Estimating monthly and yearly dependable rainfall for different climatic zones of the world

The study has demonstrated that estimating monthly or yearly dependable rainfall is not an easy task, especially where rainfall data series are not available. The world is divided into four climatic zones namely: tropical, sub-tropical, mediterranean and temperate. The results showed that no single equation or procedure is quite adequate to describe the different climatic conditions of the world. Three procedures were developed for estimating yearly and monthly dependable rainfall for yearly/monthly rainfall data series. To develop the various procedures, first a frequency-analysis using the yearly/monthly rainfall data series was conducted by means of RAINBOW software. Secondly, the results from the frequency analysis were used in an Excel program to develop the various relationships between the coefficient of variation and the mean or the log (mean) rainfall for normal and log normal distributed rainfall data series. From the results of yearly rainfall data series, all climatic zones found to be normally distributed. On the other hand, all monthly rainfall data series were assumed to be log normally distributed.