Floods: understanding, monitoring and anticipating

20 July 2021

Hydrology.

Western Europe has been hit by days of torrential rain and flooding. Several teams of researchers are monitoring flood events from the ground to the sky.

Why do heavy rains and floods occur? Can we predict such disasters? Where does Research Luxembourg stand?

The Luxembourg Institute of Science and Technology (LIST) environmental researchers use their interdisciplinary skills in hydrology, hydrogeology and remote sensing for extremely precise flood monitoring.

What caused the devastating flood events?

Heavy rainfall leads to what is known as flash flooding. In this case, a lot of rain falls locally in a very short time. So much that the soil surface is quickly saturated with water and the rest of the rain can no longer drain away. This results in flooding. Such a situation can also happen after a dry period of several weeks. But when too much rain falls at the same time, the water does not have time to reach the deeper layers of the soil.

The recent situation is different. It is not just a local phenomenon affecting individual villages, but a large region that spans several countries. The weather has been rather erratic and rainy for weeks, and rain has been falling heavily and continuously. The soils are saturated from the ground up. All the rain can hardly infiltrate or be absorbed by the soil.

“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 assessments.”

Prof. Dr. Habil. Laurent Pfister
Head of the Environmental Sensing and Modelling unit at LIST

In the Greater Region, warm and humid air masses from the Mediterranean collided with colder air masses from the Atlantic. This strong contrast eventually led to very heavy rainfall and flooding.

Collecting water pathways data to anticipate extreme events

Data collected on water pathways (infiltration into the soil, surface runoff, water residence time) are particularly relevant to better understand and anticipate extreme hydrometeorological events like floods.

“By improving our knowledge of the catchment areas’ functioning, their capacity to collect, store and redistribute rainwater, we will be able to better anticipate their response to increasingly significant climatic and anthropogenic forcing.”

Prof. Dr. Habil. Laurent Pfister
Head of the Environmental Sensing and Modelling unit at LIST

Since 1995, LIST has gradually implemented a rather unique hydro-meteorological observatory – consisting of nearly twenty nested catchments of different sizes and physiographic characteristics (geology, soil type, land use, topography), all monitored every 15 minutes for a plethora of meteorological variables, river discharge, and groundwater levels.

The observatory has become a testbed for exploring the potential for new technologies and protocols to overcome technological limitations and bottlenecks that have eventually stymied progress in water resources research for decades.

The tested innovations span from telecommunication microwave links for measuring precipitation, thermal IR imagery for mapping saturated area dynamics, portable mass spectrometers for measuring in the field stable isotopes of O and H in water, passive samplers for deriving seasonal sequences of flood event loads, terrestrial diatoms as hydrological tracers of the onset/cessation of surface runoff, to the use of freshwater mussels to reconstruct decades of signatures of stable isotopes of O in stream water.

Thanks to this dense observation network, the LIST environmental researchers have been able to exploit hydrometeorological data series dating back more than two decades – thereby demonstrating the decisive role of the geological substrates and their contrasting degrees of permeability – and thus water storage capacity – in the genesis of floods.

This information will be pivotal in the assessment of the country’s water resources resilience to global change.

Discover more about LIST Environmental Sensing and Modelling unit

LIST researchers have developed the HASARD® software, an unprecedented tool for generating real-time flood maps on a global scale. Read more about HASARD®.

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