Spatiotemporal Assessment of the NASA POWER Satellite Precipitation Product over Different Regions of Iran

Satellite products are recognized as important resources providing significant and high-resolution information on various timescales. In the present study, the precipitation data acquired from the National Aeronautics and Space Administration (NASA) POWER satellite at 0.5° resolution were investigated from 1987 to 2017 in different regions of Iran. The accuracy of satellite products was studied based on 70 meteorological synoptic stations on three timescales (daily, monthly, and annual) and four precipitation classes. The results indicate that the NASA POWER precipitation product provided acceptable performance on all three timescales. The correlation coefficient (CC) obtained for the whole country on daily, monthly, and annual scales was 0.56, 0.68, and 0.69, respectively. These values were 5.27, 3.86, and 1.03 for the fraction root mean square error (FRMSE) and 0.31, 0.41, and 0.36 for the Nash–Sutcliffe efficiency coefficient (NSE), respectively. The highest performance of the product in the whole country was verified on the monthly scale, and the daily period was found to have the lowest performance. Results indicated that the NASA product offered high accuracy on the west, northwest, and the coasts of the Persian Gulf. However, its accuracy was lowest in arid and semiarid regions, desert areas, and the Caspian Sea coast. It also demonstrated the best detection, above 90%, for rainfall less than 1 mm. The accuracy of the model decreased with increasing rainfall depth. At precipitation above 20 mm, the model detection rate was less than 18%. The results revealed that the NASA product performed very well from April to August.