Cooley, SarahPletcher, Addison2024-08-072024-08-072024-08-07https://hdl.handle.net/1794/29795The formation and breakup of lake ice plays a critical role in the hydrology, ecology, and subsistence activities of Arctic regions. However, little research has examined ice phenology in small water bodies and complex deltaic environments, areas that are particularly responsive to climate changes and could provide early indicators of broader environmental shifts. This study uses Sentinel-2 optical imagery to map the timing of lake ice breakup in the Lower Kuskokwim River Basin in southwest Alaska from 2018 to 2023. We detect ice breakup timing in 145,955 lakes, as small as 0.001 km2, filling a gap in our understanding of finer scale lake ice dynamics. Our results indicate that the average ice breakup date across the study period is May 14, with a standard deviation of 9.6 days. Breakup timing shows significant interannual variability, with the earliest mean breakup occurring on May 6 in 2019 and the latest on May 27 in 2023. The standard deviation in breakup timing also varies, with certain years exhibiting wider variability (e.g., 2019 and 2023) compared to others (e.g., 2018, 2020, 2021, and 2022). Temperature is a primary driver of breakup timing; we identify a statistically significant positive correlation between the date of the 0°C isotherm and breakup timing. Smaller lakes (defined as lakes < 1 km2) tend to break up earlier than larger lakes (6 days earlier on average), demonstrating a faster thermal response to climatic conditions. We find that the lag interval between the 0°C isotherm and breakup date averages 8.4 days, with smaller lakes exhibiting shorter lag intervals compared to larger lakes. Our analysis of 145,955 lakes over six years demonstrates the utility of Sentinel-2 imagery in accurately detecting ice breakup, typically within 2.8 days of observed dates, despite challenges such as cloud cover, sensor resolution, and temporal gaps. The significant interannual variability, along with notable differences in breakup timing between smaller and larger lakes, underscores the responsiveness of small lakes to temperature fluctuations. These findings emphasize the importance of incorporating high-resolution satellite imagery to capture rapid environmental changes, providing a more nuanced understanding of climatic impacts across diverse lake types.en-USAll Rights Reserved.Ice PhenologyRemote SensingYukon-Kuskokwim DeltaElectronic Thesis or Dissertation