Change Detection of Lakes in Pokhara, Nepal Using Landsat Data

Pokhara, city of lakes, is second largest and most beautiful tourist place in Nepal. Out of seven lakes, the large three: Phewa, Begnas and Rupa are famous for tourist attraction, whereas the rest are small and less known. Lakes are not only economic value, but are also ecological and environmental resources. But, these lakes are facing challenges due to climatic and anthropogenic activities. As these changes are slow and takes long time, the damage unnoticed to take measures. Hence, long historic data provided such as of remote sensors are concrete evidence of change, which help us understand the cause and prevent further change. Landsat series provide the continuous data with high temporal resolution freely to the scientific community. For such data, many simple and low cost index methods has been developed to identify water bodies. In this study, we use these indices to detect the change of lakes in Pokhara city using Landsat data of 25 years gap i.e., 1988–2013. Normalized Difference Vegetation Index (NDVI), Normalized Difference Water Index (NDWI), and Modified NDWI (MNDWI) were investigated for the unsupervised extraction of surface water from Landsat data. A model is developed in ArcGIS by differencing the water bodies derived form index methods and difference were calculated for positive and negative change. The results show that the area of Phewa has shrunken, whereas Rupa being increase in surface water area. Began has few changes and other small lakes except Dipang lake, were not detected. Dipang Lake showed increase in surface water area after 25 years of gap. The result can be helpful in reclaiming and restoration of lake area, preserve and maintain the wetland ecosystem in the city. Also, the model presented in the manuscript can be used for change detection of surface water due to flood, or debris blockages in disaster prone countries.