Climate change can potentially drive variations in the frequency and magnitude of hydrological extremes, and in turn the impact these events have on agriculture. Agricultural damages resulting from extreme events can significantly affect food security at multiple scales, especially in contexts where pre-existing unfavourable social and economic conditions already hinder the stability and the effectivity of the food supply chain. In these contexts, formulating approaches to directly quantify food security impacts of extreme events in a way that is compatible with local data availability, but at the same time reliable and transparent, becomes a crucial and urgent matter. Moreover, while the importance of the multifaceted repercussions of agricultural damage on food security have been highlighted in the current literature, investigation on impacts different than reduced crop availability remain understudied. Here, we propose a methodology to derive metrics of food availability and food access impacts from post-disaster assessments, by putting the affected communities at the core of the analysis. We then provide perspectives on food utilization and food stability impacts. We apply the methodology on the severe floods that affected Malawi in the early months of 2015. We find that agricultural losses correspond to food sufficient for feeding more than 300,000 people and for balancing the diet of almost 2.3 million. Food security impacts also appear to disproportionately hit poorer and less food-secure districts. The proposed methodology is easily replicable in other case studies, also moving beyond floods as the triggering extreme event.