As part of a new series, the FNR speaks to five experts about research trends in their domain. With climate change comes extreme weather: Hydrologist Laurent Pfister from the Luxembourg Institute of Science and Technology (LIST) explains the challenges this poses for weather prediction models.
Extreme weather conditions are increasingly common, as reflected in the growing number of stories about localised storms causing creeks and rivers to burst their banks and flood towns and wide areas of land, filling cellars and washing away cars.
“The frequency of such localised weather events has increased in recent years. And we assume it will continue to increase, even though the observation series are still too short for making valid statistical predictions,” says Dr. habil. Laurent Pfister, a hydrologist and head of the Catchment and Eco-Hydrology workgroup at the Luxembourg Institute of Science and Technology (LIST).
“The trouble is, the computational models we hydrologists use to model extreme weather conditions and water discharge situations are not designed for these kinds of events. We are going to have to spend the next years adapting our methods to the new conditions. For this, we need a generation of hydrologists who are very good at thinking laterally and solving technical problems; people who understand hydrology as much as they understand metrology and modelling.”
The troublemakers: sudden, localised storms
Extreme weather conditions are a result of climate change: at higher temperatures, the atmosphere can hold more water vapour and the consequences include severe storms and heavy downpours.
“What’s special about these events is not only that they are limited to small areas, but that they also occur very suddenly,” Pfister explains. “That makes it difficult to measure them with all the necessary instruments while they are still in progress. Also, the readings – such as the amount of precipitation or discharge into creeks and canals – are so high as to be off the scale of our computational models.”
This is a relatively new experience for Pfister and his colleagues, as the scientist explains: “Until now, hydrologists had assumed that water catchment areas were in a relatively static state. Sure, there are fluctuations in things like rainfall, groundwater level and other parameters. But even until a few years ago, we had still assumed these processes occur within well-defined limits over extended periods of time.”
The systems have left the stable condition
As Pfister continues, this has changed: “The systems have left the stable condition. They are progressively redefining the limits of our readings to higher or lower than ever before.”
The computational models researchers have always used to simulate the conditions of complex water systems cannot reflect this. “We need new models if we are to make any reliable predictions about the water regime in any given area.”
Numerous projects are already underway in Luxembourg to adapt the field of hydrology to the new situation.
“We are above all getting young people involved – doctoral students and post-docs,” Pfister reports. “They are learning from the outset to include different perspectives and disciplines in solving the problem.”
Tasks include developing mobile metrological networks, for example, that can be set up quickly in an area where an extreme weather event is predicted. “We also need new tracers – which are natural and artificial means of detection by which we can keep precise track of how the water flows underground and how long it stays in the rock layers.”
New methods, new data, new models
The data obtained by these new methods then has to be used for developing new models. This is a lengthy process, but well worth it, as Pfister observes:
“It is crucial to know how our water resources are developing and what influence new climatic conditions are having on them.”
Hydrology is accordingly on the verge of a revolution – one that will ensure we know everything we need to know about our most important, life-giving resource.
About Laurent Pfister
Dr habil. Laurent Pfister is Head of the Catchment and Eco-Hydrology Group at the Luxembourg Institute of Science and Technology (LIST), part of the Environmental Research and Innovation (ERIN) research department. In addition to various other grants, he is the coordinator of the Doctoral Training Unit (DTU) ‘Towards a holistic understanding of river systems: Innovative methodologies for unraveling hydrological, chemical and biological interactions across multiple scales’ (HYDRO-SCI).
INFO BOX: Luxembourg as a hydrological model region
Luxembourg as a hydrological model region
Luxembourg is a small country with a very uniform climate. Beneath its relatively uncomplicated surface, however, is a highly diverse geological substratum. This makes the Grand Duchy a place of extreme interest to hydrologists.
“We work together with research groups who come from everywhere in the world to study how groundwater currents behave here,” Laurent Pfister says.
One thing that makes this cooperation so productive is the accurate hydrological mapping of the land. “Over the last 20 years, we have built up a system of localised, nested observation areas here,” says Pfister. “These have been mapped out and characterised very accurately. Thanks to this accuracy, many hydrological processes can be fundamentally clarified here.”
Luxembourg has thus become a hydrological model region in Europe.