Intensity–Duration–Frequency (IDF) Design Rainfall Framework for Türkiye: A Practical Tool for Engineering Applications

Abstract

This study presents a new nationwide intensity–duration–frequency (IDF) framework for estimating extreme rainfall events for Türkiye. The IDF model is based on sub-daily rainfall records from 193 meteorological stations. Standard-duration annual maximum series (30 minutes to 24 hours) were analysed. Data homogeneity was evaluated using the Standard Normal Homogeneity Test, Buishand Test, and Pettitt Test and the results indicate that the maximum series are homogeneous with no significant anthropogenic influence. Trend analyses using the Mann–Kendall test reveal pronounced spatial and duration-dependent variability. Short-duration extremes (30 min–5 h) show statistically significant increasing trends, especially in western and southwestern coastal regions, whereas longer durations (6–24 h) display more heterogeneous and regionally balanced patterns. Four candidate two-parameter probability distributions (Lognormal, Gamma, Weibull, and Logistic) were assessed using the Akaike and the Bayesian Information Criterion. Results indicate a clear dominance of the Lognormal distribution across nearly all durations and regions, with the Gamma distribution serving as a secondary alternative, particularly at longer durations. Beyond statistical evaluation, the study introduces a unified and practitioner-oriented national IDF tool that enables direct extraction of design rainfall intensities for selected durations and return periods. This standardised framework enhances consistency in hydraulic design and supports climate-resilient infrastructure planning. The findings provide a robust foundation for national-scale rainfall frequency analysis while highlighting the need for future integration of non-stationary modelling approaches.

Keywords

• Intensity–Duration–Frequency (IDF)
• extreme rainfall
• lognormal distribution
• Mann–Kendall trend test
• practitioner-oriented national IDF tool
• Türkiye

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