Ngai et al. (2026) Diurnal rainfall variability over the Maritime Continent: Evaluation and future projections from CORDEX-SEA simulations

Identification

• Journal: Journal of Hydrology Regional Studies
• Year: 2026
• Date: 2026-03-09
• Authors: Sheau Tieh Ngai, Wan-Ru Huang, Tzu‐Yang Chiang
• DOI: 10.1016/j.ejrh.2026.103320

Research Groups

• Department of Earth Sciences, National Taiwan Normal University, Taipei, Taiwan

Short Summary

This study systematically evaluates present-day diurnal rainfall simulations over the CORDEX-SEA domain and projects future changes under the RCP8.5 scenario, finding that regional climate models significantly improve the simulation of diurnal rainfall characteristics and project a widespread weakening of amplitude over land and reduced coastal propagation in the late 21st century.

Objective

• To evaluate the performance and added value of CORDEX-SEA Regional Climate Models (CSEAR) in simulating present-day diurnal rainfall characteristics over the Maritime Continent compared to their driving Global Climate Models (GCMs).
• To provide the first systematic assessment of projected future changes in the diurnal rainfall cycle over the Maritime Continent under the Representative Concentration Pathway 8.5 (RCP8.5) scenario for the late 21st century.
• To diagnose the underlying dynamic and thermodynamic mechanisms driving the projected rainfall changes.

Study Configuration

• Spatial Scale: Maritime Continent within the CORDEX-SEA domain (89.49°–146.51°E, 14.81°S–26.96°N), with model outputs and observational data regridded to a common 0.25° × 0.25° grid.
• Temporal Scale: 3-hourly data for historical (1976–2005) and future (2071–2099) periods under RCP8.5. Present-day evaluation uses an overlapping period of 2001–2005. Analysis covers boreal summer (June–August; JJA) and boreal winter (December–February; DJF).

Methodology and Data

• Models used:
  • Six CORDEX-SEA (CSEAR) regional climate simulations at 0.22° resolution.
  • Driving Global Climate Models (GCMs): CNRM-CM5, HadGEM2-ES, NorESM1-M, EC-Earth.
  • Regional Climate Models (RCMs): RCA4, REMO, RegCM4.
  • Ensemble means: CSEARm (unweighted ensemble mean of six CSEAR), GCMm (ensemble of driving GCMs), RegCMm (ensemble of two RegCM models for mechanism analysis).
• Data sources:
  • Satellite observations: Integrated Multi-satellitE Retrievals for GPM Final-run V07B (IMERG) for observed 3-hourly rainfall (2001–2005).
  • Reanalysis: ERA5 (European Centre for Medium-Range Weather Forecasts) for near-surface wind fields.
  • Model outputs: 3-hourly rainfall, near-surface wind, and specific humidity from CSEAR and GCMs.

Main Results

• High-resolution regional climate models (CSEARm) significantly outperform their driving global climate models (GCMm) in capturing present-day diurnal rainfall amplitude, peak timing, and coastal-to-offshore propagation over the Maritime Continent. For the leading EOF mode, CSEARm showed a spatial correlation of 0.76 (vs. 0.59 for GCMm) and a temporal correlation of 0.52 (vs. 0.11 for GCMm) relative to observations.
• Future projections (2071–2099) under the RCP8.5 scenario indicate minimal changes in diurnal timing over most land areas but a widespread weakening of diurnal rainfall amplitude, especially in summer, with reduced coastal propagation over the Maritime Continent islands.
• Over oceanic regions, future changes in diurnal amplitude display a latitudinal pattern: increases north of approximately 10°N and decreases to the south.
• Physical mechanism analysis reveals that reduced surface specific humidity and weakened surface wind convergence jointly suppress the diurnal rainfall peak.
• The relative contributions of dynamic and thermodynamic factors vary regionally: thermodynamic effects predominantly drive diurnal rainfall changes over Sumatra, while dynamic influences are more prominent over Borneo, a pattern consistent in both boreal summer and winter.

Contributions

• Provides the first systematic evaluation of present-day diurnal rainfall characteristics and their projected future changes over the Maritime Continent using CORDEX-SEA simulations.
• Demonstrates the significant added value of high-resolution regional climate models in accurately simulating complex diurnal rainfall propagation patterns, particularly over coastal-to-offshore regions of the Maritime Continent, compared to global climate models.
• Offers new physical insights into the coupled roles of circulation and moisture in shaping the spatial heterogeneity of future diurnal rainfall changes through a moisture budget framework, identifying distinct dominant drivers (thermodynamic vs. dynamic) for different regions.
• Quantifies associated uncertainties across different RCMs and assesses the robustness of projected diurnal changes.

Funding

• National Science and Technology Council of Taiwan (NSTC 114–2111-M-003–006, NSTC 114–2625-M-003–002, NSTC 114–2811-M-003–026, NSTC 114–2811-M-003–005).

Citation

@article{Ngai2026Diurnal,
  author = {Ngai, Sheau Tieh and Huang, Wan-Ru and Chiang, Tzu‐Yang},
  title = {Diurnal rainfall variability over the Maritime Continent: Evaluation and future projections from CORDEX-SEA simulations},
  journal = {Journal of Hydrology Regional Studies},
  year = {2026},
  doi = {10.1016/j.ejrh.2026.103320},
  url = {https://doi.org/10.1016/j.ejrh.2026.103320}
}