Projected temperature and precipitation extremes over Tanzania under stratospheric SO ₂ injection

Abstract Tanzania is highly vulnerable to climate change, with rising temperatures and extreme precipitation threatening agriculture, water resources, human health, energy systems, mining, and nature-based tourism. This study provides a national-scale assessment of future climate extremes under a high-emission scenario (RCP8.5) and evaluates the potential modifying influence of stratospheric aerosol injection (SAI) using simulations from the Stratospheric Aerosol Geoengineering Large Ensemble (GLENS) project for 2075–2095. Under RCP8.5, Tanzania is projected to experience substantial warming, with maximum and minimum temperatures rising by up to +4 °C, particularly in southern and southwestern regions. Extreme temperature indices (TNN, TXX, TX90P, WSDI) intensify across all seasons, while precipitation extremes show a southeast-to-northwest gradient, with increases during the long rains (MAM) and drying during the short rains (OND). SAI deployment is projected to mitigate some of these changes by reducing temperature increases by 1.5 °C–4 °C, with localised overcooling in parts of northeastern and coastal Tanzania. However, SAI is also projected to reverse nationwide RCP8.5 increases in annual precipitation, decreasing rainfall days by up to −0.5 d month −1 during MAM and altering OND rainfall in spatially variable ways. These changes present mixed implications: SAI-induced cooling may alleviate heat stress on crops, livestock, human health, and ecosystems, while reductions in rainfall and increases in consecutive dry days could heighten water scarcity, reduce hydropower reliability, and exacerbate food and water insecurity. Overall, the findings highlight the complex, regionally uneven trade-offs associated with SAI, underscoring the need for cautious, context-specific evaluation of its potential risks and benefits for climate-sensitive sectors in Tanzania, and for careful interpretation of these outcomes as model- and design-dependent projections rather than deterministic predictions. Since GLENS applies SAI under the high-forcing RCP8.5 pathway, the magnitude of projected impacts and ‘mitigation’ may represent an upper-bound response relative to lower-emissions futures and alternative SAI strategies.