Climate Change and Change in Land Use in Luxembourg - CLIMAT

Coordinating Institution: CRP Gabriel Lippmann
From: 01/10/2003
To: 31/12/2007
Budget: 391,739.00€
Contact(s): Pfister Laurent

Summary

With the development of industrial activities since the second half of the 19th century, important landuse changes have taken place in our region (urbanisation, changes in agricultural practices, canalisation of rivers, development of modern transport infrastructures, etc.). Most of these modifications are likely to have had an influence on the rainfall-runoff transformation processes. Since the beginning of the 1970’s, significant changes in seasonal rainfall totals have been detected, characterised by a progressive increase of winter rainfall and a decrease of summer rainfall. This seasonal redistribution of intra- and interannual rainfall totals is also likely to have had a direct consquence on the hydrological regime of our river systems.

The objective of the CLIMAT project was to determine the relative weight of the changes in landuse and rainfall contributions on the hydrological regime of our rivers, with a focus on peak discharges and floods in the main alluvial floodplains of the Grand-Duchy of Luxembourg. The research focusing on a hypothetical link between landuse and/or climate changes on the one hand, and peak discharges on the other hand, had to rely on the analysis of historical hydro-climatological data series, as well as on the modelling of the hydrological behaviour of our river systems under past and future climate scenarios.

The analysis of meterological time series covering the past 150 years has shown that the daily thermal amplitude has considerably increased since the 1950’s. In the Grand-Duchy of Luxembourg, the mean annual temperature has increased at a rate of 0.6°C since 1977.

The investigations on historical meteorological data series have further shown that since the end of the 1970’s a positive NAO (North Atlantic Oscillation) phase has led to an increase of the frequency of zonal atmospheric circulation patterns, especially during winter months. The general North-North-East – South-South-West orientation of the dominating orographic obstacles in the study area has induced a zonal anisotropy, largely influencing the increase of winter rainfall contributions due to westerly atmospheric fluxes.

As a direct consequence of the changes that have affected winter rainfall totals, a clear increasing trend has been determined for maximum winter discharge in our river systems over the past 30 to 40 years. However, this trend is characterised by a strong spatial heterogeneity, which is in turn directly linked to the anisotropy that affects the trends in winter rainfall.

The investigations focusing on future climate change impacts on our river sytems have shown that currently most scenarios still have very similar occurrence probabilities. The current state of knowledge does not permit to draw reliable conclusions on the future characteristics of the hydrological regime (especially extreme events) of the Alzette and Sûre rivers. Only general features, such as increased winter discharge and lower summer discharge can be considered as being very likely to occur during the second half of the 21st century.

Collaborations:

The climate scenarios were defined and calculated in collaboration with the Ecole Polytechnique Fédérale de Lausanne (Switzerland).

Figure 1 : Discharge simulations of the Pétrusse River in Luxembourg-City for land-use conditions relative to 1770 and 1999

Figure 2 : Alzette River near Gosseldange