Developing and evaluating Impact-based Forecasting (IbF) for flooding

Overview:

Flooding affects more people globally than any other natural hazard and the number of events is

increasing with the recent 20 year period (2000-2019) recording more than double the number of

flood event than the previous 20 years. Within India, the frequency of extreme storms have

increased three-fold during the last 70 years with the storm magnitudes and occurrence of flooding

increasing too. When combined with population growth, rapid urban expansion and the value of

assets exposed to the risk of flooding, the social-economic impacts of flooding have increased

dramatically over recent decades with this only set to worsen under climate change. Improved flood

(risk) forecasting has been identified as a key priority for increasing flood resilience and supporting

effective flood risk management in India.

The international research community and research agencies have been moving towards Impact-

based Forecasting approaches that not only forecast the hazard but also the potential impact of the

hazard to help with decision making - as recommended by the World Meteorological Agency. Key

challenges are how to account for uncertainty in the hydro-meteorological forecasts, and how to

develop and evaluated the IbF end-to-end system to ensure the outputs are actionable by users. Use

of ensemble hydro-meteorological hazard forecasts are a fundamental component but there are

open research questions as to how best to form these ensemble forecasts and how to evaluated

them. Secondly, evaluating and communicating the skill in Impact-based Forecasts is a new and

emerging research area that requires novel techniques.

A particular hotspot for flooding in India is the south west coastal state of Kerala that has the

mountainous Western Ghats and catchments draining westward to the Arabian sea. During the

monsoon season (June-September), heavy rainfall can produce serious flooding with recent events

in 2018, 2019 and 2020 causing major impacts. The supervising team have been collaborating with

the UK Met Office and operational partners NCMRWF (National Centre of Medium Range Weather

Forecasting) and IMD (Indian Meteorological Department) to develop a prototype IbF system for

Kerala that will form the basis for the research and provide an exciting opportunity to work with

national Meteorological Agencies and for the research to have real-world benefits.



Methodology:

The Flood Hazard Impact Model for India (FHIM-India), co-developed by the supervising team and

Indian partners, will provide the framework for the research. It uses the Grid-to-Grid

(G2G) distributed hydrological model configured at ~1km scale over southern India and combined

with the high-resolution (<30m) HiPIMS (High-Performance Integrated hydrodynamic Modelling

System) to model city-scale flood inundation. The resulting estimates of water depth and velocity

can be linked directly to receptors in the calculation of impact severity.

The Flood Risk Matrix framework combines uncertainty from ensemble rainfall forecasts, such as

NEPS-R (NCMRWF Regional Ensemble Prediction System), together with the severity of flooding

forecast. The risk is then summarises at appropriate levels of integration in space (e.g. Ward or

Village area) and time (e.g. forecast horizon). The research will explore and evaluate alternative

ensemble forecasting methods and develop novel verification approaches for IbF outputs. Use of

HPC environments (e.g. JASMIN or BEAR at Birmingham) will be required.