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.