Missing data analysis and homogeneity test for Turkish precipitation series

Abstract

In this study, missing value analysis and homogeneity tests were conducted for 267 precipitation stations throughout Turkey. For this purpose, the monthly and annual total precipitation records at stations operated by Turkish State Meteorological Service (DMI) from 1968 to 1998 were considered. In these stations, precipitation records for each month was investigated separately and the stations with missing values for too many years were eliminated. The missing values of the stations were completed by Expectation Maximization (EM) method by using the precipitation records of the nearest gauging station. In this analysis, 38 stations were eliminated because they had missing values for more than 5 years, 161 stations had no missing values and missing precipitation values were completed in the remaining 68 stations. By this analysis, annual total precipitation data were obtained by using the monthly values. These data should be hydrologically and statistically reliable for later hydrological, meteorological, climate change modelling and forecasting studies. For this reason, Standard Normal Homogeneity Test (SNHT), (Swed-Eisenhart) Runs Test and Pettitt homogeneity tests were applied for the annual total precipitation data at 229 gauging stations from 1968 to 1998. The results of each of the testing methods were evaluated separately at a significance level of 95% and the inhomogeneous years were determined. With the application of the aforementioned methods, inhomogeneity was detected at 50 stations of which the natural structure was deteriorated and 179 stations were found to be homogeneous.