Project 4 - Flood typology – controls in a changing world

Ralf Merz and Larisa Tarasova
Umweltforschungszentrum Halle (UFZ)

The sub-project 4 “Flood typology – controls in a changing world” will focus on developing process-based flood typology, which will account for the atmospheric, catchment and river system processes of floods, as all three are important in characterising the essential flood properties. Depending on the generating processes flood event types varies in their resulting characteristics such as the shape of the flood hydrograph, their spatial coverage, time of occurrence within the year, dependence on antecedent soil moisture. Hence a classification enables to break down the plethora of different flood events in typical representatives by a clear description of similarities and differences in flood producing processes and resulting event characteristics. The classification allows us to compare only those events, which stems from similar processes and will give deeper insight in the spatio-temporal changes of differing flood producing factors.
The objective of the first phase of the project was to develop a hierarchical typology of flood events in Germany and Austria. The classification is built on indicators of flood processes and resulting event characteristics such as the intensity, duration and spatial coverage of flood producing precipitation event, weather patterns, antecedent soil moisture states and snow. Using the classification we analysed how flood types changed regionally over the study period and how flood types changed from small to more extreme floods. In the second phase we will analyse flood events in very small and very large river catchments in Germany. Very small catchments are defined in this proposal, by catchments where the typical travel time of flood events can be smaller than one day. Hence such flood events cannot be analysed on the basis of daily data. Very large catchments are defined in this proposal as catchment where flood event characteristics are mainly affected by routing effects and the coincidence of flood peaks from sub-catchment. The research will be based on the typology approach developed in the first period, but will extend the analysis by focusing on sub-daily processes in selected small catchments and routing effects in larger catchments, which requires a deeper analysing of process of the flood waves along the river network. Additionally we will analyse the drivers of changing flood types and we will tackle the question of how flood type occurrence will change in future if e.g. climatic conditions, such as the frequency of rainfall event with high intensities will change. The analysis of the future evolution of flood types will be based on a scenario approach.

References

Tarasova, L., Basso, S., Poncelet, C., and Merz, R.: Exploring Controls on Rainfall-Runoff Events: 2. Regional Patterns and Spatial Controls of Event Characteristics in Germany, Water Resources Research 54 (10), https://doi.org/10.1029/2018WR022588, 2018.
Tarasova, L., Basso, S., Wendi, D., Viglione, A., Kumar, R., and Merz, R.: A Process-Based Framework to Characterize and Classify Runoff Events: The Event Typology of Germany. Water Resources Research 56 (5). https://doi.org/10.1029/2019WR026951, 2020.
Tarasova, L., Basso, S., Zink, M., and Merz, R.: Exploring Controls on Rainfall-Runoff Events: 1. Time Series-Based Event Separation and Temporal Dynamics of Event Runoff Response in Germany. Water Resources Research 54 (10). https://doi.org/10.1029/2018WR022587, 2018.
Tarasova, L, Merz, R, Kiss, A, et al. Causative classification of river flood events. WIREs Water. https://doi.org/10.1002/wat2.1353, 2019.