Temperature stabilization using Stratospheric Aerosol Injections minimises drying over Africa only when combined with a strong decarbonization effort

Abstract. Climate change poses severe risks to African agriculture, water resources, and ecosystems. Temperature overshoot scenarios, in which global warming temporarily exceeds target thresholds such as 1.5 or 2.0 °C before declining through mitigation and carbon removal later in the century, are plausible future trajectories. Yet, their regional impacts and the reversibility of changes during the overshoot remain poorly characterized. Stratospheric aerosol injection (SAI) has been proposed as a means to limit peak warming during overshoot; however, its effects on African climate extremes and water availability require careful assessment. This study analyses different CESM2-WACCM6 simulations to evaluate changes in temperature extremes, precipitation patterns, and surface moisture budget across Africa, using two baseline scenarios, the high GHG forcing scenario (SSP5-8.5) and the SSP5-3.4-OS overshoot scenario, which includes strong decarbonization and carbon removal efforts after 2040. In addition, three SAI intervention scenarios are assessed, targeting 1.5 and 2.0 °C (for the overshoot scenario, only) above pre-industrial levels. We compute selected ETCCDI-based climate indices, including Growing Degree Days, Warm Spell Duration Index, Consecutive Dry Days, and precipitation intensity metrics for baseline and overshoot (2060–2079) periods. Our results reveal near-universal, statistically significant changes (> 90 %) in temperature indices during overshoot, with 5–30 % increases depending on the metric. Precipitation indices exhibit more heterogeneous responses, with 40–80 % of the area showing significant changes. SAI interventions consistently reduce temperature-related indices across Africa, with the strongest cooling effects in tropical regions. However, precipitation responses to SAI display substantial spatial heterogeneity and scenario dependency: West Africa’s Sahel shows increased moisture availability under high SAI compared to SSP5-8.5, Central Africa exhibits mixed responses with regional drying in parts of the Congo Basin, and East Africa demonstrates a dipole pattern of coastal wetting and interior drying that intensifies at higher warming thresholds. All these changes are magnified under high-cooling scenarios (using the high forcing baseline) compared with cooling under overshoot, in which case many precipitation differences are reduced.