Estimating the benefits of single value and probability forecasting for flood warning

Homes in this south-western suburb of Brisbane, Australia are inundated by floodwaters. Residents of the city's low-lying areas were urged to head for higher ground as the flood reached its peak (http://www.guardian.co.uk/world/picture/2011/jan/13/australia-brisbane-floods-eyewitness)

(image source: guardian.co.uk)

What is the value, expressed in flood risk, of flood warning systems? How can the benefits of a warning system be compared to those brought about by building a levee? How do single value forecasts and probability forecasts compare to one another in terms of the benefits they bring? What is the optimal lead-time for issuing a flood warning, balancing damage mitigation and forecasting uncertainty?

These are some of the questions that are explored in the first paper I published within the framework of my PhD research project on Predictive Hydrological Uncertainty. Micha Werner is my co-author. Today, the paper has been published in the special issue Latest advances and developments in data assimilation for operational hydrologic forecasting and water resources management of the open access discussion journal Hydrology and Earth System Sciences Discussions (HESSD).

The abstract:

Flood risk can be reduced by means of flood forecasting, warning and response systems (FFWRS). These systems include a forecasting sub-system which is imperfect, meaning that inherent uncertainties in hydrological forecasts may result in false alarms and missed floods, or surprises. This forecasting uncertainty decreases the potential reduction of flood risk, but is seldom accounted for in estimates of the benefits of FFWRSs. In the present paper, a method to estimate the benefits of (imperfect) FFWRSs in reducing flood risk is presented. These benefits include not only the reduction of flood losses due to a warning response, but also consider the costs of the warning response itself, as well as the costs associated with forecasting uncertainty. The method allows for estimation of the benefits of FFWRSs that use either deterministic or probabilistic forecasts. Through application to a case study, it is shown that FFWRSs using a probabilistic forecast have the potential to realise higher benefits at all lead-times. However, it is also shown that provision of warning at increasing lead-time does not necessarily lead to an increasing reduction of flood risk, but rather that an optimal lead-time at which warnings are provided can be established as a function of forecast uncertainty and the cost-loss ratio of the user receiving and responding to the warning.

HESSD is an open access discussion journal, handling discussion and peer-review of submitted papers. If and when accepted, the papers appear in HESS. For this paper, the review process is open until September 5, 2011.

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