Download Changes in the precipitation at Keszthely according to the

CHANGES IN THE PRECIPITATION AT KESZTHELY ACCORDING TO THE
MEASUREMENT OF 130 YEARS
Tímea Kocsis
Veszprém University Georgikon Faculty of Agriculture
Department of Meteorology and Waterworks
Keszthely, Festetics Str. 7.
E-mail: [email protected]
Precipitation in Hungary and its possible changes in the future
Trewartha – after viewing the climatic picture of the Earth – classified our country as a
moderate-climate zone, as continental climate with longer warm period. This climate type has
capricious temperature, and its seasonal and monthly weather is very variable. According to
the previous measurements the major part of the precipitation felt during the summer time, but
recently we can reed about the move of this state (Pálvölgyi 2000). Our country represents the
border between the wet- and dry-clime areas. In opposite of Hungary’s small area, its
precipitation-conditions show differences. The extremities are the West-Transdanubian
region’s abundance of rainfall and the Great Plain region’s low precipitation supply.
According to this state our moistest areas gets double amount than the driest regions. The
maximum value of the precipitation is expected between May and July in Hungary.
Nowadays we can hear about the decreasing level of the precipitation’s amount as one
of the possible consequence of the global warming. Especially in the temperate zone, the
falling quantity of rainfall has possibly larger dimension. In compliance with Mika (2002) for
Hungary a 0,5 K increase of global temperature will accomplish 40 mm less precipitation per
year. 1 K rise of global temperature leads to 66 mm less rainfall a year. Rakonczai (2003)
mentioned as consequences of the global climate change the modification of the yearly
dispersion of the rainfall’s value, changes of the intensity of falling and the territorial
distribution’s mutation.
The place of the research and the goal of it
Keszthely is situated in Hungary, on the Transdanubian region, in the North-West part
of it. Its climate is more balanced and wetter than the East part of the country. When we
examine the climate of the city, we should mention the nearness of Lake Balaton. The lake
has a special effect on the nearby area’s microclimate.
In the research we wanted to answer the following questions: Does the decreasing level
of the precipitation resulted from the effect of the global warming? Is there any sign on the
basis of the long-time series meteorological data of Keszthely for climate (precipitation)
change? Can we notice changes in the seasonal variation of the rainfall?
Methods
We used the monthly and yearly amounts of precipitation measured at Keszthely in the
past 130 years, between 1871 and 2000. For the research we applied the usual linear
regression and running-average regression. Simple climatic-statistic parameters were also
provided by Péczely (1998):
- The range of the temporal row (R): the difference between the maximum (xmax) and the
minimum (xmin) of the data set:
R = xmax-xmin
(1)
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- The fluctuation of the single data (x) around the average (M): the average absolute deviation
(d). We sum the differences without sign, and than we divide the sum with the data’s number
(n):
d = (|x1-M|+|x2-M|+…+|xn-M|)/n
(2)
- The standard deviation (σ): is the mean quadratic difference from the average:
σ = √{[(x1-M)2+(x2-M)2+…+(xn-M)2]/n}
(3)
Results
Simple climatic-statistic parameters describing the long time series of the yearly
precipitation at Keszthely
By studying 130-year-long temporal row of the measured precipitation at Keszthely,
we found that the driest year was 2000 with 392.6 mm, the wettest one was 1937 with 1098
mm amount of rain. The average amount of rainfall during this 130 years is 678,5 + 134,5 mm
(Fig. 1). The range of the data set is 705.4 mm and the average absolute deviation is 104.85
mm.
Precipitation (mm)
1250
1100
950
800
650
500
350
200
97
19
88
19
79
19
70
19
61
19
52
19
43
19
34
19
25
19
16
19
07
19
98
18
89
18
80
18
71
18
Time (year)
Fig. 1 Yearly amounts of precipitation at Keszthely between 1871 and 2000
Representing the yearly amount of precipitation and fitting linear regression trend-line (Fig.
2), it can be established that R2 has a very low value (R2 = 0,0138), so the result shown by the
linear regression (-0,4198) is not significant. According to the slope of the trend-line the value
of the precipitation is decreasing 42 mm in 100 years. This diminishing water-income is not a
negligible fact.
2
y = -0,4198x + 706
2
R = 0,0138
18
71
18
80
18
89
18
98
19
07
19
16
19
25
19
34
19
43
19
52
19
61
19
70
19
79
19
88
19
97
Precipitation (mm)
1200
1100
1000
900
800
700
600
500
400
300
200
Time (year)
Fig.2 The direction of change of the yearly rainfall’s amount at Keszthely
For increasing low R2, we tried to use running-average regression (k=3), but it did not serve
closer relation (higher R2), so we abstain from drawing any conclusion.
Precipitation (mm)
The next step was cutting the 130-year-long time series in 10-year-long periods (Fig.
3), and comparing them with the 130-year-mean. We can ascertain that the last 30 years were
really dry, but this dry period was not unique in the last 130 years.
800
750
10-year-mean
130-year-mean
700
650
600
80
00
0
-2
91
19
60
9
-1
71
19
40
9
-1
51
19
20
9
-1
31
19
00
9
-1
11
19
80
9
-1
91
18
8
-1
71
18
Time (decade)
Fig. 3 The formation of the 10-year-means considering the 130-year-average
The period between 1901 and 1940 had more precipitation than the 130-year-mean.
The 1881-1890 decade was the driest during the measurements, its difference from the 130year-mean is -66.5 mm. The wettest decade was 1901-1910, that’s mean is over the 130-yearmean with 101.9 mm.
Climatic-normal is wildly used index in case of the rainfall too. On the bases of the
climatic-normals we can register a notable decrease of precipitation (Table 1).
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The 30-year-means of the time
series of Keszthely (30-yearclime-normals)
Precipitation,
Peripod’s length
mm
1881-1910
685.97
1911-1940
721.77
1941-1970
664.43
1971-2000
634.15
Table 1 The values of the 30-year-climatic-normals from the beginning of the measurements
to nowadays
Changes in the seasonal amounts of the precipitation
We used linear-regression to represent the changes’ trend in precipitation of each season
(Table 2).
Season
Trend-equation
Spring y=-0.3543x+186,56
Summer y=-0.0541x+226,19
Autumn y=-0.2278x+194,42
Winter
y=0.1798x+99,352
Slope
-0.3543
-0.0541
-0.2278
0.1798
R2
0.0593
0.0008
0.0157
0.0253
Table 2 Changes of the seasonal rainfall
The marks of the slope show us that the amounts of the spring and autumn rains are
decreasing. The value of the summer’s rainfall is practically unchanged. The winter’s
precipitation is mildly increasing. However these results are not significant, also at Keszthely
seems to be proved that, whereas the seasonal dispersion of the rainfall’s yearly amount is
changing as one of the global warming’s effect.
According to the standard deviation (SD) we can state that the rainfall of the summer is
the most variable and the less alterable is the winter (Table 3).
Examining the difference between the seasonal 130-year-mean and the single year’s
data, the alteration - except the winter - is decreasing during the period. Thus the variability of
the quantity of the precipitation is falling in the spring, in the summer and in the autumn. In
opposite winter’s variability is increasing, so it is possible that there will be more or less
precipitation that expected.
Spring
Summer
[mm]
222.6
73.64
479
87
392
60.3
Autumn
Winter
Mean
163.4
179.5
111.1
SD
54.83
68.52
42.61
Maximum
347
412
229
Minimum
45
45
31
Range
302
367
198
Average absolute
42.9
53.7
34.3
deviation
Table 3 Descriptive statistical parameters of the 130-year-long time series
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Development of the monthly amount of precipitation
The value of the precipitation, after its minimum in February, is continually increasing
until its maximum in May-June. We know that this tendency is very good for the agricultural
cultivation, because with the increasing temperature it is favorable for the plant’s water
demands. After the summer maximum there is a recordable secondary maximum in the
autumn at more station in Hungary. This secondary maximum seems to vanish at Keszthely.
The monthly amounts of the precipitation seem to be equilibrated in quantity (Fig. 4).
Precipitation (mm)
1871-2000
90
80
70
60
50
40
30
20
10
0
I.
II.
III
IV.
V.
VI. VII. VIII. IX.
X.
XI. XII.
Tim e (m onth)
Fig. 4 Averages of the monthly rainfall at Keszthely
Literature
Mika, J. /2002/: About the global climate change: From the point of view of a meteorologist
In: Physical Review Vol. 52. : 258-268. (in Hungarian)
Pálvölgyi, T. /2000/: The environmental challenge of the new millennium: the climate change.
Environment and Society, Sceneries of 21th century, L’Harmattan Publisher, Budapest:
39. (in Hungarian)
Péczely, Gy. /1998/: Climatology. National Publisher of schoolbooks, Budapest (in
Hungarian)
Rakonczai, J. /2003/: Global environmental problems. Lazi Publisher, Szeged: 168-170. (in
Hungarian)
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