Rainfall Intensity-Duration-Frequency Relationships: A Robust Foundation for Urban Decision-Making and Flood Management: A Case Study

Abstract

Ahmedabad, a city in India, experiences varying climatic patterns and is prone to extreme rainfall and relies on established intensity-duration-frequency (IDF) relationships for critical infrastructure planning and flood management. While the city has existing IDF relationships, these curves were established some time ago and still lack well-established IDF Curves. To fill this research gap this study is dedicated to the development of IDF curves for Ahmedabad City, utilizing 45 years of rainfall data (1978 to 2022) sourced from the Indian Meteorological Department (IMD) making our study a pioneering effort in this direction. Employing frequency analysis methodologies, the relationships between rainfall intensity, storm duration, and return periods were established. IDF curves were generated for durations of 5, 10, 15, 30 minutes, and 1, 2, 6, 12 and 24 hours for Ahmedabad City. Short-term rainfall intensities were derived from daily rainfall values using the IMD formula. The empirical approach, Gumbel distribution, and Log Pearson Type-III distribution were applied. The Gumbel method tends to produce slightly higher rainfall intensities for shorter return periods, while the LPT III method exhibits the opposite pattern for longer return periods, such as 25, 50, and 100 years. In general, both approaches yield closely matching results across most return periods. The IDF curves produced in this study offer a versatile set of rainfall scenarios for diverse applications, including the design and modification of hydraulic structures, stormwater management infrastructure, and flood mitigation systems in Ahmedabad City. The outcomes of this research contribute not only to filling a crucial research gap but also empower decision-makers and urban planners with updated and reliable data crucial for enhancing the city’s resilience against extreme rainfall events.