3.1.1. The Spatial Pattern of Precipitation in Nepal

The spatial distributions of daily mean precipitation (mm/day) in observations and four different SBP datasets during the study period are presented in Figure 3. The observed datasets show large spatial variability of precipitation across the country. The highest mean precipitation amount (>10 mm/day) was observed in the Lumle areas (28.3ºN, 84ºE), whereas the low amount (<2 mm/day) in the high-elevation areas of central and western region (Figure 3a). Since the lowest precipitation area is located in the high-elevation areas of the central region, the high mountains remarkably block the atmospheric moisture from moving northward and considerably increase (decrease) precipitation in the southern (northern) slope of the central region. In the comparison of observed spatial distribution with the SBP datasets, all four SBP datasets generally showed the main characteristic, in which the high precipitation occurs in central Nepal. However, they differed largely in precipitation totals and location accuracy. The mean precipitation distribution from GSMaP-Gauge shows very similar characteristics, with the maximum precipitation (approximately 10–12 mm/day) at 28.3ºN, 84ºE (Figure 3e), whereas GSMaP-MVK shows the maximum precipitation (approximately 5–7 mm/day) at 28.5ºN, 84ºE (Figure 3c). In contrast, the IMERG-UC shows the maximum precipitation (approximately 10–12 mm/day) at 27.9ºN, 84.8ºE (Figure 3b), while IMERG-C shows high precipitation (approximately 4–5 mm/day) at 28.2º N, 84ºE (Figure 3d). Another area (26.5ºN, 88ºE) of the highest rainfall in IMERG-C might be associated with the monsoon trough as seen over the lower ranches of the eastern region (Figure 3d). Notably, all four datasets are drier (<2 mm/day) in the high-elevation areas of central and western region (Figure 3b–e). The large scale patterns of the precipitation such as heavier orographic precipitation along with the southern slope of mountain ranges in the central region and lower precipitation (<2 mm/day) over the northern slope of central and western region (rain-shadow areas) is also qualitatively captured

by all four satellite precipitation datasets. It is worthy to note that, IMERG-UC showed better agreement with the spatial pattern and amount of precipitation in the observations than the IMERG-C, whereas GSMaP-Gauge showed significant improvement over the GSMaP-MVK. Moreover, all four SBP datasets tend to underestimate the mean precipitation across the country. GSMaP-Gauge (Figure 3e) well reproduces the overall spatial pattern of mean precipitation followed by IMERG-UC, GSMaP-MVK, and IMERG-C, respectively. The results suggest that gauge correction scheme for IMERG product requires further improvement in the study area.

**Figure 3.** Spatial distribution of mean precipitation (mm/day) estimated by (**a**) observations, (**b**) IMERG-UC, (**c**) GSMaP-MVK, (**d**) IMERG-C and (**e**) GSMaP-Gauge averaged over March 2014 to December 2016. The magenta and black dotted lines represent the national boundary of the country and the three subregions, respectively.
