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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) 1 - 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). 3 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 4 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) 5