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Article

Significant Extremal Dependence of a Daily North Atlantic Oscillation Index (NAOI) and Weighted Regionalised Rainfall in a Small Island Using the Extremogram

1
National Laboratory for Civil Engineering (LNEC), Instituto Superior Técnico (IST), Civil Engineering Research and Innovation for Sustainability (CERIS), 1040-001 Lisbon, Portugal
2
National Laboratory for Civil Engineering (LNEC), 1700-075 Lisbon, Portugal
*
Author to whom correspondence should be addressed.
Current address: Department of Civil Engineering, Architecture and Georesources (DECivil), Instituto Superior Tecnico (IST), Universidade de Lisboa, Av. Rovisco Pais, No. 1, 1040-001 Lisbon, Portugal.
Water 2020, 12(11), 2989; https://doi.org/10.3390/w12112989
Received: 23 September 2020 / Revised: 13 October 2020 / Accepted: 20 October 2020 / Published: 25 October 2020
(This article belongs to the Special Issue Statistical Approach to Hydrological Analysis)
Extremal dependence or independence may occur among the components of univariate or bivariate random vectors. Assessing which asymptotic regime occurs and also its extent are crucial tasks when such vectors are used as statistical models for risk assessment in the field of Climatology under climate change conditions. Motivated by the poor resolution of current global climate models in North Atlantic Small Islands, the extremal dependence between a North Atlantic Oscillation index (NAOI) and rainfall was considered at multi-year dominance of negative and positive NAOI, i.e., −NAOI and +NAOI dominance subperiods, respectively. The datasets used (from 1948–2017) were daily NAOI, and three daily weighted regionalised rainfall series computed based on factor analysis and the Voronoi polygons method from 40 rain gauges in the small island of Madeira (∼740 km2), Portugal. The extremogram technique was applied for measuring the extremal dependence within the NAOI univariate series. The cross-extremogram determined the dependence between the upper tail of the weighted regionalised rainfalls, and the upper and lower tails of daily NAOI. Throughout the 70-year period, the results suggest systematic evidence of statistical dependence over Madeira between exceptionally −NAOI records and extreme rainfalls, which is stronger in the −NAOI dominance subperiods. The extremal dependence for +NAOI records is only significant in recent years, however, with a still unclear +NAOI dominance. View Full-Text
Keywords: extremal dependence; climate change; extremogram; cross-extremogram; extreme rainfall; NAOI; small island; Madeira Island extremal dependence; climate change; extremogram; cross-extremogram; extreme rainfall; NAOI; small island; Madeira Island
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MDPI and ACS Style

Espinosa, L.A.; Portela, M.M.; Rodrigues, R. Significant Extremal Dependence of a Daily North Atlantic Oscillation Index (NAOI) and Weighted Regionalised Rainfall in a Small Island Using the Extremogram. Water 2020, 12, 2989. https://doi.org/10.3390/w12112989

AMA Style

Espinosa LA, Portela MM, Rodrigues R. Significant Extremal Dependence of a Daily North Atlantic Oscillation Index (NAOI) and Weighted Regionalised Rainfall in a Small Island Using the Extremogram. Water. 2020; 12(11):2989. https://doi.org/10.3390/w12112989

Chicago/Turabian Style

Espinosa, Luis A.; Portela, Maria M.; Rodrigues, Rui. 2020. "Significant Extremal Dependence of a Daily North Atlantic Oscillation Index (NAOI) and Weighted Regionalised Rainfall in a Small Island Using the Extremogram" Water 12, no. 11: 2989. https://doi.org/10.3390/w12112989

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