ESTIMATION OF MEAN AREAL RAINFALL AND MISSING DATA BY USING GIS IN NINEVEH, NORTHERN IRAQ
Rainfall analysis is an important component of managing water resources and a key element of the national development. In this study, three methods (Arithmetic mean, Thiessen’s polygon, and isohyet), were adopted for estimating mean areal rainfall over the entire Nineveh Governorate with a total area of 35152 km2 using ArcGIS 10.5 software. The data of eight rain stations were used (Mosul, Sinjar, Zummar, Talafar, Hatra, Ba'ashiqah, Tal Abtah and Rabia) for the period from 2000 to 2019. The Normal Ratio method was used for filling missing data and consistency of the rainfall records which were tested using a double-mass curve technique. There was a significant correlation coefficient between measured and missing data at range 0.61 to 0.9. The results show that the means of areal rainfall were 298.94 mm, 230.12 mm and 260.10 mm according to Arithmetic, Thiessen polygon and Isohyet Methods receptively. The Isohyet method is the most accurate approach to estimate the mean areal rainfall.