## 3 Results
### Basin-Scale Error Intercomparison  
To facilitate direct comparison between IMERG and 3B42V7 products, the spatial resolutions of gauge- and satellite-based products should be consistent firstly. The gauge data available in each  
Figure 3: Maps of (**a,b**) Relative Bias (RB); (**c,d**) Root Mean Square Error (RMSE); (**e,f**) Correlation Coefficients (CC) and (**g,h**) scatter diagram between satellite and gauge-based three-hourly rainfall estimates in the warm season (April-September) of 2014 over the TP. Notes: the left panel, i.e., (**a,c,e,g**), stands for IMERG rainfall estimates, and the right panel, i.e., (**b,d,f,h**) stands for 3B42V7 products. basin (including the Yellow, Yangtze and Brahmaputra basins) were initially interpolated to a 0.10\({}^{\circ}\) grid with the Inverse Distance Weighting (IDW) method, which had been shown to be reliable and efficient in many previous basin-scale studies [11; 31; 32; 33; 34]. In order to make the different data comparable, the 3B42V7 data were resampled to the 0.10\({}^{\circ}\)\(\times\) 0.10\({}^{\circ}\) resolution, the same as IMERG and the interpolated gauge data, by using the standard bilinear interpolation method [35]. We adopt a consistent common 0.10\({}^{\circ}\) grid cell for both satellite rainfall comparison and validation. Note that potential errors would possibly be introduced during the resampling procedure. At the three-hourly scale, both IMERG and 3B42V7 showed similar bias patterns and bias ratio distribution in the Yellow and Yangtze River basins (Figure 4). In the Yellow River basin, the two products showed apparent underestimation in the north and south parts and overestimation in the other parts (e.g., central and southeast); whereas in the Yangtze River basin, both showed overestimation in the west and east and underestimation in the central part. Furthermore, IMERG showed lower biases than 3B42V7 for both the Yellow and Yangtze River basins. The averaged RB values in the Yellow River basin were 3.7% and 5.8% for IMERG and 3B42V7, respectively. In the Yangtze River basin, the RB values were 10.8% (IMERG) and 13.8% (3B42V7), respectively. In the Brahmaputra basin, IMERG showed obvious overestimation with an overall mean RB value of 35.6% and SD value of 49.5%, respectively. 3B42V7 showed more significant overestimation around the whole basin, and the averaged RB and SD values were 92.6% and 59.6%, respectively (Table 2). In short, both satellite products showed more acceptable performance in the Yellow and Yangtze River basins than in the Brahmaputra basin. Figure 4: Spatial patterns of averaged three-hourly relative bias (RB) (left and middle column) and its percentage of RB basin area (%) (right column) derived from satellite products and gauge observations in the three main river basins, where the top panel, i.e., (**a–c**), is the Yellow River basin; the middle panel, i.e., (**d–f**), is the Yangtze River basin; and the bottom panel, i.e., (**g–i**), is the Brahmaputra basin. The left column stands for the IMERG rainfall estimates and the middle side is the 3B42V7 data. In addition, time series analyses of IMERG, 3B42V7 and gauge-based rainfall are shown for each major river basin during the warm season of 2014 (Figure 5). Although both satellite products showed large standard deviations, IMERG did not have extreme values and appeared to be a more acceptable satellite rainfall product in each basin.