THIESSEN POLYGON AND ISOHYET CONTOUR METHODS FOR MEASURE AND COMPARE THE PRECIPITATION MEAN
THIESSEN POLYGON AND ISOHYET CONTOUR METHODS FOR MEASURE AND COMPARE THE PRECIPITATION MEAN
A brief practical report
Below is the example of the precipitation mean measurement using thiessen polygon, and isohyet contour methods. Both methods is commonly used in climatology. The result of thiessen polygon and isohyet contour methods shown in figures below :
Tabel 1. Measurement of precipitation depth using Thiessen Polygon
Station
24-hours
Total Area
Weighted ppt
(mm)
unit
(%)
(mm)
A
78
0.05
0.3
24.04438964
B
115
1.7
10.5
1205.302096
C
140
3.8
23.4
3279.901356
D
165
2.1
12.9
2136.251541
E
150
0.95
5.9
878.5450062
F
90
3.4
21.0
1886.559803
G
175
1.8
11.1
1942.046856
H
155
2.42
14.9
2312.577065
Total
1068
16.22
13665.22811
∑ Pn
The average of preciputation depth =
∑ area = 13665.23 / 16.22
= 842.4925 mm
Tabel 2. Measurement of precipitation depth using Isohyet Contour
Station
Group
Total Area
Weighted ppt
Median
unit
(%)
(mm)
80 - 90
85
0.02
0.092208391
7.837713232
90 - 100
95
0.27
1.244813278
118.2572614
100 - 110
105
2.1
9.681881051
1016.59751
110 - 120
115
2.5
11.52604887
1325.49562
120 - 130
125
3.5
16.13646842
2017.058552
130 - 140
135
5.2
23.97418165
3236.514523
140 - 150
145
3.7
17.05855233
2473.490088
150 - 160
155
1.9
8.759797142
1357.768557
160 - 170
165
0.7
3.227293684
532.5034578
170 - 180
175
1.8
8.298755187
1452.282158
Total
1300
21.69
13537.80544
∑ Pn
The average of precipitation depth =
∑ area = 13537.8 / 21.69
= 624.15 mm
CONCLUSION
The result showed the difference between both measurement. This may happen when we use a bigger grid size. The accuracy decrease since the grid cannot cover the area border precisely .
Thiessen Polygon Method is simpler than isohyets contour. Isohyet method is more complex and may...