Probability of occurence of hydrological events: Saquenay - Lake St-Jean, Quebec.

The knowledge of the probability of occurrence of hydrologic events such as flood volume, flood peak, maximum rainfall, and water equivalent of snow is essential to the optimum management of water resources and planning of hydropower production. In this paper, we present a practical approach for the selection of an adequate statistical distribution to describe a hydrometeorological variable. The selection of the distribution is based on statistical (mean absolute value of deviation between empirical and theoretical quantiles, Akaieke criterion), qualitative considerations (parsimony, representation on normal probability plot), as well as hydrometeorological criteria (regional information, spatial coherence, temporal coherence). The approach is illustrated with the hydrometeorological data of the Saguenay - Lac St-Jean basins (Quebec, Canada). The proposed procedure reduces the subjectivity in the choice of an adequate statistical distribution but does not represent a completely objective methodology.