gargantuan amplifying fluctuation in annual rainfall is an important question for understanding multidecadal climate variability. q 1999 Elsevier Science B.V. All rights reserved.
Keywords: Annual rainfall; Argentina; Multidecadal climate variability
1. Introduction
Fluctuations at decadal and interdecadal timescales are ubiquitous phenomena in time series of rainfall and other atmospheric variables. For example, annual rainfall variations
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with a quasi 20-year period were found by Hu et al. 1998 for central United States Ž
. Missouri, Illinois, Iowa, Kansas and Nebraska using running-mean analysis and Morlet
wavelet analysis. The same timescale of variability was found for precipitation in the Ž
. coastal region of central California by Haston and Michelson 1994 . Variability in the
20-year timescale is extended to climate in general as summarized by Trenberth and Ž
. Hurrel 1994 . Extensive droughts in the central plains of USA in the 1930s and the
1950s were associated to negative rainfall perturbations of a quasi 20-year precipitation Ž
. Ž
. fluctuation as found by Hu et al. 1998 . Latif and Barnett 1996 thoroughly examined
the 20-year climatic cycle in the North Pacific and North America. They found evidence that this timescale in climate variability results from coupled oceanic–atmospheric
processes.
However, despite their omnipresence, the excitation of decadal and interdecadal fluctuations of atmospheric variables, particularly rainfall, is scarcely documented.
Documenting examples of excitation of these fluctuations will provide a clearer picture of their evolution and as well as their relationship with other atmospheric and oceano-
graphic variables. Furthermore, the consequence of the excitation of interdecadal fluctuations on the evolution of annual rainfall amount is an unexplored topic.
In this research, we searched for excitation of interdecadal fluctuations in time series of annual rainfall in central Argentina. We found a case of excitation of fluctuation in
annual rainfall in the decadal and in the interdecadal timescale. These fluctuations show amplifying intensity. Furthermore, these amplifying decadal and interdecadal fluctua-
tions make a decisive contribution to the observed trend in annual rainfall in this region. Description of the characteristics of subdecadal, decadal and interdecadal fluctuations in
rainfall amounts and their relationship to a trend in annual rainfall is the purpose of this paper.
Environmental effects of the ascending trend in annual rainfall are notorious in this region in central Argentina. This trend in annual rainfall amounts is bringing about
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important effects in the hydrologic regime Lucero, 1998a, 1995 . Among these effects, Ž
. Ž
. a large part downtown of Miramar city an important resort area remained inundated
by the water of lake Mar Chiquita during the last 25 years. Lake Mar Chiquita is located in northern Cordoba. This persistent inundation led local authorities to demolish that city
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district in 1991, because it represented a danger to sport yachting, and it affected the scenery of the lake. In some parts of the territory of this province, substantially
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increased levels of the water table phreatic surface of groundwater produces inconve- niences in large agricultural areas. In other parts of the province of Cordoba, increasing
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rainfall amounts result in higher crop yields. This region is a major agricultural area, with state-of-the-art technology; weather effects on crops influence world market prices
of several agricultural products. The organization of this paper is as follows. In Section 2, data set and methods are
described. In Section 3, the excitations of amplifying fluctuation at interdecadal timescale, and trend in time series of annual rainfall are described and analyzed. In Section 4 the
seasonal variability of amplifying fluctuation and trend in rainfall amount is analyzed. Finally, Section 5 contains the conclusions.
2. Data and method
