Alpine vegetation community patterns and implications to eco-hydrology in the Khumbu region, Nepalese Himalaya

The Himalayan alpine zone (HAZ) – a high altitude zone above approximately 4100 m.a.s.l., is projected to experience strong eco-environmental changes with climate change. As plants expand their range in this region, the plant-water functioning is likely to be impacted. Satellite remote sensing provides one means of understanding the distribution pattern of HAZ vegetation communities, but the often patchy distribution of alpine vegetation creates challenges when using coarse-grained satellite data whose pixels are typically coarser than the grain of vegetation pattern. Also, the lack of in-situ measurements limits the validation of remote sensing products, and our understanding to the eco-hydrological processes within this area. Here we use fine spatial resolution satellite imagery from WorldView-2 (2 m² per pixel) coupled with elevation model data from the Copernicus GLO-30 product to produce a land cover classification for HAZ. Grassy meadows and dwarf shrubs belonging to the Rhododendron and Juniperus families dominate the ecology of HAZ in this region so we created three vegetation classes for mapping indicative major plant communities dominated by these species. Based on this land cover map, we compared in-situ measurements in shrubby and open area, to explore the impacts of Rhododendron spp. and Juniperus spp. on temperature under plant canopy. Afterwards, we coupled in-situ measurements with meteorological metrics derived from ERA5, to simulate the evapotranspiration (ET) of these two dominant plant communities. We found that altitude and aspect were dominant drivers of vegetation distribution in HAZ and that the average vegetation cover of Rhododendron spp. and Juniperus spp. reduced with increasing altitude, as expected. South- and east- facing slopes were dominated by Juniperus spp., while north- and west- facing slopes were dominated by Rhododendron spp., and the growth extent of Rhododendron spp. (between 4010 to 4820 m.a.s.l.) and meadow (between 4010 to 4680 m.a.s.l.) were vertically wider than Juniperus spp. (between 4010 to 4660 m.a.s.l.). In general, maximum temperatures under shrub canopies were lower and minimum temperatures were higher compared to unvegetated or open areas at the same location. Juniperus plants had more significant influences on temperature than Rhododendron. Results from this study demonstrate the present vegetation distribution pattern in HAZ at the plant community level, and the potential ET status relevant to the vegetation expansion trend within this area. This study provides an impetus for studies that seek further understanding to eco-hydrological interactions between dwarf plants and water flows and stores in HAZ.