Rapid-response simulation of the 2025 Hayli Gubbi eruption with an enhanced WRF-Chem v4.8 model

Volcanic ash and SO₂ clouds pose significant hazards to aviation, air quality, and downwind ecosystems, motivating rapid, physically consistent plume modeling. We present a new and improved volcanic capability in WRF-Chem v4.8 [1] that addresses key limitations of earlier implementations by (i) strengthening ash/SO₂/sulfate mass conservation and diagnostics, (ii) correcting ash gravitational settling and refining removal pathways via added wet and dry deposition for ash and sulfate, (iii) improving SO₂ oxidation to sulfate (gas-phase and in-cloud pathways), and (iv) enabling direct radiative effects of ash and sulfate for fully interactive aerosol–meteorology coupling. These developments are paired with an emission-preprocessing workflow that supports time- and height-varying volcanic source terms for rapid-response simulations.

We demonstrate the approach for the unusually explosive Hayli Gubbi eruption (Afar, Ethiopia) on 23 November 2025 by reconstructing emissions using backward-trajectory analysis and constraining the simulation with satellite and ground-based observations. The downwind plume was captured by an AERONET station in Oman, providing rare constraints on the ash size distribution, while TROPOMI retrievals constrain SO₂ columns and plume properties. The enhanced WRF-Chem reproduces the observed plume timing and structure and yields best-fit total emissions of approximately 1.0 Mt of fine ash and 0.3 Mt of SO₂. Ash is injected mainly at ~7-11 km with a brief pulse up to ~14 km, whereas SO₂ is emitted higher (~8–16 km) and remains predominantly tropospheric during the first day, implying limited near-term climate impact for the inferred SO₂ burden. Simulated deposition indicates measurable ash fallout to the southern Red Sea and Gulf of Aden within ~28 hours, consistent with satellite-observed chlorophyll anomalies suggestive of an early marine response. This workflow is readily transferable to other eruptions for near-real-time plume forecasting and impact assessment.

References:

[1] Ukhov, A., Stenchikov, G., Schnell, J., Ahmadov, R., Rizza, U., Grell, G., and Hoteit, I.: Enhancing volcanic eruption simulations with the WRF-Chem v4.8, Geosci. Model Dev., 18, 9805–9825, https://doi.org/10.5194/gmd-18-9805-2025, 2025.