Along the paper the variability of the average monthly rainfall in Warsaw and Zakopane based on empirical data from the years 1965–1990 are described. To describe that variation of rainfall the sum of harmonics was used because it better reflects the seasonality of multiple extremes. It has been proven that the total annual rainfall in Warsaw during these periods decreases significantly. It is of great importance for agriculture, when climate and the temperature increases. Next, the formula for calculating the average monthly rainfall from day t₁ to day t₂ , useful in agriculture, was introduced, in the model way. Finally, the usefulness of this model for whole months was veryfied, basing on the empirical data which were available – it must be said that very good agreement was obtained. Also it has been shown that the average monthly precipitation extremes in remote locations of Poland are not postponed, but have distinctly different values.

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