## 3 Results
### Spatiotemporal Variability
#### 3.1.3 Elevation Dependency
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Elevation Range** & **No. of Stations** & **No. of Grids** \\ \hline Below 500 m & 121 & 354 \\
500–1000 & 56 & 173 \\
1000–1500 & 90 & 185 \\
1500–2000 & 67 & 126 \\
2000–2500 & 27 & 98 \\
2500–3000 & 13 & 79 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Numbers of stations and grid boxes in different elevation ranges. Figure 5: Mean precipitation averaged over the summer monsoon season (mm/day) for the study period, (**a**) in gauge observed and four SBP datasets at station locations, (**b**) in IMERG and GSMaP product at each grid box averaged over different elevation ranges, respectively. \begin{table}
\begin{tabular}{c l c c c c c} \hline \hline
**Regions** & **Datasets** & **Mean (mm/day)** & **MB (mm/day)** & **RRMSE** & **R** & **RE (\%)** \\ \hline \multirow{3}{*}{Below 1500 m} & IMERG-UC & 10.67 & \(\mathbf{-0.85}\) & 0.57 & 0.08 & **7.36** \\  & IMERG-UC & 9.73 & \(-1.79\) & 0.47 & 0.41 & 15.58 \\ (267 stations) & GSMaP-MVK & 7.36 & \(-4.16\) & 0.58 & 0.36 & 36.08 \\  & GSMaP-Gauge & 9.14 & \(-2.38\) & **0.45** & **0.56** & 20.66 \\ \multirow{3}{*}{Between 1500} & IMERG-UC & 7.11 & \(-5.31\) & 0.70 & 0.24 & 42.75 \\  & IMERG-C & 9.34 & \(\mathbf{-3.07}\) & 0.56 & 0.46 & **24.74** \\ (95 stations) & GSMaP-MVK & 4.99 & \(-7.42\) & 0.78 & 0.49 & 59.82 \\ \multirow{3}{*}{Above 2500 m} & GSMaP-Gauge & 8.72 & \(-3.69\) & **0.53** & **0.63** & 29.72 \\  & IMERG-UC & 3.10 & \(-2.18\) & 1.15 & 0.42 & 41.28 \\ \multirow{3}{*}{Above 2500 m} & IMERG-C & 6.00 & \(\mathbf{0.72}\) & **1.07** & **0.65** & **16.63** \\  & GSMaP–MVK & 2.32 & \(-2.96\) & 1.16 & 0.59 & 56.07 \\ \multirow{3}{*}{(26 stations)} & GSMaP–Gauge & 7.78 & 1.50 & 1.44 & \(-0.02\) & 28.48 \\  & IMERG-UC & 9.29 & \(-2.03\) & 0.63 & 0.19 & 18.13 \\ \multirow{3}{*}{Whole country} & IMERG-C & 9.38 & \(\mathbf{-1.94}\) & 0.52 & 0.48 & **17.19** \\  & GSMaP-MVK & 6.44 & \(\mathbf{-4.88}\) & 0.66 & 0.40 & 43.10 \\ \multirow{3}{*}{(388 stations)} & GSMaP-Gauge & 8.88 & \(-2.44\) & **0.51** & **0.55** & 21.56 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Statistical metrics in the station mean precipitation at different elevation intervals (below 1500 m, between 1500 and 2500 m and above 2500 m), as well as in the whole study region, derived from the four SBP datasets and compared to the gauge observations during the summer monsoon for the study period. Bold font indicates the dataset with the best performance for a given metric. In high-elevation regions (above 2500 m), characterized by complex topography with low precipitation, IMERG-C showed the best performance with smaller errors (MB and RRMSE) and higher R than other datasets, demonstrating that the calibration based on GPCC data significantly improved the IMERG product. Meanwhile, the GSMaP-Gauge product overestimated summer monsoon precipitation and showed very poor correlation with the gauge observation. As mentioned in Section 2.2.1, the GPCC data merged observations from 125 gauges in Nepal, while NOAA/CPC data only merged observations from 54 gauges. Therefore, GPCC data may integrate more precipitation information, especially in high elevation regions where gauge observations are very scarce than NOAA/CPC data. This might be the reason for the improved performance of IMERG-C than GSMaP-Gauge in high-elevation regions. Overall, the gauge-calibrated products performed better than the satellite-only products on a monthly scale. IMERG-C yielded smaller MBs than GSMaP-Gauge, while GSMaP-Gauge showed the smaller RRMSE and higher R-value; indicating IMERG-C was more consistent to estimate the precipitation amount than GSMaP-Gauge, whereas GSMaP-Gauge presented more reasonable spatial distribution than IMERG-C.