Regional precipitation climates of Iran

Rainfall in Iran is complex, with unpredictable fluctuations from year to year and from region to region. At-site frequency analysis is inadequate for regional planning. Thus, it is important to determine regional rainfall frequencies. Hierarchical cluster analysis and L-moments regional frequency analysis were used in this study to find homogeneous rainfall groups and regional rainfall frequency distributions. The study showed eight homogeneous rainfall regions within Iran, which correspond with areas with differing geography and climate. A regional homogeneity measure, H1, showed that a 3-parameter log-normal distribution describes the overall distribution of rainfall within Iran, but because of substantial variations in precipitation patterns within the country, the distribution is not applicable for individual regions. Z-statistics, which are based on L-moments, were used to select the distribution that best fitted rainfall records in each homogeneous region.