Tools for the Assessment of Regional Robustness Towards Flood and Drought Events under Climate Change

Probabilities and consequences of extreme weather events are increasing worldwide. To help communities prepare for this, the primary challenge is to properly assess and value flood and drought risks in the long term. Decision making on these risks involves a discussion with communities on these risks and the weighing of the planned investment cost against the expected risk reduction. Furthermore, attention should be paid to the acceptability of the (residual) risk in terms of expected annual damage, but also on the acceptability of potential impacts of the most extreme events, which are the low-probability/high-consequence part of the risk. This presentation will focus on two recently developed methods to support discussion on acceptable flood and drought risk levels. The first one is a so-called robustness analysis method, developed to understand the sensitivity of the water management system to floods and droughts under a wide range of climate conditions. Such an analysis requires that decision-makers define two thresholds: a resistance threshold, referring to the range of event magnitudes for which impacts are avoided, and a recovery threshold, referring to the level of event impact from which society can still recover. Recent applications on floods as well as drought in The Netherlands and USA have shown the added value of this method for risk-based decision making under climate change. The second method is a risk-based cost-benefit analysis method to derive economically efficient protection levels. This method has proven its value for deriving the new flood nation-wide protection standards in The Netherlands. These two methods are currently being applied in the context of water management in a new project funded by NOAA, in the Florida Everglades and adjoining urbanized areas such as Miami, Fort Lauderdale and Palm Beaches. This project will help supporting better decisions for managing water resources in this area, thereby reducing damage and investment costs. Critical system threshold required for the robustness analysis will be defined together with the local water authority, the South Florida Water Management District. The talk will show results of earlier applications of both methods as well as discuss preliminary results of the application in South Florida.