Comparing high-resolution gridded precipitation data with satellite rainfall estimates of TRMM_3B42 over Iran

To evaluate satellite rainfall estimates of Tropical Rain Measurement Mission (TRMM) level 3 output (3B42) (TRMM_3B42) over Iran (20°-45° N, 40°-65° E), we compared these data with high-resolution gridded precipitation datasets (0.25° x0.25° latitude/longitude) based on rain gauges (Iran Synoptic gauges Version 0902 (IS0902)). Spatial distribution of mean annual and mean seasonal rainfall in both IS0902 and TRMM_3B42 from 1998 to 2006 shows two main rainfall patterns along the Caspian Sea and over the Zagros Mountains. Scatter plots of annual average rainfall from IS0902 versus TRMM_3B42 for each 0.25°x0.25° grid cell over the entire country (25°-40° N, 45°-60° E), along the Caspian Sea (35°-40° N, 48°-56° E), and over the Zagros Mountains (28°-37° N, 46°-55° E) were derived. For the entire country, the Caspian Sea region, and the Zagros Mountains, TRMM_3B42 underestimates mean annual precipitation by 0.17, 0.39, and 0.15 mm day-1, respectively, and the mean annual rainfall spatial correlation coefficients are 0.77, 0.57, and 0.75, respectively. The mean annual precipitation temporal correlation coefficient for IS0902 and TRMM_3B42 is -0.8 in the area along the Zagros Mountains, and —0.6 in the Caspian Sea and desert regions.