Vízügyi Közlemények, 2004 (86. évfolyam)

1-2. füzet - Varga György: A Balaton 2003. évi vízháztartási viszonyai

154 Varga György Virág Á.: A Balaton múltja és jelene, Eger Nyomda Kft. 1997. Virág Á. : A siófoki római kori zsilip hipotézisének története. Vízügyi Közlemények, LXXX. évfolyam 4. füzet 1998. * * * Water budget conditions of Lake Balaton, in 2003 by György VARGA, geographer Monthly controlled and thus reliable water budgets are available for Lake Balaton since 1921. This means that data series of 83 years length are available for characterising the changes of the water budget of the Lake (Table I.). The water level of the Lake stayed beyond the lower water-level control threshold value during the entire year. The annual minimum was 23 cm in the period 18-19 October, while the annual maximum of 71 cm was observed in the period of the 26

t

h of March and 12

t

h of April. (Figure 1.). In 2003 the precipitation was very low in the Balaton catchment, similarly to the weather conditions of the former 3 years. March-June and November-December were especially dry periods. Considerably more precipitation than the average had fallen only in the month October (Figure 2). Considering the spatial distribution of the precipitation-shortage the highest shortage (260-300 mm) was observed in the upper part of the catchment of the River Zala (the largest tributary, draining half of the catchment) and thus it was very important from the view point of the lack of runoff generation (Figure 3.). Considering the precipitation onto the lake surface and its distribution in time, the driest months were March, April, June and December (Figure 4.). The extreme water budget of the Lake in the year 2003 was caused, decisively, by the low inflow, which was about the third of the average only. Inflow was significantly lower than the average in all months. In the period of July-September the monthly values did not exceed 10 mm (Figure 5). In the April-October period, which is the most important for evaporation the monthly mean temperature was (between May and October) higher than the average. May, June and August were extremely warm months (Figure 6). In the period May-August the monthly evaporation was higher than the average (Figure 7). Reviewing the monthly natural changes of the water budget of the year 2003 we found that near-average value was observed in January only, while in the months of the rest of the year significantly higher negative changes than the average can be calculated. The largest anomaly was observed in the period of April-June (Figure 8).