Great Lakes monthly water balance components from the Large Lakes Statistical Water Balance Model (L2SWBM)

**Note that an updated version of the data (v2023.1) was uploaded on April 27, 2026, which supersedes earlier versions.  This is an update of v2023 with revised files. The version number now reflects the last full year of output data. In this version, file names were changed from “…_MonthlyRun.csv” to “…_AnnualRun.csv” to match the planned frequency of the update. Output remains monthly.**

These data sets are the results of leveraging bi-national data and the Large Lakes Statistical Water Balance Model (L2SWBM) specifically tailored for the Laurentian Great Lakes to produce value-added time series of water supply components, including expressions of uncertainty, that ultimately close the water balance across the interconnected Great Lakes system. 

The model serves as a new cornerstone for bi-national coordination of hydrologic data throughout this international transboundary basin, providing an improved means of capturing data patterns, revealing seasonal variabilities, as well as short-term and long-term trends.

This repository includes monthly output from the L2SWBM. Output datasets include over-lake precipitation, over-lake evaporation, lateral tributary inflow (runoff), connecting channel flow, diversion flow, change in storage, and component net basin supply. Data is included for lakes Superior, Michigan-Huron, Erie, and Ontario.

This version contains data from 1950 to 2023.