Statistical distributions of the daily rainfall regime in Catalonia (Northeastern Spain) for the years 1950–2000

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%).