Spatial and temporal variations in summer precipitation in Japanese mountain areas

We examined spatial and temporal variations in precipitation measured during summer season between 1976 and 2007 for 28 stations located in mountain areas across Japan using the amount of precipitation (Pr), the mean depth of precipitation events (η), and the inverse of the mean interval times (λ). We obtained positive correlations between the period mean Pr (Pr) and the period mean λ (λ) and between Pr and the period mean η (η) for the 28 stations. Pr was more strongly related to η than to η, indicating the spatial variations in Pr that are primarily related to the variations in η. In addition, Pr was more strongly related to η than to η for most stations on the basis of data for 1976-2007, indicating that the year-to-year variations in Pr are primarily related to η. We also examined temporal trends in Pr, λ and η for 1976-2007 and found no systematic trends for 23 of the 28 stations, suggesting long-term trends that are not common in mountain areas of Japan. The relationships between Pr and η and between Pr and η presented in this study enable us to generate a temporal precipitation distribution pattern based on only Pr and Pr data, respectively. Furthermore, probabilistic stochastic hydrological models require precipitation characteristics as input; thus, this study contributes to the determination of hydrological cycles and their possible future changes in Japanese mountain areas and therefore to water resource management.