Verification of the distributions

Chiara Marsigli

ARPA-SIM - HydroMeteorological Service of Emilia-Romagna

Bologna, Italy

Methodology

Station observation

Grid point forecast

the verification area is covered with boxes of fixed size

the distributions of both forecast and observed values falling in each box are considered

verification is made by comparing (in terms of usual scores) the parameters of the two distributions, e.g.:

• average value

• maximum value

• 50th percentile (median)

• 90th percentile

Aims method suitable for precipitation suitable for high-resolution models permit to exploit a dense network of sparse observations (raingauges) enable comparison between models with different horizontal resolution assess the forecast quality in a way helpful for the forecaster:

which is the skill of the model in predicting the average precipitation amount over an area of 50x50 km2 (e.g. a basin)? which is the skill of the model in predicting a high precipitation value located anywhere within an area of 50x50 km2?

13 May 2005 case

point (standard) verification

thresholds: 1., 5., 10., 20., 30., 50. mm = 0.04, 0.2, 0.39, 0.79, 1.18, 1.97 inchesn. points: 301101; n. occurrences: 11506, 3247, 1449,

544, 235, 46

average values - 0.5 x 0.5 ° boxes

thresholds: 1., 5., 10., 20. mm = 0.04, 0.2, 0.39, 0.79 inchesn. points: 3080; n. occurrences: 92,

26, 10, 2

maximum values - 0.5 x 0.5 ° boxes

thresholds: 1., 5., 10., 20., 30., 50. mm = 0.04, 0.2, 0.39, 0.79, 1.18, 1.97 inchesn. points: 3080; n. occurrences: 257, 85, 50,

22, 15, 5

90th percentile values - 0.5 x 0.5 ° boxes

thresholds: 1., 5., 10., 20., 30., 50. mm = 0.04, 0.2, 0.39, 0.79, 1.18, 1.97 inchesn. points: 3080; n. occurrences: 154, 45, 25,

9, 4, 1

01 June 2005 case

point (standard) verification

thresholds: 1., 5., 10., 20., 30., 50. mm = 0.04, 0.2, 0.39, 0.79, 1.18, 1.97 inchesn. points: 301101; n. occurrences: 18360, 2622, 950,

402, 257, 124

average values - 0.5 x 0.5 ° boxes

thresholds: 1., 5., 10., 20. mm = 0.04, 0.2, 0.39, 0.79 inchesn. points: 3080; n. occurrences: 132,

16, 4, 3

maximum values - 0.5 x 0.5 ° boxes

thresholds: 1., 5., 10., 20., 30., 50. mm = 0.04, 0.2, 0.39, 0.79, 1.18, 1.97 inchesn. points: 3080; n. occurrences: 390, 119,

55, 23, 8, 5

90th percentile values - 0.5 x 0.5 ° boxes

thresholds: 1., 5., 10., 20., 30., 50. mm = 0.04, 0.2, 0.39, 0.79, 1.18, 1.97 inchesn. points: 3080; n. occurrences: 242, 42, 15,

4, 4, 3