University of Oulu

Ghajarnia, N., Akbari, M., Saemian, P., Ehsani, M. R., Hosseini-Moghari, S.-M., Azizian, A., et al. (2022). Evaluating the evolution of ECMWF precipitation products using observational data for Iran: From ERA40 to ERA5. Earth and Space Science, 9, e2022EA002352.

Evaluating the evolution of ECMWF precipitation products using observational data for Iran : from ERA40 to ERA5

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Author: Ghajarnia, Navid1; Akbari, Mahdi2; Saemian, Peyman3;
Organizations: 1Department of Physical Geography, Bolin Center for Climate Research, Stockholm University, Stockholm, Sweden
2Water, Energy and Environmental Engineering Research Unit, Faculty of Technology, University of Oulu, Oulu, Finland
3Institute of Geodesy (GIS), University of Stuttgart, Stuttgart, Germany
4Department of Hydrology and Atmospheric Sciences, The University of Arizona, Tucson, AZ, USA
5Institute of Physical Geography, Goethe University Frankfurt, Frankfurt am Main, Germany
6Key Laboratory of Water Cycle and Related Land Surface Processes, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, China
7Water Engineering Department, Imam Khomeini International University, Qazvin, Iran
8Department of Sustainable Development, Environmental Science and Engineering, KTH Royal Institute of Technology, Stockholm, Sweden
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 4.1 MB)
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Language: English
Published: American Geophysical Union, 2022
Publish Date: 2023-06-08


European Center for Medium-Range Weather Forecasts Reanalysis (ERA), one of the most widely used precipitation products, has evolved from ERA-40 to ERA-20CM, ERA-20C, ERA-Interim, and ERA5. Studies evaluating the performance of individual ERA products cannot adequately assess the evolution of the products. We compared the performance of all ERA precipitation products at daily, monthly, and annual data (1980–2018) using more than 2100 Iran precipitation gauges. Results indicated that ERA-40 performed worst, followed by ERA-20CM, which showed only minor improvements over ERA-40. ERA-20C considerably outperformed its predecessors, benefiting from the assimilation of observational data. Although several previous studies have reported full superiority of ERA5 over ERA-Interim, our results revealed several shortcomings in ERA5 compared with the ERA-Interim estimates. Both ERA-Interim and ERA5 performed best overall, with ERA-Interim showing better statistical and categorical skill scores, and ERA5 performing better in estimating extreme precipitations. These results suggest that the accuracy of ERA precipitation products has improved from ERA-40 to ERA-Interim, but not consistently from ERA-Interim to ERA5. This study employed a grid-grid comparison approach by first creating a gridded reference data set through the spatial aggregation of point source observations, however, the results from a point-grid approach showed no change in the overall ranking of products (despite the slight changes in the error index values). These findings are useful for model development at a global scale and for hydrological applications in Iran.

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Series: Earth and space science
ISSN: 2333-5084
ISSN-E: 2333-5084
ISSN-L: 2333-5084
Volume: 9
Issue: 10
Article number: e2022EA002352
DOI: 10.1029/2022ea002352
Type of Publication: A1 Journal article – refereed
Field of Science: 218 Environmental engineering
Funding: The study was supported by Maa- ja vesitekniikan tuki ry (Reference no. 41878). Open access funding provided by University of Oulu.
Copyright information: © 2022 The Authors. Earth and Space Science published by Wiley Periodicals LLC on behalf of American Geophysical Union. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.