Integrated assessment of flood frequency reliability in Iraq and Australia

Abstract Flood-frequency estimates depend on observation policy, tail estimation, and temporal structure. This study evaluates these dependencies in Najaf–Kufa, Iraq, and five Australian gauges, retaining geomagnetic, event-dependence, and computational components within a common evidence framework. The Iraqi record contains 7,084 daily observations and 20 eligible annual maxima; Australian refit samples contain 51–73 annual maxima. Q100 is reported as a diagnostic comparison target, not a recommended design discharge. On identical Australian years, an inherited quality restriction reduces L-moment Q100 by 20.8–53.6%, while estimator disagreement persists. Chronological evaluation does not establish general superiority of the tested nonstationary models. In expanded independent confirmation, archived stability components accept 993 of 1,620 estimates, including 316 with an absolute relative Q100 error above 25% (31.8%); conditional error reaches 49.0% under combined trend, dependence, and peak loss. New annual re-pairing under the adopted quality and coverage policy yields no BH-adjusted rejection among 156 magnetic tests, before or after detrending; minimum adjusted p values are 0.09830 and 0.38071. The recomputed daily Kp screen contains 372 comparisons with 999 synchronized shifts; its largest absolute association is 0.06306, and the minimum global p is 0.454. New calendar-aware event extraction yields 60–287 training and 8–85 test events per station. Five genuine trivariate copula families and independence are refitted; no selected copula shows a positive simultaneous lower bound for heldout Brier improvement over independence across 18 hazard comparisons. A browser-compatible deterministic hydrological kernel matches Python on 45 return levels, but live-browser and LLM execution remain unverified. The results quantify influential analysis choices and the limits of the tested diagnostics without asserting zero magnetic effect or operational validation. Keywords: flood frequency; observation quality; Q100; geomagnetic activity; copula; reproducibility; uncertainty.