This paper explores the effects of climatic characteristics on the shape of a flow duration curves (FDCs) in Japanese watersheds. We investigated the effects by correlation analyses between climatic characteristics and index flows in 14 Japanese watersheds, where we partitioned FDCs into three sections of exceedance probability (EP) : EP=0.0-0.3, 0.3-0.7 and 0.7-1.0. As the results, we found that the shapes of FDCs of the low probability section (EP=0.0-0.3) reflects the shapes of precipitation duration curves. Also, the shapes of FDCs of the intermediate probability section (EP=0.3-0.7) and the high probability section (EP=0.7-1.0) both showed strong correlations with seasonality index. Applying the above correlations, we estimated the shapes of FDCs in two different test watersheds and found that climatic characteristics alone are useful for roughly estimating the shapes of FDCs. Our findings indicate climatic characteristics are the primary factors that control the shapes of FDCs.
