Vízügyi Közlemények, 1958 (40. évfolyam)

4. füzet - VII. Kisebb közleménye

(39) de tailed records covering a sufficiently long period for evaluation are available for no more than one of these (see Table I ). Therefore, computations based on observed meteorological data had to be relied upon in the first order. The relative evaluation of data compiled in Table IV showed the relation expressed by Eq. (1) and developed by A. F. Meyer suitable for practical compulations. The basic data necessary for the use of this relation are (a) the surface temperature of water (t' C°), i. е.* the relationship between monthly mean temperatures of water and air t' = f (t); (b) data relating to the humidity of the air, i. e. E (t' ), the saturation vapor pressure pertaining to the prevailing water temperature, and the actual vapor pressure (e, mm); and finally (c) the monthly mean wind-velocity values (v, m/sec) for the whole country. (In order to facilitate the use of the formula, graphs shown in Figs. 15 and 16. have been constructed.) A practically accurate correspondence between computed results and observation data in Table IV has been attained by adjusting water-temperature values according to Fig. 2. The exact adjustment of the formula used for computation became necessary to establish a basis of comparison for values computed for other regions of the country and for observation data used as initial values. The absence of an adequate number of w a t e r temperature data has been compensated for by determining the average annual march of the difference between the air temperature t and the water temperature I' observed in a pan having an area of 1 sq. m (Fig. 2). The series of differences thus obtained has been transferred to other regions by reducing these differences (t'

—t) according to the ratio of average annual temperature ranges characteristic for individual regions. (The annual temperature range is understood as the difference between the mean temperatures of the warmest and coldest months of the year observed for the region in question.) No detailed data on the moisture content of the atmosphere, resp. on the relative humidity were available. Furthermore, owing to differences in instruments and environment disregarding numerous faulty observations records arc frequently inhomogeneous, and, consequently, this factor too had to be determined by indirect methods. Long-period averages of monthly mean temperatures and relative humidity values were collected for 31 representative observing stations within the Carpathian Basin (Table II). A statistical relationship between corresponding t and r values has been determined as shown by the example in Fig 3. Summarizing monthly curves of best lit for individual regions, results shown in Figs. 4 and J, were obtained. These statistical relationships in addition to being simultaneously climatic characteristics as far as humidity conditions are concerned — permit the determination of the most probable relative humidity value for every observing station in the country, provided that the mean temperatures are known. Results can be represented also in the form of maps (Fig. 0). Monthly mean wind velocities have been assumed as constant over the two main regions of the country (see Table 111), since long-period averages were found to vary between but relatively narrow limits and, moreover, the effect of wind velocity is only entered with a coefficient of 0,20 into Eq. (1). Basic data, respectively statistical relationships presented in Figs. 2, 4 and 5, respectively, in Table III revealed the possibility of deriving a definite relationship between the Ion g peri od averages of monthly mean temperatures and monthly evaporation values (Fig. 7) practically for the entire country. Results of computations applying to average evaporation from a 1 sq. metre pan are compiled in the map presented in Fig. 8. These values have been transferred to natural water surfaces — primarily to fish-ponds and small reservoirs — in accordance with foreign results shown in Fig. 1, by using a correction factor of 0,70 (see Fig 9). For mountainous regions of the country the approximate value of annual mean evaporation is plotted against elevation above sea level in the lower part of Fig. U. (Curves at the left and right sides apply to the northern mountainous region and to the western parts of the country, respectively.) Having established the annual total, mean evaporation values for individual months can be computed by the proportionality numbers given in Table V, which were obtained by the method illustrated in Fig. 10. With reliable average tempe-