Harbord et al. (2026) Congo Air Boundary Breakdown Timing and Its Connection to Southern African Rainfall Onset in Reanalyses and Historical CMIP6 Models

⚠️ Warning: This summary was generated from the abstract only, as the full text was not available.

Identification

• Journal: International Journal of Climatology
• Year: 2026
• Date: 2026-10-16
• Authors: Sophie Harbord, Neil C. G. Hart, Richard Jones, Richard Washington
• DOI: 10.1002/joc.70609

Research Groups

Not explicitly stated in the abstract, but typically involves climate modeling and atmospheric science research groups.

Short Summary

This study evaluates how well 27 CMIP6 models simulate the relationship between the Congo Air Boundary (CAB) breakdown and rainfall onset in southern Africa. It finds that while models show wider variability in breakdown timing compared to reanalyses, they successfully reproduce the core association between CAB breakdown and rainfall onset, which is crucial for assessing future rainfall projections.

Objective

• To evaluate how well historical simulations from CMIP6 models represent the regional mechanisms of rainfall seasonality in southern Africa, specifically focusing on the association between the breakdown of the Congo Air Boundary (CAB) and rainfall onset timing.

Study Configuration

• Spatial Scale: Southern African subcontinent.
• Temporal Scale: Historical period, focusing on seasonal to climatological scales (annual cycle, austral summer, synoptic and climatological relationships).

Methodology and Data

• Models used: 27 CMIP6 models.
• Data sources: ERA5, ERA-Interim, and MERRA2 reanalyses.

Main Results

• ERA5, ERA-Interim, and MERRA2 reanalyses show strong agreement on CAB climatology, CAB breakdown timing, and the relationship between CAB breakdown and rainfall onset timing.
• Using two novel metrics, a clear statistically significant relationship was found in reanalyses, showing CAB breakdown is associated with rainfall onset over southern Africa at synoptic and climatological scales.
• CMIP6 model climatologies broadly reproduce the annual cycle of CAB length and frequency decreases during austral summer, as identified in reanalyses.
• CMIP6 models exhibit a much wider range (56 days) in the average CAB breakdown date across the two metrics, compared to 11 days across the reanalyses.
• CMIP6 models show the same association between CAB breakdown and rainfall onset timing as seen in reanalyses, with model climatologies having later breakdowns also having later onsets (r-value = 0.9).
• Despite high inter-model variability in season timing, individual CMIP6 models successfully simulate this core regional process linked to CAB breakdown.

Contributions

• Introduces and applies two novel metrics to quantify Congo Air Boundary (CAB) breakdown timing.
• Establishes strong agreement among ERA5, ERA-Interim, and MERRA2 reanalyses regarding CAB climatology and its relationship with southern African rainfall onset.
• Provides a comprehensive evaluation of CMIP6 models' ability to simulate the CAB breakdown and its association with rainfall onset, offering insights into their credibility for future projections of southern African rainfall.
• Highlights that while CMIP6 models have biases in the absolute timing of CAB breakdown, they successfully capture the fundamental physical link between CAB breakdown and rainfall onset.

Funding

Not specified in the abstract.

Citation

@article{Harbord2026Congo,
  author = {Harbord, Sophie and Hart, Neil C. G. and Jones, Richard and Washington, Richard},
  title = {Congo Air Boundary Breakdown Timing and Its Connection to Southern African Rainfall Onset in Reanalyses and Historical CMIP6 Models},
  journal = {International Journal of Climatology},
  year = {2026},
  doi = {10.1002/joc.70609},
  url = {https://doi.org/10.1002/joc.70609}
}