Decadal changes of flood probabilities

• Applicant: Professor Dr. Günter Blöschl
• Subject Area: Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management
• Term: from 2017 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 278017089

Recently there have been a number of major floods in Europe and it seems as if they had increased in number and magnitude. These floods suggest that we may have entered a flood rich period, i.e., a period when floods are more frequent and large than usual. Novel methods and analyses are needed to ascertain whether this is actually the case, and if so why. Specific questions include whether the probabilities of the occurrence of extreme floods have changed in recent years, what are the drivers of such changes, and what is their impact on extreme floods in the future. In the first funding period, methods have been developed for identifying flood-rich and flood-poor periods based on observed flood data in Austria and Germany. Potential drivers of changing floods, such as climate change, land use change and river works, have been identified. The aim of the second funding period is to attribute flood changes to these drivers in a spatially distributed fashion. For example, in small agricultural catchments in the North of Germany, land use change is expected to be the most relevant driver while in the Austrian Alps climate processes may be more important. A formal attribution framework will be developed that accounts for spatially different runoff processes such as short convective rainstorms, long frontal precipitation and snow melt. As large floods are more relevant to society than smaller floods, we will explore how the flood changes and the role of their drivers vary with flood magnitudes. We will expand the flood data back to the sixteenth century by including historical information which will allow us to learn, e.g., whether floods were more frequent in cold or warm periods, which will support future flood predictions. A probabilistic flood change model will be developed that explicitly accounts for flood change mechanisms, such as soil compaction, loss of flood plain retention and a transition of snowfall to rain of extreme storms. The model will be used to explore how the drivers may affect future flood probabilities. The project breaks new scientific ground in at least three ways: (a) We will develop new methods for attributing flood changes to their drivers in heterogeneous regions that differ in terms of their flood generation processes. (b) We will explore how flood probability changes and the role of their drivers vary with return period, i.e. if small and large floods have a similar behaviour or not. (c) We will develop a probabilistic flood-change model that explicitly captures change mechanisms and allows predictions of potential future flood changes and their uncertainties. The project, led by Prof. Günter Blöschl and Dr. Andrea Kiss, will improve the understanding of flood changes and their drivers, and will ultimately lead to improved flood estimation methods in both gauged and ungauged basins.

• DFG Programme: Research Units
• Subproject of: FOR 2416: Space-Time Dynamics of Extreme Floods (SPATE)
• International Connection: Austria
• Partner Organisation: Fonds zur Förderung der wissenschaftlichen Forschung (FWF)
• Co-Investigator: Andrea Kiss