Measurement

Question 1

Non-recording rainfall gauge (Hellmann)

Answer 1

 Collector (1 m above ground, opening 200 cm2, no heating)

 observation period 1 day (DWD: 7.30 previous day - 7.30 CET)

Question 2

Recording rainfall gauge (Hellmann)

Answer 2

 Collector with registration (opening: 1 m, 200 cm2)

 observation continuously analog (charts → digitizing required)

Question 3

Digitally recording gauges

Answer 3

 drop counter, tipping bucket or scale (opening: 1 m, 200 cm2)

 obs. continuously digital (digital storage, remote transmission)

Question 4

Radar rainfall observation

Answer 4

 Radar reflectivity Z estimated from receiving power

 Z-R-relationship required for estimation of rainfall

Question 5

Measurement errors for point observations :

Always underestimation of rainfall:

Answer 5

1. Wind induced error
2. Losses from surface wetting
3. Evaporation from collectors

Magnitude of errors:

• 10 - 20 % for rainfall
• about 25 % for snow

Question 6

Methods for correction of systematic error:

Answer 6

• In Germany method acc. to Richter (1995) for daily data is often applied

[equation page 6]

• Internationally different approaches are in use, see e.g. Sevruk (2005)

Question 7

When do we have to correct ?

Answer 7

1. Water balance, continuous modelling → correction always required !
2. Extremes, event based modelling → correction not mandatory !