Applicability and improvement of the Chicago storm pattern from the perspective of dimensionless storm curve shape and co-frequency probability of rainfall depths

Six cities in the middle and lower reaches of the Yangtze River Basin, China. This study addresses the structural limitations of the widely used Chicago storm pattern, whose unimodal, sharply peaked shape often misrepresents actual rainfall events, leading to uncertainties in urban flood assessment. We developed a novel methodological framework integrating Spearman correlation, copula functions, and Bayes’ theorem to qualitatively and quantitatively re-evaluate the pattern’s applicability. Subsequently, we proposed improved storm patterns based on a “relaxed equiprobability” concept and a dual-pattern strategy. (1) A significant correlation exists between total rainfall depth and storm pattern shape in the region. As depth increases, rainfall temporal distribution becomes more uniform, rendering the Chicago pattern structurally unsuitable for high-volume events, which are critical for regional flood control. (2) The applicability of the Chicago pattern significantly decreases with increasing return period and duration difference, exposing the risk of its misapplication in the region’s infrastructure design. (3) The newly developed framework overcomes the rigid assumptions of traditional methods. A case study demonstrates that the improved patterns provide more realistic representations of both short-duration downpours and prolonged rainfall, optimizing drainage design efficiency while maintaining safety standards. This offers a scientifically-grounded and cost-effective approach for targeted flood prevention in the Yangtze River Basin and similar hydroclimatic regions. • Reveals rainfall pattern correlation: uniformity increases with depth. • Chicago pattern applicability decreases with return period, revealing design risks. • New “relaxed equiprobability” framework overcomes traditional method limitations. • Dual-pattern strategy optimizes drainage design while maintaining flood standards.