A universal multifractal description applied to precipitation patterns of the Ebro River Basin, Spain

Abstract

Water supplies in the Ebro River Basin are increasingly stressed, especially during the summer season. The year-to-year fluctuations in rainfall over this area exert vital influence on the regional hydrology, agriculture and several related industries in the region. Repeated anomalous rainfall in recent decades has had a devastating impact on this region, both socially and economically. We characterised the change in the rainfall variability pattern in the Ebro River Basin using universal multifractal (UM) analysis, which estimates the concentration of the data around the precipitation average (C 1 , codimension average), the degree of multiscaling behaviour in time (α index) and the maximum probable singularity in the rainfall distribution (γ s ). Fourteen meteorological stations were selected based on the length of rainfall series and the climatic classification to obtain a representative untreated data set from the river basin. Daily rainfall series from 1957 to 2002 were obtained from each meteorological station and subdivided (1957-1980 and 1981-2002) to analyse the difference between the 2 periods. The general scenario observed in this study, through the UM parameters, can be summarised as follows: the range of variation of precipitation amounts was spatially more homogenous in 1980-2002 than in 1957-1979; at the same time, there is higher frequency of dry periods at different scales in 1980-2002; and in almost all of the stations, the range of precipitation over the years has been decreasing at a lower rate than the rainfall average. We then analysed the evolution of the UM parameters from 1957 to 2002. Continuous variations in C 1 and α were found for 2 of the stations, indicating that a precipitation regime change has begun in the last few decades and should be considered in the agricultural development of the region.

Change of extreme rainfall indexes at Ebro River Basin

“…They concluded that the cause of this pattern is a high frequency of high pressure over Iberia, which they proved using teleconnection indexes. In contrast, Valencia et al (2010), using multifractal analysis, showed that there are no rainfall variations at the Ebro River Basin. Our data consist of 14 data series from several meteorological stations located at different sites in the Ebro River Basin using daily rainfall data from .…”

Spatial Modeling of Rainfall Patterns over the Ebro River Basin Using Multifractality and Non-Parametric Statistical Techniques

“…Therefore, it is difficult to compare the absolute results obtained by these two studies. However, although Valencia et al [49] observed that the value of α increased at some stations and the intermittency C1 increased at more than half of the stations (reaching values above those obtained in the present study), the parameter γs showed a general slightly increasing pattern at 12 of the 14 stations with values that were very similar to the values of the square geographical areas containing the analyzed stations. Thus, it seems that the γs parameter best reflects the evolution of the multifractal properties of rainfall distribution.…”

“…Thus, the southeast region of the watershed has the greatest expected multifractality. This result indicates that the parameter γs could be used as an indicator for detecting climate change from a multifractal perspective [24,49].…”

“…Previously, one study has been conducted on the precipitation patterns of the Ebro River Basin by using multifractality, the study of Valencia et al [49]. The data used for this previous study were directly obtained from a group of irregular rainfall stations scattered across the territory over the period of 1957 to 2002.…”

“…For further details see Lavallée et al [32] and Tessier et al [18]. This technique was applied separately for each one of the 132 daily precipitation series relative to the square areas with similar amplitudes over the two selected periods of 1931-1975 and 1965-2009 by using previously described methods [49].…”