SPATIAL-TEMPORAL EVALUATION OF MAXIMAL QUANTITY OF PRECIPITATIONS FOR HYDROLOGICAL CALCULATIONS AND FORECASTS Nataliia Pryimachenko, Mykhaylo Sosedko Ukraіnіan Hydrometeorologіcal Research Institute Pr. Nauky 37, Kyіv 03028 Ukraіne [email protected]; [email protected] Abstract The score of the maximal precipitations only then have a value if it is known their repeatability or probability of approach. Such estimations can be received through statistical generalization of homogeneous data in time and space. Nevertheless in many publications and directories it is not attending appropriate attention to data which are processed. Therefore value of similar generalizations is not enough high, as data are lost on intensity of precipitations. Keywords: maximum quantities, precipitations, mountain part, homogeneous districts. 1 HETEROGENEITY OF THE MAXIMAL DAILY QUANTITIES OF PRECIPITATIONS Widespread enough characteristic of precipitations is the maximal daily quantity. This value is estimated by summation of quantities of precipitations for terms of observation during a meteorological day. Therefore separate parts of the same rain can get in P m contiguous day. Thus daily quantities of precipitations d mainly will be smaller, than maximal for 24 hours, which cover the interval of their fall which has been not attached P m to constant initial time reckoning - 24 . A ratio between these values of the maximal precipitations is defined by an inequality (Sosedko, 1980): m m m 5,0 P24 Pd P24 . (1) In table 1 are resulted comparisons of daily and 24-hours maximum quantities of precipitations for a flood in November, 1998 in the Tisza river basin. So, for the values of the maximal daily quantities of precipitations is inhere the uncertainty caused by the way of their receiving. 2 SPATIAL GENERALIZATION OF MAXIMUM QUANTITIES OF PRECIPITATIONS At generalization of the maximal precipitations quite often mixes up the variation in space with variation in time. If are analyzed data about precipitations within the limits of homogeneous physiographic area where weather situations are predetermined for the long-term period by the same atmospheric processes, genetically and statistically wrongfully to carry sequences of the given separate items of observation to different general totality. In such cases statistical sequences of data of each station which are in one area, it is necessary to consider as realization of one general totality. P m Table 1. Maximum quantities of precipitations for meteorological day d and 24-hours P m interval 24 in the Tisza river basin (4-5.11.1998) Measurement items of m m Difference Pd P24 precipitations m m P24 - Pd Rakhiv 64 78 14 Jasinia 53 76 23 Luhy 47 59 12 Ust-Chorna 135 137 2 Ruska Mokra 163 171 8 Kolochava 95 117 22 V.Bystry 57 95 38 Mizhhiria 113 157 44 Maidan 73 119 46 Repinne 84 133 49 N.Studeny 43 86 43 Pidpolozia 63 89 26 Mukacheve 59 67 8 Chop 25 34 9 Zniacovo 47 59 12 V.Berezny 26 41 15 Zaricheve 44 60 16 Uzhhorod 22 35 13 Simer 43 51 8 N.Vorota 45 72 27 Plai 83 107 24 In such cases it is possible to receive precise representation about temporal and spatial distributions of the maximal precipitations through the regional curve distributions of the probabilities constructed by a period’s method on incorporated sequence of homogeneous temporal sequences, i.e. by unification of several items of observation [1- 3]. Such unification is possible, as intensive precipitations in different items of area practically are not connected among themselves. Means, that in the certain area is observed the same mode of precipitations, they are only distributed on territory casually. The same exceedance probability of maximum precipitations is characteristic for the territory of all area (Alekseev, 1971; Gruza et al.,1982; Kobysheva et al. 1980). According to the method of period-ststions elements of partial sequences are united in uniform space-time variation. If the dimension of everyone extracts (realization) is N equaled to ni , the incorporated regional totality reaches volume : im (2) N ni , 1 where m - quantity of extracts (partial sequences, items of observations). The further processing are carried out, as usual, by data ranging on their value and construction of theoretical or empirical curve of exceedance probability. As an example, is resulted distribution of the maximal precipitations for a mountain part of the Dnister river basin (the area is 14 thousand square kilometers). Here are allocated 6 homogeneous areas behind the precipitations, caused by features of an arrangement of Carpathians mountains: (1) Upper Dnister, (2) Middle Podnistrovye, (3) East Beskidy, (4) Skolevski Beskidy, (5) Gorgany, (6) Vododilno-Verhovyna area. The quantity of observations items after precipitations represents in each area 4-6. Estimations of the maximal precipitations of 1 % exceedance probability for 12 hours calculated for these areas by the period’s method are within the limits of 69-110 mm (table 2). The maximal precipitations of 5 % exceedance probability are oscillated on the allocated areas from 50 up to 75 mm for 12 hours. Table 2 - Maximum quantity of precipitations on a right bank of Dnister Exceedance Precipitation total for 12 hours, mm probability 1-st area 2-nd area 3-rd area 4 area 5 area 6 area 0,2 % 100 145 155 160 162 103 0,5 % 83 110 126 124 128 86 1 % 69 88 107 103 110 76 2 % 60 71 90 84 93 67 5 % 50 56 72 64 75 57 The incorporated regional sequences described above statistically more steady, they consider probabilities of the rare values of the maximal precipitations which were observed only in separate items. And these rare values, undoubtedly, are the most valuable in theoretical and practical attitudes. They display conditions of heavy shower activity and characterize intensity of processes which predetermine a mode of precipitations in the certain physiographic area. 3 CONCLUSIONS 1. Statistical representation of totality of the maximal daily quantities of precipitations wrongfully as their elements are generated from non-uniform values in the genetic attitude and is not displayed with the rare sizes of precipitations. 2. Representation of maximal for the certain time interval quantities of precipitations in separate items of observations without estimation of their probabilities and spatial distinctness cannot serve as a climatological parameter. 3. To obtain valuable data in the informative attitude about maximum quantities of precipitations for the certain time interval (12, 24 h.), it is necessary to work on them by period’s method on homogeneous areas in the physiographic attitude. Such generalization allows obtaining authentic data concerning space-time mode of precipitations. References Alekseev G. A. (1971): Objective methods of smoothing and normalization of correlation connections. - L.: Gidrometeoizdat. - 364 p. Gruza G.V., Reytenbach R.G. (1982): Statistics and analysis of hydrometeorological data. - L.: Gidrometeoizdat. - 216 p. Kobysheva N.V., Kostin S.I., Strunnikov E.A. (1980): Climatology. - L.: Gidrometeoizdat. - 344 p. Sosedko M.N. (1980): About principles of definition of the maximal layer of precipitations for a calculated time interval // Meteorology and hydrology. - № 10. - 39-43 pp..