Vízügyi Közlemények, 1998 (80. évfolyam)
3. füzet - Csepregi A.-Liebe P.-Varga Gy.: Magyarország vízkészleteinek állapotértékelése
416 " Csepregi A— Liebe P.-Varga Gy. Assessment of the state of water resources of Hungary by András CSEPREGI, Päl LIEBE, György VARGA The overall assessment of the long term past changes of the state of water resources and the annual upgrading of this assessment was necessitated by the changes of hydrometeorological and hydrological conditions, which determine the water resources management options of the nation, and also by the gaining of new knowledge in this field. Investigation of the water budget requires the analysis of a series of meteorological and hydrological elements as well (solar radiation, air temperature, vapour content and pressure of the air, wind etc.). Among these the most frequently utilized element is the air temperature, changes of which are deterministic in the assessment of hydrometeorological elements and in the analysis of the elements of the water budget. The national monthly, half-yearly and annual average air temperature values are given in Table I. on the basis of the data of 37 stations. Precipitation conditions were investigated on the basis of the data of 83 stations, including the 30 stations used for the great plains of Hungary, the Alföld. Time series of 45 years length are shown in Figure 1. for the country and for the Alföld. Under Hungarian climatic conditions actual évapotranspiration is the largest negative element of the water budget (Figure 1.). Time series of annual potential evaporation are shown in Figure 2 for the country and separately for the Alföld. Differences between the national average precipitation and the actual évapotranspiration are shown in Figure 3. for the country and separately for the Alföld, together with the linear trend of this value. It can be concluded from Figure 3 that the zero difference corresponds, in the case of the Alföld area, to 540 mm annual precipitation. The water regime of water courses is characterized by the time series of water stages and stream discharges. Time series of major rivers show a much varying picture in the period 1950-1995. Flows that were entering and leaving the country in 1995 are summarized in Table II. From the point of view of water resources management the possible most detailed and most reliable knowledge on the characteristics of low flow periods is required for the determination of the chances of meeting water demands and/or the priorities of meeting these demands. Low flow conditions are evaluated in Table III. for a fully Hungarian river system (River Koppány at Tamási) and for a mostly Hungarian one (River Zagyva at Jásztelek). In evaluating the water budget conditions of large lakes data of Lake Balaton and Lake Velence (the two largest lakes of Hungary) are presented in Tables V. and VI. Figure 4. shows the variation of actual water demands in August for the period 1981—1995. It can be concluded for the country as a whole that water demands were increasing until 1990 then dropped dramatically after 1991 to a constant level. Details of the water intakes and their role in the water budget of the month August are given in Table VII. Subsurface water resources are influenced, in addition to the conditions of surface waters which provide for recharge and drainage, by the withdrawals from the aquifers. Time variation of water abstraction rates are shown in Figure 5. Analyzing the variation of the water table the authors concluded that subsidence exceeded 3 meters in the area between the rivers Danube and Tisza. Other areas characterized by smaller rates of the subsidence of the water table are found in the alluvial cone of the River Maros and in the western rim of the Nyírség area. However, substantial rise of the water table can be observed in the middle of the Alföld and in the Nagykúnság. Joint effects of the diversion of the River Danube and the subsidence of the channel bed resulted in 0.5—2.0 m drop of the water table in the Szigetköz area. Relationships between precipitation and the shallow groundwater level are shown in Figures 6. and 7. relationships between shallow ground water levels and surface waters and confined aquifers are shown in Figures 8. and 9. respectively. Variation of the water levels of confined aquifers have been measured since the late seventies only. Data of water abstraction wells indicate that the subsidence of the water levels of confined
