A 51 years Rainfall Frequency Analysis and Development of Intensity–Duration–Frequency (IDF) Curves for Riyadh, Saudi Arabia

Rainfall Frequency Analysis and Development of Intensity–Duration–Frequency (IDF) Curves for Riyadh, Saudi Arabia presents a rigorous 51-year hydrometeorological analysis (1964–2014) of annual maximum daily rainfall for Riyadh, applying the Weibull plotting-position method and Gumbel Extreme Value Type I distribution to derive statistically validated design rainfall depths for return periods of 2 to 100 years. Sub-daily design storms are developed using Bell's generalised disaggregation ratios and the SCS Type II temporal distribution, producing a complete family of Intensity–Duration–Frequency curves alongside a generalised IDF equation — i = 105.4·T^0.285 / (t + 2.78)^0.629 — fitted with R² = 0.999. The study provides, for the first time from a long local record, locally calibrated design tools directly applicable to storm-water infrastructure design, hydraulic modelling, and flood-risk assessment across Riyadh's rapidly expanding urban environment. Raw data from seven gauge stations, goodness-of-fit statistics, ranked probability tables, and 30-minute Type II design hyetographs are fully documented, making the results immediately usable in HEC-HMS, SWMM, and rational-method calculations. This work addresses a critical gap in arid-region engineering hydrology and establishes a reproducible methodological framework suitable for extension to other data-scarce cities across the Arabian Peninsula and wider hyper-arid zones