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September 17, 2026HydrologyOpen Access

Evaluating Rainfall Forecast Skill in Numerical Weather Prediction Models and the Effects of Bias Correction on the PCJ (Piracicaba-Capivari-Jundiaí) River Basins in Brazil

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Authors

VIViolet IshakDFDanieli Mara FerreiraMLMaria Fernanda D. d. S. Lima

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Overview

Comparative evaluation reveals variable impacts of statistical bias correction across river basins, highlighting that post-processing gains depend strongly on observational reference choices.

Key Points

  • To assess the skill of operational numerical weather prediction precipitation forecasts and determine whether statistical bias correction improves dry/wet occurrence and rainfall magnitude estimates across river basins.
  • Evaluated two operational precipitation forecasting systems against two observational reference datasets across three basins in São Paulo State, Brazil, covering seven lead times.
  • Applied four logistic-regression-based methods to adjust dry/wet occurrence and Quantile Delta Mapping (QDM) to correct precipitation amounts.
  • Assessed occurrence shifts using exact McNemar tests with Holm adjustment, evaluated metric changes via exact paired permutation tests and bootstrap 95% confidence intervals, and measured magnitude skill using RMSE skill score and KGE.
  • Occurrence correction significantly altered individual event classifications in some configurations per McNemar testing, but paired permutation tests revealed no systematic metric improvements across lead times.
  • HBLR-AR1 exhibited the most balanced overall performance among occurrence correction techniques, whereas LR-Seasonal was the least consistent.
  • Quantile Delta Mapping improved RMSE skill scores—particularly at extended forecast lead times—without delivering consistent improvements in KGE.

Cite This Study

Ishak et al. (2026) studied this question.

synapsesocial.com/papers/6aabb7275f706d05830e612chttps://doi.org/10.3390/hydrology13090254
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