Evaluation of IMERG precipitation product over various temporal scales in a semi-arid region of southern Iran

Abstract

In the recent decades, poor spatial coverage of rain gauges and weather radars, mostly in less developed countries, has caused satellite-based precipitation products to gain more popularity. However, they are considered less precise compared to traditional rain gauges and weather radars. Therefore, their thorough evaluations are essential before implementing these products in practice. In this study, IMERG satellite-based precipitation product was evaluated in the Fars province, Iran, using daily rain gauges as reference data to find the relationships between the uncertainties in the product and various factors such as elevation, temperature, and rainfall intensity by employing continuous and categorical statistical metrics. The findings revealed that: a) The IMERG product overestimates light rainfall and underestimates heavy rainfall, while showing the best performance in the range 40–80 mm/day. b) The accuracy of the product tends to vary in different months of the year and it is less biased in ones with milder temperatures. c) Higher correlation in mid-elevated areas (up to 0.96), positive bias in low-elevated areas (up to 2.5) and negative bias in high-elevated areas (down to −0.4) were observed. d) A considerable improvement in the IMERG estimates was observed for longer time scales for almost all validation indices. Overall, IMERG products show potential for hydrological and atmospheric decision-making, but further improvements in retrieval algorithms and developing local correction models, considering the trends found in this study, are needed for increased reliability.