*3.3. Global View of GSMaP\_NRT and GSMaP\_Gauge\_NRT*

In the previous section, we compared the GSMaP\_NRT with GSMaP\_Gauge\_NRT satellite precipitation products over the Mainland China. The results showed that the GSMaP\_Gauge\_NRT effectively reduced the error in GSMaP\_NRT and was more consistent with gauge observations. To obtain a much broader view of GSMaP\_Gauge\_NRT at other regions, we extended the comparison to the global scale. Operationally, it is usually difficult to validate the satellite precipitation products on the global scale using gauge observations, due to the fact that the ground gauge networks are sparse or nonexistent in many regions like oceans, deserts, and mountains. In order to provide a globally consistent evaluation, we chose the GSMaP\_Gauge product as the reference data for global comparison. Figure 6 displays the spatial difference between the two near-real-time GSMaP products and the standard GSMaP\_Gauge product. It can be seen that the GSMaP\_NRT underestimated the precipitation in the southeastern China, which was consistent with the evaluation results when using CGDPA as a reference. The calibrated GSMaP\_Gauge\_NRT substantially decreased this underestimation and was closer to the GSMaP\_Gauge. Globally, the GSMaP\_NRT exhibited positive bias over most parts of the world. Most notably, along the intertropical convergence zone (ITPC) extending toward Central America, eastern United States, southern parts of South America, and West Africa, the GSMaP\_NRT tended to overestimate precipitation. After the real-time calibration, these positive biases were effectively reduced. Besides, compared to the GSMaP\_Gauge, the GSMaP\_Gauge\_NRT only had slight underestimations over most parts of world, except for the ITPC, with an overestimation (Figure 6b). Considering that the development of GSMaP\_Gauge\_NRT intended to make the GSMaP near-real-time

products as close to the GSMaP\_Gauge product as possible, we believe that the parameterized gauge calibration effectively reduced the errors in GSMaP\_NRT, and that the calibrated GSMaP\_Gauge\_NRT is a better product than GSMaP\_NRT.

**Figure 6.** Global map of mean daily precipitation difference between (**a**) GSMaP\_NRT and GSMaP\_Gauge and (**b**) GSMaP\_Gauge\_NRT and GSMaP\_Gauge.
