A framework for assessing multi-hazard risk dynamics: Application to South African maize production

Source Agritrop Cirad (agritrop.cirad.fr) International audience Climate change amplifies extreme weather events, posing critical risks to South African agriculture, where rainfed farming and climatic variability heighten vulnerability. Maize, the country's staple crop, is sensitive to compounded hazards. However, current risk assessments largely consider hazards in isolation and often fail to capture their interactions across time, space, and crop development stages, limiting their usefulness for decision-making. Therefore, this paper presents a novel risk-scoring system within a multi-hazard assessment framework applied to South African maize production. This system integrates irrigation-defined clusters, climatic indices, and crop-stage-specific dynamics. Climatic hazards—including droughts, heatwaves, cold spells, heavy rainfall, diseases, and frost—were profiled, and risk scores calculated from their correlations with yield. Statistical models, linking spatio-temporal yield variability to multi-hazard risk scores, captured how hazard interactions compound across regions, irrigation levels, and phenological stages. Results show that yield losses are not driven by the number of hazards occurring each year, but by specific hazard interactions across phenological stages. Yield gaps between rainfed and moderately irrigated systems narrow from 41% at a risk score of 0 (lowest) to 9% at 8 (highest), suggesting that moderate irrigation cannot fully mitigate high risks. Yield gaps between rainfed and highly irrigated systems widen from 47% to 71%, indicating greater stability under higher risk conditions. Normalized average risk scores (0–1) were lower in highly irrigated systems (0.13–0.14), moderate in moderately irrigated systems (0.23–0.36), and highly variable in rainfed systems (0.00–0.90). In rainfed systems, all hazard profiles negatively impact yields, with the drought-heatwave combination presenting the highest risks. While irrigation reduces drought stress, it can also amplify challenges under combined heat and high-moisture conditions by promoting waterlogging and disease outbreaks. These findings identify the most critical hazard interactions, across irrigation levels and growth stages, supporting more targeted and context-specific risk management strategies.