The water discharge of the Rhine river could increase by 30% in the winter and spring by the end of the century. Even more remarkable, however, is that during the summer and autumn, the discharge could be around 30% lower. These extremely low water levels will primarily result from the decreasing Alpine snow pack, which will also begin to melt earlier in the year. These are the results of a hydrological study using extreme climate scenarios conducted by Ruud Hurkmans of Wageningen University as part of his PhD research; he defended his thesis on 15 June.
Previous studies with shorter term scenarios already showed that the average discharge of the Rhine, measured at Lobith (the Netherlands), will increase in the winter and spring and decrease in the summer and autumn. The hydrological models with input for the entire 21st century have now shown that the change can amount to approximately 30%. This means that during certain periods, the transport of goods on the river will be seriously threatened.
Although the snowmelt in the spring is still providing a substantial contribution to the river discharge, this will decrease strongly in the future. Nevertheless, the models predict that more frequent and higher discharge peaks will occur in the spring. The opposite will occur in the autumn, with longer and more frequent dry periods, with corresponding low river levels.
PhD student Ruud Hurkmans studied the expected river discharge for the Rhine for the entire 21st century. For this purpose he used a hydrological model in which he inputted the expected developments in climate and land use. The three climate scenarios cover the entire 21st century and have a high spatial resolution of approximately 10 x 10 km.
The three scenarios used in the model were based on different technological and societal developments. in addition, three forms of land use were worked out according to the same 'storylines'. These land-use scenarios differ primarily concerning increasing urbanisation and the conversion of agricultural land to forest or nature reserves.
The consequences of these developments for the water level and the Rhine appear to partially counteract each other. However, at the regional level, which comprises the river basin area of a tributary to the Rhine, such as the Lahn in Germany, the changes in land use can have a significant effect. These changes are visible in the scenarios and model due to its high spatial resolution; as a result the effects of local precipitation extremes with high discharge peaks are included.