Risk mapping major Danish roads for flooding – Blue Spot model and results

21/04/2015 / 1 kommentti / Tagit :

The task of ensuring safety and mobility on roads can be challenged by various factors such as accidents, wildlife, and weather extremes. The latter has over recent years, even decades, gained more focus due to an evident increase in incidents of road flooding due to a higher frequency of extreme weather phenomena, leading to flooded roads.

Prognostics, published by scientific authorities, e.g. IPCC, unambiguously point to a continued trend in increasing global temperatures which, prospectively, will result in accelerated numbers of extreme precipitation phenomena. Thus, incidents of flooded roads will undoubtedly rise in future, provided that no adaptation measures are implemented.

Adapting roads to the future climate is in most cases expensive initiatives which, furthermore, oftentimes will lead to disruption and hindering of traffic flow due to construction. Thus, adapting roads to climate change is only considered feasible when resources can be allocated in an optimum manner.

In this context, the Danish Road Directorate has developed a model which can identify stretches of roads particularly vulnerable to floods and, equally important, where there is a significant consequence of a flood. By incorporating both vulnerability and consequence, stretches of roads in particular need of adaptation is identified including a socio-economical perspective.

The Blue Model was developed in this very context where a Blue Spot is defined as a stretch of road where the likelihood of flooding is high and the consequence hereof is significant.

Key to this model is the integration of climate factors, enabling the model to identify not only Blue Spots for present day climate scenarios but likewise for the prognosticated climate scenarios for the year 2050. We, in the Danish Road Directorate build our roads to be able to drain precipitation occurrences up to the equivalent of a 25 year return period. Figure 1 illustrates how the future climate will cause more frequent extreme precipitation events in a Danish context.

PRESENT DAY RETURN PATTERN (RP) RP 2050 RP 2100
mm years years year(s)
45 5 2 1
47,5 10 5 2
54,6 20 10 5
58 25 20 10
65,2 50 25 20
74 100 50 25
97,3 500 100 100
142,8 1000 500 500

Figure 1 – Illustration on how climate change will affect precipitation patterns to more frequent extreme precipitation events. Based on Danish statistical data on precipitation patterns and climate factors found in the IPCC report of 2007

 

In this figure, it is evident that with no adaptation actions, in particular at road stretches identified as Blue Spots, road flooding will become more recurring in the future, compromising safety and mobility.

As written previously, adaptation measures of roads are oftentimes expensive initiatives but also necessary to maintain safety and mobility both now and in the future. Blue Spot identification enable a vital risk map that can act as the chief factor to allocate resources in the most cost-effective, focused and smartest manner in order to make climate change adaptation more feasible, both in technical and political terms.

On the basis of multiple data types, among these are the data found in figure 1 to conduct analysis for the year 2050, analyses to determine the factors Likelihood and Consequence to identify Blue Spots are possible. The results are illustrated in figure 2 and figure 3 with respectively 11 and additional 17 identified Blue Spots. Please note that the Blue Spots identified in 2050 are all additional identifications. Hence, Blue Spots illustrated in figure 1 are likewise Blue Spots the year 2050.

 

 

Axelsen_Figure 2

 

Figure 2 – Illustration of the geographical distribution of identified Blue Spots for present day climate scenarios

 

Axelsen_Figure 3

Figure 3 – Illustration of the geographical distribution of identified Blue Spots for climate scenarios in 2050

Tämä artikkeli on osa Ilmastonmuutokseen sopeutuminen -juttusarjaa, joka julkaistaan Fintripin sivuilla kevään 2015 aikana. Lue sarjan esittely tästä.

Kirjoittanut: Christian Axelsen, Danish Road Directorate, Dept. of R&D and innovation. CAX(at)vd.dk
Kuva: Anders Ekström

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