Evaluation of the TRMM-3B43 V7 rainfall products on a monthly scale in the Northwest of Iran

Satellite rainfall estimate systems can produce data for areas for which other sources areunavailable. Without referring to ground measurements, satellite-based estimates cannot beused directly before bias correction. This study aims to evaluate the performance of theTRMM-3B43 V7 rainfall products in the Northwest of Iran. The evaluation was carried outusing monthly data obtained from 21 meteorological stations during 1998–2015. Themonthly and annual spatial distributions of the Pearson correlation coefficient between thestation and satellite-based observations as well as the statistical error measure werecalculated. The results revealed that the correlations between TRMM 3B43 and rain gaugedata were high (R> 0.80) in October and small (R < 0.55) in August. Moreover, meanannual spatial distribution of R showed that the small values of R occurred in the Northeastand the southern mountainous regions. We found that the TRMM-3B43 V7 overestimatedrainfall in the Northeast, in September, October and November (> 30 mm) and in Decemberto May (> 20 mm). On the contrary, an underestimation was found in the Southwest regionswhere summer season (June, July & August) is generally characterized by small anomaliesin terms of R values. Generally, the satellite products applied in this study underestimatehigher rainfall values while showing overestimation for lower rainfall records. The measureof Root Mean Square Error (RMSE) showed that a large spatial variability takes place inSeptember, October and November in most of the stations, particularly when rainfallrecords is less than 50 mm. Meanwhile, the lowest variability occurred in June, July andAugust with a slight increase in the Northeast. Our findings imply that satellite productshave poor performance for estimating higher rainfalls in the Northwest of Iran on a monthlyscale.

Keywords:

TRMM-3B43 V7 , Rainfall variability , Northwest of Iran