Environmental Engineering Reference
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Short Exercise 2: Wind Correction of Precipitation Data
Table 3.3 shows daily mean air temperature and wind speed, and daily total
precipitation recorded by a weighing precipitation gauge with an Alter wind shield
(similar to Fig. 3.5a ), at a hydrological research station in Calgary, Alberta, Canada,
in 2008. There were two precipitation events, on December 7 and 12.
1. Based on the air temperature, determine the form of precipitation (rain or snow).
2. If the precipitation occurs as snow, then a correction must be made to account for
the gage-catch deficiency (see Fig. 3.6 ). Use the following equation (Dingman
2002 :111-112) to compute the catch deficiency factor (CD) from wind speed
( u ,ms 1 ) for each day.
036 u 1 : 75
CD
ΒΌ
100 exp
4
:
61
0
:
(3.56)
3. Divide the uncorrected precipitation by CD to estimated true (i.e., corrected)
precipitation.
4. Calculate the total of two precipitation events for both uncorrected and corrected
data. What is the degree (percentage) of underestimate by not correcting the
data?
5. Many winter precipitation data sets available on the internet have not been
corrected. Discuss the potential problem of using such data for a water-budget
analysis.
Table 3.3 Daily mean air temperature and wind speed, and daily total precipitation
Date
Air temp. ( C) Wind spd. (m s 1 ) Recorded pcp. (mm) CD Corrected pcp. (mm)
Dec. 7
1.4
1.7
13
___ ___
Dec. 12
5.4
3.7
17
___ ___
Total
___
___
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