LIST is conducting research on rainfall and extreme flooding

The summer of 2016 has been marked thus far by particularly abundant rainfall. Due to a high potential for stormy weather conditions, there have been multiple resurgences of extreme rainfall events. This was particularly evident on Friday 22 July 2016, a day on which total rainfall reached 49mm at the Bettendorf station and 69mm at the Christnach station (source: the Administration of Technical Services for Agriculture). Such high accumulated rainfall is usually only reached in Luxembourg on a monthly basis. The maximum intensity of the rainfall was exceptional in Christnach, with 53mm recorded over an hour, and no less than 20mm in 10 minutes. According to initial statistical calculations, this kind of intensity was last seen more than 90 years ago. Similar levels of intensity were recorded last Friday at the Bettendorf station (44mm over an hour, with this kind of intensity last seen 80 years ago, and 16mm recorded in 10 minutes, last seen approximately 20 years ago).

During rainfall events of this kind, soil infiltration capacity is quickly reached and most of the rainwater flows over the ground surface. This leads to overflowing of small streams, which, in turn, causes flooding of larger rivers. Exceptional water levels were observed on Friday in the White Ernz River in the west of the country (source: Administration of Water Management). The Larochette limnigraph recorded a maximum level of 2.23m. At the Reisdorf station, the maximum water level observed was 3.11m, while the highest water level ever recorded to date has been 1.81m!

The exceptional rainfall events and floods over the last few days and weeks of July 2016 have rapidly amplified the current challenges faced in terms of forecasting and the management of exceptional weather and hydrological events. In particular, the reaction of streams and rivers to extreme rainfall inflows cannot be fully captured by current observation systems. Therefore, the phenomena that lead to flooding of such magnitude and speed can only be reproduced based on extensive estimations made by water level rise and flooding forecasting models. In these conditions, these are applied well beyond their usual scope of application.

Hydroclimatology researcers working around the clock

This last aspect is currently hydroclimatology researchers' main concern.  Indeed, the concept of the lack of stability of hydrosystems (waterways, rivers) goes hand in hand with changes in ground occupancy (e.g. waterproofing large urbanised surface areas and certain types of agricultural activities) as well as climate change. These changes lead to changes in the hydrological behaviour of waterways. They react increasingly quickly to extreme rainfall inflows, leading to peak flows rarely achieved, if ever, until very recently. In this context, mention must be made of the fact that climate change goes hand in hand with a reconsidered energy policy, while adaptation to climate change is closely linked, in our region, to aspects of water management.

In order to take into account these aspects as best as possible, it is imperative to develop measurement tools and protocols (e.g. rainfall and flow meter measurements, etc.) capable of displaying unparalleled spatial and temporal resolution. At the Luxembourg Institute of Science and Technology (LIST), research is conducted to better understand and limit the impact of extreme weather and hydrological events. Besides the development of measuring tools that must provide up-to-the-minute information on rain-flow transformation processes, new concepts dedicated to modelling and forecasting extreme weather events are being developed and tested. In this domain, several research projects are currently under way with the support of the National Research Fund, in close collaboration with the Water Management Administration and the Administration of Technical Services for Agriculture. The catastrophic events of the last few days have shown more than ever the benefit of this type of research and collaboration between public research and government stakeholders responsible for managing our natural resources.