Modelling annual maxima of daily rainfall in Madeira Island

Réis, Délia Gouveia; Lopes, Luiz; Mendonça, Sandra

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http://hdl.handle.net/10400.13/5373

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Authors

Réis, Délia Gouveia

Lopes, Luiz

Mendonça, Sandra

Abstract(s)

Madeira Island is located in the Atlantic Ocean off the coast of Northwest Africa, between latitudes 32º30'N–33º30'N and longitudes 16º30'W–17º30'W. Extreme rainfall events have triggered a significant number of flash floods, landslides and debris flows in this volcanic island along its past and recent history. One of the most significant events was the one that happened on the 20th of February 2010, which caused 45 casualties, six missed people and extensive damage to properties and infrastructures. Madeira Island is therefore a natural laboratory for the study of extreme precipitation events and its consequences. In this study, tests based on the likelihood ratio statistic and the probability-weighted moments were used to test the hypothesis of a Gumbel distribution for the annual 1-day maximum rainfall data, from 19 rain gauge stations, provided by the Department of Hydraulics and Energy Technologies of the Madeira Regional Laboratory of Civil Engineering. The rainfall records, with 22, 23 and 31 years of extension, were drawn from rain gauge stations located in the northern and southern hillsides of the island. The estimates for the generalised extreme value distribution (GEV) obtained by the methods of maximum likelihood and probability-weighted moments revealed the influence of the proximity to the sea and altitude on the spatial distribution of extreme rainfall, in addition to the natural differences observed on the windward and lee sides of any mountainous island. Estimates for 50- and 100-year return levels were also obtained. The existence of trends in the parameters’ values was also analysed, revealing a significant evidence of a linear trend, both in location and scale parameters, for one location in the north side of the island.