Abstract
Abstract. Extreme rainfall events are a serious concern for regional hydrology and agriculture in the Ebro River Basin. Repeated anomalous rainfall in recent decades has had a devastating impact on this region, both socially and economically. Some studies developed in Italy and USA have shown that there is a change in seasonal patterns and an increasing frequency of extreme rainfall events, whereas other studies have pointed out that no global behaviour could be observed in monthly trends due to high climatic variability. The aim of this work is to test which of these scenarios is the case for the Ebro River Basin. For this purpose, 14 meteorological stations were selected based on the length of the rainfall series and the climatic classification to obtain a representative untreated dataset from the river basin. Daily rainfall series from 1957 to 2002 were obtained from each meteorological station. First, classical climatic indexes were analysed with an autoregressive test to study possible trends in rainfall. The results can be explained following the evolution of the NAO and WeMO indexes, which indicate that the initial period should be subdivided in two periods (1957–1979 and 1980–2002) to assume stationarity and to analyse the rainfall distribution functions. The general results obtained in this study for both sub-periods, through the generalised Pareto distribution (GPD) parameters and the maximum expected return values, do not support the results previously obtained by other authors that affirm a positive trend in extreme rainfall indexes and point to a slight reduction indicated by others. Three extreme precipitation indexes show negative statistical significant trends. GPD-scale parameters decrease except for only one rain gauge, although this decrease is only statistically significant for two rain gauges. Another two locations show statistical significance decreased for maximum expected return values.
Highlights
Several researchers have pointed out that climate change is expected to increase temperatures and lower rainfall in Mediterranean regions, simultaneously increasing the intensity of extreme rainfall events (Raisanen et al, 2004)
The highest total precipitation amounts are found for the Pyrenees at the north of the Ebro River Basin
Rainfall data from 1975 to 2002 from 14 stations located at different places in the Ebro River Basin and under different climatic conditions were used to study extreme rainfall trends in the area
Summary
Several researchers have pointed out that climate change is expected to increase temperatures and lower rainfall in Mediterranean regions, simultaneously increasing the intensity of extreme rainfall events (Raisanen et al, 2004). If the rainfall distribution has changed, it is necessary to determine whether there are specific sub-periods of time with a similar distribution This type of treatment was not carried out in certain works that studied the evolution and probability of rainfall exceeding dangerous thresholds (Gallego et al, 2006; Rodrigo, 2010; Muller et al, 2009). These authors found a lack of stationarity in rainfall during the 1951–2002 period, especially in terms of extreme values
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