Trend Analysis of Annual Rainfall Time Series in Northwest Libya

Abstract

This study is based on historical total annual rainfall recorded at eleven meteorological stations located in the northwestern part of Libya. The data were analyzed to study long term temporal trends on annual scale. The rainfall time series data were tested for homogeneity and randomness in order to be confident that the measurements were taken at the time with the same instruments and location. After testing, Mann–Kendall test was applied to detect the trends in rainfall data. TheilSen's slope estimator test was used for finding the magnitude of change over a time period. The results of Mann–Kendall test detected statistically significant trends of increasing and decreasing rainfall in two out of eleven stations at 95% and 99% confidence levels, namely Sirt and Tripoli Airport stations. During the study period of observation, Sen’s Slope and change percentage were estimated as 0.829 mm/year rainfall increase (36.88 %) in Sirt station and -0.686 mm/year (20.04 %) rainfall decrease in Tripoli Airport station.