Thirty years of change of Pekalongan coastline based on Landsat imagery

Abstract

The northern coastal area of Java Island is where many economic and industrial centers are located. Many big cities are located in this area, such as Jakarta, Semarang, and Surabaya. One of the problems in this area is the occurrence of tidal flooding. One of those affected by the tidal flood is Pekalongan, where the city also experienced land subsidence which is more severe than other big cities in Indonesia. One of the impacts of tidal flooding is the occurrence of coastal abrasion, where land areas are increasingly disappearing. This research objective is to see how big the coastline changes occurred in the Pekalongan area for 30 years through remote sensing data. Landsat image was used to see changes in coastlines from 1988 to 2021 on an annual basis. NDWI (Normalized Difference Water Index) was used to clarify the difference between land and water areas. Moreover, to reduce subjectivity, Otsu’s method was used for thresholding. The results show that most Pekalongan area is subject to abrasion, with the most severe conditions up to around 232 m. In addition, there are also problems related to tidal flooding, whose conditions are increasingly widespread every year.