Abstract
Abstract. The purpose of this work is to investigate trends in annual and monthly precipitation in mainland Portugal by studying long time series. The data are from ten measuring stations scattered over mainland Portugal; some of the time series date back from the 19th century. Trends in these precipitation series were examined using the Mann-Kendall non-parametric trend test and the Sen's non-parametric method. Both full monotonic trends (i.e., over the record period) and partial trends were investigated. Results provide no evidences for rejecting the null hypothesis of no trend in annual precipitation, when a monotonic linear model was used. On the other hand, the analyses of partial trends in the time series identified a sequence of alternating decreasing and increasing trends in annual precipitation, which are sometimes statistically significant. This type of behaviour was also observed for the monthly precipitation.
Highlights
The impact of climate change on precipitation is one of the major concerns in many scientific research studies (e.g. Wentz et al, 2007; Zhang et al, 2007)
The statistics of the Shapiro-Wilk and Kolmogorov-Smirnov tests, applied to the annual precipitation time series, provided evidences to reject the null hypothesis of normality for only one data set: Sao Bras de Alportel
The analyses of the historical precipitation records did not provide statistical evidence for rejecting the null hypothesis of no trend in annual precipitation in mainland Portugal, when the monotonic linearity of trends was tested over the full record period
Summary
The impact of climate change on precipitation is one of the major concerns in many scientific research studies (e.g. Wentz et al, 2007; Zhang et al, 2007). The impact of climate change on precipitation is one of the major concerns in many scientific research studies Quite often the limiting factor is the short length of many existing precipitation records; the majority of the studies on this topic are based on relatively short time series, covering a few decades, over periods of about 40–50 years. For the Iberian Peninsula, Lionello et al (2006) give an interesting review of several studies of precipitation trends. The debate about the different results that are sometimes reported triggered the study presented here, where the main purpose is to complement previous studies for mainland Portugal (e.g. de Lima et al, 2007, reporting trend analysis of annual and monthly point precipitation data from 1941– 2000, for 107 stations scattered over the territory) by investigating precipitation trends in mainland Portugal using the longest records available. This study explores the statistical analyses of annual and monthly precipitation, searching for the presence of linear monotonic trends in the temporal structure of precipitation
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