Wavelet analysis of multi-scale drought variability and climate teleconnections in Penang, Malaysia

Understanding the multi-scale variability of drought is critical for improving climate diagnostics in tropical coastal regions. This study investigates the temporal dynamics of meteorological drought and its linkage with large-scale climate teleconnections in Penang, Malaysia, using a wavelet-based time–frequency framework. The Standardized Precipitation Index (SPI-3) was derived from six meteorological stations for the period 1986–2020 to characterise short-term drought variability at a fine spatial scale. Findings indicate that trend and homogeneity analyses reveal weak yet spatially heterogeneous changes, with a tendency towards wetter conditions on the mainland compared to Penang Island. Time–frequency analysis reveals distinct periodicities at intra-annual (3–6 months), seasonal (6–12 months), and interannual (> 12 months) scales, with dominant oscillations in the 6–10-month band across multiple stations. Prolonged drought episodes, lasting up to 20 months, were identified, particularly during 2001–2002, highlighting the persistence of low-frequency variability. Wavelet coherence analysis demonstrates significant and non-stationary relationships between SPI-3 and large-scale climate drivers. The El Niño–Southern Oscillation (ENSO) exhibits stronger and more persistent coherence at interannual scales, indicating its dominant influence on regional hydroclimatic variability, whereas the Indian Ocean Dipole (IOD) shows comparatively weaker and intermittent effects. Overall, this study reveals the scale-dependent and non-stationary nature of drought dynamics in a humid tropical coastal environment. By integrating station-level analysis with wavelet-based diagnostics, it provides new insights into the multi-scale structure of drought variability and advances the understanding of teleconnection-driven hydroclimatic processes in Southeast Asia.