In 1982 hydrological observations were started in the small mountain basin of Valle della Gallina in north-western Italy (1.08 km^2). The results were analysed to evaluate variability in the water balance during the period between 1982-2008. Variations in the ratio of runoff to rainfall at yearly and monthly scales were considered, with reference to the rainfall patternin the north-western Italian environment. In that region the seasonal rainfall maxima are recognized in autumn (October-November) and late spring (May). The seasonal rainfall distribution is typical of the zone encompassing the basin and is considered representative of the continental-Mediterranean climate. This small basin contributes to one of the Alpine tributaries of the River Po, whose basin has seen a decrease in the amount of annual precipitation and number of wet days, together with increasing storm intensities. Forest cover is increasing in mountain lands.
In the Valle della Gallina small research basin, the annual runoff coefficient is observed to have decreased during the last period 1999-2008, with the runoff decrease being higher than the rainfall decrease.
Variability in monthly runoff coefficients showed increasing values in the summer season. At the same time, rainfall intensity related to flash flood events increases, being characterized by higher hourly values.
