Data Sources

These are the data sources for the Sustained Assessment of the Great Lakes: Lake Climatology pages.

Note: since the publication of this resource in 2021, many data sources below have moved or been updated. GLISA will be updating the Climatology pages and this data sources list in the coming months to reflect up-to-date information.

Lake Levels

• Data for the analysis of water levels in each of the lakes was originally from the GLERL Dashboard, but the data is now housed through the Coordinating Committee on Great Lakes Basin Hydraulic and Hydrologic Data. 
  • Source: https://www.greatlakescc.org/en/coordinating-committee-products-and-datasets/
  • For each lake there is a separate file with monthly water levels from 1918 to 2020 (now 2024)
  • Each file is a csv with the lake in the filename (ex.LakeSuperior_MonthlyMeanWaterLevels_1918to2024.csv)
• The water levels are lake-wide averages calculated based on a network of gauges in each respective lake.  
  • There are currently 53 gauges in the United States and 33 in Canada. 
  • For more information: https://www.glerl.noaa.gov/data/wlevels/#monitoringNetwork

Evaporation 

• Data used in the analysis of over-lake evaporation in each of the Great Lakes is part of GLERL Great Lakes Monthly Hydrologic Data 
  • File used: evaporation_shortlakename.csv
  • Source: https://www.glerl.noaa.gov/pubs/tech_reports/glerl-083/UpdatedFiles/
  • For each lake, there is a separate file with monthly evaporation amounts in millimeters from 1950 to 2019. 
  • Each file is a csv with the word evaporation, an underscore, and a shortened version of the name of the individual lake (ex. evaporation_sup.csv).
• Evaporation is calculated by estimating “total monthly evaporation over each lake by aggregating daily simulations from NOAA-GLERL’s one-dimensional Large LakeThermodynamics Model” 
  • From Hunter et al., 2015

Precipitation

• Data used in the analysis of over-lake precipitation in each of the Great Lakes is part of GLERL Great Lakes Monthly Hydrologic Data 
  • File used: prc_shortlakename_lake_mon.csv
  • Only 1950 to 2019 is used in the analysis, to match the period of record of evaporation
  • Source: https://www.glerl.noaa.gov/pubs/tech_reports/glerl-083/UpdatedFiles/
  • For each lake, there is a separate file with monthly precipitation amounts in millimeters from 1940 to 2019 
  • Each file is a csv with the name prc_ the shortened lake name _lake_mon (ex. prc_sup_lake_mon.csv)
• Precipitation totals are estimated using daily monitoring station data from NOAA’s National Climate Data Center data set
  • Data from all stations within each lake basin are used in the estimations
  • For more information see Hunter et al., 2015

Runoff

• Data used in the analysis of runoff in the basin of each Great Lake is part of GLERL Great Lakes Monthly Hydrologic Data 
  • File used: runoff_shortlakename_arm.csv
  • The data must be converted from cubic meters per second to millimeters per month to be used in the analysis, as precipitation and evaporation are recorded in millimeters. 
  • Source: https://www.glerl.noaa.gov/pubs/tech_reports/glerl-083/UpdatedFiles/
  • For each lake there is a separate file with monthly runoff rates in cubic meters per second from 1908 to 2019. 
  • Each file is a csv with the name runoff_ the shortened lake name _arm (ex. runoff_sup_arm.csv). 
• Runoff is estimated through the extrapolation of daily streamflow measurements from USGS and WSC in the lake basins. 
  • A flow-per-unit area ratio approach is used.
  • For more information see Hunter et al., 2015 

Net Basin Supply

• Data used in the analysis of component net basin supply of each Great Lake is part of GLERL Great Lakes Monthly Hydrologic Data 
  • File used: lakenameNBSLakemmMo.csv
  • Source: https://www.glerl.noaa.gov/data/dashboard/data/hydroIO/nbs/
  • For each lake there is a separate file with the monthly net basin supply in millimeters over the lake surface from 1950 to 2015.
  • Each file is a csv with the name of the lake followed by NBSLakemmMo.csv (ex. superiorNBSLakemmMo.csv)
• Net basin supply is calculated as the sum of over-lake precipitation, over-lake evaporation, and runoff values 
  • For more information see Hunter et al., 2015

Water Temperature

• Data used in the analysis of water surface temperature of each Great Lake is part of the Great Lakes Surface Environmental Analysis
  • Files used: glsea-tempsyear_1024.dat
    • Each year has to be downloaded individually from the section called “Average GLSEA Surface Water Temperature Data (by year)”
  • Source: https://coastwatch.glerl.noaa.gov/statistic/
  • Yearly water temperatures for each lake are in one file named glsea-temps with the year and _1024 (ex. glsea-temps1995_1024.dat)
  • Data is available from 1995 to 2019
• Water surface temperatures are derived from NOAA AVHRR imagery which is obtained through the Great Lakes CoastWatch program
  • For more information see https://coastwatch.glerl.noaa.gov/glsea/doc/

Basin Air Temperature

• Data used in the analysis of Air Temperature in the basin of each Great Lake is part of GLERL Great Lakes Monthly Hydrologic Data 
  • File used: lakeLakeAirTempMeanAnn.csv
  • Source: https://www.glerl.noaa.gov/data/dashboard/data/hydroIO/temps/
  • For each lake basin there is a separate file with yearly average air temperatures from 1948 to 2010
  • Each file is a csv with the name of the lake followed by LakeAirTempMeanAnn.csv (ex. superiorLakeAirTempMeanAnn.csv).
• Basin air temperature is estimated using daily monitoring station data from NOAA’s National Climate Data Center data set
  • Data from all stations within each lake basin are used in the estimations
  • Average air temperature is calculated using areally-weighted averages
  • For more information see Hunter et al., 2015

Maximum Ice Cover

• Data used in the analysis of maximum ice cover in each of the Great Lakes is from GLERL Great Lakes Ice Cover Database. 
  • File used: dates_AMIC.txt
  • Source: https://www.glerl.noaa.gov/data/ice/#historical
  • One file contains the yearly maximum ice coverage for all of the lakes from 1973 to 2020
• Ice cover on each of the lakes has been monitored by NOAA/GLERL since the early 1970s
  • U.S. National Ice Center and the Canadian Ice Service products were used in the monitoring
  • For more information see https://www.glerl.noaa.gov/data/ice/#historical

Daily Ice Cover

• Data used in the analysis of daily ice cover in each of the Great Lakes is from GLERL Great Lakes Ice Cover Database. 
  • File used: lakename.txt
  • Source: https://www.glerl.noaa.gov/data/ice/#historical
  • For each lake, there is a file with daily ice concentrations from 1973 to 2020
  • Each file is a txt file with a shortened version of the lake name followed by .txt (ex. sup.txt)
• Ice cover on each of the lakes has been monitored by NOAA/GLERL since the early 1970s
  • Ice charts are created based on all available information about ice cover including weather and oceanographic information, visual observations from shore, ship, and aircraft, airborne radar, satellite imagery, and climatological information. 
  • Data from 1973 to 1988 data is from the Canadian Ice Service
  • Data from 1989 on is from the U.S. National Ice Center (NIC)
    • Data from both Canadian and U.S. Sources are combined by the NIC
  • Specific publication: https://www.glerl.noaa.gov/pubs/tech_reports/glerl-155/tm-155.pdf
  • U.S. National Ice Center and the Canadian Ice Service ice charts were used to create the GLERL data set
  • For more information see https://www.glerl.noaa.gov/data/ice/#historical

Bathymetry

• Data used in the creation of the bathymetry maps for each Great Lake is from NCEI
  • File used: lakename_Ild.grd.gz 
  • To access data, go to the above link, click on the name of the lake, and click NetCDF
  • Source: https://www.ngdc.noaa.gov/mgg/greatlakes/greatlakes.html
  • For each lake, there is a separate file with its bathymetry in meters
  • Each file is a NetCDF file with the lake name followed by _Ild.grd.gz (ex. superior_Ild.grd.gz)
• Bathymetry data for the Great Lakes was compiled by NOAA’s National Geophysical Data Center 
  • 150 years of nautical charting by the US Army Corps of Engineers (pre 1970)
  • NOAA National Ocean Service (after 1970)
  • Canadian Hydrographic Service
  • Bathymetry data was collected from three separate sources:
  • For more information see: https://www.ngdc.noaa.gov/mgg/greatlakes/greatlakes.html

If you have questions, comments, or feedback on the Sustained Assessment of the Great Lakes, please contact Kim Channell (kimchann@umich.edu)