The case of Lake Balaton: how can we exercise precaution?

Balaton is the largest shallow lake in Central Europe and the most important recreational area in Hungary. Water balance of the lake is positive, while natural water level fluctuation has been significant. In 2000, an extreme drought period started. Until 2003, water level dropped about 70 cm (about 20% of the average depth). Public concern grew and the idea of water transfer from the Rába River was raised. To examine possible impacts a comprehensive study was prepared. The main question was whether water transfer was really needed and what criterion should be applied. For developing the methodology, three pillars were used: the potential climate change, the precautionary principle and the EU Water Framework Directive. The study covered impacts of the planned water transfer on the Rába–Balaton system in terms of changes of the water regime, water demands and quality, nutrient loads and ecosystems. The Thomas–Fiering ARMA model was used for characterizing monthly change of the natural water resources of the lake. A Monte Carlo generator was developed to analyze the occurrence of extreme events, uncertainties, possible climate change impacts and water level control strategies.