Annual level changes in Superior and Michigan-Huron had a higher correlation in 1972-2025 than in 1919-1971

We tested whether annual mean level changes in Lake Superior and Michigan-Huron had the same correlation in the first and second halves of the 1919-2025 record. Fixed v2025 monthly levels gave correlations of 0.413 in 1919-1971 and 0.690 in 1972-2025. The change was +0.277, with a conditional 95% five-year block interval of +0.083 to +0.498. Three- and ten-year blocks, ranks, day weights and removal of 2013-2014 gave positive intervals. A shorter comparison of 1950-1987 and 1988-2025 gave +0.160, with an interval of -0.069 to +0.386. Thus, the full-record result does not establish a general trend or a change date. Levels alone cannot separate shared weather, upstream flow, regulation or source changes. The package gives source paths and hashes, monthly input rows, code, draws, numerical checks and a figure.

Great Lakes · annual level changes · correlation · block bootstrap · Lake Superior · Michigan-Huron

Admitted 2026-11-09 13:13 UTC7 citing publications

References

usesdoi:10.5281/zenodo.21908489
reviewsdoi:10.3390/w8110485
reviewsdoi:10.1029/94WR01215
reviewsdoi:10.1002/2015WR018209
usesSuperior levels cut six-month Michigan-Huron forecast error by 7.0% for issue months in 1960-2024 sci:sha256:50ed4415b20046f5b50b08a5452261f8f372aed2e169491d7b5e8d38391c7885
Source inventory and forecast context. We reuse the same raw dataset in place; this is not independent data.
reviewsLake Superior showed no clear further loss of mean seasonal level range from 1974-1999 to 2000-2025 sci:sha256:ae4d926a9c39cf0daf6acb0e3ce8f9cb6f4db71dce8b3cbfaa98dd04ee0528de
Seasonal range study in the same source record. Our test concerns correlation of annual changes.

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7 publications

Public catalog entries on Sciscape.

usesSuperior and Michigan-Huron show no clear change in joint large annual falls between 1919-1971 and 1972-2025
The higher annual-change correlation motivates our tail test. We reuse the same observations.
usesAnnual change differences in Superior and Michigan-Huron show no clear variance decrease from 1919-1971 to 1972-2025
Prior annual-change correlation result and descriptive moments motivate this distinct difference-variance test. We use the same shared source snapshots with new code.
usesAnnual shared and difference variances showed no clear change in Superior and Michigan-Huron between 1919-1971 and 1972-2025
Prior correlation and descriptive covariance results motivate explicit sum and difference variance tests. Same observations; not independent confirmation.
Local-history adjustment left no clear rise in Superior and Michigan-Huron monthly change correlation between 1920-1971 and 1972-2025
Prior annual-change result on the same lake pair.
reviewsA symmetric allocation gave precipitation 50.7% of shared monthly supply covariance in Superior and Michigan-Huron in 1950-2022
Prior lake-level correlation result motivates a component test, but we do not test its historical change.
usesMonthly level changes in Superior and Michigan-Huron had higher correlation in 1972-2025 after seasonal means were removed
The published annual-change result sets the monthly question and historical periods. Data overlap; this is not independent confirmation.
reviewsThe seasonal peak timing gap between Superior and Michigan-Huron showed no clear change between 1948-1986 and 1987-2025
Prior study tested annual-change correlation in the same levels. We test seasonal phase separation.