Variability of low monthly rainfall in La Plata Basin

PENALBA O., VARGAS W.

METEOROLOGICAL APPLICATIONS

JOHN WILEY & SONS INC

Año: 2008 p. 313 - 323

1350-4827

Water resources management and agriculture planning models require a statistical synthesis of some rainfallfeatures, in particular those representing dry atmospheric conditions. The bigger the basin, the more important these featuresbecome, as is the case of the La Plata Basin (LPB).This paper focuses on the precipitation variability in the large LPB in South America, analysing the number of monthsper year with low rainfall and the sequences of months with low rainfall, their theoretical distributions and stability, whichare needed as input for the models mentioned above.Long time series are used to analyse the low-frequency variability and the relative importance of decadal variability.Changes are evident in the number of months per year with low rainfall, with a decrease of about 20% in the period after1970.Theoretical distribution models (binomial and geometric) are fitted to these empirical distributions, and the regionalvariability of the fitting parameters is shown. In practically the entire region, the goodness-of-fit of the two theoreticalmodels considered is statistically satisfactory.The temporal variability of the parameters of the theoretical binomial (p) and geometric (α) distributions is analysed, inexcluding sub-periods of 10 and 5 years, respectively. The results show low-frequency variability overlapped on a decadalvariability, with low homogeneous regional behaviour.The distribution models have proven to be efficient for frequency adjustments of the rainfall properties studied. Theseresults are an acceptable and necessary input to decision models in LPB. They also make it possible to infer effects ofclimate change. Copyright  2008 Royal Meteorological Society