INTERNATIONAL JOURNAL OF CLIMATOLOGY Int. J. Climatol. 25: 1381–1403 (2005) Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/joc.1197 STATISTICAL DISTRIBUTIONS OF THE DAILY RAINFALL REGIME IN CATALONIA (NORTHEASTERN SPAIN) FOR THE YEARS 1950–2000 A. BURGUE ˜ NO, a M. D. MART ´ INEZ, b X. LANA c, * and C. SERRA c a Departament d’Astronomia i Meteorologia, Facultat de F´ ısica, Universitat de Barcelona, C. Mart´ ı Franqu` es 1, 08028 Barcelona, Spain b Departament de F´ ısica Aplicada, Universitat Polit` ecnica de Catalunya, Av. Diagonal 649, 08028 Barcelona, Spain c Departament de F´ ısica i Enginyeria Nuclear, Universitat Polit` ecnica de Catalunya, Av. Diagonal 647, 08028 Barcelona, Spain Received 2 February 2004 Revised 16 March 2005 Accepted 16 March 2005 ABSTRACT A database of daily rainfall, compiled from 75 gauges covering the period 1950–2000, that was previously considered for analysing spatial and temporal patterns of the daily pluviometric regime in Catalonia is used to obtain new statistical patterns of the daily rain amounts. First, the annual number of rainy days, its coefficient of variation and time trends affecting this number are evaluated for every rain gauge, with the aim of complementing previous analyses concerning the average amount per rainy day and its absolute and relative dispersions. Second, empirical cumulative amount X and time Y distributions are obtained for every rain gauge and fitted with exponential and Weibull models respectively. Third, a normalized rainfall curve is obtained for every rain gauge and modelled in two ways. One of them is based on the relationship X = Y exp[−b(1 − Y) c ] and the other on the beta distribution of X given by Y . It is noticeable that there is a relationship between the parameters of both models and the coefficient of variation of the daily rainfall. Additionally, a strong spatial variability is deduced after a review of the results. This variability is characterized by spatial gradients of the parameters of the exponential and Weibull distributions and of the threshold levels that define different percentiles of the X and Y distributions. A more homogeneous spatial behaviour is observed when the contribution to rain amounts of a specific type of daily episode is analysed. Thus, a relatively low ratio of rainy days (25–35%), with daily amounts exceeding average values, generates a good part of the rain amounts (75–85%) for most gauges (80%). Copyright  2005 Royal Meteorological Society. KEY WORDS: northeastern Spain; cumulative amount and time distributions; normalized rainfall curves; spatial variability; daily rainfall amounts 1. INTRODUCTION The spatial complexity of the daily rainfall regime in Catalonia (northeastern Spain) is to be expected, given the varied orography of Catalonia (Figure 1), and its vicinity to the Mediterranean Sea. From the point of view of the atmospheric circulation patterns and their effects on the rain episodes, the Pyrenees, Pre-Pyrenees, Littoral and Pre-Littoral ranges and the Central Basin strongly condition rain amounts. For instance, under the effects of eastern advections, gauges along the coast record higher rain amounts than gauges in the western face of the Transversal, Littoral and Pre-Littoral Ranges, given that these latter gauges are sheltered by the mountain ranges. Similarly, gauges in the Central Basin are not usually affected by eastern advections. Consequently, a noticeable spatial variability appears in addition to the characteristic time irregularity of the Mediterranean climate. This spatial feature has been made clear through different processes of spatial clustering in terms of daily and monthly amounts (Periago et al., 1991; Fern´ andez-Mills et al., 1994; Serra et al., 1996, 1998; Lana et al., 2001, 2004). * Correspondence to: X. Lana, Departament de F´ ısica i Enginyeria Nuclear, Universitat Polit` ecnica de Catalunya, Av. Diagonal 647, 08028 Barcelona, Spain; e-mail: francisco.javier.lana@upc.edu Copyright  2005 Royal Meteorological Society