Homogeneity Analysis of Rainfall Series in the Upper Blue Nile River Basin, Ethiopia

Abstract

Reliability and quality Assessment of historical rainfall records are required in the hydrological modelling, water resource processes and for climatic studies. The homogeneity of the annual rainfall data sets throughout the Upper Blue Nile River Basin (UBNRB) was examined using four absolute homogeneity tests namely; Standard Normal Homogeneity Test (SNHT), Buishand Range (BR), Pettitt test and Von Neumann ratio tests (VNR). The rainfall records from 30 meteorological stations during the period between 1901 and 2013 were considered. Results of SNH and BR tests showed that the annual series of the considered stations are homogeneous and classified as “useful“at 95% significance level. However, the Von Neumann ratio test detected inhomogeneity at six stations. Moreover, only 16 out of 30 stations were classified as homogenous based on the Pettitt test which confirmed that Pettitt test is more sensitive to detect the non-homogeneity for the time series. On the basis of results of the performed tests, SNHT and BRT were able to detect breaks at the series’ end. Overall, the data set is representing a reliable climatic series to be considered in the subsequent trend analysis.

Keywords

• standard normal homogeneity test
• buishand range test
• pettitt test
• von neumann ratio test
• upper blue nile