In-field rainwater harvesting (IRWH), a runoff farming system, is a beneficial water management technique for crop production in arid and semi-arid areas. In-field rainwater harvesting is influenced by rainfall characteristics, and hence this study aimed to identify and characterize rainfall events, and determine rainfall parameters that were of significance in in-field runoff. Two algorithms of event identification were developed. The algorithm that identified events spanning over a 24-h day limit as a single event, gave better identification results which were then characterized. This enabled systematic grouping of rainfall parameters. About 33% of the total rainfall amount received had zero potential to be harvested as runoff in the IRWH system. Therefore, a runoff harvesting practice needs to use the remaining 67%. Rainfall events that lasted 30 min or longer were of water-harvesting importance. This could be the minimum duration guideline when simulating rainfall for rainwater harvesting studies. Rainfall event amount and intensity were of significant importance for IRWH runoff determination.