The flood that struck Germany this summer is the largest flood in Western Europe since 1985. The flood water caused major damage to infrastructure, loss of life and created challenges for emergency preparedness and business. Society can benefit from being well prepared for the weather, including the extreme events we have today and the weather we expect in the future. To help us be prepared for the next extreme weather event, researchers on flood, extreme rainfall and statistical modeling, together with key infrastructure owners and representatives from municipalities,, have formulated a set of research questions that will be answered in the ClimDesign project:
Why do we experience a 100-year flood much more often than every 100 years?
How much water can come in one minute or one hour, either in the form of extreme rainfall or flooding?
How often can we experience extreme rainfall or flooding in a city or along a stretch of road?
How extreme will these events be in a changing climate?
To answer these questions we will use observations of extreme rainfall and floods to establish statistical models that estimate design rainfall and floods. Furthermore, results from climate models will be used to estimate how large changes we can expect in extreme events in the future 50-100 years. The researchers in ClimDesign will address four important challenges: (i) creating statistical models for extremes with durations of one minute to several days, (ii) creating models that can be used where there are no direct measurements, (iii) creating models that describe the relationship between extreme events at different locations (iv) explain how extreme events change as the climate changes.
During the first year of the project, new statistical models have been developed for both extreme precipitation and floods for durations from one minute to several days. For precipitation, new intensity-duration-fequency (IDF) curves that include uncertainty in design rainfall estimates are developed. A newly developed approach ensures that accumulated design precipitation increases with duration provide good results. These recent developments will be available to the public through services provided by the Meteorological Institute. For floods, flood-duration-frequency (QDF) curves with similar properties have been developed.
In ClimDesign, researchers and practitioners collaborate to develop models and tools so that the results can be used in community planning. The new IVF and QDF curves will be made available as tools for practitioners. Through several case studies, we want to exemplify 'best practices' for the use of new methods.
The main objective of ClimDesign is to generate user-relevant design values based on intensity-duration-frequency (IDF) and flood-duration-frequency (QDF) curves that account for a changing climate at individual locations and across regions. A project team of experts on floods, extreme precipitation and statistical methods together with major infrastructure owners, will collaborate to handle the challenges emanating from this objective. ClimDesign will move the frontier of knowledge by (i) improved understanding of temporal changes in extreme events and handling non-stationarity in estimating design values, (ii) quantifying the risk of extreme events within a region and (iii) incorporating projected changes in extremes into design values. A particular challenge related to climate changes effects is the expected changes in seasonality of extremes. Spatial analysis of extremes is important for the estimation of an area reduction factor of extreme precipitation, i.e. what is the ratio of a 200-year precipitation event for an area of 1000 km2 compared to a rain gauge? Spatial analysis of extremes is also important for assessing the spatial extension of a 200-year flood and for assessing how often one of the culverts along a road might experience a 200-year rainfall event. The high-dimensional extreme value modelling needed for analysing spatial extremes is a methodological challenge.
Selected project findings will be implemented in operational tools, and the project team will suggest updates of existing guidelines for flood estimation. Infrastructure owners, areal planners, municipalities and consultancies’, will use the project results for climate change adapted estimates of design values. This will reduce flood risks and thereby reduce the vulnerability to floods and increase infrastructure resilience. The research tasks will be carried out on case-studies suggested by the stakeholders, ensuring that there is a close link between research questions and user needs.