Wetter, weaker, and more frequent monsoon low-pressure systems in CMIP6 future scenarios

Hunt, K. M. R. ORCID: https://orcid.org/0000-0003-1480-3755 and Turner, A. G. ORCID: https://orcid.org/0000-0002-0642-6876 (2025) Wetter, weaker, and more frequent monsoon low-pressure systems in CMIP6 future scenarios. Journal of Climate. ISSN 1520-0442 doi: 10.1175/JCLI-D-25-0389.1 (In Press)

Abstract/Summary

The South Asian monsoon is strongly influenced by synoptic-scale low-pressure systems (LPSs), which deliver the majority of seasonal and extreme rainfall. Here, we provide a robust synthesis of future LPS characteristics by analysing 13 models from the Coupled Model Intercomparison Project Phase 6 (CMIP6). We develop a novel, multi-component skill score (FLIP: Frequency, Location, Intensity, Precipitation) to evaluate and weight model performance against reanalysis benchmarks. Our weighted multi-model projections reveal a consistent narrative for future monsoons: LPSs are projected to become more frequent and dynamically weaker in terms of low-level vorticity as global warming levels increase. Per-LPS precipitation is projected to increase, with a super-Clausius-Clapeyron scaling for the most intense storms, despite a general weakening of their circulation. We attribute this apparent paradox to a projected increase in the background meridional moisture gradient and a structural change whereby boundary layer winds weaken less than those in the free troposphere, maintaining strong frictional moisture convergence. Furthermore, LPSs are projected to penetrate deeper inland, with a significant increase in post-landfall duration between 1.5°C and 2°C of warming. To deconstruct inter-model uncertainty, we employ a storyline approach based on unsupervised clustering of circulation and moisture anomalies. This reveals four physically self-consistent yet distinct future pathways that explain model diversity in LPS frequency, track, and precipitation changes. For example, a storyline with enhanced easterlies over Southeast Asia leads to a 36% increase in LPS frequency by transporting more precursor disturbances into the Bay of Bengal. Averaging over these diverse futures, the consistent outcome is a monsoon dominated by more numerous and wetter LPSs that track deeper into the subcontinent, expanding the risk of extreme rainfall and flooding to western parts of India.

Item Type	Article
URI	https://centaur.reading.ac.uk/id/eprint/127004
Identification Number/DOI	10.1175/JCLI-D-25-0389.1
Refereed	Yes
Divisions	Science > School of Mathematical, Physical and Computational Sciences > NCAS Science > School of Mathematical, Physical and Computational Sciences > Department of Meteorology
Publisher	American Meteorological Society
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