Construction of IDF curves based on NRCS synthetic rainfall hyetographs and daily rainfall records in arid regions

Construction of intensity-duration-frequency (IDF) curves is crucially important for the design and management of hydro-systems and hydraulic structures. The existence of long-term records of short-duration rainfall is essential for the development of IDF curves. In arid regions, short-duration rainfall records are usually scarce and daily rainfall data are the most commonly available. However, synthetic rainfall hyetographs can afford a simple and suitable tool for extracting short-duration rainfall from daily rainfall data. This study aims to evaluate the ability of the four standard NRCS synthetic rainfall distributions to generate short-duration rainfall data from daily data that might be used to construct IDF curves for an arid region in western Saudi Arabia. The historical intensity and daily rainfall records are collected from 10 recording rainfall stations in Jeddah-Makkah-Taif (JMT) hydrologic region located in western Saudi Arabia. In this study, 2-, 3-, 6-, 12-, and 24-h types I, IA, II, and III NRCS dimensionless rainfall time distributions are used to convert the observed daily rainfall data into shorter duration data. The generated data are used to develop IDF curves and they were compared with those constructed from the available observed rainfall intensity data. Values of the mean absolute percentage error (MAPE) for the used gauge stations range between 5 and 11%. The comparison shows that the NRCS synthetic rainfall distributions are capable to generate short-duration rainfall data that can be used to construct IDF curves for the JMT region. The results also suggest that the 6-h type II NRCS distribution produced IDF curves that are very comparable with those extracted from the observed data. The results also indicate that the 3-h types I and III NRCS distributions have relatively low overall mean values of MAPE (10 to 12%). They can be considered the second-best choice after the 6-h NRCS distribution for developing IDF curves for the study region. This may highlight the applicability of the proposed technique in the JMT region.