Diurnal rainfall variability over the Maritime Continent: Evaluation and future projections from CORDEX-SEA simulations

Study region: This study focuses on the Maritime Continent within the Coordinated Regional Climate Downscaling Experiment–Southeast Asia (CORDEX–SEA) domain. Study focus: This study provides the first systematic evaluation of present-day diurnal rainfall simulations over the CORDEX–SEA domain, and projects future changes under the Representative Concentration Pathway 8.5 scenario, emphasizing the Maritime Continent islands and adjacent coastal–offshore environments. The analysis covers both boreal summer and winter seasons and includes a diagnosis of the underlying dynamic and thermodynamic mechanisms driving the projected rainfall changes. New hydrological insights for the region: High-resolution regional climate models better capture present-day diurnal rainfall amplitude, peak timing, and coastal-to-offshore propagation than their driving global climate models, with particularly marked improvements in propagation over the Maritime Continent. Future projections in the late 21st century indicate minimal change in diurnal timing over land but a widespread weakening of amplitude, especially in summer, with reduced coastal propagation. Over oceans, changes display a latitudinal pattern, with amplitude increases north of 10°N and decreases to the south. Physical mechanism analysis further reveals that reduced surface specific humidity and weakened surface wind convergence jointly suppress the diurnal rainfall peak, with thermodynamic effects dominating over Sumatra and dynamic effects over Borneo. These results provide new physical insights into the coupled roles of circulation and moisture in shaping the spatial heterogeneity of future diurnal rainfall changes over the Maritime Continent.