I was struck by the presentation of Carlos Velasco-Forero at the recent EGU General Assembly when he referred to a ‘critical need to develop defensible flood forecasts’ in Australia. He mentioned the uncertainties involved when dealing with decision making when rainfall and flood forecasts rapidly unfold and the challenges associated with communicating these uncertainties with responders. So what were some of the take home points from presentations across EGU19 and how can they support the scientist and decision maker through improved flood forecasting?
Integrating the disciplines of meteorological and hydrological science to improve the end-to-end framework for forecasting intense rainfall and flash flooding was presented by Linda Speight. Linda summarised the work that has been delivered as part of the recently completed NERC and Met Office funded Flooding from Intense Rainfall (FFIR) programme which included improved knowledge of catchment vulnerability to ﬂash ﬂooding, improved rainfall (radar) and river observations during events, improved forecasting of convection, and real time ﬂood inundation modelling.
Taking over from FFIR as a research initiative attempting to improve flash flood forecasting is the French ANR PICS project which will run through to 2021. As presented by Olivier Payrastre, the project aims to couple the disciplines and actors involved in flash flood nowcasting, from the meteorologist through to the decision maker. The aim is to integrate short-range forecasting chains incorporating high resolution precipitation forecasts, distributed rainfall-runoff modelling across ungauged catchments, DTM-based modelling of impacts including dynamic population exposure and vulnerability.
Whilst these highlighted papers were concerned with the forecasting timescales in the short range, Louise Arnal described the potential role for seasonal forecasting in flood early warning and an ‘autopsy’ technique to understand the relative contributions of various hydro-meteorological variables. Whilst unlikely to offer immediate operational benefit for most rivers, it did present some suitability for understanding the contribution to flooding on large-scale river systems such as the Danube. On a similar scale, Gabriela Guimaraes Nobre – who was awarded an outstanding student poster and PICO Award – described that whilst there had been great advancements in flood forecasting, it remains a challenge to provide useful impact-based forecast information and presented an approach for linking large-scale indices of climate variability and flood losses.
But back to the theme of flash flooding – Steven Boeing presented work on dealing with the uncertainties in urban scale surface water flood predictions. As part of the iCASP initiative (Integrated Catchment Solutions Programme), work is being carried out to understand how probabilistic rainfall forecasts can be linked to high resolution hydrodynamic modelling to produce hyper-local forecasts over short lead times. One key element of the work is to understand how responders are able to respond to such complex information.
As for the Australian case study, forecasting science developments are now supporting the availability of STEPS (Short-term Ensemble Prediction System) every few minutes compared to the current operational set-up of updating the hydrological forecast a few times per day which is now providing a framework for a probabilistic approach to flood warnings. However, as Carlos concluded (and matching a theme across other hydrological forecasting presentations at EGU19), whilst increasing the resolution of flood forecast information can be seen as a positive development, it in turn creates its own challenge of where science development meets the operational reality of delivering flood forecasting services.