Decision support to client

For pluvial flash flood hazard assessment the definition of representative scenarios is an important topic. This includes the choice of appropriate precipitation-scenarios and their spatial distribution as well as initial conditions (e.g. antecedent soil moisture content, disposition of different areas of land use and soil types to produce surface runoff). Depending on the scale of a study the choice of scenarios can be either pragmatic (e.g. regional scale hazard indicator maps) or has to be more elaborate (e.g. design of mitigation structures). In either case information about the availability and quality of respective datasets is indispensable for the involved stakeholders.

Regardless of scale also possible future developments concerning the intensity and frequency of potential triggering events are of interest for developing sustainable coping and adaption-strategies.

Currently in Austria design-precipitation sums are available in approx. 6kmx6km resolution for return-periods between 1 and 100 years and durations ranging from 5 min up to 6 days. On national level currently no future projections of climate change are included in theprovided datasets. However some pan-European climate services provide projected change rates that might be utilized.

Temporal and spatial scale

Pluvial Flash Floods are often triggered by convective rainfall events featuring heavy rainfall with short-durations. Thus, the affected areas are in many cases confined to a few km² and their typical event-durations range from around 15min to only a few hours.

Thus, process scales of pluvial flash flooding are usually small with regard to spatial and temporal extends. In contrast, scales and responsibilities for decision making processes are varying and take place at different scales ranging from national and provincial (national and federal government authorities) to municipal and local level (municipalities and property owners).

Climate Indicators

Pan-European and local indicators

The most important climate indicators for pluvial flash flood assessment are statistical values characterizing extreme precipitation sums for short-duration precipitation events (“design-rainfall” for short-duration events). These indicators are available on national level in Austria based on extreme-value analysis of time-series from meteorological stations.

Projections of future developments for short-duration rain events are not available on the national level, but might be supplemented with data from pan-European climate-services.

However, given the local nature of convective storm-cells, there are well-known challenges in reliably measuring peak precipitation intensities. Therefore the usability and quality of the data from both national and pan-European climate-services with respect to pluvial flash flood impact studies should be carefully evaluated.

Case study workflow