2.1.2. Satellite-Based and Reanalysis Precipitation Datasets

In this study, considering the precipitation datasets availability and time span (study period of 2004–2017), we collected twelve sets of gridded precipitation data, including six satellite-based and six reanalysis products, for evaluation. Detailed information of these datasets is shown in Table 1. Of the selected satellite-based precipitation products, both the TRMM (i.e., TRMM3B42RT and TRMM3B42 adjusted with gauge observations), and the GSMaP (i.e., GSMaP-RNL and GSMaP-RNLG adjusted with gauge observations) precipitation datasets are produced through merging VIS/IR and MW information but are based on different algorithms [32,36]. In contrast, PERSIANN and PERSIANN-CCS belong to the VIS/IR family of satellite-based precipitation products [13,33–35,87]. The main differences in the two PERSIANN products are that the PERSIANN-CCS system enables the categorization of cloud-patch features based on cloud height, areal extent, and variability of texture estimated from satellite imagery, which is optimized for observing extreme precipitation, particularly at a very high spatial resolution. The six reanalysis precipitation products include JRA-55, ERA-Interim, ERA-5, NCEP1, NCEP2, and MERRA-2. These reanalysis products are produced based on different forecasting systems by assimilating many of the basic surface and upper-atmospheric fields from multiple sources, e.g., the surface humidity, radiosonde-based specific humidity, wind fields, and satellite-derived radiance. Among them, different data assimilation techniques are employed. For example, the ERA-Interim, ERA-5, and JRA-55 adopt four-dimensional variational (4D-VAR) data assimilation systems, whereas the MERRA-2, NCEP1, and NECEP2 utilize 3D-VAR assimilation systems. For more details about these datasets, the reader can refer to the product-specific user guide and the related literature.


**Table 1.** Summary of the selected satellite and reanalysis rainfall products.

**Note:** CPCU: the NOAA Climate Prediction Center (CPC) Unified Gauge-Based Analysis of Global Daily Precipitation (CPCU) product. CMAP/GPCPv2.1: the CPC Merged Analysis of Precipitation (CMAP)/Global Precipitation Climatology Project product, version 2.2. GPCC: Global Precipitation Climatology Centre. CAMS: Climate Assessment and Monitoring Systems.

As shown in Table 1, datasets had different temporal and spatial resolutions, so it is necessary to process them before evaluation. First, the satellite-based and reanalysis Pd and Pn were summed from the 1-hourly, 3-hourly, or 6-hourly accumulated precipitation at product-specified grids. Then, based on the bilinear interpolation method, the Pd and Pn for all products (except for TRMM-3B42RT, TRMM-3B42, PERSIANN, and ERA-5) were resampled to the spatial resolution of 0.25◦. This was mainly because most products correspond to a spatial resolution of 0.25◦ or higher, so the resampling-induced uncertainties could be reduced to some extent. For Pwd, its values were obtained using the sum of Pd and Pn from the resampled maps. The grids with at least one site were extracted to conduct performance evaluations. If any grid included more than one site, the average precipitation value at these sites was calculated to represent the final reference value of that grid.
