# Journal of Flood Risk Management

Version of Record online: 14 JAN 2010

DOI: 10.1111/j.1753-318X.2009.01059.x

© 2010 The Author. Journal Compilation © 2010 Blackwell Publishing Ltd

Additional Information

#### How to Cite

Hall, J. (2010), Journal of Flood Risk Management. Journal of Flood Risk Management, 3: 1–2. doi: 10.1111/j.1753-318X.2009.01059.x

#### Publication History

- Issue online: 4 FEB 2010
- Version of Record online: 14 JAN 2010

Risk analysis lies at the heart of flood risk management. Of course flood risk management amounts to much more than analysis. It also entails the framing of relevant policy objectives, the identification of the problem domains that are the targets for analysis and the assimilation of that analysis into decision-making processes. Most important of all, management requires some actions, which, in the context of flood risk management, are intended to reduce flood risks at present and/or in the future. These are followed by processes of monitoring, which can initiate new management cycles.

Yet, as the papers in the *Journal of Flood Risk Management* attest, flood risk analysis is now generating a great deal of attention, in particular among the technical professions and academics interested in flood risk management. Flood risk analysis provides a rational basis for prioritizing resources and management actions. It is intimately embedded in the flood risk management cycle: in problem identification, ranking of options and prioritization of targets for data acquisition. Moreover, there are now illuminating examples of how risk analyses have become the focal point for development of collective understanding of complex flooding problems. In situations where different actors in flood risk management have different perspectives and objectives (consider, e.g., land-use spatial planners, urban drainage engineers and flood defence engineers), flood risk analysis can provide a common platform for the development of collective understanding and the multipurpose solutions that were the subject of my previous Editorial in the *Journal of Flood Risk Management* (Volume 1, Issue 3). Moreover, flood risk analysis can provide the basis for targeting of flood warning and evacuation activities and for awareness raising among the general public.

Risk analysis can take many forms, from informal methods of risk ranking and risk matrices to fully quantified analysis. In the context of flood risk, in which many of the salient variables are continuous rather than discrete events and system responses are nonlinear, it is widely accepted that dependable risk analysis must incorporate some quantified representation of the main processes that contribute to flood risk, namely flood-generating mechanisms, the processes by which floods materialize at points where they can cause harm and the main processes of consequential damage.

The concepts and structure of flood risk analysis have now become so widely accepted around the world that it is easy to forget that essentially deterministic approaches, based on the estimation of a design flood and identification of flood defence designs to resist that flood, have persisted, in many places until rather recently. The deficiencies of such an approach are well recognized. Blinkered focus on a design event neglects consideration of the effects of loading conditions greater or less than the chosen event. In floods greater than the design event, it may not be justifiable to seek to prevent flooding, but mechanisms should be in place to minimize the effects of flooding should it occur and some consideration should be given to modes of failure in very extreme events in order to avoid the most fragile and catastrophic failures. Even in events less than the design event, there is still a finite probability of system failure, which should be accounted for in decision making. To this end, the application of reliability theory to flood defence systems has been an enormously fruitful endeavour, which is still incomplete, given the scarcity of information about the material properties of flood defences, their correlations and cross correlations. Moreover, quantified flood risk analysis provides a structure for systematic analysis of uncertainties and their implications for decision making.

However, notwithstanding the inevitable gaps in data that will confront anyone applying the methods of flood risk analysis to a flooding system for the first time, the framework of theory is well established and actually rather thoroughly elaborated upon. Witness the number of papers on flood risk analysis in journals and conferences that adopt basically the same systems framework and mathematical structure. Yet, in most of these applications broadly the same, and sometimes more or less identical, mathematical structures have been re-implemented in different countries and different times. In a sense, this is reassuring. It represents a convergence and maturation of the relevant science, which will certainly engender confidence in the users of quantified flood risk analysis that they are basing their decisions on a process that is mature and well tried (even if not in the location they have in mind). It does also begin to suggest that there may be wasteful reimplementation (if not reinvention) going on around the world, or maybe in the same country and for the same decision makers. It would be easy to leap to the conclusion that some generic risk analysis tool would be useful to avoid the inefficiencies of reimplementation, and indeed there are a number of developments along these lines, namely in the HEC-FRM program from the US Army Corps of Engineers, the UK Environment Agency's Modelling and Decision Support Framework (MDSF2) and the PC-Ring program developed for Rijkswaterstaat (Dutch Department of Public Works). However, all of these systems have been developed with particular configurations of the flooding systems in mind, while the scope of flood risk analysis is rapidly expanding. In the United Kingdom, for example, the widespread floods of 2007 have placed a new focus upon flooding in urban areas and interactions with sewer systems, which do not readily fit into the conceptualization of the flooding system on which MDSF2 is based, because of the high dimensionality of the boundary conditions, the increasing use of synthetic–spatial temporal rainfall simulations (as opposed to explicit joint probability distributions of boundary conditions) and the possibilities of sewer failure. Another direction of future development is to ever broader scales, to consider correlation of extreme floods on national and even continental domains in order to generate full loss-probability functions rather than mathematical expectations of damage. This upscaling is motivated in part by the reinsurance industry, but also by the need for national planning for very widespread events. These are developments that are inherently interesting and show great practical promise, and yet once again they fall outside a one-size-fits-all conceptualization of the flood risk analysis calculation.

Is there a middle ground that can be located between persistent reimplementation of well-established probabilistic calculations and a futile aspiration to encode every necessary variant on the flood risk calculation within a monolithic tool? The solution surely lies in careful and freely available implementation of the basic *structures* of flood risk computations, which are now well settled, from which customized implementations can be constructed. Moreover, as the foregoing arguments indicated, flood risk analysis is actually a component in broader processes of decision analysis (under uncertainty). Thus, we need risk analysis components from which broader decision analyses can be constructed. Given the well-established status of the core flood risk analysis structure and the basic integrals, there seems to be little to be gained from proprietary ownership and much to be lost from a lack of transparency. Yet, to reach a point in which there is an open global community working and exploiting a common basic framework for flood risk analysis requires an up-front investment in initiative and time. Something of this seems to have been achieved with OpenMI, which is now gaining impressive international attention, but the intersection between OpenMI (which is focused on time-step coupling of simulation models) and flood risk analysis, which is a structured probabilistic integration wrapped around simulation models, is at most partial. Can we do the same for flood risk analysis?

In the *Journal of Flood Risk Management*, we will continue to welcome innovative papers on every aspect of flood risk analysis, alongside case studies that can provide new insights that are of relevance and interest to the flood risk management community. We expect papers on analysis to clearly adumbrate the means by which the proposed analysis can be expected to improve flood risk management decision making. We hope that over the coming years, the Journal can enable a global community of flood risk management professionals to develop open, flexible and dependable approaches to the calculations that underpin good flood risk management decisions.