Is daily precipitation Gamma-distributed?: Adverse effects of an incorrect use of the Kolmogorov–Smirnov test

The applicability of the Gamma distribution for the description of daily precipitation amounts within a single season is tested on 90 European stations. The test is carried out separately for winter, spring, summer, and autumn seasons. The Lilliefors (LI) modification of the Kolmogorov–Smirnov (KS) test is used to assess the goodness-of-fit of the Gamma distribution to daily precipitation in every year and season of the reference period. The possible rejection of the Gamma distribution for a particular station and season is based on the number of years in which the distribution is rejected. The results are compared with those obtained from the non-modified KS test, whose application is incorrect when the fit to the theoretical distribution is tested on the same data from which its parameters were estimated. We confirm that the two tests yield considerably different results. The validity of the Gamma distribution is not as wide as it is commonly believed: in winter, precipitation at more than 40% of the examined stations is not Gamma-distributed.