Geospatial analysis of wetland dynamics and watershed monitoring in Pokhara Valley, Nepal

Abstract

Lakes are essential components of ecosystems and serve as important indicators of climate change and human impact. This study employed historical remote sensing images and geospatial analysis to examine the dynamics of three significant wetlands (Phewa, Begnas, and Rupa lakes) in the Pokhara Valley of Nepal, which are designated as Ramsar sites. Changes in land use land cover (LULC) and soil erosion within the watersheds of these lakes were also monitored using Landsat images and soil erosion dataset, respectively. Additionally, climatic trends in the Pokhara Valley were analyzed using data from ground-based monitoring stations. The results highlight a notable 11.39 % decline in the surface area of Phewa Lake since 1989, while the surface areas of Begnas and Rupa have remained relatively stable. Changes in LULC show an increase in forest cover (+47 to 64 %) and decrease in croplands (−36 to 59 %) across all watersheds. Urbanization is most pronounced in the Phewa watershed, leading to increased pollution and shoreline encroachment. The decline in cropland may improve water quality by decreasing agricultural runoff. However, soil erosion is most severe in cropland areas, resulting in Phewa lake receiving the highest sediment influx among the three lakes. The lake regions have been experiencing changes in temperature (0.3 °C per decade) and rainfall (insignificant slight increase). Changes in these lakes are primarily driven by watershed dynamics and human activities. These results underscore the necessity for integrated watershed management and further in-depth investigation into the effects of climate change on these ecosystems for regional sustainability.