Monthly and annual validation of TRMM Mulitisatellite Precipitation Analysis (TMPA) products in the Caspian Sea Region for the period 1999–2003

Two Tropical Rainfall Measuring Mission (TRMM) Multisatellite Precipitation Analysis (TMPA) products i.e. 3-hourly TRMM 3B42 and monthly 3B43 data were validated using 39 rain gauge stations in the Caspian Sea Region (CSR) in Iran with complex topography. The period 1999-2003 were selected. The validations were performed at monthly and annual scales. Results showed that both TRMM 3B42 and 3B43 can provide similar monthly rainfall distribution pattern with rain gauge data. Both 3B42 and 3B43 data overestimated precipitation when the rainfall amount is small while underestimated for large amount rainfall. The 3B42 data were in poor agreement with rain gauge data at both monthly and annual scales. In contrast, the 3B43 data performed significantly better than the 3B42 with higher R² and reduced RMSE values. Nevertheless, the 3B43 data were still unreliable in the CSR for most months and years for the period 1999-2003 as the relative RMSE are larger than 50%. Locate calibration should be carried out first to improve TRMM 3B42 and 3B43 data for further applications in the CSR.