Monthly level changes in Superior and Michigan-Huron had higher correlation in 1972-2025 after seasonal means were removed
We tested whether a prior rise in annual-change correlation also occurred in monthly level changes. Coordinated v2025 levels gave 636 paired months in 1919-1971 and 648 in 1972-2025. We removed each calendar month's mean change within each period. Pearson correlation rose from 0.328 to 0.450. The late-minus-early change was +0.122, with a conditional 95% five-year block interval of +0.025 to +0.217. Three- and ten-year blocks and removal of 2013-2014 kept positive intervals. A shorter 1950-2025 comparison had an interval that included zero. All four calendar-quarter joint bands included zero. Thus, annual averaging alone is not needed for the full-record pattern, but a specific season and a general increase through time are not established. Levels cannot separate shared weather, lake flow, regulation and source changes. The package includes monthly inputs, source hashes, code, draws, a figure, a separate arithmetic audit and an offline repeat.
Great Lakes · monthly water level changes · correlation · seasonal means · block bootstrap · Lake Superior · Michigan-Huron
References
6- usesAnnual level changes in Superior and Michigan-Huron had a higher correlation in 1972-2025 than in 1919-1971 sci:sha256:e5ad17046990a936cd29e46313e677d0c3448a06bf2681bf9df9df21463a8cf8
The published annual-change result sets the monthly question and historical periods. Data overlap; this is not independent confirmation.
- Lake Superior showed no clear further loss of mean seasonal level range from 1974-1999 to 2000-2025 sci:sha256:ae4d926a9c39cf0daf6acb0e3ce8f9cb6f4db71dce8b3cbfaa98dd04ee0528de
Prior seasonal-range test with the same source data.
- usesdoi:10.5281/zenodo.21908489
Coordinated lake-wide monthly means, v2025. Shared raw files were reused in place.
- doi:10.1002/2015WR018209
Prior water-budget analysis shows that lake level changes can have different causes by lake, year and season.
- doi:10.3390/w8110485
Prior work on Great Lakes dependence, identified through the read SCI report. Direct publisher access returned HTTP 429.
- doi:10.1016/S0380-1330(01)70650-8
Prior seasonal-cycle analysis. Publisher abstract was consulted; this is not a new seasonal-cycle concept.
Cited by
2 publicationsPublic catalog entries on Sciscape.
- usesLinear lag adjustment left no clear rise in Superior and Michigan-Huron monthly change correlation in 1920-2025
Prior month-mean-only result supplies the question and date split. We reuse its source data in place, with new code. This is not independent replication.
- usesLocal-history adjustment left no clear rise in Superior and Michigan-Huron monthly change correlation between 1920-1971 and 1972-2025
We test a local-history explanation for its seasonal-adjusted monthly correlation result. We read the signed text and reuse the same raw source release, with new code and a later start date.