Evaluation of the accuracy of the ERA5-Land database in estimating climatic parameters, evapotranspiration, and drought index in the Varamin region

Behizadi, Negar; Soltani, Jaber; Hashemi Garmdare, Seyed Ebrahim; Massah Bavani, Ali Reza; Azadegan, Behzad

doi:10.22059/jwim.2026.408285.1276

Evaluation of the accuracy of the ERA5-Land database in estimating climatic parameters, evapotranspiration, and drought index in the Varamin region

Articles in Press

Document Type : Research Paper

Authors

Negar Behizadi ¹

Jaber Soltani ²

Seyed Ebrahim Hashemi Garmdare ³

Ali Reza Massah Bavani ⁴

Behzad Azadegan ⁵

¹ PhD Student -Department of Water Engineering - Abu Raihan Faculty of Agricultural Technology - University of Tehran - Tehran - Iran

² Department of Water Engineering, University of Tehran,

³ Department of Water Engineering -University of Tehran

⁴ Department of Water Engineering - University of Tehran

⁵ Department of water Engineering-University of Tehran

10.22059/jwim.2026.408285.1276

Abstract

In this study, the accuracy of the ERA5-Land reanalysis dataset in estimating climatic parameters (precipitation, temperature, wind speed, and evapotranspiration) over the Varamin Plain was evaluated by comparison with data from the Varamin synoptic station during the common period of 2007–2023. The validation results indicated that ERA5-Land shows satisfactory performance in estimating daily maximum, minimum, and mean temperatures (R² > 0.95), daily evapotranspiration (R² > 0.85), and monthly precipitation (R² > 0.70) in the study area. However, the dataset demonstrated lower accuracy in estimating daily precipitation and wind speed. Given the acceptable performance of ERA5-Land, the drought indices SPI-1 and SPEI-2 were calculated at 3-, 6-, 12-, and 24-month time scales for the long-term period of 1990–2023 (33 years) using data from this dataset. The drought monitoring results indicate that the Varamin Plain has entered a regime of severe and persistent drought since approximately 2014. Furthermore, the findings suggest that in warm and semi-arid regions of Iran, the SPEI index—due to its consideration of warming effects and increased evapotranspiration—provides a more accurate and reliable tool than SPI for drought monitoring and water resources management.

Keywords

Reanalysis data

Statistical validation

Synoptic station

Water resources management

Subjects