Lake Urmia water level has fluctuated during many years. We investigated water level data (annual maximum, minimum and average series in the period of 1966–2012) to evaluate changes based on long-term and seasonal patterns over time, data characteristics and temporal change analysis. Our tools for the mentioned analyses included seasonal trend decomposition using loess (STL); normality and independence; change point and trend analysis. The results of STL revealed a sustained decline occurring after the last 1990s and loess trend line confirmed it. The analyses of data characteristics showed that the observed data do not fulfil the assumptions of being independent and identically normal-distributed. Therefore, the non-parametric Pettitt’s test was applied to identify an abrupt change point in the data series, followed by trend analysis using the non-parametric Mann-Kendall test. Results showed that there is a significant decreasing trend in water lake level and the beginning of change point is in 1996.
Keywords: long-term pattern, data characteristics, non-parametric test, change point analysis, trend analysis, Lake Urmia