Impact of Rainfall Temporal Heterogeneity on Relationship between Curve Number and Rainfall Depth in the Zagros Mountain Region,Iran

The impact of temporal variation of rainfall on the relationship between rainfall and catchment response is investigated in a catchment with high temporally variable rainfalls and a high percentage of permeable soils in the southwest of Iran.Twenty-nine storm events are classified into two classes, High Temporal heterogeneous(HT) and Low Temporal heterogeneous(LT) events using the variogram technique and the storm events of each class are analyzed to detect the relationship between Curve Number(CN) and rainfall depth. It is found that there is not a similar correlation between CN values and rainfall depths for both temporally variable classes, and hence, two different responses can be observed in the catchment according to rainfall temporal heterogeneities. For HT events, a complacent behavior is detected in which the CNs decline as rainfall depth increases while a different response, violent behavior, is observed for LT events in which the CNs rise and asymptotically approach a constant value with increasing storm size. This considerable difference between CN-P relationships derived from the two temporally variable classes of rainfall is attributed to the provocation of different runoff generation mechanisms, infiltration-excess and saturation-excess caused by rainfall temporal heterogeneities. Moreover, the results support the validity of variogram technique to classify storm events into two LT and HT classes.