and serious damage. This high number leads to the need for a methodology to classify them, on the basis of their surface rainfall distribution, their internal organization and their physical features. The aim of this paper is to show a methodology to analyze systematically the convective structures responsible of those heavy rainfall events on the basis of the information supplied by the meteorological radar. The proposed methodology is as follows. Firstly, the rainfall intensity and the surface rainfall pattern are analyzed on the basis of the raingauge data. Secondly, the convective structures at the lowest level are identified and characterized by using a 2-D algorithm, and the convective cells are identified by using a 3-D procedure that looks for the reflectivity cores in every radar volume. Thirdly, the convective cells (3-D) are associated with the 2-D structures (convective rainfall areas). This methodology has been applied to the 43 heavy rainfall events using the meteorological radar located near Barcelona and the SAIH automatic raingauge network.

A limited area model intercomparison on the "Montserrat-2000" flash-flood event using statistical and deterministic methods

In the scope of the European project Hydroptimet, INTERREG IIIB-MEDOCC programme, limited area model (LAM) intercomparison of intense events that produced many damages to people and territory is performed. As the comparison is limited to single case studies, the work is not meant to provide a measure of the different models' skill, but to identify the key model factors useful to give a good forecast on such a kind of meteorological phenomena. This work focuses on the Spanish flash-flood event, also known as "Montserrat-2000" event. The study is performed using forecast data from seven operational LAMs, placed at partners' disposal via the Hydroptimet ftp site, and observed data from Catalonia rain gauge network. To improve the event analysis, satellite rainfall estimates have been also considered. For statistical evaluation of quantitative precipitation forecasts (QPFs), several non-parametric skill scores based on contingency tables have been used. Furthermore, for each model run it has been possible to identify Catalonia regions affected by misses and false alarms using contingency table elements. Moreover, the standard "eyeball" analysis of forecast and observed precipitation fields has been supported by the use of a state-of-the-art diagnostic method, the contiguous rain area (CRA) analysis. This method allows to quantify the spatial shift forecast error and to identify the error sources that affected each model forecasts. High-resolution modelling and domain size seem to have a key role for providing a skillful forecast. Further work is needed to support this statement, including verification using a wider observational data set.

Radar analysis of the life cycle of mesoscale convective systems during the 10 June 2000 event

The 10 June 2000 event was the largest flash flood event that occurred in the Northeast of Spain in the late 20th century, both as regards its meteorological features and its considerable social impact. This paper focuses on analysis of the structures that produced the heavy rainfalls, especially from the point of view of meteorological radar. Due to the fact that this case is a good example of a Mediterranean flash flood event, a final objective of this paper is to undertake a description of the evolution of the rainfall structure that would be sufficiently clear to be understood at an interdisciplinary forum. Then, it could be useful not only to improve conceptual meteorological models, but also for application in downscaling models. The main precipitation structure was a Mesoscale Convective System (MCS) that crossed the region and that developed as a consequence of the merging of two previous squall lines. The paper analyses the main meteorological features that led to the development and triggering of the heavy rainfalls, with special emphasis on the features of this MCS, its life cycle and its dynamic features. To this end, 2-D and 3-D algorithms were applied to the imagery recorded over the complete life cycle of the structures, which lasted approximately 18 h. Mesoscale and synoptic information were also considered. Results show that it was an NS-MCS, quasi-stationary during its stage of maturity as a consequence of the formation of a convective train, the different displacement directions of the 2-D structures and the 3-D structures, including the propagation of new cells, and the slow movement of the convergence line associated with the Mediterranean mesoscale low.

The cases of June 2000, November 2002 and September 2002 as examples of Mediterranean floods

Four flood events that affected three different countries are here described in terms of meteorological genesis and in terms of consequences on the population and on the territory. Each event is a good representative of a class of phenomena that produce important effects on the urban and extra-urban tissue and that must be taken into account in an optic of civil protection and risk evaluation. This is the subject of the HYDROPTIMET project, part of the Interreg IIIB program, which is collocated in the framework of the prevention of natural hazards and, in particular, those related to severe meteo-hydrological events. This paper aims at being a general introduction of the four events which are the subject of more detailed studies, already published or under submission.

Statistical analysis and modelling of weather radar beam propagation conditions in the Po Valley (Italy)

Ground clutter caused by anomalous propagation (anaprop) can affect seriously radar rain rate estimates, particularly in fully automatic radar processing systems, and, if not filtered, can produce frequent false alarms. A statistical study of anomalous propagation detected from two operational C-band radars in the northern Italian region of Emilia Romagna is discussed, paying particular attention to its diurnal and seasonal variability. The analysis shows a high incidence of anaprop in summer, mainly in the morning and evening, due to the humid and hot summer climate of the Po Valley, particularly in the coastal zone. Thereafter, a comparison between different techniques and datasets to retrieve the vertical profile of the refractive index gradient in the boundary layer is also presented. In particular, their capability to detect anomalous propagation conditions is compared. Furthermore, beam path trajectories are simulated using a multilayer ray-tracing model and the influence of the propagation conditions on the beam trajectory and shape is examined. High resolution radiosounding data are identified as the best available dataset to reproduce accurately the local propagation conditions, while lower resolution standard TEMP data suffers from interpolation degradation and Numerical Weather Prediction model data (Lokal Model) are able to retrieve a tendency to superrefraction but not to detect ducting conditions. Observing the ray tracing of the centre, lower and upper limits of the radar antenna 3-dB half-power main beam lobe it is concluded that ducting layers produce a change in the measured volume and in the power distribution that can lead to an additional error in the reflectivity estimate and, subsequently, in the estimated rainfall rate.

An observational study of the 7 September 2005 Barcelona tornado outbreak

This paper presents an observational study of the tornado outbreak that took place on the 7 September 2005 in the Llobregat delta river, affecting a densely populated and urbanised area and the Barcelona International airport (NE Spain). The site survey confirmed at least five short-lived tornadoes. Four of them were weak (F0, F1) and the other one was significant (F2 on the Fujita scale). They started mostly as waterspouts and moved later inland causing extensive damage estimated in 9 million Euros, three injured people but fortunately no fatalities. Large scale forcing was provided by upper level diffluence and low level warm air advection. Satellite and weather radar images revealed the development of the cells that spawned the waterspouts along a mesoscale convergence line in a highly sheared and relatively low buoyant environment. Further analysis indicated characteristics that could be attributed indistinctively to non-supercell or to mini-supercell thunderstorms.

Modelling of weather radar echoes from anomalous propagation using a hybrid parabolic equation method and NWP model data

Contamination of weather radar echoes by anomalous propagation (anaprop) mechanisms remains a serious issue in quality control of radar precipitation estimates. Although significant progress has been made identifying clutter due to anaprop there is no unique method that solves the question of data reliability without removing genuine data. The work described here relates to the development of a software application that uses a numerical weather prediction (NWP) model to obtain the temperature, humidity and pressure fields to calculate the three dimensional structure of the atmospheric refractive index structure, from which a physically based prediction of the incidence of clutter can be made. This technique can be used in conjunction with existing methods for clutter removal by modifying parameters of detectors or filters according to the physical evidence for anomalous propagation conditions. The parabolic equation method (PEM) is a well established technique for solving the equations for beam propagation in a non-uniformly stratified atmosphere, but although intrinsically very efficient, is not sufficiently fast to be practicable for near real-time modelling of clutter over the entire area observed by a typical weather radar. We demonstrate a fast hybrid PEM technique that is capable of providing acceptable results in conjunction with a high-resolution terrain elevation model, using a standard desktop personal computer. We discuss the performance of the method and approaches for the improvement of the model profiles in the lowest levels of the troposphere.

Enhanced radar precipitation estimates using a combined clutter and beam blockage correction technique

Weather radar observations are currently the most reliable method for remote sensing of precipitation. However, a number of factors affect the quality of radar observations and may limit seriously automated quantitative applications of radar precipitation estimates such as those required in Numerical Weather Prediction (NWP) data assimilation or in hydrological models. In this paper, a technique to correct two different problems typically present in radar data is presented and evaluated. The aspects dealt with are non-precipitating echoes - caused either by permanent ground clutter or by anomalous propagation of the radar beam (anaprop echoes) - and also topographical beam blockage. The correction technique is based in the computation of realistic beam propagation trajectories based upon recent radiosonde observations instead of assuming standard radio propagation conditions. The correction consists of three different steps: 1) calculation of a Dynamic Elevation Map which provides the minimum clutter-free antenna elevation for each pixel within the radar coverage; 2) correction for residual anaprop, checking the vertical reflectivity gradients within the radar volume; and 3) topographical beam blockage estimation and correction using a geometric optics approach. The technique is evaluated with four case studies in the region of the Po Valley (N Italy) using a C-band Doppler radar and a network of raingauges providing hourly precipitation measurements. The case studies cover different seasons, different radio propagation conditions and also stratiform and convective precipitation type events. After applying the proposed correction, a comparison of the radar precipitation estimates with raingauges indicates a general reduction in both the root mean squared error and the fractional error variance indicating the efficiency and robustness of the procedure. Moreover, the technique presented is not computationally expensive so it seems well suited to be implemented in an operational environment.

A flood geodatabase and its climatological applications: the case of Catalonia for the last century

Floods are the natural hazards that produce the highest number of casualties and material damage in the Western Mediterranean. An improvement in flood risk assessment and study of a possible increase in flooding occurrence are therefore needed. To carry out these tasks it is important to have at our disposal extensive knowledge on historical floods and to find an efficient way to manage this geographical data. In this paper we present a complete flood database spanning the 20th century for the whole of Catalonia (NE Spain), which includes documentary information (affected areas and damage) and instrumental information (meteorological and hydrological records). This geodatabase, named Inungama, has been implemented on a GIS (Geographical Information System) in order to display all the information within a given geographical scenario, as well as to carry out an analysis thereof using queries, overlays and calculus. Following a description of the type and amount of information stored in the database and the structure of the information system, the first applications of Inungama are presented. The geographical distribution of floods shows the localities which are more likely to be flooded, confirming that the most affected municipalities are the most densely populated ones in coastal areas. Regarding the existence of an increase in flooding occurrence, a temporal analysis has been carried out, showing a steady increase over the last 30 years.

A press database on natural risks and its application in the study of floods in Northeastern Spain

The aim of this work is to introduce a systematic press database on natural hazards and climate change in Catalonia (NE of Spain) and to analyze its potential application to social-impact studies. For this reason, a review of the concepts of risk, hazard, vulnerability and social perception is also included. This database has been built for the period 1982¿2007 and contains all the news related with those issues published by the oldest still-active newspaper in Catalonia. Some parameters are registered for each article and for each event, including criteria that enable us to determine the importance accorded to it by the newspaper, and a compilation of information about it. This ACCESS data base allows each article to be classified on the basis of the seven defined topics and key words, as well as summary information about the format and structuring of the new itself, the social impact of the event and data about the magnitude or intensity of the event. The coverage given to this type of news has been assessed because of its influence on construction of the social perception of natural risk and climate change, and as a potential source of information about them. The treatment accorded by the press to different risks is also considered. More than 14 000 press articles have been classified. Results show that the largest number of news items for the period 1982¿2007 relates to forest fires and droughts, followed by floods and heavy rainfalls, although floods are the major risk in the region of study. Two flood events recorded in 2002 have been analyzed in order to show an example of the role of the press information as indicator of risk perception.