Mohammed et al. (2025) Comprehensive Assessment of GPM-IMERG and ERA5 Precipitation Products Across Ireland

Identification

• Journal: Remote Sensing
• Year: 2025
• Date: 2025-09-11
• Authors: Safa Mohammed, Ahmed Nasr, Mohammed Mahmoud
• DOI: 10.3390/rs17183154

Research Groups

• School of Transport and Civil Engineering, Technological University Dublin, D01 K822 Dublin, Ireland

Short Summary

This study comprehensively assesses the accuracy and reliability of GPM-IMERG (Early, Late, Final) and ERA5 precipitation products against ground observations across Ireland (2014–2021). It finds ERA5 superior for low-to-moderate rainfall and seasonal consistency, while IMERG-Final excels in detecting high-intensity, short-duration events, suggesting a hybrid approach for enhanced hydrological applications.

Objective

• To evaluate the accuracy and reliability of GPM-IMERG (Early, Late, Final runs) and ERA5 precipitation datasets across Ireland (2014–2021) using ground-based observations, considering multiple temporal resolutions (hourly, daily), seasonal variations, and rainfall intensity classes, with a focus on extreme event detection.

Study Configuration

• Spatial Scale: The entire Republic of Ireland (approximately 70,273 km²), located between latitudes 51°23′–55°26′N and longitudes 5°59′–10°40′W. Evaluation conducted at 25 synoptic weather stations.
• Temporal Scale: January 2014 to September 2021 (8 years). Data analyzed at hourly and daily resolutions, and across four meteorological seasons (Spring, Summer, Autumn, Winter).

Methodology and Data

• Models used:
  • GPM-IMERG (Integrated Multi-satellitE Retrievals for the Global Precipitation Measurement) version V06B: Early Run, Late Run, Final Run.
  • ERA5 (European Centre for Medium-Range Weather Forecasts Reanalysis-5).
• Data sources:
  • Reference data: Ground-based precipitation observations from 25 synoptic weather stations operated by Met Éireann, Ireland’s national meteorological service.
  • Satellite data: NASA Precipitation Measurement Missions (PMM) GPM-IMERG portal.
  • Reanalysis data: Copernicus Climate Data Store (CDS) for ERA5.
  • Methodology: Grid-to-point matching approach (nearest grid cell centroid within half the grid resolution) and evaluation using seven statistical and categorical metrics (Probability of Detection (POD), False Alarm Ratio (FAR), Critical Success Index (CSI), Mean Absolute Error (MAE), Root Mean Squared Error (RMSE), Relative Bias (BIAS), and Pearson Correlation Coefficient (CC)).

Main Results

• ERA5 consistently demonstrated strong detection skills and climatological stability for low-to-moderate rainfall, particularly during autumn and winter frontal systems, showing strong temporal agreement and low bias in coastal regions.
• ERA5 tended to underestimate very heavy rainfall events (e.g., up to 73.5% underestimation of peak rainfall at Mullingar) and exhibited elevated false alarm rates at finer temporal scales, especially in spring and summer.
• IMERG-Final showed enhanced responsiveness to short-duration, high-intensity events, particularly when aggregated to daily resolution, and performed more reliably at daily resolution, especially during summer convective activity.
• During very heavy rainfall events, IMERG-Final achieved up to 18% lower MAE, 17% lower RMSE, and 13% higher correlation compared to ERA5.
• IMERG-Early and IMERG-Late generally exhibited comparable performance to IMERG-Final within a narrow margin, but tended to overestimate rainfall in mountainous regions and showed weaker correlations, particularly in winter (CC < 0.2).
• At the hourly scale, ERA5 had the lowest average MAE (~0.16 mm) and RMSE (~0.45 mm), with negligible bias. At the daily scale, ERA5 remained the most accurate (RMSE ~2.8 mm, MAE ~1.5 mm).

Contributions

• Provides the first systematic intercomparison of ERA5 and IMERG datasets over Ireland, addressing a regional gap in the evaluation of these widely used precipitation products.
• Offers a scientific basis for the appropriate use of these datasets in operational and research applications within the Irish context.
• Supports the recommendation of adopting a hybrid approach, combining ERA5’s seasonal consistency with IMERG-Final’s event responsiveness, for enhanced rainfall monitoring and hydrological applications in Ireland.

Funding

• Irish Research Council under 2021 Government of Ireland Postgraduate (GOIPG) Scholarship, grant number [GOIPG/2021/1388].

Citation

@article{Mohammed2025Comprehensive,
  author = {Mohammed, Safa and Nasr, Ahmed and Mahmoud, Mohammed},
  title = {Comprehensive Assessment of GPM-IMERG and ERA5 Precipitation Products Across Ireland},
  journal = {Remote Sensing},
  year = {2025},
  doi = {10.3390/rs17183154},
  url = {https://doi.org/10.3390/rs17183154}
}