It is expected that climate change will affect important natural inland waterways in Europe, among others, the Rhine River. Inland waterway transport is one of the main economic activities developed in the Rhine, and the effects of climate change on this activity are of great concern for skippers, the industry and policy-makers. This paper aims to identify whether longer and more frequent dry periods projected in the Rhine River will turn into a physical limitation that prevent inland waterway transport companies from guaranteeing reliable transportation to their customers, and – if so – when such a situation might take place. Based on the adaptation turning point approach, we propose a four step method to identify critical time periods for future climate change adaptation. According to our results, the inland waterway transport sector will start facing insurmountable problems associated with low water levels within the time span 2081–2095. The adaptation turning point approach provides analysts with a dynamic appraisal method that allows options to be ranked with timing of period of effectiveness and the time span needed for implementation as criteria. This increases flexibility of planning and allows for uncertainty about changing future conditions.

INTRODUCTION

Currently, the Rhine main stream, its tributaries and canals, constitute one of the most important commercial inland waterways worldwide (Cioc 2002). Its geographical location and well-developed infrastructure allow transportation of about 300 million tons of cargo and 2 million containers each year, connecting important industrial areas, such as the Ruhr and Basel, with main European ports such as Rotterdam and Antwerp (Pauli 2010).

Most probably climate change will alter the Rhine hydrological cycle (Middelkoop et al. 2001; Barnett et al. 2005; Görgen et al. 2010; Flörke et al. 2011). Increased precipitation is projected during winter, leading to higher average runoff and more frequent peak flows during winter (Middelkoop et al. 2001). Moreover, warmer winter temperatures in the Alps will trigger precipitation to fall as rain instead of snow, resulting in lesser snow storage. Lower snow storage, together with increased evaporation during summer, will result in lower discharges during summer and autumn (Hurkmans et al. 2010; Middelkoop et al. 2001).

The normal functioning of inland waterway transport depends on the Rhine hydrological regime. High water levels limit air draft (Zigic 2003), and increased peak flow frequency halts navigation traffic more often (Middelkoop & Kwadijk 2001; Flörke et al. 2011). Alternatively, reduced water levels during summer set lower ships' carrying capacity (Middelkoop & Kwadijk 2001), raising the freight prices per ton transported (Jonkeren et al. 2007). Also, shallow waters restrict vessels' speed, causing higher fuel consumption (Flörke et al. 2011) and increasing the risk of grounding.

The consequences of climate change on inland navigation have become an increasing concern among policy-makers (Krekt et al. 2011; Middelkoop & Kwadijk 2001). The Dutch government – through the ‘Kennis voor Klimaat’ project – has been working to identify potential impacts of climate change on navigation and alternatives for adaptation (Krekt et al. 2011). In Germany, similar efforts have been made through the KLIWAS research program led by the Federal Ministry of Transport, Building and Urban Development (Törkel 2009).

Despite these institutional efforts, scarce research has been carried out about the impacts of low water levels on inland waterway transport (Koetse & Rietveld 2009, 2012). Moreover, the literature available on climate change and navigation in the Rhine is mainly concerned with the economic implications of climate change on the inland freight transport market (see Jonkeren et al. 2007, 2011; Scholten et al. 2011). However, no research has been done about how the prospect changes on the Rhine hydrological regime may translate into physical limitations for navigation.

This paper aims to identify whether the longer and more frequent dry periods projected in the Rhine River may turn into a physical limitation that prevent inland waterway transport companies from guaranteeing reliable transport to their customers, and – if so – when such a situation might take place.

Based on different approaches to deal with adaptation planning under uncertainty, we propose a four step method to offer an answer to these questions. For the analysis, interviews with experts and inland waterway transport companies are performed. After identifying the physical factors that determine a limitation for navigation, we ask stakeholders to describe how a critical situation would be described in terms of frequency and length of dry periods. We answer the question about when this critical situation might occur by translating the parameters into timescale, using hydrological projections obtained by Hurkmans et al. (2010) and Haasnoot et al. (2013a). Finally, we present an overview of adaptation options for the inland waterway transport sector.

METHODS

Study area

The Rhine River is one of the most important rivers of Europe, about 1,320 km long and with a catchment area covering about 200,000 km2 within nine states (ICPR 2009). The region addressed in this study is the lower Rhine from the Ruhr area to Rotterdam through the Waal River which is the main Dutch branch of the Rhine (Figure 1).
Figure 1

Rhine stretch between Ruhr area and Rotterdam.

Figure 1

Rhine stretch between Ruhr area and Rotterdam.

Along this stretch, the fairway is invariably 150 meters wide and with 2.80 m minimum depth (CCNR 2012). This level of performance is guaranteed in the Netherlands by the Ministry of Infrastructure and the Environment (van der Velde et al. 2012). Hydrological data used in this study are based on measurements taken at the Lobith gauging station (Figure 1), which is representative for all the study area.

Climate adaptation under uncertainty

A new way of thinking has appeared in climate change studies to deal with adaptation planning as an alternative to the traditional ‘predict-then-adapt’ method (Gersonius et al. 2012). This new paradigm accepts that there is unavoidable uncertainty attached to climate change projections mainly due to our knowledge gap about the Earth's system functioning, model oversimplification, and our inability to anticipate future societal preferences (Dessai & Hulme 2004; Haasnoot et al. 2011). Consequently, adaptation strategies must be flexible in time in such a way that adaptation options are left open according to how the future unfolds (Reeder & Ranger 2010).

Within this framework, Reeder & Ranger (2010) proposed a ‘context-first’ approach to deal with adaptation planning by identifying alternative adaptation pathways suitable for different potential future scenarios. A similar perspective was used by Kwadijk et al. (2010) to develop the concept of ‘adaptation tipping point’ to address long-term water management planning in the Netherlands. The authors defined an adaptation tipping point as the moment when the extent of the impacts of climate change is such that ‘the current management strategy will no longer be able to meet the objectives’ (Kwadijk et al. 2010).

This notion was used by Werners et al. (2012) as the starting point to propose the concept of ‘adaptation turning point’ as a moment when ‘a socio-political threshold is reached, due to climate change induced changes in the biophysical system’. The adaptation turning point assessment provides insights about how long a socio-ecological system maintains its routines under growing impacts of climate change, the effects of climate change that may drive its collapse, and what adaptation measures can be displayed (Werners et al. 2012). The difference between the adaptation tipping point and the adaptation turning point approaches lies in the nature of the threshold to be reached. The first approach considers solely those thresholds related to formal policy objectives (Kwadijk et al. 2010) and this implies changes may have a discrete character much like state transformations in physical systems. The adaptation turning point approach involves a broader definition of threshold in order to include social preferences, stakes, and interests (Scheffer 2009; Werners et al. 2012). Turning points are characterized by a growing realization among stakeholders that climate change results in conditions they consider unacceptable, resulting in periods of discussion and policy transformation at often multiple levels (Werners et al. 2012). The inland waterway transport sector involves inland waterway transport companies, skippers, customers, port authorities, and river managers, each with their own objectives and preferences. Turning points will occur only after coordination between these parties.

Based on the ideas proposed by the previous authors, Table 1 shows the four practical steps we follow to assess adaptation turning points on the inland waterway transport sector.

Table 1

Steps for assessing adaptation turning points on inland waterway transport sector

Step Objective Methods 
1. Threshold value To identify water depth threshold value after which physical limitations for inland waterway transport begin Literature review, and semi-structured interviews applied to experts and policy-makers (8 interviewees) 
2. Stakeholders' preferences To identify how long stakeholders can handle a dry period, in terms of length and frequency of low water events Literature review, and semi-structured interviews applied to inland waterway transport companies' representatives (5 interviewees) 
3. Adaptation turning points To translate the parameters found out in step 2 into timescale by using hydrological projections and climate scenarios to assess when an unacceptable situation may occur 
  1. Analysis of two sets of transient discharge series at Lobith gauging station:

  2. Sensitivity analysis (±10% discharge)

 
4. Adaptation
measures 
To explore alternative adaptation strategies that the inland waterway transport sector may take to cope with future low water level events Literature review and semi-structured interviews 
Step Objective Methods 
1. Threshold value To identify water depth threshold value after which physical limitations for inland waterway transport begin Literature review, and semi-structured interviews applied to experts and policy-makers (8 interviewees) 
2. Stakeholders' preferences To identify how long stakeholders can handle a dry period, in terms of length and frequency of low water events Literature review, and semi-structured interviews applied to inland waterway transport companies' representatives (5 interviewees) 
3. Adaptation turning points To translate the parameters found out in step 2 into timescale by using hydrological projections and climate scenarios to assess when an unacceptable situation may occur 
  1. Analysis of two sets of transient discharge series at Lobith gauging station:

  2. Sensitivity analysis (±10% discharge)

 
4. Adaptation
measures 
To explore alternative adaptation strategies that the inland waterway transport sector may take to cope with future low water level events Literature review and semi-structured interviews 

Hydrological projections and climate change scenarios

During the last decade, several studies have been carried out to simulate the potential effects of climate change on the stream flow dynamics in the Rhine River Basin (see Middelkoop et al. 2001; van den Hurk et al. 2005; Te Linde 2006; Hurkmans et al. 2010). In most cases, the experiment setup consists of a model chain composed of a global climate model (GCM), a regional climate model (RCM) for downscaling GCM simulations, and a hydrological model for translating atmospheric data into stream flow responses. The models as well as their parameterization depend on the objective of the study, the study area, and timescales. Moreover, a trend towards a multi-model ensemble approach is observed in some recent studies (see Törkel 2009; Görgen et al. 2010).

Some studies focus on the accurate forecasting of extreme hydrological events, which provides more relevant insights for the design of adaptation measures than the accurate simulation of future mean hydrological values. Van Pelt et al. (2012) project future extreme precipitation events in the Rhine Basin for the IPCC SRES A1B scenario (Van Pelt et al. 2012). Te Linde et al. (2010) compared three different methods for simulating low probability flood peak events in the Rhine Basin on a time span of 1,000 years. Other studies focusing on flooding events can be found in Te Linde et al. (2011, 2012). Unlike studies on high water events, research on future droughts is scarce. Bisterbosch (2010) estimated low water discharges in the Rhine River by integrating the Hydrologiska Byråns Vattenbalansavdelning (HBV) model to four different model chains (GCM-RCM) in order to generate datasets of daily discharge values for the periods 2020–2050 and 2070–2100 for the IPCC SRES A1B scenario.

The objective of the third step of this study (see Table 1) is to identify critical low water periods projected over a time series, therefore the use of transient projections of daily water discharges is required (Haasnoot et al. 2012). We analyze two sets of transient projections obtained by two different methods: Hurkmans et al. (2010) and Haasnoot et al. (2013a). Hurkmans et al. (2010) assembled the variable infiltration capacity (VIC) model to the atmospheric datasets resulting from the RCM REMO to simulate future Rhine discharges at different locations within the Rhine from 2002 to 2100 for three IPCC SRES scenarios: A2, A1B, and B1. Haasnoot et al. (2013a) used the delta method (Te Linde 2006) to generate transient time series of atmospheric data which were coupled to the HBV-Rhine model to generate daily transient discharge projections for the G and W+ KNMI'06 scenarios (van den Hurk et al. 2006; Haasnoot et al. 2013a).

RESULTS

Low water threshold

Several threshold values have been previously proposed to analyze the effects of low water levels on inland waterway transport in the Rhine (see Törkel 2009; Bisterbosch 2010; Klijn et al. 2011). These are based on policy or economic criteria defined by the analysts themselves or based on preferences of one sector only. Our interviews showed that stakeholders disagree. Consensus on economic threshold values is difficult to identify because the elasticity of the demand of inland waterway transport is low (Jonkeren et al. 2007, 2011). This means that under low flow conditions ships have to reduce loading capacity with the resulting increase on freight prices; however, this does not have a significant effect on the amount of cargo demanded to be transported. Elasticity might vary between bulk cargo and container transportation. It is reasonable to assume that the elasticity of the demand of container transport is higher since it is possible to shift from inland transport to rail or road if needed; nevertheless, the higher prices of rail or road transport together with limitations in carrying capacity make the elasticity of the demand of container transport still lower than 0 (Jonkeren et al. 2011).

The only threshold value that stakeholders we consulted agree is critical, occurs when shipping becomes physically impossible during extended periods, when coal stocks of power plants and goods for other critical industries become depleted.

Low water depths in the fairway set draft restrictions that limit ships loading capacity. It is estimated that a ship can be fully loaded from 4.3 m water depth (Klijn et al. 2011) and its loading capacity decreases on a rate of around 85 tonnes per 10 cm of lost draft, as it is the case of Europe II type pushed barges commonly used along the Rhine. Then, skippers adapt to water levels variability by regulating the amount of cargo, with the resulting variability of freight prices (see Jonkeren et al. 2007).

However, low water levels trigger insurmountable problems for the inland waterway transport sector when they impede the normal performance of ships' propellers. Ships allowed to navigate along the Rhine fairway require a minimum draft that fluctuates between 1.4 and 1.8 m with minimum cargo. Considering a minimum safety clearance of 0.3 m, we estimate the minimum water depth for navigation fluctuates between 1.7 and 2.1 m (see Figure 2). We took the upper depth value to carry out our analysis: 2.1 m. This value corresponds to the requirements of the biggest ships allowed to navigate along the Rhine.
Figure 2

Schematic cross section showing the main variables of vessel position in the fairway.

Figure 2

Schematic cross section showing the main variables of vessel position in the fairway.

This water depth value must be converted into equivalent water discharges for further comparisons with hydrological projections. We used the OLR standard (RWS 2011) and the rating curve kindly provided by the Rijkswaterstaat to relate water discharge (m3/s), water level (m+ NAP) and water depth (m). Then, water depth of 2.1 m occurs at a water discharge of approximately 754 m3/s. Such low discharges have not been measured in the field, so this section of the rating curve is theoretical.

Stakeholders' preferences

Once the threshold value was defined, the next step is to determine when such a dry period becomes unacceptable from the point of view of the stakeholders. This issue was addressed during the semi-structured interviews with inland waterway transport companies. We performed a ‘what if’ exercise to determine how long these companies can cope with a dry period. The interviewees agreed when affirming that the acceptable length of a dry period is given by their customers, which are those companies whose inputs are transported by inland waterway transport. Our results indicate that the acceptable length of a dry period varies according to the production process of each of these companies, ranging from 3–4 days to 1–2 weeks in most cases, and from 6 to 10 weeks in the case of power plants which have large coal storage capacity. Also, three out of the five inland waterway transport companies interviewed estimated an average between 7 and 10 days. These lengths consider the security storage capacity that customers usually display when a dry period is announced.

Similar results were obtained by Scholten et al. (2011). They analyzed the impact of low water levels on industries which rely on inland waterway transport along the Rhine as part of their supply chain (Scholten et al. 2011). Storage capacity was one of the variables analyzed to measure companies' vulnerability to low water periods. The authors applied a survey to 58 firms located at different sections along the Rhine. The results indicated that storage capacity varies widely among companies, industries, and locations, ranging from 1 or 2 days, in the case of the food industry and semi-finished producers, to 1 month or even more in the case of the energy industry (Scholten et al. 2011).

In this study, we analyze the occurrence of a dry period of 7 days in a row. We chose this time frame since it provides problems for most of the companies except for the energy industry.

Adaptation turning points

An adaptation tuning point is related to a major change in the socio-political system as a result of a climate change-induced alteration in the bio-physical system (Werners et al. 2012); hence, the alteration in the bio-physical system should be sustained enough to not only trigger crisis but also to trigger major change.

Then, not an isolated dry event but only a sustained alteration in the Rhine hydrological regime can trigger change in the inland waterway transport sector. For the analysis, we assume that an alteration in the Rhine hydrological regime will be sustained when it results in at least one dry period every year. In other words, an adaptation turning point on inland waterway transport will be triggered when the inland waterway transport sector has to face at least one unacceptable long dry period (≥7 days) annually.

We present here the results obtained from the analysis of the hydrological projections of Hurkmans et al. (2010) for the A1B, A2, and B1 SRES scenarios, and Haasnoot et al. (2013a) for the G and W+ KNMI'06 scenarios. With the exception of the series for the G scenario, all transient projections indicate a reduction of the lowest yearly discharges as well as an increase in length and frequency of low water periods at Lobith, the tendency particularly accentuated after the second half of the 2070s. Figure 3 indicates the frequency of low water periods as the number of events per 5-year period according to the transient series for the different climate scenarios. We define an event as 7 days in a row of water discharges lower than 754 m3/s. Since we assumed an adaptation turning point would be triggered when – on average – at least one event occurs per year, here we look for the moment when the frequency of occurrence goes beyond five events per 5-year period (horizontal dot-dashed line in Figure 3). In the figure, the data have been adjusted to sixth-degree polynomial trend lines to generate tendency lines of frequency of low water events. The tendency lines indicate that such frequency is reached during the period 2081–2085 in the case of A1B and W+ scenarios and during the period 2091–2095 for the A2 scenario. According to the B1 scenario, the threshold would not be reached. The results obtained for the G KNMI'06 scenario are not shown since no event was found within the series.
Figure 3

Frequency of low water period events.

Figure 3

Frequency of low water period events.

According to the G climate scenario, no low water-related problem should be expected for the inland waterway transport sector in the Netherlands. Despite the fact that the KNMI'06 scenarios are not linked to probability of occurrence (van den Hurk et al. 2006), the scientific community gives scarce reasons to rely on this future development pathway. The G scenario is the most moderate of the four KNMI climate change scenarios for the Netherlands, assuming an increase in global temperature of +1 °C by 2050 together with a weak change of atmospheric circulation (van den Hurk et al. 2006). Haasnoot et al. (2013a) assumed a linear scaling up of the climate change effects to generate the transient discharge series by 2100; hence, the G scenario series presumes an increase of global temperature of +2 °C by 2100. Currently, such small variation by the end of the century is a challenging target given the observed trajectory of global carbon emissions (Bernstein et al. 2007; UNEP 2010; Smith et al. 2011; Guivarch & Hallegatte 2013; Peters et al. 2013). We can make similar remarks for scenario B1 since it presumes a global temperature rise of 1.8 °C (range of 1.1–2.9 °C) by the end of the 21st century (IPCC 2007). The observed emissions are consistent with the scenarios A1B and A2 SRES scenarios (Peters et al. 2013) and the bandwidth of projected global temperature rise assumed in W+ KNMI'06 scenario is coherent with both SRES scenarios (van den Hurk et al. 2006).

Despite the fact that the frequency curves corresponding to scenarios W+ and A1B coincide in the 5-year period when crossing the threshold, they describe two different trajectories. On the one hand, the A1B series shows high inter-annual variability on the lowest yearly discharges as well as a gradual increase in the frequency and length of low water periods, indicating that problems related to low water will show up earlier but sporadically, and will become more recurrent by the end of the century. On the other hand, the W+ series shows low inter-annual variability and a clear declining tendency on the lowest yearly discharges; thus, the events are concentrated at the end of the century, indicating a later but persistent increase in frequency and length of low water periods.

We performed a sensitivity analysis to study the effect of varying the discharge value considered as threshold: 754 m3/s. Figure 4 shows the time spans when an adaptation turning point may take place, given a variation of ±10% with respect to the original discharge value analyzed.
Figure 4

Sensitivity of the turning point's time span when varying the discharge value by ±10%.

Figure 4

Sensitivity of the turning point's time span when varying the discharge value by ±10%.

We performed a similar analysis to study the effect of varying the length of the period considered as critical: 7 days in a row. Figure 5 shows the time spans when an adaptation turning point may take place, given a variation of ±3 with respect to the original length analyzed.
Figure 5

Sensitivity of the turning point's time span when varying the length of a critical low water period.

Figure 5

Sensitivity of the turning point's time span when varying the length of a critical low water period.

Adaptation measures

A summary of the main adaptation measures to face the impacts of low water levels on inland waterway transport is presented in Table 2. Unless a different source is indicated, this summary is based on information collected from the interviews we performed. The assessment is done in terms of advantages and disadvantages of the different measures; however, determining the best adaptation measure is beyond the scope of this study. Where possible, estimates on delay effects of measures are made on the basis of adjustments to the threshold parameter value (increase or decrease of required minimum draft or unacceptable length of a dry period) and re-comparison with the transient projections.

Table 2

Adaptation measures to face low water periods on inland waterway transport

  Strategy Advantages Disadvantages Estimate of effectiveness to postpone ATP 
Shipping companies/Ship owners Lighter and wider vessels (new materials and/or design) Up to 20% higher transport capacity during low water periods (Blaauw 2009Ships that offer better performance during low water conditions perform less optimally during normal conditions Assuming -Δ 0.2 m draft required: W+ [2091–2095]. It postpones ATP about 10 years 
Extra buoyancy aside of a common ship to decreased draft requirements (Krekt et al. 2011Higher transport capacity during low water periods The feasibility of implementing this measure in modern ships depends on technical issues like the room available in the shipping lanes, because with less river discharge there is usually less navigable width available Assuming -Δ 0.1 m draft required: A1B [2081–2085]; W+ [2086–2090]. No postponement 
Customers Increased storage capacity Safety stock available during low water periods, avoiding production halt because of inputs shortage (a) Higher storage costs. (b) Extra claims on land use and possibly higher environmental pressures +Δ 1 day: A1B and W+ [2081–2085]. No postponement 
    +Δ 3 days: W+ [2081–2085]; A1B [2096–2100]. No postponement 
    +Δ 5 days: W+ [2086–2090]. It postpones ATP between 0 and 10 years 
 Mixed transport modes Greater supply reliability (a) Higher transport costs; (b) due to economic and/or technical reasons, not all kinds of goods can be transported by rail or road; (c) modal split to rail and road causes higher environmental pressures No effect. No postponement 
Water managers Dredging In case of irregular riverbed (a) local thresholds are removed increasing navigation depth; (b) it is the cheapest measure to improve navigability (a) In case of regular riverbed, dredging will just lower the riverbed level and, at the same discharge, water level will lower at equivalent extent, with null result. (b) Execution causes alteration on river traffic and increases risk of accident; (c) due to the fixed layers located at Nijmegen, Erlecom, and Sint Andries, dredging does not guarantee increased available draft (Havinga et al. 2006No effect. No postponement 
 Canalization (implementation of weirs and lock-complexes) Increased navigation depth (a) High economic and institutional/political cost; (b) slower river traffic; (c) negative ecological consequences; (d) it may increase flood risk Long-term effects 
 Longitudinal dams (a) Increased navigation depth; (b) unlike groynes, longitudinal dams do not increase hydraulic roughness (Giri 2011); (c) formation of additional flow area to reduce flood levels and easy readjustment to avoid negative morphodynamic effects (Huthoff 2011(a) Higher economic costs in comparison with groynes; (b) it is a local solution, it cannot be implemented along the entire river stretch due to river bends (e.g., Nijmegen area); (c) it may increase flood risk Theoretically, it may postpone ATP indefinitely on those river sections where it can be implemented 
  Strategy Advantages Disadvantages Estimate of effectiveness to postpone ATP 
Shipping companies/Ship owners Lighter and wider vessels (new materials and/or design) Up to 20% higher transport capacity during low water periods (Blaauw 2009Ships that offer better performance during low water conditions perform less optimally during normal conditions Assuming -Δ 0.2 m draft required: W+ [2091–2095]. It postpones ATP about 10 years 
Extra buoyancy aside of a common ship to decreased draft requirements (Krekt et al. 2011Higher transport capacity during low water periods The feasibility of implementing this measure in modern ships depends on technical issues like the room available in the shipping lanes, because with less river discharge there is usually less navigable width available Assuming -Δ 0.1 m draft required: A1B [2081–2085]; W+ [2086–2090]. No postponement 
Customers Increased storage capacity Safety stock available during low water periods, avoiding production halt because of inputs shortage (a) Higher storage costs. (b) Extra claims on land use and possibly higher environmental pressures +Δ 1 day: A1B and W+ [2081–2085]. No postponement 
    +Δ 3 days: W+ [2081–2085]; A1B [2096–2100]. No postponement 
    +Δ 5 days: W+ [2086–2090]. It postpones ATP between 0 and 10 years 
 Mixed transport modes Greater supply reliability (a) Higher transport costs; (b) due to economic and/or technical reasons, not all kinds of goods can be transported by rail or road; (c) modal split to rail and road causes higher environmental pressures No effect. No postponement 
Water managers Dredging In case of irregular riverbed (a) local thresholds are removed increasing navigation depth; (b) it is the cheapest measure to improve navigability (a) In case of regular riverbed, dredging will just lower the riverbed level and, at the same discharge, water level will lower at equivalent extent, with null result. (b) Execution causes alteration on river traffic and increases risk of accident; (c) due to the fixed layers located at Nijmegen, Erlecom, and Sint Andries, dredging does not guarantee increased available draft (Havinga et al. 2006No effect. No postponement 
 Canalization (implementation of weirs and lock-complexes) Increased navigation depth (a) High economic and institutional/political cost; (b) slower river traffic; (c) negative ecological consequences; (d) it may increase flood risk Long-term effects 
 Longitudinal dams (a) Increased navigation depth; (b) unlike groynes, longitudinal dams do not increase hydraulic roughness (Giri 2011); (c) formation of additional flow area to reduce flood levels and easy readjustment to avoid negative morphodynamic effects (Huthoff 2011(a) Higher economic costs in comparison with groynes; (b) it is a local solution, it cannot be implemented along the entire river stretch due to river bends (e.g., Nijmegen area); (c) it may increase flood risk Theoretically, it may postpone ATP indefinitely on those river sections where it can be implemented 

DISCUSSION

Our results suggest that insurmountable problems associated with low water depths will appear during the first half of the 2080 decade in the case of the W+ and A1B scenarios or during the first half of the 2090s in the case of A2 scenario. We recognize that moment as an adaptation turning point because after this point is reached, inland waterway transport companies could not guarantee transportation to their customers and adjustments by means of reducing cargo will not be feasible anymore due to technical limitations.

The loss of reliability of the inland waterway sector, together with the higher freight prices (Jonkeren et al. 2007), should trigger a change in the distribution of freight transport market shares, favoring rail and road transport sectors. Jonkeren et al. (2011) claims that this change will gradually take place, reaching up to 5.4% loss in tonnes transported as a response to an increment of 27% in freight prices by 2050, according to W+ scenario. Consequently, we may speculate that economic constraints will lead to a critical situation for the inland waterway transport sector before physical limitations become an issue. However, the low elasticity of the demand in this market makes it difficult to estimate an increment in prices that proves to be strong enough to trigger a substantial loss in tonnes transported. Besides, the loss of demand due to modal shift is limited because the carrying capacity offered by the inland waterway transport sector is far higher than the carrying capacity of rail or road transport.

Efforts from the different actors within the inland waterway transport sector are needed to face the effects of low water levels (Koetse & Rietveld 2012). However, the level of urgency for adaptation seems to differ between stakeholders. Since the demand in the inland waterway transport market is inelastic (Jonkeren et al. 2007), inland waterway transport companies and skippers have no economic incentives to invest in adaptation measures because their income is not affected by the loss of transport capacity during low water periods. This is because the loss of transport capacity is compensated by the higher prices they can charge per freight; whereas, the companies depending on shipping services are the ones bearing the higher transport costs. Furthermore, our results are sensitive to negative variations in the length of a critical low water period. In fact, a variation of −3 days in length of a critical low water period leads to a difference of up to 15 years in the estimated time span (see Figure 5), indicating that companies with slightly lower storage capacities should expect problems in raw material supply much earlier. Therefore, companies depending on shipping services are the ones that need to display adaptive capacity by making their supply chains more flexible and enlarging security storage capacity.

In this study we consider sectoral adaptation measures. Yet, any measure to improve navigation under low water conditions must be embedded in cross-sectoral strategies intended to avoid potential conflicts of interests between navigation, safety, and environment. The possible conflicts between inland navigation interests and the measures contemplated in the Room for the River program, such as the impact of floodplains on the discharge in the main channel, are discussed in detailed by Havinga et al. (2009). Some experiences in the implementation of cross-sectoral strategies in the Mississippi River have been documented (DuBowy 2010).

Our results are unavoidably associated with sources of uncertainty. In addition to uncertainty in climate and hydrological models, our results are based on transient discharge series not specifically designed for the accurate forecast of low water events (Hurkmans et al. 2010; Haasnoot et al. 2013a). Furthermore, our results are sensitive to variations in discharge and length threshold. In fact, a variation of 10% in the discharge threshold leads to a difference of up to 15 years in the estimated time span. The water level values we related to water discharge were extremely low and so never observed; hence, there is an inherent uncertainty associated with the use of a model-based section of the rating curve, which added to the sensitivity of our results, creates a large amount of uncertainty. However, the trend towards increased frequency and length of low water periods indicated by the hydrological projections is clear and uncertainty should not be taken as an excuse to not carry out actions.

The added value of adaptation turning point identification as a planning tool for uncertain futures is not in the assessment of when turning points exactly occur (although this is relevant information for stakeholders too). The main value lies in the appraisal of adaptation options. Comparison of turning points of different adaptation strategies shows the sustainability of strategies and uncovers potential lock ins (e.g., continuation of the current practice of dredging has limited effects on climate proofing and cannot be reversed and excludes other measures) and makes it possible to rank options in terms of timing of implementation and expected time of effectiveness. On the basis of adaptation tipping point analyses, Haasnoot et al. (2013b) developed adaptation pathways, consisting of a flexible set of measures, adaptable to changing conditions in the future. The same can be done with adaptation turning point analyses.

CONCLUSIONS

In the Lobith area, the inland waterway transport sector probably will face longer and more frequent dry periods driven by climate change. Our results suggest that decision-makers should expect a threshold situation to occur during the first half of the 2080 decade, when water depths resulting from low water discharges will impose a physical limit to inland waterway transport during at least 7 days in a row every year. After this threshold is reached, shipping companies will no longer be able to guarantee transportation to their customers.

For the identification of the threshold we used the adaptation turning point analysis. This methodology starts with an inventory of stakeholder opinions on when they consider impacts of climate change on their sector intolerable. As such, this methodology takes stakeholder concerns as problem definition instead of the usual climate impact or risk assessments. By doing so, this approach aims at bridging the gap between policy-makers and stakeholders on one side and experts on the other side.

There is no straightforward answer to the question about the best adaptation measure to face the impacts of low water periods on inland waterway transport. The uncertainty attached to climate change studies makes it difficult to estimate the actual severity of the consequences associated with low water levels in the Rhine River. However, following earlier work on adaptation pathways (Haasnoot et al. 2013b), the adaptation turning point approach provides analysts with a dynamic appraisal method of adaptation options, meaning that options may be ranked with timing of period of effectiveness and timing of the period needed for implementation as criteria. This increases flexibility of planning and allows for uncertainty about changing future conditions.

ACKNOWLEDGEMENTS

This research has been developed in the framework of MEDIATION Project, ‘Methodology for Effective Decision-making on Impacts and AdaptaTION’, funded by the European Commission, 7th Framework Program, Theme 6 (Environment, including Climate Change).

REFERENCES

REFERENCES
Barnett
T. P.
Adam
J. C.
Lettenmaier
D. P.
2005
Potential impacts of a warming climate on water availability in snow-dominated regions
.
Nature
438
(
7066
),
303
309
.
Bernstein
L.
Bosch
P.
Canziani
O.
Chen
Z.
Christ
R.
Davidson
O.
Hare
W.
Huq
S.
Karoly
D.
Kattsov
V.
Kundzewicz
Z.
Liu
J.
Lohmann
U.
Manning
M.
Matsuno
T.
Menne
B.
Metz
B.
Mirza
M.
Nicholls
N.
Nurse
L.
Pachauri
R.
Palutikof
J.
Parry
M.
Qin
D.
Ravindranath
N.
Reisinger
A.
Ren
J.
Riahi
K.
Rosenzweig
C.
Rusticucci
M.
Schneider
S.
Sokona
Y.
Solomon
S.
Stott
P.
Stouffer
R.
Sugiyama
T.
Swart
R.
Tirpak
D.
Vogel
C.
Yohe
G.
2007
Climate Change 2007. Synthesis Report
,
IPCC
,
Geneva
.
Bisterbosch
J.
2010
Impacts of climate change on low flows in the Rhine basin
.
MSc Water Engineering & Management
,
Universiteit Twente
,
The Netherlands
.
Blaauw
H.
2009
Potential for the inland navigation fleet to adapt to changes in the water discharge. In Navigation on the Rhine and Climate Change: A Challenge and an Opportunity. Congress of the Central Commission for the Navigation of the Rhine, 24–25 June
,
Bonn, Germany
.
CCNR
2012
Navigation Channel Clearances of the Rhine. Waterway Profile of the Rhine
.
Central Commission for the Navigation of the Rhine, Strasbourg, 3
.
Cioc
M.
2002
The Rhine: An Eco-biography, 1815–2000
.
University of Washington Press
,
Seattle and London
.
Dessai
S.
Hulme
M.
2004
Does climate adaptation policy need probabilities?
Clim. Policy
4
(
2
),
107
128
.
DuBowy
P. J.
2010
Navigation, flood risk management and Mississippi River ecosystem rehabilitation. In Watershed Management Conference 2010: Innovations in Watershed Management under Land Use and Climate Change – Proceedings of the 2010 Watershed Management Conference, 23–27 August
,
Madison, WI
.
Flörke
M.
Wimmer
F.
Laaser
C.
Vidaurre
R.
Tröltzsch
J.
Dworak
T.
Stein
U.
Marinova
N.
Jaspers
F.
Ludwig
F.
Swart
R.
Giupponi
C.
Bosello
F.
Mysiak
J.
2011
Final Report for the project Climate Adaptation – modelling water scenarios and sectoral impacts
,
Center for Environmental Systems Research (CESR)
,
Kassel
.
Gersonius
B.
Nasruddin
F.
Ashley
R.
Jeuken
A.
Pathirana
A.
Zevenbergen
C.
2012
Developing the evidence base for mainstreaming adaptation of stormwater systems to climate change
.
Water Res.
46
(
20
),
6824
6835
.
Giri
S.
2011
River engineering measures to improve navigability. Appendix 7 Project Knowledge for Climate – HSRR08. The effects of climate change on inland water transport via the Port of Rotterdam: 7
.
Görgen
K.
Beersma
J.
Brahmer
G.
Buiteveld
H.
Carambia
M.
Keizer
O. D.
Krahe
P.
Nilson
E.
Lammersen
R.
Perrin
C.
Volken
D.
2010
Assessment of Climate Change Impacts on Discharge in the Rhine River Basin: Results of the RheinBlick2050 Project
.
International Commission for the Hydrology of the Rhine Basin, Lelystad
.
Guivarch
C.
Hallegatte
S.
2013
2C or not 2C?
Global Environ. Change
23
(
1
),
179
192
.
Haasnoot
M.
Middelkoop
H.
van Beek
E.
van Deursen
W. P. A.
2011
A method to develop sustainable water management strategies for an uncertain future
.
Sustain. Dev.
19
(
6
),
369
381
.
Haasnoot
M.
Middelkoop
H.
Offermans
A.
Beek
E.
van Deursen
W. A.
2012
Exploring pathways for sustainable water management in river deltas in a changing environment
.
Clim. Change
115
(
3–4
),
795
819
.
Haasnoot
M.
Beersma
J.
Schellekens
J.
2013a
Change Ahead: Transient Scenarios for Long-term Water Management. EGU General Assembly, Vienna, Austria
.
Haasnoot
M.
Kwakkel
J. H.
Walker
W. E.
ter Maat
J.
2013b
Dynamic adaptive policy pathways: A method for crafting robust decisions for a deeply uncertain world
.
Global Environ. Change
23
,
485
498
.
Havinga
H.
Taal
M.
Smedes
R.
Klaassen
G. J.
Douben
N.
Sloff
C. J.
2006
Recent training of the lower Rhine River to increase Inland Water Transport potentials: a mix of permanent and recurrent measures. In: Proceedings of the International Conference on Fluvial Hydraulics – River Flow 2006, 6–8 September 2006
,
Lisbon, Portugal
.
Havinga
H.
Schielen
R. M. J.
van Vuren
S.
2009
Tension between navigation, maintenance and safety calls for an integrated planning of flood protection measures. In: Proceedings of River, Coastal, Estuarine Morphodynamics – RCEM Conference, 21–25 September, 2009
,
Santa Fe, Argentina
.
Hurkmans
R.
Terink
W.
Uijlenhoet
R.
Torfs
P.
Jacob
D.
Troch
P. A.
2010
Changes in streamflow dynamics in the Rhine basin under three high-resolution regional climate scenarios
.
J. Climate
23
(
3
),
679
699
.
Huthoff
F.
2011
Longitudinal Dams as an Alternative to Wing Dikes in River Engineering
.
Smart Rivers 2011
.
PIANC, New Orleans, LA, USA
.
ICPR
2009
Internationally Coordinated Management Plan for the International River Basin District of the Rhine
.
International Comission for the Protection of the Rhine
,
Koblenz
.
IPCC
2007
Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. S. Solomon, D. Qin, M. Manning, M. Marquis, K. Averyt, M. M. B. Tignor, J. Henry LeRoy Miller & Z. Chen, Cambridge University Press, Cambridge, UK and New York, 966 pp
.
Jonkeren
O.
Rietveld
P.
van Ommeren
J.
2007
Welfare effects of low water levels on the river Rhine through the Inland Waterway Transport Sector
.
J. Transp. Econ. Policy
41
(
3
),
387
411
.
Jonkeren
O.
Jourquin
B.
Rietveld
P.
2011
Modal-split effects of climate change: the effect of low water levels on the competitive position of inland waterway transport in the river Rhine area
.
Transport. Res. A-Pol.
45
(
10
),
1007
1019
.
Klijn
F.
ter Maat
J.
van Velzen
E.
2011
Zoetwatervoorziening in Nederland: landelijke analyse knelpunten in de 21e eeuw [Fresh water supply in the Netherlands. National analyses of bottlenecks in the 21st century]. Deltares, 162 pp
.
Koetse
M. J.
Rietveld
P.
2009
The impact of climate change and weather on transport: an overview of empirical findings
.
Transport. Res. D-Tr E
14
(
3
),
205
221
.
Koetse
M. J.
Rietveld
P.
2012
Adaptation to climate change in the transport sector
.
Transport Rev.
32
(
3
),
267
286
.
Krekt
A.
van der Laan
T.
van der Meer
R.
Bas Turpijn
O.
van del Toorn
A.
Mosselman
E.
van Meijeren
J.
Groen
T.
2011
Climate change and inland waterway transport: impacts on the sector, the Port of Rotterdam and potential solutions. Report Knowledge for Climate, 74 pp
.
Kwadijk
J. C. J.
Haasnoot
M.
Mulder
J. P. M.
Hoogvliet
M. M. C.
Jeuken
A. B. M.
van der Krogt
R. A. A.
van Oostrom
N. G. C.
Schelfhout
H. A.
van Velzen
E. H.
van Waveren
H.
de Wit
M. J. M.
2010
Using adaptation tipping points to prepare for climate change and sea level rise: a case study in the Netherlands
.
Wiley Interdiscip. Rev.: Clim. Change
1
(
5
),
729
740
.
Middelkoop
H.
Kwadijk
J. C. J.
2001
Towards integrated assessment of the implications of global change for water management – The Rhine experience
.
Phys. Chem. Earth Pt B
26
(
7–8
),
553
560
.
Middelkoop
H.
Daamen
K.
Gellens
D.
Grabs
W.
Kwadijk
J. C. J.
Lang
H.
Parmet
B. W. A. H.
Schädler
B.
Schulla
J.
Wilke
K.
2001
Impact of climate change on hydrological regimes and water resources management in the Rhine basin
.
Clim. Change
49
(
1–2
),
105
128
.
Pauli
G.
2010
Sustainable transport: a case study of Rhine navigation
.
Nat. Resour. Forum
34
(
4
),
236
254
.
Peters
G. P.
Andrew
R. M.
Boden
T.
Canadell
J. G.
Ciais
P.
Le Quéré
C.
Marland
G.
Raupach
M. R.
Wilson
C.
2013
The challenge to keep global warming below 2C
.
Nat. Clim. Change
3
(
1
),
4
6
.
Reeder
T.
Ranger
N.
2010
How do you adapt in an uncertain world? Lessons from the Thames Estuary 2100 project. World Resources Report 2010–2011
.
Washington, DC
.
RWS
2011
Waterway Guidelines 2011
.
J. U. Brolsma & K. Roelse. Delft, Directorate-General for Public Works and Water Management, Rijkswaterstaat, Centre for Transport and Navigation
.
Scheffer
M.
2009
Critical Transitions in Nature and Society
.
Princeton University Press
,
Princeton, NJ
.
Scholten
A.
Rothstein
B.
Baumhauer
R.
2011
Critical parameters for mass-cargo affine industries due to climate change in Germany: impacts of low water events on industry and possible adaptation measures
. In:
The Economic, Social and Political Elements of Climate Change
(
Leal Filho
W.
, ed.).
Springer
,
Berlin, Heidelberg
, pp.
267
287
.
Smith
M. S.
Horrocks
L.
Harvey
A.
Hamilton
C.
2011
Rethinking adaptation for a 4°C world
.
Phil. Trans. R. Soc. A
369
(
1934
),
196
216
.
Te Linde
A. H.
2006
Effects of Climate Change on the Rivers Rhine and Meuse: Applying the KNMI 2006 Scenarios Using the HBV Model
.
WL Delft Hydraulics
,
Delft
.
Te Linde
A. H.
Aerts
J. C. J. H.
Bakker
A. M. R.
Kwadijk
J. C. J.
2010
Simulating low-probability peak discharges for the Rhine basin using resampled climate modeling data
.
Water Resour. Res.
46
(
3
)
W03512
.
Te Linde
A. H.
Bubeck
P.
Dekkers
J. E. C.
De Moel
H.
Aerts
J. C. J. H.
2011
Future flood risk estimates along the river Rhine
.
Nat. Hazard. Earth Syst. Sci.
11
(
2
),
459
473
.
Te Linde
H. A.
Moors
E. J.
Droogers
P.
Bisselink
B.
Becker
G.
t. Maat
H.
Aerts
J. C.
2012
ACER: developing Adaptive Capacity to Extreme events in the Rhine basin, National Research Programme Climate Changes Spatial Planning
.
Törkel
B
.
2009
An Introduction to the KLIWAS Research Programme. In: Proceedings of KLIWAS: Impacts of Climate Change on Waterways and Navigation in Germany – First Status Conference, 18–19 March 2009
,
Bonn, Germany
.
UNEP
2010
The Emissions Gap Report: Are the Copenhagen Accord pledges sufficient to limit global warming to 2°C or 1.5°C? A preliminary assessment, United Nations Environment Programme, 52 pp
.
van den Hurk
B.
Hirschi
M.
Schär
C.
Lenderink
G.
van Meijgaard
E.
van Ulden
A.
Rockel
B.
Hagemann
S.
Graham
P.
Kjellström
E.
Jones
R.
2005
Soil control on runoff response to climate change in regional climate model simulations
.
J. Climate
18
(
17
),
3536
3551
.
van den Hurk
B.
Klein Tank
A.
Lenderink
G.
van Ulden
A.
van Oldenborgh
G.
Katsman
C.
van den Brink
H.
Keller
F.
Bessembinder
J.
Burgers
G.
Komen
G.
Hazeleger
W.
Drijfhout
S.
2006
KNMI Climate Change Scenarios 2006 for the Netherlands
.
KNMI
,
De Bilt, 82 pp
.
van der Velde
J.
Klatter
L.
Bakker
J.
2012
A holistic approach to asset management in the Netherlands
.
Struct. Infrastruct. Eng.
9
(
4
),
340
348
.
Van Pelt
S. C.
Beersma
J. J.
Buishand
T. A.
Van Den Hurk
B. J. J. M.
Kabat
P.
2012
Future changes in extreme precipitation in the rhine basin based on global and regional climate model simulations
.
Hydrol. Earth Syst. Sci.
16
(
12
),
4517
4530
.
Werners
S. E.
Swart
R.
van Slobbe
E.
Bölscher
T.
Pfenninger
S.
Trombi
G.
Moriondo
M.
2012
Turning Points in Climate Change Adaptation
.
The Governance of Adaptation
,
Amsterdam, The Netherlands
.
Zigic
B.
2003
Particularities of navigation on inland waterways
.
SPINletter: Strat. Promote Inland Navig.
1
,
6
.