Bivariate gamma distributions have been used successfully on modeling hydrological processes. In this work, supposing that X: and Y: follow the gamma beta II bivariate gamma model, we deduce the exact distributions of the functions U = X + Y P = XY: and Q = X/ (X + Y),: as well as their respective moments. Those functions describe important hidrological variables. An application of the results is provided to rainfall data from Passo Fundo - RS.
Gamma beta II distribution; combination of random variables; rainfall
