Fitting Statistical Distributions of Monthly Rainfall for Some Iraqi Stations

Abstract

In this study three statistical distributions were fitted to thirteen Iraqi stations of monthly rainfall observations: Mosul, Kirkuk, Khanaqin, Ramadi, Baghdad, Karbala, Hilla, Najaf, Diwaniya, Samawa, Nasiriyah, Amara and Basrah for the period (1970-2010) for all stations except Ramadi (1981-2010) and Hilla (1980-2010). These distributions were: Normal, Gamma and Weibull distributions. Method of moments was used for estimating parameters and two goodness of fit test were used: Chi-Square and Kolmogorov-Smirnov tests. Chi-Square test showed that Gamma distribution was suitable for five stations which were Ramadi, Baghdad, Hilla, Najaf and Samawa stations while, Normal and Weibull distributions were not suitable for any station. Kolmogorov-Smirnov test showed that none of the three distributions was suitable for any station.

Keywords: Rainfall in Iraq, Statistical distributions, Normal distribution, Gamma distribution, Weibull distribution