How do the Drava, Tisza, and Sava rivers affect the Danube River's flow?

The Drava, Tisza, and Sava rivers are among the most significant tributaries of the Danube River, and their confluence with the main river substantially alters its hydrological regime.1

As the Danube flows through its middle course across the Great Alfold plain, it absorbs the waters of these three major tributaries, which contribute to a significant increase in the river's average runoff—rising from approximately 83,000 cubic feet (2,400 cubic metres) per second north of Budapest to 200,000 cubic feet (5,600 cubic metres) per second by the time it reaches the Iron Gate.1

The impact of these tributaries is particularly notable in their capacity to influence water levels. For instance, when high water conditions in the Tisza coincide with similar conditions in the Danube, the Tisza can be forced back into its own course, which has historically resulted in severe flooding. Collectively, these tributaries are vital to the expansion of the Danube's drainage basin, which grows to 228,000 square miles (590,000 square km) following their confluences.21