Spatial and Temporal Patterns in Northern Hemisphere Lake Ice Phenology, 2000-2018

The timing of lake ice phenology is a robust indicator of climate change. Variations in lake ice timing also affect ecological processes and land-atmosphere energy fluxes associated with lakes. To understand the temporal and spatial patterns of lake ice timing variations in the past 20 years, as well as the climate drivers of these changes, we developed a boreal lake ice phenology dataset, including time series of lake ice breakup/freezeup dates and lake ice durations over 138,000 lakes (>1 km ² ) across the Northern Hemisphere. This dataset is based on MODIS daily surface reflectance (2000- 2018) at 250 m spatial resolution. The lake ice phenology timing was validated against in situ data in Maine, US, with mean absolute error of 5.34 days and 7.20 days for breakup and freezeup, respectively. We compare the lake ice phenology time series with climate modes that can influence the Northern Hemisphere temperature, such as the North Atlantic Oscillation (NAO) and Pacific-North American Pattern (PNA). By doing so, we identify the most substantial climate drivers of lake ice variations and assess the impact of climate modes on lake ice over different regions and periods.