التحليل التكراري للأمطار في العراق باستخدام النماذج الإحصائية دراسة تطبيقية على محطات الموصل وبغداد والبصرة

Abstract

The study aims to analyze the temporal and spatial variability of annual rainfall totals in Iraq and to identify the most appropriate probability models for estimating precipitation amounts at different return periods. The study relied on rainfall data for the 30-year period from 1994 to 2024. Descriptive statistics and the Chi-square goodness-of-fit test were employed to evaluate the suitability of the Normal, Log-Normal, and Gumbel distributions. Rainfall amounts were subsequently estimated for return periods of 5, 10, 25, 50, and 100 years, and the results were spatially represented using the Inverse Distance Weighted (IDW) interpolation method in ArcGIS 10.8.1. The results showed that Mosul recorded the highest annual mean rainfall, reaching 328.76 mm, with a standard deviation of 143.16 mm, whereas the mean annual rainfall amounted to 121.17 mm in Baghdad and 119.30 mm in Basra. Baghdad recorded the highest relative variability, with a coefficient of variation of 57.30%, compared with 43.55% in Mosul and 42.08% in Basra. The goodness-of-fit test indicated that the Gumbel distribution was the most suitable for Baghdad, the Normal distribution for Basra, and the Log-Normal distribution for Mosul. The Exponential distribution was not adopted in the final estimations. The estimated rainfall amounts for the 100-year return period reached 338.95 mm in Baghdad, 236.07 mm in Basra, and 794.63 mm in Mosul, compared with 171.12, 161.54, and 428.04 mm, respectively, for the 5-year return period. The spatial maps revealed a clear rainfall gradient from northern Iraq toward the central and southern regions. The study concludes that adopting a single probability distribution for all stations does not adequately reflect the local characteristics of rainfall within the study area.