Joint low and high annual supply counts were equal in two Great Lakes reconstructions for 1950-2022

We tested whether low annual supplies occur together more often than high annual supplies in Lake Superior and Michigan-Huron. We used L2SWBM V3.0 monthly component medians for 1950-2022. Each lake had 14 years in each tail. There were eight joint low years and eight joint high years. Both joint frequencies were 10.96%. The low-minus-high difference was 0.00 percentage points, with a conditional 95% five-year block interval of -8.22 to +4.11 points. The data do not resolve a difference. Equal observed counts do not establish equal population risks. At a smaller tail size of seven years, there were zero joint low and four joint high years, but the interval also included zero. The 73-year record, selected thresholds, shared reconstruction constraints and omitted posterior uncertainty limit inference. The package gives code, source hashes, aggregate evidence, all planned checks, a figure and repeat instructions. Raw data and annual record-level tables remain in external storage.

Great Lakes · joint extremes · net basin supply · tail asymmetry · block bootstrap · null result