## 6 Conclusions  
This study conducted a comprehensive evaluation of the accuracy of the IMERG series products on multiple time scales (daily and monthly scales) and three spatial scales (grid cumulative scale, basin scale, and grid scale) in the mountainous XRRB of China. Subsequently, the hydrological utility of these products is assessed in streamflow simulations using the SWAT model, and an assessment of the impact of the FR product as forcing data in hydrological applications in the XRRB is derived. The main conclusions are described as follows. 1. At the daily scale, the FR outperforms the ER and LR products and has better CORR values (0.61/0.71) than the ER (0.59/0.69) and LR (0.59/0.69) at both the grid accumulation scale and the basin scale. At the monthly scale, the FR also has a higher CORR value (0.94/0.99) than the ER (0.88/0.93) and LR (0.88/0.92) products at both the grid accumulation scale and the basin scale. The RMSEs of the FR (48.03/18.99 mm) are also lower than those of the ER (71.50/54.88 mm) and LR (73.13/58.34 mm) products. For the systematic error, the ER and LR products generally tend to underestimate the precipitation, with BIASs of \(-0.14\) and \(-0.16\), respectively, while the FR tends to overestimate the precipitation, with a relatively low BIAS of 0.01. In terms of detection indicators, at the grid accumulation scale, the POD of IMERG series products is above 0.8 at the daily and monthly scales, the FAR is below 0.37, and the HSS is above 0.56. The results at the average scale of the basin show that the detection effect of each product is also satisfactory. 2. For the hydrological evaluation, two experiments based on different parameter calibration scenarios are conducted over the XRRB. In Scenario I, the IMERG-based simulation shows acceptable hydrological prediction skill in terms of the NSE (0.25-0.39) and CORR (0.50-0.61) at the daily scale and performs fairly well at the monthly scale (an NSE of 0.69-0.72 and a CORR of 0.71-0.87), especially for the FR product. 3. For the hydrological evaluation in Scenario II, the hydrological simulation performance improved. The hydrological prediction skill of the FR product in the validation period is acceptable (CORR = 0.64, BIAS = 0.01, and NSE = 0.43), and it is significantly better at the monthly scale than the simulation results in Scenario I (CORR = 0.85, BIAS = \(-0.02\), and NSE = 0.84). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **STA** & **ER** & **LR** & **FR** &
\begin{tabular}{} **Average** \\ **(ER, LR, and FR)** \\ \end{tabular} \\ \hline
**Precipitation (mm)** & 1938.9 & 1721.5 & 1681.3 & 1975.1 & 1792.6 \\
**Relative change rate** & \(-0.11\) & \(-0.13\) & 0.02 & 0.09 \({}^{*}\) \\
**Discharge (m3/s)** & 221.6 & 208.6 & 203.1 & 245.9 & 219.2 \\
**Relative change rate** & \(-0.06\) & \(-0.08\) & 0.11 & 0.08 \({}^{*}\) \\ \hline \hline \end{tabular} \({}^{*}\): Absolute relative change rate.  
\end{table} 
Table 6: Average annual precipitation and discharge simulated for the year of 2014–2017. In summary, the IMERG products have certain hydrological application potential in tropical watersheds in data-deficient areas and may be able to replace ground station observations for hydrological modeling. This research is useful for hydrological, meteorological and disaster studies in developing countries or remote areas with sparse or low-quality networks of ground-based observation stations. Notably, the IMERG products show overestimations in the non-flood season. To reduce the uncertainty of hydrological simulations based on satellite data, deviation correction studies of the IMERG satellite products in the XRBB should be carried out in the future. [PERSON] conceived of the original design of this paper. [PERSON] improved the structure of the paper. [PERSON], [PERSON], and [PERSON] provided comments on this paper. All authors have read and agreed to the published version of the manuscript. This research was funded by the National Key Research and Development Program of China  
* [PERSON] et al.