Previously, each region, climate or meteorological institute relied on its own analysis, often from one border to another, or even from one team to another. In the present case, the aim of the project was to harmonize theories by taking account of a maximum number of possible factors. Predictions were therefore dealt with from a hydrological and then a hydraulic point of view before including an assessment of economic damage by including urban factors. Thus predictions made it possible to suggest a better way of managing the impact of the effects of climate change on the river Meuse. 

A climate model between two extremes

Projections about future flooding of the river Meuse were divided into two main climate scenarios. The “dry-climate” scenario, which is the most optimistic one and the “wet-climate” scenario which is more pessimistic and which predicts a 30% increase in the one-hundred year flood peak flow.  The reality is certainly somewhere beween the two but it is difficult to be more precise using current means of projection. 

“2100, is a long time away”, says Arnaud Beckers, a doctoral student in geography and the first author of the publication. “We are obliged to establish several scenarios to define possible future events and observe the implications of each of these”.“Another difficulty”, continues Benjamin Dewals, “is that the scenario that will occur will not only depend on physical processes linked to climate. Political, economic and social decisions will also have an influence and these are an unknown quantity. All we can do is to take stock of all possibilities and to work with that in mind. According to what we find, we will be able to develop adaptation measures for protection or management which although they will not work in an optimal way for a given scenario, will be satisfactory when weighed against the range of possibilities”.

It is also important to specify that the two climatological extremes were not just randomly selected.“For example, explains Pierre Archambeau, a research engineer at the HECE unit, “the most optimistic theory of no cimate change was formed after a series of precise calculations resulting from a chain of models taking account of greenhouse gas emissions, political decisions, climate models on a grand scale such as the evolution of the atmosphere, temperature and precipitation. These results were then integrated into a more precise hydrological model which made it possible to calculate the evolution of the water runoff in the river Meuse basin. This is not a theory that we could have anticipated at the outset. It is a result in itself.”

By estimating the likely patterns of flooding, and by concurrently developing an urban planning model, it became possible to predict the economic damage that will be caused by these future natural catastrophes. 

What is the level of vulnerability of flood-risk areas?

One of the original aspects of this course is therefore the inclusion of the urban question as well as climatological considerations. “We realized ”, explains Benjamin Dewals, “that previous research studied climate evolution, but it did not attribute equal importance to other important factors such as the development of urbanization. And yet, this factor is of the utmost importance. Urbanization in the river basin, for example, changes groundwater flow dynamics. Rainwater seeps into the ground or flows more or less quickly into the rivers and in time, changes the intensity of flood peaks”. This is a first aspect of urbanization which does not require models with a high level of precision. However, it is not this aspect that is dealt with in this publication. The aim was to observe what happened in terms of damage by restricting access to flood-risk areas. In order to do this, it was neccessary to perfect models that made it possible to work on a small scale to reproduce dwellings, roads or protection walls.