Seasonal Modulation of Diurnal Precipitation over the Mentawai Islands

Abstract

One important aspect of tropical climates is the diurnal precipitation cycle, which is strongly modulated by seasonal dynamics and atmospheric processes. This study investigates the diurnal variation of precipitation over the Mentawai Islands, a small-island region off western Sumatra that is highly exposed to heavy rainfall and hydrometeorological hazards. Hourly precipitation accumulation (PA), frequency (PF), and intensity (PI) were analyzed using IMERG V07 and GSMaP V08 satellite datasets for the wet season (November–March; NDJFM) and dry season (May–September; MJJAS) during the period 2000–2022. In addition, ERA5 reanalysis was employed to examine the associated vertical velocity, relative humidity, and surface wind convergence. The results show that PI is generally higher during the dry season (1.5–3.3 mm/h) than during the wet season (1.5–2.6 mm/h), particularly over smaller islands (Sipora and North Pagai) and adjacent coastal seas, whereas both PA and PF are greater in the wet season. Seasonal variations in vertical velocity (ω) and offshore low-level winds enhance nocturnal convection over the Mentawai Strait, leading to earlier diurnal peaks of PA and PI during MJJAS (23–01 LT) compared to NDJFM (01–03 LT) over the Mentawai Islands. In contrast, the large-scale monsoon circulation regulates the seasonal pattern of PF amplitude without significantly altering the timing of its diurnal peak. These findings not only elucidate the complex diurnal mechanisms in maritime island climates but also suggest the need for localized rainfall monitoring and early-warning systems to support ecosystem sustainability and the livelihoods of Mentawai communities that depend on nature.