Interannual variability of precipitation in Sri Lanka

Abstract

Two different spectral analysis methods, the multitaper method (MTM) and the maximum entropy method (MEM) were applied to investigate the presence of low-frequency periodicities in precipitation records of 14 climatological stations in Sri Lanka. The spectral analysis revealed statistically significant periodicities in the range of 2–3 year and 3–6 year periods in all parts of Sri Lanka irrespective of the climatic variability. The 2–3 year band corresponds to the Quasi-Biennial oscillation (QBO), while the 3–6 year band corresponds to the El-Nino/Southern oscillation (ENSO) higher and lower frequency bands. Cross spectrum analysis showed statistically significant (at 5%) coherencies for the Indian Ocean dipole (IOD) and Southern oscillation index (SOI) in the 2–3 year band and the 3–6 year band, respectively for most of the regions. Thus, it is concluded that the IOD and SOI play important roles as modulators of precipitation in Sri Lanka.