The Probability Distribution of Daily Precipitation at the Point and Catchment Scales in the United States

Abstract

Abstract. Choosing a probability distribution to represent daily precipitation depths is important for precipitation frequency analysis, stochastic precipitation modeling and in climate trend assessments. Early studies identified the 2-parameter Gamma (G2) distribution as a suitable distribution for wet-day precipitation based on traditional goodness of fit tests. Here, probability plot correlation coefficients and L-moment diagrams are used to examine distributional alternatives for the full-record and wet-day series of daily precipitation at the point and catchment scales in the United States. Importantly, the G2 distribution performs poorly in comparison to either the Pearson Type-III (P3) or Kappa (KAP) distributions. The analysis indicates that the P3 distribution fits the full record of daily precipitation at both the point and catchment scales remarkably well; while the KAP distribution best describes the distribution of wet-day precipitation at the point scale, and the performance of KAP and P3 distributions is comparable for wet-day precipitation at the catchment scale.