Akbary et al. (2026) Projected changes in sub-daily extreme precipitation: comparing temperature-scaling approaches and convection-permitting models across an Alpine gradient

Identification

• Journal: Journal of Hydrology
• Year: 2026
• Date: 2026-03-22
• Authors: Rashid Akbary, Eleonora Dallan, Marco Marani, Francesco Marra, Marco Borga
• DOI: 10.1016/j.jhydrol.2026.135356

Research Groups

• Department of Land Environment Agriculture and Forestry, University of Padova, Padova, Italy
• Department of Civil, Environmental, and Architectural Engineering, University of Padova, Padova, Italy
• Research Center on Climate Change Impacts, University of Padova, Rovigo, Italy
• Department of Geosciences, University of Padova, Padova, Italy

Short Summary

This study evaluates the reliability of temperature-scaling approaches for projecting sub-daily extreme precipitation changes by comparing them against convection-permitting model (CPM) outputs across a complex Alpine region. It finds that optimal scaling rates vary with duration and return period, and their reliability is modulated by local variability, seasonality, and elevation.

Objective

• Evaluate the reliability of temperature-scaling approaches by comparing their projections of extreme precipitation to outputs from convection-permitting models (CPMs) across a complex mountainous region in northeastern Italy, considering factors like duration, return period, elevation, and seasonal shifts.

Study Configuration

• Spatial Scale: Northeastern Italy (Eastern Alpine crests to Po River and Adriatic Sea), approximately 32,000 km², ranging in altitude from -5 m to 3990 m above sea level. CPM simulations were remapped to a common 3 km spatial resolution.
• Temporal Scale: Historical period: 1996–2005. Future period: 2090–2099, under the Representative Concentration Pathway (RCP) 8.5 climate change scenario. Data resolution: 1 hour.

Methodology and Data

• Models used:
  • Ensemble of five Convection-Permitting Models (CPMs) from the FPS-CORDEX project (CCLM, COSMO-crCLIM, HARMONIE-Climate, CCLM5, HCLIM38-AROME41).
  • Simplified Metastatistical Extreme Value (SMEV) approach for estimating precipitation return levels.
  • Clausius-Clapeyron (CC) equation for temperature-scaling relationships.
• Data sources:
  • Hourly precipitation and temperature projections from the FPS-CORDEX CPM ensemble.
  • Quality-controlled, 5-minute temporal resolution precipitation data from 174 heated rain gauges (aggregated to hourly resolution).

Main Results

• Optimal temperature-scaling rates for sub-daily extreme precipitation vary with duration and return period. For moderate extremes (2- and 5-year return period), rates are typically between 5.5% K⁻¹ and 6% K⁻¹. For more severe events (return periods > 10 years), rates are higher, peaking at approximately 8.4% K⁻¹ for 3-hour, 100-year events.
• Projected temperature increases (ΔT) are higher in high-elevation areas (median ΔT ~3.5–4 °C) compared to lowlands (~1.5–2.5 °C), and higher for shorter precipitation durations.
• Temperature-scaling estimates align closely with CPM outputs in high-elevation areas where extreme events remain summer-dominated and seasonal shifts are minimal (Pearson correlation coefficients exceeding 0.5 for 1- and 3-hour events).
• Poorer performance (lower correlation, below 0.3) is observed in lowland areas and for longer durations, where significant shifts in the seasonality of extremes (e.g., towards late summer or fall) are expected.
• Using event-specific pre-storm temperatures (average of 24 hours prior to the event) for scaling yields substantially better agreement with CPMs compared to using mean annual temperature.

Contributions

• Provides the first comprehensive evaluation of temperature-scaling approaches against an ensemble of high-resolution convection-permitting models (CPMs) for projecting sub-daily extreme precipitation changes in a complex mountainous region.
• Quantifies optimal temperature-scaling factors that are dependent on precipitation duration and return period, demonstrating departures from a fixed Clausius-Clapeyron rate.
• Highlights that the reliability of temperature-scaling methods is significantly modulated by local variability, elevation, and projected shifts in the seasonal timing of extreme events.
• Emphasizes the critical importance of selecting event-specific pre-storm temperatures over mean annual temperatures for more accurate scaling.

Funding

• Fondazione Cassa di Risparmio di Padova e Rovigo (Excellence Grant 2021 to the Resilience Project).
• European Union Next-GenerationEU (National Recovery and Resilience Plan – NRRP, Mission 4, Component 2, Investment 1.3—D.D. 1243 2/8/2022, PE0000005) for ED within the RETURN Extended Partnership.
• European Union - Next Generation EU in the framework of PRIN (Progetti di ricerca di Rilevante Interesse Nazionale) programme (Grant 2022ZC2522) for FM and MM (INTENSE project).

Citation

@article{Akbary2026Projected,
  author = {Akbary, Rashid and Dallan, Eleonora and Marani, Marco and Marra, Francesco and Borga, Marco},
  title = {Projected changes in sub-daily extreme precipitation: comparing temperature-scaling approaches and convection-permitting models across an Alpine gradient},
  journal = {Journal of Hydrology},
  year = {2026},
  doi = {10.1016/j.jhydrol.2026.135356},
  url = {https://doi.org/10.1016/j.jhydrol.2026.135356}
}