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Validation of the CHIRPS and CPC-Unified products for estimating extreme daily precipitation over southwestern Iran

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Abstract

Although gridded precipitation products (GPPs) are essential when evaluating weather and climate systems, their reliability must be known before application for scientific works. This study assessed the correspondence of observed daily precipitation data over southwestern Iran and the corresponding precipitation values from two well-known GPPs, CHIRPS and CPC-Unified (CPC), from 1998 through 2018. The datasets were for the Jan-Mar period, which contributes to 30 to 80% of annual precipitation in northwestern Iran and Persian Gulf coastal areas. Principal component analysis was used to divide 218 rain-gauge stations in the study area into three main zones, the western and northwestern (Zone 1), south-central (zone 2), and coastal areas (zone 3). The area-averaged time series of zonal precipitation data were then compared with the corresponding zonal GPPs values. All precipitation data that was equal to or greater than 1 mm (wet day) and equaled or exceeded the 95th or 99th percentiles (very wet or extremely wet days, respectively) were compared for each zone. The comparison was repeated for 3-day cumulative precipitation data. The statistical tests demonstrated significant relationships between the observational-based and model-based GPPs. The results were more robust for the CPC and 3-day cumulative datasets than for CHIRPS and the daily records. The strongest results were for estimation of extremely wet days and were significant for CPC estimations of the three-day cumulative precipitation in zone 3.

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The authors used different software such as R statistic and Microsoft Excel for preparation or analyzing data and producing maps.

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Acknowledgements

The authors would like to thank the I.R of Iran Meteorology Organization (IRIMO) for providing the daily precipitation data. We are grateful to the NOAA/OAR/ESRL PSL, Boulder, Colorado, USA, developers for providing the daily CPC Global Unified Precipitation dataset. We also acknowledge the University of California Santa Barbara’s Climate Hazards Group (CHG) to make the daily CHIRPS precipitation data available to international users that made this study possible. It is a pleasure to acknowledge helpful comments from anonymous reviewers for their helpful comments and suggestions. A great thank you to Professor Dr. Hartmut Graßl from the journal editorial board for his useful comments and advice.

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All authors, including Habib Allah Ghaedamini, Saeed Morid, Mohammad Jafar Nazemosadat, Ali Shamsoddini, and Hossein Shafizadeh Moghadam, contributed the design and implementation of the research. Habib Allah Ghaedamini and Saeed Morid performed the analysis. Habib Ghaedamini wrote the first draft of the manuscript, and all authors commented on previous versions of the manuscript. Habib Ghaedamini, Saeed Morid, and Mohammad Jafar Nazemosadat read and approved the final manuscript.

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Correspondence to Saeed Morid.

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The paper is part of doctoral theses and is not currently being considered for publication elsewhere. It reflects the authors’ own research and analysis truthfully and completely credits the meaningful contributions of co-authors.

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Ghaedamini, H.A., Morid, S., Nazemosadat, M.J. et al. Validation of the CHIRPS and CPC-Unified products for estimating extreme daily precipitation over southwestern Iran. Theor Appl Climatol 146, 1207–1225 (2021). https://doi.org/10.1007/s00704-021-03790-y

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