Ensemble verification Quantile score and decomposition Generalization to CRPS Ensemble verification: Old scores, new perspectives Sabrina Wahl, Petra Friederichs, Jan Keller WMO Verification Workshop Berlin, May 2017 Sabrina Wahl Ensemble verification
Ensemble verification Quantile score and decomposition Generalization to CRPS equally probable simulations ensemble forecast of numerical model ➡ calibration: rank (pit) histogram, beta score ➡ discrimination: generalized discrimination score translation, interpretation, ➡ sharpness: prediction interval post-processing pdf, cdf, mean, sd, probabilistic forecast quantiles, probabilities,… xf M p(x |y ) i i ➡ proper scoring rules: p(x ) f xi -1 -1 CRPS, Brier score, quantile score, H G model space logarithmic score, MSE, MAE, … p(y ) N i p(y |x ) f f observation space ti tf time Fig. 1 from Stephenson et al. (2005) Sabrina Wahl Ensemble verification
Ensemble verification Quantile score and decomposition Generalization to CRPS 35 ● 30 ● temperature (°C) ● 25 ● ● ● ● ● ● ● ● ● ● ● ● 20 ● ● ● ● ● ● ● ● ● 15 ● ● ● ● ● 10 ● ● 5 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 days ensemble forecast in terms of empirical distribution boxplot represents forecast distribution in terms of quantiles evaluation of ensemble members as quantiles Sabrina Wahl Ensemble verification
Ensemble verification single quantile Quantile score and decomposition multiple quantiles Generalization to CRPS Verification-framework for quantiles score for quantile forecasts q τ when y is the event that materializes, with τ ∈ ( 0 , 1 ) the probability level � | y − q τ | τ if y ≥ q τ S Q ( q τ , y ) = ρ τ ( y − q τ ) = | y − q τ | ( 1 − τ ) if y < q τ empirical quantile score from a set of N forecast-observation pairs N QS ( τ ) = 1 � ρ τ ( y i − q τ, i ) N i = 1 decomposition of the quantile score (Bentzien and Friederichs, 2014) N QS ( τ ) = 1 � ρ τ ( y i − q τ, i ) = UNC ( τ ) − RES ( τ ) + REL ( τ ) N i = 1 Sabrina Wahl Ensemble verification
Ensemble verification single quantile Quantile score and decomposition multiple quantiles Generalization to CRPS 50.00 ● ● ● Calibration : quantile 20.00 ● ● ● ● ● ● ● ● ● reliability diagram ● ● ● ● 10.00 ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● 5.00 ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● forecast intervals I k ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ●● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● observation ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● 2.00 ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● y ( k ) ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● τ : conditional observed ● ● ● ● ● ● ● ● ● ● ● ● ● ● 1.00 ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● quantile in I k ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● 0.50 ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ●● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● 0.20 ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● discrete values y ( k ) τ , q ( k ) ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● with ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● τ ● ● ● ● ● ● 0.10 ● ● ● ● ● ● ● ● ● k = 1 , ..., K ≤ N ● ● ● ● ● ● ● ● ● ● ● 0.05 ● 0.05 0.20 0.50 2.00 5.00 20.00 quantile forecast Sabrina Wahl Ensemble verification
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