The relation between interannual storage and frequency of droughts, with particular reference to the Pantanal Wetland of South America

Abstract

A large volume of natural storage within a drainage basin has a marked effect on its regime of hydrologic extremes. In this paper, the carry-over effects from one year to the next that result from large interannual storage are quantified for the Ladário gauging site below the Pantanal, the world's largest wetland, in the drainage basin of the River Paraguay. The presence of carry-over effects introduces correlation between extremes in successive years, with the consequence that commonly used methods for calculating the frequencies of extreme events, all of which assume that values in successive years are statistically independent, are no longer appropriate. When serial correlation between annual flood peaks at Ladário is allowed for, the estimated mean length of longest drought period in a 100-year period is extended by two years. The possibility that other factors contribute to the serial correlation in Ladário flood peaks is considered: no evidence was found of correlation with ENSO events as defined in the literature. Copyright 2005 by the American Geophysical Union.