DOWNLOAD A PDF VERSION OF THIS CASE STUDY >
Outline
The province of Zuid Holland (Netherlands) is a low-laying delta province that is susceptible to climate change. It is densely populated and also contains nationally important infrastructure and industry as well as the Dutch government. The province wants to ensure safe and comfortable living and working circumstances, also during times of changing climate.
Therefore, even before the national law that determined that all levels of government must conduct a climate stress test, the province had started work on assessing climate risks to its infrastructure. The province is responsible for the main (provincial) through-roads, main waterways and associated structures e.g. tunnels, bridges, shore protection. The case study consists of several steps/ projects that were conducted separately but integrated for presentation.
Analysis of climate hazards
The stress-test was based on available knowledge, combined with model outputs of several knowledge institutes and engineering companies. In some cases, the stress-test was conducted qualitatively, in others in a more (semi) quantitative fashion. More detail is given below:
Roads:
For heavy precipitation (100mm in 2hours), the water depth was determined on the road using a hydrologic model. This leads to an indication of maximum water depth during a precipitation event, the impact of the maximum water depth on the ‘passability’ for various vehicle types, and a semi quantitative determination of the reduced traffic flow.
The conclusion for roads and heavy precipitation was that low-laying areas and areas where the capacity of roadside ditches was limited are exposed and vulnerable. Approximately 90% of the roads in the province are expected to have little to no effects caused by heavy precipitation. The remaining approximately 10% may be affected by heavy precipitation. Especially tunnels and viaducts are indicated as vulnerable.
The extreme temperature hazard was analysed by taking the temperature increase for the most extreme climate scenario for 2050. It was determined that the effects of heat stress on the roads were insignificant and/ or manageable during regular maintenance e.g. using a different asphalt mix when the driving surface is replaced.
The effects of drought were assumed to lead to forest fires. Therefore the exposure of the province’s infrastructure to drought was indicated by overlaying the forest fire map with the infrastructure map. This resulted in a few locations, mostly in the dunes being exposed to forest fires.
There is a lot of information available in the Netherlands concerning flooding due to failure of levees. This information also takes the effects of climate change into account. As such, the water depth on roads was determined for flood events with a medium-high probability (1:100 – 1:1000 per year), similarly to the heavy precipitation events (see above). This analysis shows that ~65% (~440km) of the provincial roads will have less than 20cm of water depth and thus be available for all traffic; ~11% (73km) will only be available to emergency vehicles and ~24% (161km) of the roads will be unavailable.
The exposure of the roads to subsidence was based on the pre-existing subsidence map and the map of the road network. This analysis led to ~60% (400km) of the provincial roads not being susceptible to subsidence, 10% (75km) as susceptible and 30% (200km) as very susceptible. For roads that were designated as having a potentially high susceptibility for subsidence, it was recommended to do additional research into the road design.
Waterways
Heavy precipitation and high precipitation amounts can potentially lead to the water level in waterways increasing to the point that bridges may become unnavigable. At the same time, the water levels in the waterways are regulated by Waterboards (Waterschappen). The most extreme water levels permissible by the Waterboards were determined and the effects on shipping then ascertained. In all cases, the effects were insignificant except for one specific case where some flooding of adjacent gardens, houses and sheds may occur.
High water levels on adjacent rivers can be the result of extreme weather and/ or climate change. Effects on shipping may occur during high water levels on adjacent rivers, linked to the provincial waterways, specifically for one waterway. The analysis suggests monitoring the effects of high water on adjacent river systems on shipping to determine if this is a significant problem.
Extreme temperatures do not pose a significant risk to waterways.
The effects of drought on the waterways of the province originate from the water levels in adjacent river systems that feed the waterways. As such effects of drought are strongly influenced by decisions made by the Waterboards. During droughts, the water quality (salinity) in the rivers increases. This can lead to Waterboards decreasing or completely shutting down lock operations. The stress-test does not mention how often this occurs nor how often it will occur in the future due to climate change. The expectation is that such situations will happen more often in the future.
Similarly, the effects of climate change on the probability of flooding are not quantified, yet the stress-test does mention that an increase is expected. Subsidence may lead to unequal settlement of quays and shores. The effect of unequal settlement on the strength of levees is not clear. To determine the effects on quays and shores, the subsidence map was combined with the location of quays and shores. 16% (71km) of the total length of quays and shores are indicated as vulnerable; 13% (59km) are indicated as extra vulnerable.
Structures
Extreme temperature may affect the functioning of movable bridges, e.g. bascule bridges, drawbridges, swing bridges, and vertical lift bridges. As temperatures increase due to climate change, the number of bridges becoming jammed will also increase. However, the susceptibility to problems occurring due to high temperatures depends on many variables and is not further discussed. Extreme temperatures are considered the most important hazard.
For flooding the water level due to a flooding event was determined at the location of the control systems of the structure, using flood maps. The return period for these flooding events is not given. Most structures are not susceptible to subsidence as they are built on piled foundations. This stress-test provides the information needed to establish an Implementation Agenda that links to all the processes that Rijkswaterstaat uses for the management of the road network, including design, maintenance, renewal and renovation. In total, the stress-test covered 13 hazards, including pluvial flooding of the road due to intense rainfall, uplift of tunnels and lightweight materials, dike breaches (river and coastal flooding), heat expansion of bridges, heat effects on road foundations, drought-, nature- and roadside-related fires and road deformation caused by soil subsidence. Climate change effects were considered by keeping the damages and losses per climate event equal, but by changing the return period based on climate statics data delivered by the Royal Netherlands Meteorological Institute (KNMI) Dutch meteorological institute. The susceptibility of structures to drought is not relevant.
Resilience assessment
The first step was to conduct a climate stress test. The conducted stress test falls somewhere in between the determination of exposure and a (semi) quantitative risk assessment for the impact of extreme weather (precipitation, high temperatures, drought, flooding and subsidence) on the province’s roads, waterways and structures. The results of the stress test are presented on maps on https://klimaat-informatiehub-pzh.hub.arcgis.com/.
Subsequently, the impact of these hazards has been indicatively/ qualitatively investigated, alongside discussions with stakeholders on how to move on from there have been held.
Based on the assumed impact, the hazards were prioritized and the scope of possible measures was determined for the hazards with the highest priority.
How are adaptation solutions considered?
Based on the stress test results, a follow-up to determine the scope of available measures for the most important threats was undertaken. This was done for 4 specific cases:
1. Waterway affected by subsidence
2. Waterway affected by drought
3. Road affected by subsidence
4. Road affected by heavy rainfall
For these cases, the unwanted events were visualised through bowties. The Bowtie method is a risk evaluation method that can be used to analyse and demonstrate causal relationships in high-risk scenarios. It shows how various chains of events can lead to a top event (e.g. subsidence) and the chain of possible effects on the infrastructure. Such a bowtie allows for a better understanding of how unwanted effects on the infrastructure may occur and how measures can lessen the effects and/ or decrease the probability of an unwanted event occurring.
How is the adaptation strategy implemented in practice?
The results of the analyses are deemed valuable and effort has been made to integrate the recommendations into an adaptation strategy. The results are used to inform new construction projects of relevant hazards and provide an overview of possible measures.
Currently, the adaptation strategy is not followed in our projects, only using the basic findings. The legal framework to justify the additional costs for climate adaptation is missing. Without this framework, climate adaptation is considered a relevant topic, but no action is taken. At a project level, a set of quantitative requirements is defined as a starting point in each project. Also, a standard set of effective measures is collected to inform new projects. Input from the adaptation strategy is used for this.
At present, risk assessments are only undertaken for heavy rainfall. In addition, other issues (e.g. heat, drought) are of interest, assuming this will be increasingly relevant based on recent climate forecasts.
Lessons learned?
Due to the practical approach, a good overview of climate and weather-related hazards was provided. However, to make this actionable, the effects of the hazards need to be better understood and preferably quantified. This allows for prioritizing locations and having a more solid grip on the size of the risk. Based on this, a cost-benefit analysis can be conducted for measures for the high-priority locations. As some of these steps have not yet been taken, and legislation requiring the implementation of climate resilience-building measures has not been issued, uptaking the results into a Climate adaptation strategy is very challenging.
