<p>S1. Stochastic model validation; S1 Fig.</p>

Climate change poses a significant threat to food production in Tanzania, particularly for smallholder farmers who rely on rain-fed agriculture. This study examines the role of improved seeds and fertilizers as climate adaptation strategies to boost rice productivity and food security. Using data from the 2019/20 National Sample Census of Agriculture (NSCA), the study analyzed 6,025 rice farms from Mainland Tanzania and Zanzibar. A Stochastic Simulation model was used to account for yield variability and uncertainty. Farms were classified by seed type (local or improved) and fertilizer use (organic, inorganic, or none). Findings show that using improved seeds with inorganic fertilizers significantly enhances productivity, with a 16% chance of achieving yields above 4.5 t/ha. This combination also reduced the risk of falling below food security thresholds. In contrast, farms using local seeds, even with fertilizers, had only a 10% chance of reaching that yield level. The impact was more notable in Mainland Tanzania (25%) than in Zanzibar (6%). While organic fertilizers improve soil health, they offer limited short-term yield gains. The study concludes that promoting access to improved seeds and inorganic fertilizers is crucial for enhancing rice productivity and achieving the SDG 2 goal of Zero Hunger in Tanzania.