Doktorarbeit

Climatic changes in heavy precipitation on a European scale

Heavy precipitation events can have large impact on several regions in Eu-
rope as they are often associated with some of the most destroying natural
hazards, like, for example, floods in the riverine regions or severe land slides
in the mountainous areas. The result often represents a threat of human life,
property, and infracstructure.

In a warming climate due to enhanced greenhouse gas concentrations in the
atmosphere, precipitation in general and its upper percentiles in particular
are expected to increase. Whereas the mean precipitation is proposed to
change due to the global energy budget, the heavy precipitation is expected
to change due to the increased amount of column integrated water vapour
which the atmosphere can hold when the air temperature is increasing. This
dependence is decribed by the Clausius-Clapeyron relation which suggests
an increase of the atmospheric moisture content by about 7% per degree of
warming. Also, the availability of moisture is expected to steer the intensity
of heavy precipitation events.

Europe is characterized by a variety of regional factors, such as, for example,
the Alps or the Mediterranean Sea, which have a large impact on the regional
weather and climate. Therefore the investigation of climatic changes on a
regional scale is indespensable and high-resolution regional climate models
represent an appropriate tool. For extreme precipitation events, regional
modeling is of special importance as they are often forced by convection
on small scales. The quality of representing heavy precipitation in regional
climate models is mainly dependant on the spatial resolution on the one
hand and the cumulus convection scheme on the other hand. Therefore it is
important to investigate how well the models are able to reflect the processes
responsible for the formation of heavy precipitation.

To understand the nature of heavy precipitation and its changes in the fu-
ture, one has to investigate both thermodynamical and dynamical processes
and their alterations in as most detail as possible. Thermodynamical factors
include for example the possibility of strong convection formation which is
described by the convectively available potential energy (CAPE), the avail-
ability of moisture in the air, or the latent heat flux. On the other hand, dy-
namical factors, that is, changes in the atmospheric circulation cause changes
in the transport of moisture.

This study shall tackle the following major research questions:
• Which trends in heavy precipitation can we see in Europe? How are
they distributed regionally and seasonally?
• How can the trends be explained physically? Which are the dynamic
and thermodynamic causes for changes in heavy precipitation?

Forschungsinteressen

• Starkniederschläge und deren Variabilität
• Klima der Polarregionen