Abstract
Annual rainfall records of 20 stations for 30 years are used in order to detect rainfall regimes and climatic features of Saudi Arabia using harmonic analysis techniques. In this study, the percentages of variance, amplitudes, and phase angles are calculated in order to depict the spatial and temporal characteristics of the country's rainfall. The first harmonic explains 42 % of rainfall variation in the western (W) region. This percentage increases toward east (E) and north (N) with 69 and 67 %, respectively. In the southwest (SW) region, the percentages explain 43 % of rainfall variation. The percentages of variance in W and SW are lower than in the E, NW, and central (C) regions. This implies significant contributions of the second harmonic in W and SW regions with 26 and 16 %, respectively. The high percentages of the second and third harmonics in W and SW regions suggest that these two regions are affected by different weather systems at different times. The SW region has the highest amplitudes of the first, second, and third harmonics. The amplitude of the first harmonic reaches to 21 mm in SW and 9 mm in both C and E regions. The time of maximum rainfall is calculated using phase angle; the result reflects that maximum rainfall is shifted forward on the time axis toward the spring season in SW and C regions, January in E and NW regions, and October and November in the W region. This reveals that the SW region is a completely different climatic region, though some of what affects this region also affects the central region. Conditions in the E and NW regions are mainly affected by Mediterranean weather systems, while the W region is affected by unstable conditions caused by the active Red Sea Trough (RST) in October and November.