UNIVERSITY OF THE FREE STATE
MAIN CAMPUS
LWR 314
DEPARTMENT: SOIL, CROP AND CLIMATE SCIENCES
CONTACT NUMBER : 401-2388
EXAMINATION: JUNE 2008
PAPER 1
ASSESSOR(S): 1. Mrs. L. De Wet
2. Mr. S. Steyn
MODERATOR(S): Prof. S. Walker
TIME: 3 hours
MARKS: 100
Instructions:
1. Answer all the questions in SECTION A.
2. Answer only 5 questions from SECTION B.
SECTION A
COMPULSORY QUESTIONS
[50]
QUESTION 1
TEMPERATURE HUMIDITY INDEX (THI)
(10)
You have inherited some money and decide to use it to purchase a livestock farm
in Kwazulu-Natal. Two possible farms near stations A and B become available, in
different parts of the province. Use the data in Table 1.1 and your knowledge of
THI to
a)
Calculate THI for Nov to February only, for each station.
(8)
b)
Make the best choice, taking into consideration that the livestock need
the most favourable conditions possible in order to be able to produce at
their highest levels. Motivate your answer.
(2)
Table 1.1
THI for farms near stations A and B for the months of January to
December.
STATION A
JAN
Tmx
RHmn
es
e
Td
THI
o
C
%
kPa
kPa
o
C
FEB
MRT
APR
MAY
JUN
Lat. 2040S
JUL
AUG
35.3
45.3
5.7
2.6
34.3
44.2
5.4
2.4
33.9
42.8
5.3
2.3
31.6
33.9
4.6
1.6
29.5
27.8
4.1
1.1
27
25.1
3.6
0.9
27.5
25.6
3.7
0.9
31.7
27.6
4.7
1.3
35.1
32.8
5.7
1.9
21.7
20.4
19.5
82
13.8
78
9.0
74
5.4
70
6.1
71
10.7
77
16.3
82
FEB
MRT
APR
MAY
JUN
Lat. 2935S
JUL
AUG
25.0
50.6
3.2
1.6
25.0
49.1
3.2
1.6
24.3
46.5
3.0
1.4
22.7
38.4
2.8
1.1
20.8
33.0
2.5
0.8
19.0
28.4
2.2
0.6
19.2
27.7
2.2
0.6
20.8
29.4
2.5
0.7
22.3
35.2
2.7
0.9
14.0
13.6
12.1
70
7.8
67
4.0
63
0.3
60
0.1
60
2.3
63
6.2
66
STATION B
JAN
Tmx
RHmn
es
e
Td
THI
o
C
%
kPa
kPa
o
C
Long. 3024E
SEP
OCT
Alt. 775 m
NOV
DEC
35.3
40.6
5.7
2.3
34.9
42.4
5.6
2.4
35.4
44.3
5.7
2.5
19.9
84
20.2
21.4
Long. 3017E
SEP
OCT
Alt. 1075 m
NOV
DEC
22.6
43.4
2.7
1.2
23.5
46.8
2.9
1.4
24.7
48.4
3.1
1.5
9.5
67
11.5
13.1
1
QUESTION 2
IRRIGATION – SAPWAT
(10)
Describe the steps followed to use SAPWAT model to select best irrigation
scheduling programme.
QUESTION 3
REMOTE SENSING
(20)
a) Describe how LANDSAT-7 satellite imagery can be used to identify and monitor
the state of agricultural crop production in a certain region.
(7)
b) Tabulate the differences between polar orbiting and geostationary satellites.
(8)
c) Study the Radar image in Figure 3.1. What type of weather is occurring in the
vicinity of Ixopo (100 km west of Durban) at the time of the image? Motivate
your answer by referring to the observed reflectivities, associated rainfall rate,
special echo structures and your theoretical knowledge of rainfall-producing
weather systems.
(5)
Figure 3.1: Radar reflectivity image of southern KwaZulu Natal at 14:00 UTC on 2007-0221 (copyright, SAWS).
QUESTION 4
INTEGRATED PROBLEM-SOLVING
(10)
Study the information given (Tables 4.1, and 4.2) for a mixed farming-setup in
location A and explain how the microclimate can be manipulated for optimum farm
management. Following steps a) and b), include crops, stock and human activities
and give at least three examples. You may tabulate your answers.
a)
Identify possible problems.
b)
Describe how you would manipulate the climate/circumstances to solve
each problem.
2
Table 4.1
Long term data for station A.
Station
A
198m
3234S
1859E
34y
JAN
FEB
MRT
APR
MAY
JUN
JUL
AUG
SEP
OCT
NOV
DEC
Tmx
oC
27.70
28.30
27.40
26.90
22.50
19.10
18.50
19.60
22.40
23.50
25.20
26.10
Tmn
oC
17.10
17.40
16.20
13.10
9.40
6.80
5.90
7.10
8.90
11.60
14.20
16.00
Rain
mm
7.10
8.50
14.70
36.30
52.90
77.60
66.10
57.10
31.10
22.90
13.40
13.60
Epan
mm
362.30
302.10
268.40 165.60
91.30
58.40
61.30
91.80
139.50
224.90
298.40 342.80
Sunhr
h
km.d-1
10.80
10.00
8.70
7.20
5.90
5.10
5.40
6.20
6.80
8.20
9.80
Wind
8.02
7.28
6.39
4.95
3.73
3.48
3.60
4.67
5.23
6.36
7.34
7.73
RHmx
%
77.70
76.70
78.40
82.30
90.20
93.00
93.30
91.20
89.70
83.00
78.20
78.10
RHmn
%
30.10
31.70
32.30
36.40
41.20
45.90
45.20
42.90
39.20
34.20
30.40
31.40
Tavg
oC
24.80
24.90
23.50
20.00
16.00
13.00
12.20
13.30
15.70
18.70
21.60
23.50
satvap
kPa
3.71
3.85
3.65
3.54
2.73
2.21
2.13
2.28
2.71
2.90
3.21
3.38
vappres
kPa
1.12
1.22
1.18
1.29
1.12
1.01
0.96
0.98
1.06
0.99
0.97
1.06
Tdew
oC
8.61
9.89
9.39
10.74
8.67
7.19
6.42
6.66
7.85
6.83
6.60
7.85
THI
72
73
72
72
67
63
62
63
66
67
69
70
Lowveld FDI
Yellow
Yellow
Yellow
Green
Green
Green
Green
Yellow
Green Green Green Green
10.40
DI
88
90
88
88
78
71
69
72
78
79
82
84
TT
444
447
405
300
180
90
66
99
171
261
348
405
Table 4.2
Crop requirement information for Station A.
First frost date
Last frost date
Planting date
TT - Germination
TT - Crop growth season
Length of crop growth season
Date
12-Jun
23-Aug
-
Maize
01-Nov
300
1700
120 d / 4 mnths
Wheat
01-Jun
110
1200
180 d / 6 mnths
__________________________________________________________________
SECTION B
CHOICE QUESTIONS
[50]
You must answer 5 questions from this section. Choose between:
QUESTION 5
OR
QUESTION 6
QUESTION 7
OR
QUESTION 8
QUESTION 9
OR
QUESTION 10
QUESTION 11
OR
QUESTION 12
QUESTION 13
OR
QUESTION 14
AND
AND
AND
AND
QUESTION 5
DISCOMFORT INDEX
(10)
You are required to organize an event for farmers and their families in the Limpopo
Province. The event is scheduled for one of the months from November to
February.
a)
Calculate Discomfort Index (DI) from November to February.
(8)
b)
Pick the correct month and correct place for the event, from the two possible
locations given, using the data in Table 5.1. Motivate your answer. (2)
3
Table 5.1
JAN
Station X
FEB
MRT
APR
MAY
JUN
JUL
AUG
1345m
SEP
2644S
OCT
2705E
NOV
84y
DEC
C
28.0
27.0
27.1
24.6
21.6
18.8
19.2
22.1
25.9
27.8
25.0
27.0
C
mm
mm
h
%
%
o
C
15.8
109.6
227.7
8.7
84.5
24.0
15.2
94.1
185.1
8.7
86.1
23.0
13.4
81.5
170.3
8.1
87.6
35.0
9.1
46.0
133.1
8.2
88.4
33.1
4.1
19.0
114.0
8.6
84.4
29.5
0.4
7.5
93.1
8.4
83.9
29.6
0.3
7.2
112.0
8.8
80.1
29.4
3.1
9.5
156.3
9.4
73.3
27.3
7.8
17.7
208.2
9.4
70.6
27.2
11.6
53.0
235.5
9.0
77.1
30.3
13.4
80.6
231.8
9.0
81.0
20.0
15.0
101.0
246.9
9.2
83.9
22.0
22.6
21.9
20.3
88
16.9
81
12.9
74
9.6
67
9.7
68
12.6
74
22.1
Station Y
FEB
MRT
APR
MAY
JUN
JUL
AUG
19.7
88
2305S
OCT
20.9
JAN
16.9
83
610m
SEP
3017E
NOV
30y
DEC
C
29.3
28.6
28.0
26.5
25.0
22.7
22.8
24.5
26.9
27.2
27.8
28.7
C
mm
mm
h
%
%
o
C
19.3
174.0
148.3
7.3
87.5
43.2
19.1
162.0
131.6
6.9
90.7
44.5
18.1
121.0
131.3
7.1
90.8
44.0
15.8
57.6
113.3
7.4
86.0
38.8
12.8
22.4
112.6
8.2
80.3
34.8
10.1
17.0
101.5
8.0
75.8
32.2
10.0
10.2
111.4
8.2
76.3
31.4
11.7
13.5
132.6
8.2
74.2
30.8
14.2
30.8
157.3
8.3
74.1
31.9
15.9
64.1
157.6
7.5
79.0
37.4
17.3
102.4
154.0
7.3
82.8
40.7
18.5
147.7
157.9
7.4
84.9
41.4
24.3
23.9
23.1
92
21.2
87
19.0
83
16.4
77
16.4
77
18.1
81
20.5
86
21.6
89
22.6
23.6
Tmx
o
Tmn
Rain
Epan
Sunhr
RHmx
RHmn
o
Tavg
DI
Tmx
o
Tmn
Rain
Epan
Sunhr
RHmx
RHmn
o
Tavg
DI
Discomfort Index (DI) for January till December for Stations X
and Y.
OR
QUESTION 6
PESTS AND DISEASES
(10)
Consider the study by Johrar, et al., 1997 on the prediction of Asochyta blight
disease of chickpea in India and discuss how the humid thermal ratio (HTR) was
used in the prediction. Include in your discussion objectives, methods, results,
analyses, conclusions and topics such as disease index (DI), correlations, SMW
(standard meteorological week), graphs, prediction, observation, model testing,
timely warning, etc.
(10)
__________________________________________________________________
AND
QUESTION 7
FROST
(10)
A frost transect was done for 4 stations in the winter of 2006 in a South African city
suburb (Table 7.1). Station E shows the data from the South African Weather
Service (SAWS) for the city. Using the table and your knowledge of frost in different
environments and with changing weather conditions, explain the differences
between the stations in terms of topography, altitude, aspect and site.
4
Table 7.1
Date
Maximum (Tmx) and minimum (Tmn) temperatures for two days in
2006 (08/05/06 and 10/05/06) for a city suburb with stations A - D
situated along a transect (slope on a hill) and station E
representing South African Weather Service (SAWS).
Temperature
(oC)
Station
A
B
SAWS
C
D
E
Height above sea-level (m)
08-05-06
10-05-06
1000
1200
1350
1400
1351
Tmx
8.53
9.42
14.47
19.04
14.9
Tmn
-4.82
-2.44
-0.61
0.29
-4
Tmx
17.52
21.71
22.86
24.79
22
Tmn
-1.51
-1.06
2.46
5.4
-2.9
OR
QUESTION 8
HEAT AND COLD UNITS
(10)
Suppose you are given a long-term weather data set with daily minimum and
maximum temperatures, as well as rainfall in an Excel spreadsheet program.
Explain how you would go about determining the germination, emergence and
harvest dates of the wheat cultivar in Table 8.1 Planting should commence on 1
June 2008.
Table 8.1
Requirements for a wheat cultivar.
Crop
Tb
TT Germination
TT Emergence
TT harvest
Wheat
2 ºC
20
61
900
AND
QUESTION 9
SHORT TERM FORECASTING
(10)
You are appointed as an agricultural consultant and one of your clients farm with
broiler chickens in the south-western Limpopo Province. Study the short-term
forecast (Table 9.1) and attached synoptic weather chart before answering the
following questions:
a) Describe the weather that is expected over the particular area and explain the
problems that it may have in store for the specific farming activity.
(2)
b) Identify and describe the weather system(s) responsible for the weather
described in (a).
(4)
c) Discuss the possible management decisions that can be made in order to
alleviate the negative impacts of the weather or to make optimal use thereof
(whatever the case may be).
(4)
5
Discussion
Issued on 2001-01-12
Currently, very hot conditions are experienced over most of the interior with
isolated thundershowers expected to the east of the surface trough located
over the central interior. Cloudy conditions with rain is moving in along the
Cape south coast where strong south-westerly winds are blowing ahead of an
approaching cold front to the southwest of the country.
On the 13th the cold front, associated with strong winds, is expected to move in
over the western interior producing cloudy conditions with scattered showers
over the western and south-western parts of the country, spreading to the
Eastern Cape. Partly cloudy and hot conditions with isolated thundershowers
are expected over the north-eastern interior.
By the 14th the cold front should have moved to the eastern Free State and
southern KwaZulu Natal with the onshore flow behind it causing cloudy, cool
and rainy conditions over the Eastern Cape. Strong south-westerly winds are
expected along the southeast coast, reaching gale force at times. Scattered
thundershowers are expected over Mpumalanga and KwaZulu Natal to the
east of the surface trough. Cloudy conditions with light rain are expected along
the Cape south coast due to an onshore flow.
The cold front will slide out to the east of the country by the 15th with fresh to
strong south-westerly winds along the southeast coast where it will be cloudy.
Cool conditions are expected to continue over the southern parts, whilst hot
conditions should persist over the northern interior.
On the 16th an influx of moist air from the east will cause cloudy and cool
conditions in the Lowveld with drizzle along the eastern escarpment. It will be
partly cloudy over the Highveld, otherwise fine and hot becoming cloudy along
the southwest coast due to the onshore flow ahead of a new approaching cold
front.
6
Table 9.1
5-Day Forecast for Thabazimbi (SW Limpopo Province).
Date
Cloud
cover
Weather
Tmin
Tmax
Wind
2001-01-12
Partly
cloudy
Isolated
thundershowers
23
40
Light NE
2001-01-13
Partly
cloudy
Isolated
thundershowers
23
38
Light becoming
moderate NE
2001-01-14
Partly
cloudy
Nil
23
40
Light NE becoming
moderate NW
2001-01-15
Partly
cloudy
Nil
24
41
Moderate NW
becoming SW
2001-01-16
Cloudy
Nil
26
37
Moderate NE
OR
QUESTION 10
FIRE DANGER INDEX
(10)
a) Make use of the attached nomogram and the data supplied in Table 10.1 in
order to calculate the expected Lowveld Fire Danger Index (FDI) for Wellington.
(3)
Tomorrow’s weather forecast for Wellington.
Table 10.1
Parameter
Unit
Forecast value
Tmx
ºC
32
Tmn
ºC
14
RHmx
%
56
RHmn
%
38
Rain
mm
0
Wind
km/h
16
NOTE: The last rainfall in Wellington was 13 mm and occurred 5 days ago.
b)
The following cut-off values are employed in the Lowveld Fire Danger Index:
0 - 20:
21 – 45:
Blue
Green
46 – 60:
61 – 75:
≥ 76:
Yellow
Orange
Red
7
State which fire danger rating you would allocate to Wellington for tomorrow and
discuss the expected fire behaviour and recommended fire control measures which
apply.
(7)
AND
_
QUESTION 11
DROUGHT
(10)
Use your knowledge of the “10-point Drought Plan” to answer the following:
a)
List government departments and parastatals (at all levels) that need to be
involved in the task team.
(5)
b)
Compare and contrast the different aims and objectives one would need for
a rural versus an urban area.
(5)
OR
QUESTION 12
SEASONAL FORECASTING
(10)
Describe the procedure (or steps) needed to help farmers to be able to use the
seasonal forecasts.
AND
_
QUESTION 13
MICROCLIMATE MANAGEMENT
(10)
Consider the course presented by Prof. C.J. Stigter and answer the following
questions:
a)
Give an example of a cropping system where tillage is preferred.
(1)
b)
Give an example of a live mulch.
(1)
c)
Briefly explain 2 ways, other than tillage or live mulch in which heat- and/or
moisture flow can be manipulated.
(8)
OR
QUESTION 14
AGMET SERVICES
[10]
Consider the course presented by Prof. C.J. Stigter from 25/02/08 to 29/02/08 titled
“Agrometeorological Services: Theory and Practice.” Select one of the themes
discussed and describe how you would apply the knowledge gained, to develop an
Agromet service for a group of farmers in an area of your choice.
8
FORMULA SHEET
FORMULEBLAD
p  RT
R  287 Jkg 1 K 1
E  T 4
E  T 4
 1
2897
 max 
T
Rn  S t  r S t  S e   tSe  Ld  Le  Lb  0
  5.67  10 8 Wm 2 K 4
S  aS  rS  tS  vS
St  Sb  S d
 va     Ta  Tw 
aC p
 
 0.5 gm 3 K 1  0.066 kPaK 1
Lv
e  es   Ta  Tw 
1 Atmosphere  1013.3 hPa
'
va
C p  1010 Jkg 1  C 1
Lv  2.50  10 6 Jkg 1
e

RH  a  100  va'  100
es
 va
es  0.6108  e
ea  A  B
A  0.6108  e
ea
0.6108
ea
1  0.0579 ln
0.6108
273.16  2.0765 ln
 psy  a psy P
 17.2694Tw 


 237.3Tw 
B  0.066Ta  Tw 1  0.00115Tw 
SD  es  ea     va  VT
'
va
Td  273.16 
 17.2694Ta 


 237.3Ta 
ea  e 0 Tw    psy Ta  Tw 
for ventilated Asmann type psychrometer apsy = 0.622×10-3
900
u 2 e s  ea 
0.408Rn  G 
T

273
ET0 

   1  0.34u 2 
   1  0.34u 2 

es at Ta
Rn  Rns  Rnl
All radiation parameters are in MJm-2d-1
Rns  1 0.23Rs
0.23 is the albedo for a well-watered short grass surface
n

Rs   a s  bs  Ra where
N

bs  0.50

no
calibrated
values
are
available,
a s  0.25

Rs 0  0.75  2  10 5 z Ra


Tmax K  Tmin K 4 


Rs
Rnl  
 0.35 
 0.34  0.14 ea 1.35
2
Rs 0




ETc  K c  K s  ET0
ET  P  I  S  SF  CR  R  DP
4
 T  Tmn

TT   mx
 Tb   t
2


FDI  BGI  BI  WF   RCF
 RH mn

DI  OBI  2  Tmx   
 Tmx   24
 100

THI  Tmx  0.36Td  41.2
old WCI  nou WVI  (0.2136 V  0.2637  0.0183V )(1.8T  59.4)  33



new WCI  nuwe WVI  13.12  0.6215T  11.37 V 0.16  0.3965T V 0.16

9
10