Hourly-scale modeling of storm transitions in Southern Brazil with Markov Chains

Abstract

Abstract. Southern Brazil faces escalating flood risk, yet intraday storm dynamics remain under-characterized. This study aims to characterize the temporal dynamics of storm intensity and persistence at the intraday scale. To achieve this, we apply a season-resolved Markov chain framework for storm state transitions, using hourly precipitation from 15 stations in situ from 2007 to 2024. Storms were identified and quantified by depth, duration, and intensity, then classified into Moderate, Strong, and Very Strong states. Peak mean intensities reach 9 to 11 mm h−1 in mountainous units, compared with maxima near 7 mm h−1 on the coast. Storms last roughly 11 to 13 h in the Southern Plateau and Southern Shield, and 15 to 17 h in the Central Depression and Coastal Plain, indicating greater lowland persistence. Transition probabilities indicate enhanced persistence of intense storms in orographic regions, while lowland areas exhibit faster dissipation. Storm transitions show consistent behavior within each season and are well represented by a first-order Markov chain. These intraday, spatially resolved probabilities link geomorphology to storm persistence and provide actionable inputs for early warning, zoning, and climate risk management.