## 3 Results
### Spatiotemporal Variability
#### 3.1.3 Elevation Dependency  
The knowledge of the elevation gradient of precipitation is vital for many hydro-meteorological applications. As known that a larger portion of the precipitation occurs during the summer monsoon season, thus the elevation dependency was investigated based on monthly data from the summer monsoon season. The mean precipitation data from observed and four SBP were averaged over summer monsoon at different elevation ranges in every 500 m from 60 m to below 3000 m during the study period (Figure 5). The number of stations above 3000 m is very limited; thus, the elevation dependency was only calculated below 3000 m. The gauge observations reveal an evident elevation dependency of precipitation, as shown in Figure 5 for the monsoon period. Gauge observations show that precipitation gradually increases with increasing elevation up to 2000 m, and then decreases rapidly (black line, Figure 5a). The highest precipitation (approximately 13 mm/day) occurs in the range 1500-2000 m during the summer monsoon. These patterns are similar to the results revealed by the previous study conducted using gauge observations [72]. IMERG-C moderately captured this evident elevation-dependent pattern, with the highest precipitation (approximately 10 mm/day) in the elevation range of 1500-2000 m. In contrast, other three SBP products failed to capture this pattern; IMERG-UC and GSMaP-MVK showed the highest precipitation at the lowest elevation (below 500 m), and GSMaP-Gauge shows the highest precipitation in the elevation range 500-1000 m. In the higher elevation areas (above 3000 m) with limited stations (14), GSMaP-Gauge and both IMERG datasets overestimated the observed precipitation (not shown in Figure 5). This could be associated with the complex terrain and orographic effect [73; 74]. It is worth to note that, orographic rain corrected GSMaP-Gauge showed the variation in precipitation amount for different elevation intervals (i.e., precipitation increase and decrease pattern) [75]. Additionally, we calculated the elevation dependency of SBP datasets by averaging the precipitation across all grid boxes within different elevation ranges (Figure 5b). The numbers of stations and grid boxes in different elevation ranges are listed in Table 4. Grid-based elevation dependency of SBP showed a similar pattern to that of the point-pixel results, but with slightly different precipitation amounts. Overall, both gauge satellite-only IMERG-UC and GSMaP-MVK significantly underestimated the monsoonal precipitation amount. However, after gauge correction, the precipitation estimates of gauge calibrated datasets were more consistent with the gauge observation than the satellite-only datasets. Therefore, the procedure of calibrating SBP products with rain gauge data is the reason for their increased accuracy. Table 5 gives the statistical metrics of errors for the four SBP datasets across three different geographic regions, based on summer monsoon mean values at each station. In lowland areas (below 1500 m) the error metrics indicate that IMERG-UC showed smallest MBs of \(-0.85\) mm/day; indicating the estimated precipitation amount was more consistent with the observed datasets; meanwhile, GSMaP-Gauge showed better overall performance than other three datasets with lower RRMSE (0.45) and a higher R-value (0.56). In the highest precipitating mid-elevation areas (between 1500 and 2500 m), both gauges calibrated datasets showed a more consistent performance to observed datasets than satellite-only datasets. IMERG-C showed the best performance to estimate the precipitation amount with lowest MBs of \(-3.07\) mm/day, while GSMaP-Gauge presented the evident lowest RRMSE and higher R-value, indicating better performance in reproducing the spatial distribution of gauge observed precipitation among all. However, all four datasets underestimated the monsoon precipitation amount below 2500 m.