Modelling spatial and temporal rainfall and their relationship to climatic indicators in South Australia
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ORIGINAL PAPER
Modelling spatial and temporal rainfall and their relationship to climatic indicators in South Australia M. Kamruzzaman 1
&
A. Metcalfe 2 & S. Beecham 1
Received: 7 December 2018 / Accepted: 3 July 2020 # Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract A spatial model for daily rainfall based on an ordinal logistic regression for the number of wet sites and an ordinary regression for average depth of rainfall at wet sites is presented. The model is fitted to daily rainfall records from a cluster of seven meteorological stations, at the meso-gamma meteorological scale, in South Australia. Data covering a 55-year period from 1958 to 2012 is analysed. The model is used to identify associations between rainfall and four climatic indicators, namely the Southern Oscillation Index (SOI), the Southern Annular Mode (SAM), the Indian Ocean Dipole (IOD) and the Pacific Decadal Oscillation (PDO), and also to monitor changes in rainfall patterns. The results show that there is strong evidence of seasonal variations, in both depth and spatial extent of rainfall, and of persistence of the rainfall pattern from day to day. There is no evidence of trends, but there is evidence of a spatial association between rainfall and SOI, SAM and IOD. There is also evidence of an association between rainfall depth and PDO.
1 Introduction Monitoring average rainfall may miss changes in the rainfall intensity if there is a tendency towards fewer but more intense rainfall events. For example, in a comprehensive study of daily rainfall in the Mediterranean region over the period 1951–1995, Alpert et al. (2002) found evidence of an increase in extreme light and extreme torrential rainfall in Spain despite a slight decrease in the overall mean. In contrast, they did not find evidence of trends in either the mean or variance in Israel and Cyprus. Alpert et al. (2002) also noted that the link between torrential rainfall and El Niño seemed to strengthen over the period. Ghosh et al. (2012) discussed the lack of consistent trends but also identified increasing variability in observed Indian rainfall extremes. Pingale et al. (2014) reported statistically significant positive and negative trends in mean and
* A. Metcalfe [email protected] M. Kamruzzaman [email protected] 1
Natural and Built Environments Research Centre, University of South Australia, Mawson Lakes, SA 5095, Australia
2
School of Mathematical Sciences, University of Adelaide, Adelaide, SA 5005, Australia
extreme rainfall in Rajasthan. There are many other reports of trends in rainfall which vary with the region investigated, but the consistent feature appears to be an increase in variability. Australian rainfall is linked to various climatic processes and their interactions (Risbey et al. 2009). The El Niño-Southern Oscillation (ENSO) over the Pacific Ocean is the principal influence on the east coast of Australia, where it accounts for nearly half of the annual variance of rainfall, with El Niño being associated wi
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