Vízügyi Közlemények, 2001 (83. évfolyam)
3. füzet - Nováky B.-Goda L.-Domokos M.-H. Bergmann: Éghajlatváltozási hatások keresése a Felső-Rába vízgyűjtőjében
Eghaj latváltozási hatások keresése a Felső-Rába vízgyűjtőjében 425 The typifying of the runoff regime of the watercourses has been carried out, first, in the traditional way, i.e., on the basis of the wthin-the-year distribution of the monthly mean discharges (Table /): the regions of the three types of runoff regime are identified on the map of Fig. 2. The second method of typifying was based on the so-called discriminant-periods , i.e. on the fact, in which of these three-months-periods the first, second and third biggest and the first, second and third lowest monthly discharge of a given river section occurs with the highest frequency (Table II, Fig. 3). There are three well-known indices — all of them also based on the discriminant-periods — characterizing the stability of runoff regime: the entropy-index H of Shannon [Eqs. (1) and (2)], the index CS of СогЬщ [Eqs. (3) and (4)] and the modified version of the Shannon -index, H*. introduced by the Authors of this paper [Eqs. (5) and (6)]. From these three indeces, CS and H* have been used, by taking into account the empirical intervals of Table III. The qualification of the stability of the the investigated 24 sub-catchments is displayed in the Tables IV, V and VI while a regional generalization of a CS-based qualification can be seen in Fig. 4. In order to compare the trends existing in the observed data series a (possibly long) basis period had to be found; finally the period 1966-1968 was selected. Consequently, the discharge data series of the 11 gauging stations (out of 25), where observation had been started after 1966, had to be extended backwards by using the optimal ones of the regressions established between the not sufficiently long data series and the longer ones in their neighbourhoods (Fig. 5, Table VII). For the annual and seasonal mean values observed at the 20+66+25 stations, trend equations according to Eq. (8) have been determined, for which a graphical example is shown in Fig. 6. The standardized steepnesses, expressed in %/year, of the trend equations of the 25 discharge data series are shown in Table VIII. It is seen that although the steepnesses of most annual, winter, spring and summer trend equations are negative, their absolute values cannot be called significant. A survey of the signs of the steepnesses of the trend equations of the temperature, precipitation and discharhe data series is offered in Table IX. Beside the data series beginning in 1966, also the 48 years long series (starting in 1951 ) of the annual mean discharges of 10 stations have been investigated (Table X). A comparison of these data with those of Table VIII shows that while the sign of steepness raemined negative at most stations, its absolute value further diminished with the increasing length of observation. In order to establish relationships between the multiannual mean runoff of the sub-catchments of the Upper Raab River and the related climatic elements, first areal mean values of temperature and precipitation had to be computed. When computing the temperature values, use has been made of the relationship (9) between the mean temperature т and the hight Z above sea level as well as of the data of hypsographic distribution of the sub-catchments (Table X/).The areal mean values of precipitation P have mostly been computed as arithmetic averages of the values measured in the rather dense network of stations, and if necessary, by using the empirical relationship ( 10). The potential évapotranspiration £ ma x was estimated from Eq. (15) (Fig 7), while the value of (specific) runoff R could be derived directly from the observed values of the gauging stations. Table XII contains the thus computed values R. P and E m m as well as the runoff coefficients r| and the aridity coefficients a for all the 24 sub-catchments investigated. (The relationship between the latter two coefficients is displayed in Fig. 8). The final scope was to calibrate the formula of Budiko for the Upper Raab Catchment. The result is Eq. (16) whose reliability can be checked by comparing the values in the fourth and last column of Table XII. The equation (16), describing, according to Fig. 9, the structure of the average water household of the catchment, has also been adopted in Table XIII to estimate the impact of a hypothetical scenario of climate change onto the runoff conditions. # * *
