# Utilizing Sentinel-2 Satellite Imagery for LULC and NDVI Change Dynamics for Celephu, Bhutan
## 3 Results and Discussions
### LULC Change Detection  
Additionally, change detection on the LULC was performed (see Figure 6) using the postprocessing tools in SCP in QGIS. The main goal of change detection mapping is to identify the change or transition of each land-use class to each other in the study area. Gelephu's LULC change detection map is shown in Figure 6a. The colors of the legend in Figure 6 indicate quantification of the current state of the land classes in 2023 (Figure 6a) that have already transitioned within the assessment period of the 2016 study, with some of the classes with no changes. Further, the LULC change detection map is rendered in Figure 6b to visually depict the delineation of land-use class change spots and represent the actual land-use transition through the year 2023. In Figure 6b, a white background is assigned to the land-use class to represent the no-change land-use class.  
Figure 5: A subset of the Gelephu LULC map. (**a**) Gelephu Thromde LULC map of 2016; (**b**) Gelephu Thromde LULC map of 2023.  
The LULC change detection results from Gelephu show several significant transitions (Figure 7). The largest land cover class, vegetation, was fairly stable, with an area of 34.95 km\({}^{2}\). This provides information about the notable change in the vegetation areas over just a seven-year study period. The changes between water and vegetation are relatively small. The water-to-vegetation transition covers an area of 0.04 km\({}^{2}\), indicating slight dispersal of vegetation into water bodies. Similarly, transitions involving water and built-up areas are relatively small in scale. Conversely, the transition from vegetation to water covers an area of 0.05 km\({}^{2}\), indicating a slight decrease in vegetation cover and an increase in water bodies. A total area of 2.62 km\({}^{2}\) shows a transition from barren land to vegetation. The conversion of vegetation into built-up areas covers an area of 4.82 km\({}^{2}\), indicating urban expansion and reflecting the conversion of natural vegetation into built-up infrastructure, such as residential, commercial, or industrial facilities. The conversion of vegetation to barren land covers an area of 4.48 km\({}^{2}\), suggesting possible land degradation or land-use changes. This transition between barren land and built-up areas illustrates urban expansion into previously unproductive or degraded areas. The conversion of barren land to built-up areas covers 1.16 km\({}^{2}\), indicating land utilization for urban development purposes. Conversely, the conversion of developed land to barren land covers an area of 1.34 km\({}^{2}\). The barren land cover class remained relatively stable, with an area of 3.38 km\({}^{2}\), indicating the persistence of unproductive or degraded areas within the study area.  
Figure 6: LULC change detection map of Gelephu. (**a**) Gelephu LULC map of 2023 quantifying the transition area of each land class to one another, including those classes with no changes. The quantifications are represented by the legend colors (Green: Vegetation; Blue: Water; Red: Built-up; Yellow: Barren land), (**b**) Change detection map of Gelephu delineated with ’No change classes’ on a white background. This map represents transitional classes only.