A realistic assessment of floodrisk includes understanding the potential for harm stemming from multiple hazards, such as combined inland and coastal flooding, or flooding in multiple locations, such as in recent regionally and nationally significant events.

A quantitative assessment of the risk of these types of events requires joint probability analysis, which has been applied in the latest flooding scenarios developed within the Cabinet Office’s National Risk Register(NRR) process, bringing together the latest assessments of hazards and threats to increase national resilience and preparedness.

The development of widespread flood risk scenarios considered within the NRR involved the application of new statistical methods using complex and specialist software. Working in close partnership with Defra and supply chain partners, those advances in statistical methodology have been translated into a practical tool – the Multivariate Event Modeller (MEM) – for the analysis of joint probability within flood risk management.

The MEM is designed to be applied more readily by trained practitioners for joint probability analysis in operational flood risk management, with case studies and supporting guidance. The MEM is a demonstration tool that allows practitioners to start analysing spatial or multivariate joint probability problems in more than 3 variables and combinations of up to 10 variables. It provides an alternative to use alongside existing methods, and does not supersede or take priority over other methods.

This user guide places the MEM within the context of existing good practice in joint probability analysis, listing some possible uses within flood and coastal risk management while noting some caveats and limitations to be borne in mind. Instructions are given on how to install the required software and how to run to MEM tool. Guidance is provided on the process of using the tool and what each of the 6 tabs within the tool does. Numerous screenshots (some annotated) are included.

Five case studies offer examples of how the MEM tool can be used in a range of environmental applications. The guide ends with a series of FAQs and a glossary.