Monthly rain amounts (MRA) recorded at Fabra Observatory (Barcelona, NE Spain) since 1917–2010, are analysed from two complementary points of view. First, mono- and multifractal characteristics of MRA are compared with those corresponding to the monthly Western Mediterranean Oscillation index (WeMOi), which affects the rainfall regime at the western Mediterranean region. Monofractality is analysed through Hurst and Hausdorff exponents, and a power law describing the dependence of MRA power spectra on frequency. The reconstruction theorem permits to quantify the complexity of the physical process by means of the correlation dimension and the Kolmogorov entropy. In agreement with this theorem, the predictive instability is also evaluated through the Lyapunov exponents. The multifractality is characterized by the critical Hölder exponent, as well as by the asymmetry and spectral width of the multifractal spectrum. Second, three predictive processes for MRA are tested. One of them is based on the assumption that MRA could be simulated by fractional Gaussian noise. The other two are, by one hand, an ARIMA(p,1,0) process for MRA; on the other hand, an adaptation of the ARIMA process for MRA taking as arguments preceding WeMOi. Finally, relationships between MRA and WeMOi confirm that outstanding MRA use to be coincident with negative WeMOi. An explanation is also proposed for the non-negligible number of MRA corresponding to positive WeMOi.
The complexity, predictability and predictive instability of the Western Mediterranean Oscillation index (WeMOi) at monthly scale, years 1856-2000, are analysed from the viewpoint of monofractal and multifractal theories. The complex physical mechanism is quantified by: (1) the Hurst exponent, H, of the rescaled range analysis; (2) correlation and embedding dimensions, mu* and d(E), together with Kolmogorov entropy, kappa, derived from the reconstruction theorem; and (3) the critical Holder exponent, alpha(o), the spectral width, W, and the asymmetry of the multifractal spectrum, f(alpha). The predictive instability is described by the Lyapunov exponents, lambda, and the Kaplan-Yorke dimension, D-KY, while the self-affine character is characterized by the Hausdorff exponent, H-a. Relationships between the exponent beta, which describes the dependence of the power spectrum S(f) on frequency f, and the Hurst and Hausdorff exponents suggest fractional Gaussian noise (fGn) as a right simulation of empiric WeMOi. Comparisons are made with monthly North-Atlantic Oscillation and Atlantic Multidecadal Oscillation indices. The analysis is complemented with an ARIMA(p,1,0) autoregressive process, which yields a more accurate prediction of WeMOi than that derived from fGn simulations.
Rodriguez, R.; M. Carmen Casas-Castillo; Navarro, J.; Redaño, A. International journal of climatology Vol. 37, num. 2, p. 770-780 DOI: 10.1002/joc.4738 Data de publicació: 2016-04-20 Article en revista
A methodology based on the fractal properties of rainfall has been applied to obtain the intensity-duration-frequency, IDF, curves for 100 pluviometric Spanish stations over the Iberian Peninsula and the Balearic Islands from their daily precipitation series. The scaling behaviour of maximum rainfall intensities has been investigated and simple scaling has resulted suitable. This methodology has been verified in three emblematic observatories with available sub-daily registers and current known generalized IDF relationships: the Fabra Observatory of Barcelona, the Ebre Observatory near Tortosa (Tarragona) and the Retiro Observatory of Madrid. Despite some general concordance with the mean annual rainfall distribution over Spain, the spatial distribution of the scaling parameter found for the 100 stations shows some discrepancies in diverse areas probably due to the influence of other features, as the inter-annual rainfall variability and the contribution of convective rainfall to total precipitation, on the characteristic rainfall pattern in these areas.
Air-sea interaction in the region of the South Atlantic Convergence Zone (SACZ) is studied using Granger causality (GC) as a measure of directional coupling. Calculation of the area weighted connectivity indicates that the SACZ region is the one with largest mutual air-sea connectivity in the south Atlantic basin during summertime. Focusing on the leading mode of daily coupled variability, GC allows distinguishing four regimes characterized by different coupling: there are years in which the forcing is mainly directed from the atmosphere to the ocean, years in which the ocean forces the atmosphere, years in which the influence is mutual and years in which the coupling is not significant. A composite analysis shows that ocean-driven events have atmospheric anomalies that develop first and are strongest over the ocean, while in events without coupling anomalies develop from the continent where they are strongest and have smaller oceanic extension.
A circulation-type classification is derived for the 1983-2012 climatic period to characterize air quality dynamics over the Iberian Peninsula (IP). Sensitivity tests to automatic classification techniques and other factors affecting the classification (number of patterns, temporal and spatial resolution, domain size, etc.) are performed to objectivize the set-up that maximizes its quality. The ERA-Interim reanalysis and the cost733class classification software are used. The identified circulation types (CTs) are described in terms of frequency, persistence, transitions, and location of isobaric systems. The temporal stability of the classification is evaluated following a cross-validation process that compares the results of the climatic and yearly classifications, leading to the identification of a representative year. Moreover, a representative day for each CT is identified using an objective score that minimizes the absolute value difference of the daily grid with respect to the average CT grid. The reference set-up uses a cluster-based technique (Ck-means) on a daily mean sea-level pressure database. Six CTs are identified, which are consistent with synoptic patterns found in the literature. Furthermore, the CTs of the climatic period are temporally stable showing similar characteristics in terms of frequency and location of high- and low-pressure systems as those of the representative year (2012). As a first application of the CT classification, 1h-maximum NO2 concentration maps from the CALIOPE Air Quality Forecasting System is analysed for the representative days. Synoptic circulation controls the origin and strength of advection explaining transport and NO2 background concentration over the IP. However, there is a strong spatial heterogeneity: in central, northern, and southern IP; NO2 concentrations are controlled by the synoptic circulation, whereas in Spanish Mediterranean coastal areas, a combination of synoptic and mesoscale dynamics explains the NO2 concentration patterns.
In this work, the wind patterns in high mountain areas with complex orography are characterized using hourly data provided by a network of weather stations. The key novelty of the study is the methodology. Data are grouped separately by wind speed and wind direction using two cluster analyses. The groups are analysed and described according to measurements at key stations in the network and their hourly presence. Both classifications are subsequently compared using contingency tables, and the main wind patterns are identified. The uncertainties associated with the average values of each wind pattern are quantified by principal component analysis of the wind vectors at each station. One year of data from nine stations located in the area of La Oroya, Peru was used to validate the proposed method. The local wind behaviour was characterized, the wind patterns were compared with respect to the seasons, and the winter morning transitions were analysed in detail. The methodology allows quantitative description of the local wind patterns and their temporal dynamics in complex mountain valleys. Both wind speed and direction were found to be relevant in wind pattern characterization. In particular, both parameters have proven helpful in identifying and quantifying the prevailing winds during cold dawns and thermal inversion periods.
Rodriguez, R.; Navarro, J.; M. Carmen Casas-Castillo; Ribalaygua, J.; Russo, B.; Pouget, L.; Redaño, A. International journal of climatology Vol. 34, num. 3, p. 643-654 DOI: 10.1002/joc.3712 Data de publicació: 2014-03-15 Article en revista
The evaluation of the possible climate change influence on extreme precipitation is very interesting in the Mediterranean area due to the usual and characteristic high intensities of its rainfall pattern. This analysis is also very important in urban zones, especially those densely populated with complex sewer systems, generally vulnerable to torrential rainfall. In this work, a total of 114 simulated daily rainfall series, 84 for the period 2000-2099 and 30 for the control period 1951-1999, have been analysed. These series were obtained for six thermo-pluviometric stations located in the metropolitan area of Barcelona using the information provided by five general circulation models under four future climate scenarios of greenhouse gas emissions and applying statistical downscaling methods. The potential changes in the intensity-duration-frequency relationships due to climate change have been investigated. For the last third of the 21st century, under A1B, A2 and B2 climate scenarios, an increase of at least 4% has been found on the expected daily rainfall with return period longer than 20years. Using a temporal downscaling based on scaling properties of rainfall, future hourly extreme rainfall has been estimated. For almost all the scenarios and periods considered, the increase on the expected hourly rainfall has resulted slightly higher than the corresponding daily rainfall. The greatest differences between the future hourly and daily rainfall estimated have been found in the second third of the century under scenarios A1B (8%) and A2 (9%). (c) 2013 Royal Meteorological Society
The evaluation of the possible climate change influence on extreme precipitation is very interesting in the Mediterranean area due to the usual and characteristic high intensities of its rainfall pattern. This analysis is also very important in urban zones, especially those densely populated with complex sewer systems, generally vulnerable to torrential rainfall. In this work, a total of 114 simulated daily rainfall series, 84 for the period 2000–2099 and 30 for the control period 1951–1999, have been analysed. These series were obtained for six thermo-pluviometric stations located in the metropolitan area of Barcelona using the information provided by five general circulation models under four future climate scenarios of greenhouse gas emissions and applying statistical downscaling methods. The potential changes in the intensity–duration–frequency relationships due to climate change have been investigated. For the last third of the 21st century, under A1B, A2 and B2 climate scenarios, an increase of at least 4% has been found on the expected daily rainfall
with return period longer than 20 years. Using a temporal downscaling based on scaling properties of rainfall, future hourly
extreme rainfall has been estimated. For almost all the scenarios and periods considered, the increase on the expected
hourly rainfall has resulted slightly higher than the corresponding daily rainfall. The greatest differences between the future
hourly and daily rainfall estimated have been found in the second third of the century under scenarios A1B (8%) and A2
The main objective of this study is to estimate the probable maximum precipitation (PMP) in Barcelona for durations ranging from 5 min to 30 h. To this end, rain records from the Jard´ı gauge of the Fabra Observatory located in Barcelona (1927–1992) and the urban pluviometric network supported by Clavegueram de Barcelona, S.A.
(CLABSA, 1994–2007) were analysed. Two different techniques were used and compared: a physical method based on the maximization of actual storms, and the Hershfield’ statistical method. The PMP values obtained using the two techniques are very similar. In both cases, the expected increasing behaviour of the PMP with duration was found, with the increase especially notable for the mesoscale durations 2–9 h, and not significant from 12 h on up. This result seems to be related to the scale of the meteorological situations producing high intense rainfall amounts over our territory.
M. Carmen Casas-Castillo; Herrero, M.; Ninyerola, M.; PONS, X.; Rodriguez, R.; Rius, A.; Redaño, A. International journal of climatology Vol. 27, num. 3, p. 399-409 Data de publicació: 2007-03 Article en revista
Martín, M.; Cremades, L.V.; Santabàrbara, J. International journal of climatology Vol. 19, num. 2, p. 197-209 DOI: 10.1002/(SICI)1097-0088(199902)19:2<197::AID-JOC360>3.0.CO;2-H Data de publicació: 1999-02 Article en revista