Global Characteristics of Ultra-Extreme Precipitation in Major Cities

Climate change is reshaping the statistical characteristics of precipitation, leading to an increased probability of precipitation events that exceed the range of historically observed extremes. Such ultra-extreme precipitation events are exceedingly rare with limited representation in observational record. However, they pose substantial risks to urban systems and hydrologic infrastructure. The scarcity of observations makes it challenging to robustly quantify their frequency and intensity, constraining the scientific basis for climate risk assessment and long-term adaptation planning. To address these challenges, we propose a statistical framework to characterize ultra-extreme precipitation by integrating observational records and climate model projections. The probability of ultra-extreme precipitation events is estimated at each station by counting the number of occurrences with a standardized deviation from the station mean that exceeds a specified threshold. These exceedances are divided by the total number of observations to derive the regional probability of exceedance. In order to evaluate changes under future climate, daily precipitation from Coupled Model Intercomparison Project Phase 6 (CMIP6) models is statistically downscaled to individual station using observation-based quantile mapping. This ensures consistency between modeled and observed precipitation distributions. The framework is applied to approximately 200 global major cities with populations exceeding one million and Gross Domestic Product (GDP) over 100 billion USD. Using this framework, we evaluate changes in ultra-extreme precipitation characteristics between historical and future climate conditions. We expect this framework to facilitate the analysis of spatial and temporal patterns of ultra-extreme precipitation and their potential changes in future. The framework further supports the interpretation of rare but high-impact precipitation events and provides insights for urban flood risk management. Therefore, this study contributes to the development of hydrologic infrastructure design and adaptation strategies that are robust to increasing precipitation extremes under climate change.

 

Acknowledgment

This work was supported by Korea Environment Industry & Technology Institute(KEITI) through R&D Program for Innovative Flood Protection Technologies against Climate Crisis Program(or Project), funded by Korea Ministry of Environment(MOE)(RS-2023-00218873).