A quantitative assessment of crop vulnerability to tephra hazard at Tungurahua volcano, Ecuador: understanding the effect of volcanic and biological factors

Crops are regularly impacted by tephra from explosive volcanic eruptions, causing significant economic losses and jeopardising farmers’ livelihood at the local to regional scales. Crop vulnerability to tephra remains poorly understood, impeding the construction of robust risk models for agriculture. Previous studies of crop vulnerability to tephra are semi-quantitative and consider tephra accumulation as the only hazard intensity metric. Here, we provide a robust evaluation of crop vulnerability based on the analysis of 700 sets of quantitative data, allowing for the assessment of the influence of various volcanic and non-volcanic factors. We collected farmers’ perceptions of damage to fodders, root and tuber crops, leafy crops, legumes, cereals, tree fruits, non-tree fruits, and estimations of their yield loss due to the August 16–17, 2006, October–November, 2015, and February–March, 2016, eruptions of Tungurahua volcano, Ecuador. Crop yield loss increased with tephra loads (48 ± 35, 69 ± 33, and 76 ± 34% for < 0.5, 0.5–5, and 5–50 kg m⁻², respectively), and we found that exposure to tephra led to a greater decline in yield compared to existing predictions. The results further highlight the plant phenological stage as a key factor of vulnerability. Exposure to tephra during the flowering period of legumes, cereals, and tree fruits caused a median yield loss ≥ 80%. Legumes, tree fruits, and non-tree fruits are more vulnerable to tephra than onions. Quantitative knowledge on crop vulnerability to tephra can be obtained from post-eruption impact assessments provided that a large population sample is collected and careful uncertainty analysis is conducted.