Work Description

Date: May 2025

Dataset Title: Great Lakes Ice Duration Geodatabase

Dataset Creators: King, Katelyn; Fujisaki-Manome, Ayumi; Brant, Cory; Alofs, Karen

Dataset Contact: Katelyn King kingk42@michigan.gov

Funding: Coregonine Restoration Template and Great Lakes Restoration Initiative

Research Overview:
Ice cover on the Great Lakes plays an important role in regional climate, supports tourism and recreation, and provides ecological habitat. As the climate warms, ice cover in the Great Lakes is expected to decline, which in turn will create more lake effect precipitation, reduce ice cover for recreation, and alter habitat for fishes. Therefore, it is important to understand historical ice patterns to better understand and predict future ice cover on the lakes. However, Great Lakes ice cover data prior to 1973 is scarce, due to the limited routine satellite observations. Our dataset aims to fill this gap by providing historical spatial ice duration layers to be used for modeling species distributions.

This geodatabase contains a raster layer for each of the Great Lakes for mean ice duration of the historical period and coefficient of variation (CV) of ice duration across years of the historical period. GDB editing template tables were automatically created when the GDB was exported and these system tables contain and manage metadata required to implement geodatabase properties.

Methodology:
We created a continuous air temperature data record based on select coastal stations across the Great Lakes that consistently collected surface weather data since the 1890s. Then, we derived historical cumulative freezing degree-days (CFDD) and net melting degree-days (NMDD) from October 1 to April 30 each winter. CFDD is the estimated cumulative continuous days average temperatures were below-freezing. NMDD is the difference between the ice season’s days above-freezing temperatures and days below-freezing temperatures. We found that CFDD and NMDD are correlated to ice duration (the number of days per year when the lake was frozen).

We downloaded geographic information system (GIS) raster data layers (i.e. spatial data that define space as an array of equally sized cells with each cell containing a value) of ice duration from 1979-2014 from Great Lakes Aquatic Habitat Framework (GLAHF) (hub.glahf.org). Ice duration layers from GLAHF were generated from geospatial analysis of daily ice charts to determine the number of days per year when each grid cell was frozen. This analysis applies a criterion of 10 % ice cover at the individual cell level. This means a cell is counted in the duration metric for each day it had an ice cover of 10 % or higher. Therefore, “duration” represents the total number of days during the season that met the threshold; the days need not all be consecutive or contiguous.

We averaged the maximum CFDD for each winter across the historical time period (1898-1960). We used the mean historical max CFDD plus or minus 20% of the standard deviation across years to select contemporary years (post 1979) where the predicted maximum CFDD fell within this range. For each lake, we selected the spatial ice duration raster layers for years within this range and created two rasters: 1) mean ice duration of the years to be representative of historical ice duration and 2) coefficient of variation (CV) of ice duration across years to be representative of ice consistency across years. The CV is the ratio of the standard deviation to the mean, with the higher the CV, the greater the level of dispersion around the mean.

Instrument and/or Software specifications: ArcGIS Pro (https://www.esri.com/en-us/arcgis/products/arcgis-pro/overview), QGIS (https://qgis.org/) or other spatial data software will be required to view this dataset.

Files contained here:
historical_ice.gdb

Related publication(s):
King, K., Fujisaki-Manome, A., Brant, C., Cohn, D., Peng, I., Alofs, K., Reconstructing Great Lakes air temperature and ice dynamics data back to 1897. Under Review

Use and Access:
This data set is made available under a Creative Commons Public Domain license (CC0 1.0).

To Cite Data:
King, K.B.S., Fujisaki-Manome, A., Brant, C., & Alofs, K. (2025). [Data set]. Great Lakes Ice Duration Geodatabase. University of Michigan - Deep Blue.