Monitoring the changes in the extent of glacial lakes in the Southern Alps, New Zealand from 2000-2023 using an Object-Based Image Analysis (OBIA) approach in Google Earth Engine (GEE)

Glacial lakes are growing rapidly, driven by climatic change and glacier retreat. The growth of glacial lakes may increase the magnitude and frequency of glacial lake outburst floods (GLOFs), posing a hazard to downstream populated regions. Therefore, an automatic method is needed to test on a region to understand whether it can accurately calculate and monitor lake area changes globally to
have a clearer understanding of their future trajectory. In this study we use an Object-Based Image Analysis (OBIA) applied to multispectral Landsat 4-9 satellite imagery in Google Earth Engine (GEE) to monitor the changes of four lake-terminating glacial lakes (Tasman, Hooker, Mueller and Murchison)
in the Southern Alps of New Zealand during the ablation season (December-March) between 2000-2023. The areal extent of the Tasman Lake increased on first (2000) and last observation (2023) by 175%, while Hooker Lake increased by 91%, Mueller Lake by 241.5%, and Murchison Lake by 175%. The accuracy of this method was evaluated by comparing automatically generated lake outlines with
random manually corrected reference data, resulting in an overall accuracy of 93%. This suggests that the method has the potential to map glacial lakes accurately and rapidly and can be applied to other glaciated regions.