• Review of existing methods for (i) detecting trends and shifts in time series of hydrological extremes, and (ii) non-stationary flood frequency analysis. A list of methods for use in Europe will be identified.
• Guidelines for development of regional procedures for flood frequency analysis in a
changing environment under the different climatic conditions in Europe.
• New framework for risk-based design under environmental change by introduction of non-stationary design estimates.
• Collection of open-source computer programs for non-stationary flood frequency analysis.
Standard statistical procedures for flood frequency analysis are based on the assumption of stationary; that is, the extreme flood statistics do not change in time, and hence past observations can be used to estimate design flood events. In a changing environment the assumption of stationary might not be reasonable, and more advanced statistical methods are required that explicitly accounts for the non-stationary of extreme flood characteristics. Flood frequency analysis for non-stationary processes has become highly relevant in the light of climate change, as it is expected that most parts of Europe will experience more frequent and more severe floods in the future. Besides climate related changes in flood frequencies also direct anthropogenic changes in the hydrological regime (e.g. land use changes, urbanisation, wetland draining) and river infrastructure developments need to be addressed.
A key-component of FloodFreq is to develop a scientific framework for assessing the impact of environmental change on flood frequency characteristics. The framework will be based on analysis of trends in historic data, combined with projections of future climate conditions from Global and Regional Climate Models (GCM/RCM) and analysis of historical developments of human induced changes in hydrological and hydraulic conditions. Process based modelling can be used to analyse human induced changes and isolate climatological changes in flood frequency characteristics. Powerful statistical tools are required to detect changes or trends in extreme flood characteristics and to model time dependent statistical properties. In addition, a changing environment calls for a completely new paradigm for risk-based design guidelines and standards.
Working Group 4 Report. A Review of Applied Methods in Europe for Flood-Frequency Analysis in a Changing Environment.