Spatiotemporal Variability of Defined Extreme and Convective Rainfall in Sabah Malaysia from 2000 to 2024 Using GPM IMERG and JAXA GSMaP

Abstract Short-duration high-intensity rainfall poses substantial challenges for hydrocli-matic hazard assessment in tropical regions, yet its spatial, seasonal and temporal variability remains insufficiently characterised across Sabah, Malaysian Borneo. This study characterises threshold-defined extreme and convective rainfall occurrence across Sabah during 2000–2024 and evaluates its consistency between GPM and JAXA in relation to monsoon seasons and large-scale climate variability. Rainfall occurrences were identified using operational thresholds adopted from Malaysia’s Department of Irrigation and Drainage and analysed at hourly resolution on a common 0.1° grid. Frequencies were evaluated during the Northeast Monsoon (NEM) and Southwest Monsoon (SWM) across 27 administrative districts grouped into five geographical Zones. The results reveal pronounced spatial and temporal heterogeneity, with the Sandakan and Kudat Zones repeatedly exhibiting relatively high rainfall-occurrence frequencies across multiple five-year periods. Sandakan was particularly prominent during the SWM, whereas Kudat showed greater prominence during the NEM. Convective rainfall was generally more frequent and spatially extensive than hourly extreme rainfall. GPM and JAXA broadly agreed on the recurrent geographical concentration of rainfall occurrence but differed in its magnitude, spatial extent and temporal evolution, particularly for extreme rainfall. Inter-product correlations were sparse and spatially fragmented for extreme rainfall but more extensive for convective rainfall, particularly during the NEM. Comparisons with ENSO, the Indian Ocean Dipole and the Madden–Julian Oscillation showed no consistent correspondence between individual climate phases and periods of enhanced rainfall frequency, indicating that these large-scale modes alone do not explain the observed variability. Overall , the study provides a 25-year spatially explicit baseline of threshold-defined rainfall occurrence across Sabah, identifies the Sandakan and Kudat Zones as recurrent high-frequency areas, and demonstrates the importance of accounting for satellite-product uncertainty when assessing short-duration rainfall variability and associated hazards.