An interesting article from Rahman Khatibi [thanks Rich] about the role of flood forecasting and warning in sustainability of flood defence.
The core of the paper, if I understand correctly, is
- The idea that structural defence ("hard", "preventative", "bounded", "finite" measures) tend to lead to a positive feedback cycle where value at risk increases as probability of flooding is reduced.
- Looking at flood forecasting and warning as part of the overall system of response to flood risk encourages a more balanced system where the natural negative feedback (risk leads to people living elsewhere) isn't so severely suppressed.
I like this idea, and it fits with my earlier comment that
Systems without negative feedback tend to spiral out of control. [Hamish Harvey]
Khatibi argues that particular types (categories) of model are a better fit to particular types of physical system. Intuitively apparent, but establishing with any confidence what those appropriate combinations are would surely require a very large amount of data.
… research activities are promoted by the NFWC to produce prescribed Pf values [measures of the probability that an accurate forecast is made and disseminated] for each category of modelling techniques. [Rahman Khatibi]
How well can these values be defined? How clear a categorisation of physical system type is possible? Many different categorisation schemes are clearly possible, such as
… characterising these systems based on the significance of a particular term(s) in the Saint-Venant equations … using the lead-time as the basis for classification of catchment systems … there are other possible approaches [Rahman Khatibi]
This all suggests that a faceted classification system is needed, and this in turn provides a potential combinatorial explosion in the number of Pf values to be calculated.
Update 2006-02-24: broken links fixed.
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