In this paper, we develop a conceptual model capable of decomposing supply variations into yield effects and cultivation area effects. The dataset includes supply, yield and cultivation area information on Chinese cabbage, highland Chinese cabbage, pepper, garlic, green onion, onion and radish, collected in a Farm Product Survey from the year of 2009 to the year of 2013 by the National Statistical Office. Applying this model to vegetable production data, we found that cultivation area effects are dominant in explaining vegetable production variations except the case of highland Chinese cabbage. This implies that the production variability of vegetables is mostly affected by the cultivated area variability: the size of yield variability in explaining production variability of vegetables is smaller than that of cultivation variability. Moreover, we found that yield effects decreased over time; comparing decomposition results before and after the year of 2000 showed that yield effects in explaining production variation of vegetables decreased for all vegetable products considered except green onion. This implies that the major source of production variabilityof vegetables has shifted from yield variability to cultivation area variability. However, inrecent 5 years (2009-2013), yield effects are found to be getting stronger reflecting climate change (i.e., extreme weather events) effects. This generates important policy implications on taylor-made interventions for production stability of each vegetable given its decomposition results.