Homogeneity of Time Series and the General Trend of Rainfall in the King Salman Royal Reserve, Northern Saudi Arabia
Abstract
To investigate the trends of monthly and annual rainfall in the King Salman Royal Reserve in northern Saudi Arabia, four homogeneity tests were applied: the Pettitt test, the Standard Normal Homogeneity Test (SNHT), Buishand’s test, and the Von Neumann ratio test. These tests were conducted to assess data homogeneity and ensure data quality according to the Wijngaard classification. Subsequently, monthly and annual rainfall trends were analyzed using non-parametric methods, namely the Mann–Kendall test and Sen’s Slope estimator to quantify the magnitude of trends. The homogeneity tests indicated that five stations were classified as homogeneous and categorized as “Useful.” Four additional stations exhibited homogeneity levels ranging between 75% and 90%. Among the 96 monthly time series examined, five series were classified as “Doubtful,” while only two series were classified as “Suspect.” The results of the Mann–Kendall test for annual rainfall trends revealed four statistically significant trends. Only one station (Jubbah) exhibited a significant positive trend, whereas three stations (Hail, Dumat Al-Jandal, and Nabk Abu Qasr) showed significant negative trends, indicating a decrease in annual rainfall amounts. The remaining stations showed no statistically significant trends. Regarding monthly rainfall trends, the correlation values were generally weak across most months and largely statistically non-significant, suggesting that many of the detected monthly trends do not represent meaningful or robust temporal changes in the rainfall time series.
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