Struglia et al. (2025) Impact of spatial resolution on multi-scenario WRF-ARW simulations driven by the CMIP6 MPI-ESM1-2-HR global model: a focus on precipitation distribution over Italy

Identification

• Journal: Geoscientific model development
• Year: 2025
• Date: 2025-09-17
• Authors: Maria Vittoria Struglia, Alessandro Anav, Marta Antonelli, Sandro Calmanti, Franco Catalano, Alessandro Dell’Aquila, Emanuela Pichelli, Giovanna Pisacane
• DOI: 10.5194/gmd-18-6095-2025

Research Groups

• ENEA Italian National Agency for New Technologies, Energy and Sustainable Economic Development, Rome, Italy
• ICSC Italian Research Center on High-Performance Computing, Big Data and Quantum Computing, Casalecchio di Reno, Italy

Short Summary

This study dynamically downscales CMIP6 global climate projections over Italy and the Mediterranean to 5 km resolution, demonstrating the added value of high resolution for precipitation, and projects a general warming, mean precipitation reduction over the Mediterranean, and a strong increase in extreme precipitation intensity over the Italian Peninsula by 2100, especially under SSP5-8.5.

Objective

• To dynamically downscale CMIP6 global climate projections to local scales (5 km) over the Mediterranean and Italian regions to produce high-resolution climate information for assessing climate change signals, with a focus on precipitation extreme events, and to evaluate the performance of a scale-aware convection parameterization in the "gray zone" (5 km resolution).

Study Configuration

• Spatial Scale: Double-nesting approach: a parent domain (D01) covering Europe at 15 km horizontal resolution, and an innermost nested domain (D02) covering Italy and the northwestern Mediterranean at 5 km horizontal resolution.
• Temporal Scale:
  • Hindcast simulations (ERA5-driven): 1980–2023 (evaluation period 1984–2014).
  • Historical simulations (MPI-ESM1-2-HR driven): 1980–2014.
  • Future simulations (MPI-ESM1-2-HR driven): 2015–2100, under SSP1-2.6, SSP2-4.5, and SSP5-8.5 scenarios.

Methodology and Data

• Models used:
  • Weather Research and Forecasting model with the Advanced Research core (WRF-ARW) version 4.2.2.
  • Grell–Freitas cumulus parameterization.
  • Thompson microphysics scheme.
  • MYNN 2.5 Planetary Boundary Layer (PBL) scheme.
  • Noah_MP Land surface model.
  • RRTMG Radiation scheme.
  • Driving Global Climate Model: CMIP6 MPI-ESM1-2-HR (T127 grid, approximately 103 km resolution).
• Data sources:
  • Forcing for hindcast: ERA5 reanalysis.
  • Forcing for historical/future: CMIP6 MPI-ESM1-2-HR.
  • Evaluation benchmarks: E-OBS (11 km resolution), ERA5 (25 km resolution), ERA5-Land (11 km resolution), and CERRA (5 km resolution) reanalysis products.

Main Results

• The 15 km hindcast simulation closely reproduced ERA5 seasonal mean temperature (T2m) and precipitation (P) with biases generally within 0.5–1.5 °C and 1 mm d⁻¹, respectively.
• Increasing resolution to 5 km significantly improved precipitation representation, particularly in summer, by reducing a wet bias present at 15 km. The 5 km simulation, utilizing a scale-aware Grell–Freitas scheme, demonstrated convection-permitting model-like behavior, with parameterized convective precipitation being an order of magnitude lower than resolved precipitation.
• The 5 km resolution enhanced the representation of extreme precipitation events, reducing overestimation compared to CERRA and better capturing the tail of the precipitation probability density function.
• Future projections (2071–2100 vs 1985–2014) indicate a general warming across all scenarios and seasons. The 5 km resolution showed reduced warming in summer and autumn over most of the Italian Peninsula and in winter and spring in the Po Valley compared to 15 km, while highlighting larger warming over mountainous areas in summer and autumn for higher emission scenarios.
• Mean precipitation projections show an intensification of the hydrological cycle over continental Europe and a reduction over the Mediterranean. Over Italy, SSP1-2.6 projects positive changes in winter and spring (exceeding 0.5 mm d⁻¹ in mountains) but a significant reduction in summer. SSP2-4.5 and SSP5-8.5 project a generally drier climate, especially in summer, with increased mean precipitation in the Alpine region in winter and autumn.
• Extreme precipitation events (P99) are projected to increase in both frequency and intensity under SSP2-4.5 and SSP5-8.5, with the 5 km resolution exacerbating the frequency of very extreme events. A strong increase in extreme precipitation intensity is particularly relevant for the SSP5-8.5 scenario during autumn over the Italian Peninsula, with complex spatial patterns strongly influenced by local orography, a significant improvement over global model projections.

Contributions

• Presents the first coherent set of high-resolution multi-scenario (SSP1-2.6, SSP2-4.5, SSP5-8.5) climate simulations for Italy using the latest generation CMIP6 global models (MPI-ESM1-2-HR) dynamically downscaled to 5 km resolution.
• Demonstrates the added value of 5 km resolution (within the gray zone) for improving the representation of mean and extreme precipitation over complex terrain like the Italian Peninsula, correcting biases from coarser resolutions.
• Validates the effective use of a scale-aware cumulus parameterization (Grell–Freitas) at 5 km resolution, showing it mimics convection-permitting behavior, enabling computationally feasible long-term simulations over wide domains.
• Provides robust statistics for climate change impacts, particularly for extreme precipitation events, which are crucial for national risk assessment plans.
• The generated simulations can serve as boundary conditions for future convection-permitting (finer than 4 km) downscaling studies.

Funding

• Project KNOWING (European Union’s Horizon Europe research and innovation program, grant agreement no. 101056841, GA Project 1011056841).
• RETURN Extended Partnership (European Union Next-GenerationEU, National Recovery and Resilience Plan – NRRP, Mission 4, Component 2, Investment 1.3 – D.D. 1243 2/8/2022, PE0000005).
• ICSC Italian Research Center on High-Performance Computing, Big Data and Quantum Computing (European Union Next-GenerationEU, National Recovery and Resilience Plan – NRRP, Mission 4, Component 2, Investment 1.4 – D.D: 3138 16/12/2021, CN00000013).

Citation

@article{Struglia2025Impact,
  author = {Struglia, Maria Vittoria and Anav, Alessandro and Antonelli, Marta and Calmanti, Sandro and Catalano, Franco and Dell’Aquila, Alessandro and Pichelli, Emanuela and Pisacane, Giovanna},
  title = {Impact of spatial resolution on multi-scenario WRF-ARW simulations driven by the CMIP6 MPI-ESM1-2-HR global model: a focus on precipitation distribution over Italy},
  journal = {Geoscientific model development},
  year = {2025},
  doi = {10.5194/gmd-18-6095-2025},
  url = {https://doi.org/10.5194/gmd-18-6095-2025}
}