Since climate change became an issue potential changes in the hydrology of the river have been subject of research. Most of this research was directed at floods and as a result adaptation strategies for flood security infrastructure are being developed now. The need to anticipate with changes in low flow events however has received insufficient attention. We define low flow as the lowest 7-day mean discharge per year (NMQ7) ¹. Water users are accustomed to average low flows, and they usually can deal with the damaging impacts of extreme low flows, like in 2003, on the condition these do not occur too often. But what if average low flow discharges diminish? And what if the frequency of extreme low flows increases? The aim of this case study is to assess when, from the perspective of water users, changes become intolerable and water use practices will fail as well as to make an inventory of adaptation options for water users.

Methods and tools to analyse impacts of changing low flows are being developed and applied, but uncertainties in results are high, and more work needs to be done (for references see under heading 'Details'). This case study takes three water use practices to assess their vulnerability to climate induced changes in low flows and to asses possible adaptation strategies (see figure 2 for locations): Reintroduction policies of the salmon. The salmon is used as a symbol and an indicator species for the ecological quality of the river. We selected this policy to address the large investments made for environmental and ecological restoration 2. Navigation on the river. The river is facilitating transport of over 200 million tons of goods annually. We selected this sector because riparian economies depend on it. The region addressed in this study is the river section between Duisburg and Rotterdam, because it is the busiest transport section 3. Irrigation water. The map shows the study area in the east of the Netherlands called Twente. Water is taken from the Ijssel river through a pumping station at Eefde (near Zutphen on the map) and distributed through a system of canals 4.

Figure 2: Master Plan Migratory Fish Rhine. With location indications added of the Rotterdam - Duisburg navigation section and the Twente water allocation area.

Figure 3: Change of low flow characteristics of Rhine River in near future (2021 to 2050; red; 20 members) and far future (2071 to 2100; purple; 17 members) with reference to control period (1961 to 1990 = zero line); expressed as NM7Q in the hydrological summer 6.

Currently, the Rhine River is a mixed snowfed - rainfed system. Due to climate change, the Rhine River is expected to transform itself into a predominantly rainfall driven system. Higher temperatures will trigger precipitation to fall as rain instead of snow, resulting in lesser snow storage in the Alps during winter. Lower snow storage, together with increased evaporation during summer, will result in lower discharge volumes during summer and autumn. Model projections show no significant low flow changes in the near future (2021-2050). But they do show an increase of the frequency of low flow events and a reduction of discharge during such events in the distant future (2071-2100) 5. See figure 3.

---

¹ ICPR (International Commission for the Protection of the Rhine) (2011) Study of Scenarios for the Discharge Regime of the Rhine state. State April 2011. Report No. 188. ICPR. Koblenz; www.IKSR.org.

² See: Bölcher T. Van Slobbe E. Van Vliet M. Werners S. (2013) Adaptation turning points in river restoration? The Rhine salmon case Sustainability 2012, 4, 1-x manuscripts; doi:10.3390/su40x000x. (Under review).

³ See: Riquelme-Solar M. Van Slobbe E. Werners S.E. Adaptation Turning Points on Inland Waterways Transport in the Rhine River (to be submitted)

⁴ Research based on MSc. thesis H. de Groot, Wageningen University 2012

⁵ Middelkoop, H., K. Daamen, et al. (2001). "Impact of climate change on hydrological regimes and water resources management in the Rhine basin." Climatic Change 49(1-2): 105-128.

Te Linde, A. H. (2006). Effects of climate change on the rivers Rhine and Meuse: Applying the KNMI 2006 scenarios using the HBV model. Delft, WL¦delft hydraulics.

Hurmans R. Terink W. Uijlenhoet R. Torfs P. (2010). Changes in Streamflow Dynamics in the Rhine Basin under Three High-Resolution Regional Climate Scenarios. American Meteorological Society. DOI: 10.1175/2009JCLI3066.1

Görgen, K., Beersma, J., Brahmer, G., Buiteveld, H., Carambia, M., de Keizer, O., Krahe, P., Nilson, E., Lammersen, R., Perrin, C. and Volken, D. (2010) Assessment of Climate Change Impacts on Discharge in the Rhine River Basin: Results of the RheinBlick2050 Project, CHR report, I-23, 229 pp.

⁶ Taken from: International Commission for the Hydrology of the Rhine Basin( 2010) Assessment of Climate Change Impacts on Discharge in the Rhine River Basin: Results of the RheinBlick2050. Project Report No. I-23 of the CHR. p. 117.