Simulation and Projection of Diurnal Rainfall over the Maritime Continent Using High-Resolution CORDEX-SEA Simulations

Rainfall over Southeast Asia exhibits a pronounced diurnal cycle driven by complex land–sea interactions, particularly over the Maritime Continent, where mesoscale processes play a key role in shaping regional climate variability and predictability across spatial and temporal scales. Understanding how these processes respond to climate change remains challenging due to uncertainties in their representation in climate models and the complex interplay between thermodynamic and dynamical factors. This study evaluates the spatial and temporal characteristics of diurnal rainfall over the Maritime Continent and their projected changes during boreal summer and winter using six high-resolution regional climate model (RCM) simulations from the Coordinated Regional Climate Downscaling Experiment (CORDEX) Southeast Asia project. Evaluation against observations shows that the RCMs more accurately reproduce key features of present-day diurnal rainfall, including amplitude, peak timing, and coastal-to-offshore propagation, than their driving global climate models (GCMs), with the greatest added value in representing propagation over Maritime Continent islands. Future projections under the Representative Concentration Pathway 8.5 scenario for the late 21st century indicate minimal changes in diurnal phase timing over most land areas, but a widespread weakening of amplitude over the Maritime Continent in both seasons. The reduction is more pronounced in summer, accompanied by a weakening of coastal-to-offshore propagation. Inter-model agreement is robust over land areas of the Maritime Continent, increasing confidence in the projected weakening of the diurnal cycle. Analysis of physical mechanisms suggests that both reduced surface specific humidity and weakened surface wind convergence contribute to the suppression of the diurnal rainfall peak, with thermodynamic components dominating over Sumatra and dynamic components influencing more pronounced over Borneo. These findings highlight the importance of coupled circulation–moisture processes in shaping future changes of the diurnal rainfall cycle and demonstrate the added value of high-resolution regional modeling for advancing understanding of mesoscale meteorology and climate change in regions with complex land–sea interactions.