January-March basin water volume change gave no clear added winter ENSO forecast gain in 2000-2024

We tested whether January-to-March change in equatorial Pacific warm water volume adds winter ENSO forecast value beyond March volume, March Nino 3.4 temperature, and recent surface temperature change. We used NOAA GODAS and ERSSTv5 snapshots. Each linear fit used only earlier issue years, with training from 1980 and 25 test issues in 2000-2024. Adding the volume change raised mean squared error by 2.94%. The conditional 95% three-year block interval for error reduction was -26.32% to +13.39%. Root mean squared error rose from 1.110 to 1.126 C. Trend, rolling-window, shorter-change, and western-region checks also gave intervals that include zero. Removing the 2015 and 2023 issues from scoring changed the point gain to +4.92%, still uncertain. This result does not establish added forecast value or reject the physical recharge process. Few test years, revised data, simple linear models, and uncertainty conditional on stored forecasts limit inference. The package includes exact source bytes, hashes, annual inputs, forecasts, code, uncertainty draws, a numerical audit, and a figure.

ENSO · warm water volume · recharge · forecast validation · null result · GODAS · ERSSTv5