Abstract
Flood modelling and mapping, underpinned by hydraulic modelling, are typically used to define flood hazard and allow a quantification of risk and associated Expected Annual Damages (EAD). At a regional or national scale, such modelling is often a lengthy process, which does not allow changes in risk resulting from new science such as revised rainfall frequency estimates or climate projections to be readily quantified by policy makers. A framework of interpolation and extrapolation methods has been developed in the R language via practical application to the city of Perth in central Scotland. These methods allow existing flood mapping, design rainfall estimates and property receptor datasets combined with revised design rainfall estimates to be used to rapidly assess the consequences of change in risk and EAD. The results are evaluated against detailed hydraulic modelling and are shown to provide a good approximation of changes in flood depth and EAD for properties previously modelled as at risk of flooding, particularly residential properties, with lower confidence for non-residential properties. In the Scottish context, the methods are considered to be robust for regional and national scale application and would allow policy makers with a means to rapidly determine the consequence of changes in design rainfall estimates without the immediate requirement to undertake complex hydraulic modelling.
Highlights
Academic Editor: Momcilo MarkusSurface water flooding is a significant problem within urban areas during heavy rainfall
The number of discrete events analysed for the Expected Annual Damages (EAD) calculation is often limited to a few annual exceedance probabilities and a linear interpolation is performed between each damage-exceedance probability point of the curve, high probability, low damages events contributing the most to the EAD [23]
For 77 catchments across Scotland (Figure 2), pluvial flood hazard data based on detailed 2D hydraulic modelling [14], property-level flood depths, and EAD values [6] are available for this study; these are known as ‘Regional Pluvial’ catchments to distinguish them from broadscale national modelling that exists
Summary
Academic Editor: Momcilo MarkusSurface water flooding is a significant problem within urban areas during heavy rainfall. Climate change projections suggest such rainfall is likely to increase, and without significant adaptation, in many cities, drainage systems will be unable to cope leading to greater damages [1,2]. Future projections show that across Europe, flood average annual losses could increase by 5% to 10%, according to seasonality per decade under a 1.5 ◦ C global warming scenario [3]. Property exposure to frequent flooding in the UK could increase by 20% with an associated increase in expected annual damage of 25% by 2050 under a 2 ◦ C global warming scenario [4]. In Scotland, there are approximately 210,000 properties at risk of surface water flooding at the 200-year return period (0.5% annual exceedance probability) equating to GBP 310 million of potential annual average damages [6]
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