Seasonal Distribution Analysis of Extreme Precipitation in Iran using AgERA5 dataset

Document Type : Research Paper


1 Department of Geography, Ferdowsi University of Mashhad

2 Department of Geography, Ferdowsi University of Mashhad,


Extreme precipitation is considered as a serious hazard, especially in arid and semi-arid regions as they increase the risk of flooding and leave limited time for warning. The aim of this study is to evaluate precipitation of the fifth-generation reanalysis (AgERA5) of the European Centre for Medium-RangeWeather Forecasts (ECMWF) and to investigate the seasonal distribution of extreme precipitation in Iran. In this study, the accuracy of AgERA5 precipitation is evaluated using NRMSE, MBE, and PCC statistics. The error analysis shows that AgERA5 has the highest NRMSE in the humid climate of the northern coasts as well as the rainy regions of Zagros and Northwest of Iran. In contrast, this dataset estimates precipitation in arid and semi-arid regions of Iran more accurately. Three indices, including SDII, RX1day, and R10mm, were used to examine seasonal precipitation. The evaluation of extreme indices shows that the AgERA5 dataset is underestimated R10mm in large parts of the country, and in contrast, the two indices RX1day and SDII are overestimated in most parts of Iran. Like the average precipitation, the maximum error and bias of extreme precipitation are seen on the Southern Caspian Sea coast. The results showed that the maximum one-day precipitation (RX1day) in Iran is 80.5 mm in winter. The maximum daily precipitation intensity (SDII) is observed in southeastern Iran, with 19.2 mm/day in summer. The Southern Caspian Sea coasts show the highest continuity of days with heavy precipitation in all seasons. Despite the fact that this region has the highest number of heavy precipitation days in all seasons, the maximum continuity of heavy precipitation is seen in the high Zagros mountains. Precipitation intensity in all regions of Iran is directly related to altitudes. In this regard, the southern coast of the Caspian Sea is an exception throughout the year.


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