Xu et al. (2025) Applicability and improvement of the Chicago storm pattern from the perspective of dimensionless storm curve shape and co-frequency probability of rainfall depths

Identification

• Journal: Journal of Hydrology Regional Studies
• Year: 2025
• Date: 2025-12-09
• Authors: Wenbin Xu, Zheng Fang, Hanjie Zhou, Wentao Xu, Liang Lai
• DOI: 10.1016/j.ejrh.2025.103018

Research Groups

• School of Civil Engineering, Wuhan University, Wuhan, China
• Nanchang Urban Planning & Design Institute Group Co., Ltd., Nanchang, China
• The National Key Laboratory of Water Disaster Prevention, Hohai University, Nanjing, China
• JiangXi Climate Center, Nanchang, China

Short Summary

This study re-evaluates the applicability of the Chicago storm pattern, finding its fixed shape unsuitable for high-volume rainfall events, and proposes improved storm patterns that offer more realistic representations for urban flood assessment and drainage design optimization.

Objective

• To qualitatively and quantitatively re-evaluate the applicability of the Chicago storm pattern, which has structural limitations for urban flood assessment, and to propose improved storm patterns based on a "relaxed equiprobability" concept and a dual-pattern strategy.

Study Configuration

• Spatial Scale: Six cities in the middle and lower reaches of the Yangtze River Basin, China (Yichang, Wuhan, Nanchang, Hefei, Nanjing, and Ganzhou).
• Temporal Scale: Rainfall time series data with a 5-minute temporal resolution. Nanchang data spanned 40 years (January 1981 to December 2020), while other cities had 9 years of data (July 2015 to June 2024). Storm events were uniformly sampled to a 120-minute duration.

Methodology and Data

• Models used: Spearman correlation, copula functions (Gaussian, t-copula, Clayton, Gumbel, Frank), Bayes’ theorem, log-normal, logistic, Weibull, gamma, and log-logistic distributions (for marginal probability), MIKE integrated modeling suite (for 1D-2D coupled hydrodynamic modeling), Kolmogorov–Smirnov test, Akaike’s information criterion, and Euclidean square distance.
• Data sources: Rainfall time series data from 43 national meteorological stations across the six study cities.

Main Results

• A statistically significant correlation was established between total rainfall depth and storm pattern shape, showing that as total rainfall depth increases, the rainfall temporal distribution becomes more uniform, rendering the unimodal, sharply peaked Chicago storm pattern structurally unsuitable for high-volume events.
• The applicability of the Chicago pattern diminishes significantly with increasing design return period (DRP) and duration difference. For Nanchang, with a 50% co-frequency probability of rainfall depths (CFPRD) threshold, the Chicago pattern is applicable only for total durations of 120, 120, 60, 30, 30, and 30 minutes for DRPs of 2, 3, 5, 10, 20, and 50 years, respectively.
• The proposed improved storm patterns (Improved pattern A for short-duration intense rainfall and Improved pattern B for long-duration continuous rainfall) provide more realistic representations of actual rainfall events compared to the Chicago, Huff, and Pilgrim & Cordery patterns.
• Flood simulations in Nanchang demonstrated that the Chicago storm pattern consistently overestimated waterlogging areas. For a 50-year DRP, the Chicago pattern simulated a waterlogging area 52% larger than that simulated by Improved pattern A, suggesting potential for significant overinvestment in drainage infrastructure.

Contributions

• Developed a novel methodological framework integrating Spearman correlation, copula functions, and Bayes’ theorem to qualitatively and quantitatively re-evaluate the applicability of the Chicago storm pattern.
• Proposed improved storm patterns based on a “relaxed equiprobability” concept and a dual-pattern strategy, overcoming the rigid structural assumptions and selective storm sampling limitations of traditional methods.
• Demonstrated that the improved patterns provide more realistic representations of rainfall events, optimizing drainage design efficiency and safety standards, offering a scientifically-grounded and cost-effective approach for targeted flood prevention.
• Introduced a dual-pattern approach (Pattern A for short-duration intense rainfall, Pattern B for long-duration events) to provide comprehensive risk coverage, moving beyond "one-size-fits-all" limitations and excessive conservatism of traditional methods.

Funding

• Jiangxi Meteorological Bureau
• Jiangxi Eco-meteorological Center
• Jiangxi Province Technology Innovation Guidance Program (project number S2022KJSLE0002)

Citation

@article{Xu2025Applicability,
  author = {Xu, Wenbin and Fang, Zheng and Zhou, Hanjie and Xu, Wentao and Lai, Liang},
  title = {Applicability and improvement of the Chicago storm pattern from the perspective of dimensionless storm curve shape and co-frequency probability of rainfall depths},
  journal = {Journal of Hydrology Regional Studies},
  year = {2025},
  doi = {10.1016/j.ejrh.2025.103018},
  url = {https://doi.org/10.1016/j.ejrh.2025.103018}
}