Trends in Daily Precipitation Regimes and their Extremes at Three Observatories in the Iberian Peninsula

Abstract

The daily precipitation series of San Sebastián, Valencia and Badajoz are analysed for each of the annual seasons and for the hydrological year (Sep-Aug). To this end several indices descriptive of the precipitation distribution are computed: number of days of precipitation and rainfall within limits marked by the quartiles of the whole series, the shape and scale parameters γ and β of the fitted Γ biparametric distribution. The most significant trends found are: a decrease in the number of days and precipitation in days in the inter-quartile range in San Sebastian for the year, summer and winter; an increase in the precipitation and number of days in the first quartile in summer and the year at Valencia; and in Badajoz a drop in spring of precipitation and of the number of days in the last quartile, whereas the precipitation and number of days rise in the year for the first quartile range. The parameter γ drops significantly in San Sebastián (year and winter), Valencia (year and spring) and Badajoz (spring). The drop in γ for the year is especially pronounced in San Sebastián and Badajoz since the sixties.

For the extremes study, the trends in the number of days with precipitation greater than the 90%, 95% and 99% percentiles are analysed, and only a significant decreasing trend was found for the autumn in San Sebastián (Q90). When those percentiles themselves are computed for each year, a clearly increasing trend is detected in San Sebastián for the spring.