Geoscience Reference
In-Depth Information
The interpolation of the different statistical parameters characteristic of rainfall,
which are used as geographical information, is a method that is recognized and used
globally. The same is also true for the method used to calculate the different
averages of the rainfall levels (such as arithmetic average and median), and for the
method used to calculate dispersion parameters (or gradex), as well as the method
used to work out the decennial total rainfall.
7.2.3.3. Plotting rainfall levels on a map for a particular month
For the long-term stations (those which have been used more than 20 times to
provide information on rainfall levels for a given month, and in our case this is the
month of December), it is possible to evaluate the median value and with this value
it is possible to generate a map showing the rainfall levels for that particular month.
If the median value is known, it is possible to estimate the value of
σ by using
the following equation:
P
σ
0.2188
P
+
1.5852 (1
e
0.5489
)
P
X
y
Name
Code
Calculated
Median
Median
plotted on
map
Rainfall
Dec 94
Gaussian
(U)
variable
412.3
426.5
459.7
430.2
444.7
464.5
403.6
434.5
465.9
470.6
72.8
79.8
116.3
111.6
91.1
177.8
214.5
234.5
213.3
229.6
BRIDA
SEBGAG
CENTER
SIDI BOUZID
GUELTAT SIDI
SAAD
AFLOU SECTOR
ZMALET EL
AMIR AEK
AIN BAADJ
RECHAIGA
KSAR
CHELLALA
SIDI BOUDAOUD
10101
10102
10204
10205
10208
10502
10701
10703
10704
10706
14.67
9.81
8.11
0
0.2
0
0
3.5
0
12.4
11.4
3.9
10.6
-1.58
-1.19
-1.29
-1.32
-0.34
-0.92
-0.65
-0.36
-0.48
0.22
8.56
6.74
3.10
28.28
18.31
7.72
9.35
Table 7.2. An extract taken from the observations that were recorded in December 1994
In this section we will focus on rainfall levels for the month of December 1994,
which can be seen in Table 7.2. The same type of table was generated for the other
359 months that were used in the study that took place between September 1965 and
August 1995. For each measurement that was recorded in the month of December
1994 the median value for rainfall was known. This value was known, irrespective
of whether the measurement was taken from a long-term station or from a station
that was only used for a particular month.
For example, if we take a closer look at the long-term station of Rechaïga, we
can see that the total level of rainfall for the month of December 1994 was 11.4 mm.
The median rainfall value for the month of December (and which was measured
 
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