Autumn DMI gave no clear added Pacific spring volume forecast gain in 2000-2024

We tested whether autumn Indian Ocean Dipole Mode Index (DMI) adds forecast value for Pacific warm water volume the next spring. The baseline used autumn volume and Nino 3.4 plus summer volume. Fits used only earlier years from 1980. In 25 target springs in 2000-2024, adding DMI raised mean squared error by 25.73%. The conditional 95% three-year block interval for error reduction was -102.51% to +24.41%. RMSE rose from 0.540 to 0.606 in units of 10^14 cubic metres. Removing spring 2008 from scoring changed the estimated reduction to +9.56%. All six planned model checks had intervals that included zero. Thus this small test gives no clear added forecast gain. It does not exclude a physical Indian Ocean effect. A short test, revised data, small linear fits and uncertainty conditional on saved forecasts limit inference. The package gives fixed monthly inputs, source hashes, forecasts, code, bootstrap evidence, a figure and a successful separate numerical audit and offline repeat.

Indian Ocean Dipole · warm water volume · Pacific · forecast test · null result · event influence