Multi-Hazard Early Warning Systems: The Coastal Inundation Forecasting Initiative

Multi-Hazard Early Warning Systems: The Coastal Inundation Forecasting Initiative

By Val Swail, Emeritus Associate, Environment and Climate Change Canada

The Coastal Inundation Forecasting Demonstration Project (CIFDP) and its subprojects aimed to improve safety from flooding in communities at risk, a fundamental priority of WMO. CIFDP was unique in facilitating the design and development of a comprehensive alert and warning system for coastal flooding caused by multiple sources.

Coral Coast Fiji (SPC).png

Coral Coast, Fiji is one of the well-known tourist areas, where beachside resorts are located. The tourist beaches are prone to coastal inundation from long range swell from the southern ocean – the top image shows the event in 2011, and the second image shows the same umbrella, damaged after the event (Source: SPC)

Four separate and disparate CIFDP subprojects were undertaken, in Bangladesh, the Caribbean, Fiji and Indonesia (see WMO Bulletin 68(2), Early Warnings for Coastal Inundations). Each had a different set of forcing mechanisms which, coupled with the varying degrees of capacity and emergency management structure within the country, made them unique. Their successful implementation showed that integrated coastal inundation forecasting and warnings can be improved and coordinated by National Meteorological and Hydrological Services (NMHSs). In the following paragraphs, we describe the general considerations required to undertake a coastal inundation forecasting (CIF) early warning system, with some illustrative examples from the most recently completed project, Fiji1.

What to predict? Fiji experiences tropical storms that bring heavy rains and river flooding along with large storm surges and high seas and damaging inundation due to long period swells from extratropical storms in the southern ocean off New Zealand. When other factors – such as the tide and sea surface height anomaly and a fringing reef along the south coast – are taken into account, the forecast problems for a coastal inundation system in Fiji are very complex, requiring innovative modelling approaches and impact-based products. This is further complicated by the need for timely forecasts and warnings, usually with more limited capacities associated with Small Islands Developing States (SIDS).

It is very rare that the required accuracy of bathymetry and topography information is available, particularly in SIDS and Least Developed Counties (LDCs). Necessary meteorological and oceanographic information – waves, water level, river levels and flow – is also usually inadequate. As part of the Fiji project, improvements were made through detailed surveys to the bathymetry and topography information on the coral coast, vital for mapping coastal inundation (note that in the Caribbean subproject topography enhancements were achieved through the use of the TANDEM-X satellite, which provided data equivalent to the gold-standard LiDAR surveys). Wave measurements from buoys deployed on the Coral Coast as part of the CIFDP provide early warning of damaging swells coming from the south; they also provide vital information for the validation of the forecast systems. New water level measurements also provide valuable information for coastal flooding. Unfortunately, these buoys are often subject to damage, either by accident or through vandalism. A new WMO video (available here) was developed to raise awareness in local communities by highlighting the value of this critical ocean infrastructure for their own safety and livelihoods.

Forecasts and warnings are not useful unless they reach the “last mile”, i.e. the general population. In addition to radio and TV broadcasts, the Internet and social media are used extensively in Fiji for warning dissemination. Social media were widely used for warnings about TC Harold; the total reach of Facebook peaked to 172 864 according to Fiji Meteorological Service (FMS). Twitter had 6 404 impressions, and Instagram warnings were also issued.

Capacity development for FMS operations covered all the components of the forecast system and life cycle management of the new measurement systems for waves, ocean and river levels. Institutional end users, such as the disaster managers, were also trained to use the new forecast products. In addition, public awareness of coastal inundation was addressed by the development of a WMO video (available here) on the dangers and actions to be taken when fleeing or if caught in rising waters.

In April 2020, Severe Tropical Cyclone Harold carved a path through several Pacific Islands. As the storm approached, FMS issued its first ever wave and storm surge warnings during a cyclone, enabled by a new coastal inundation forecasting system of the CIFDP Fiji-subproject. Mr. Misaeli Funaki, Director of the FMS, reported that “the new coastal inundation forecasting system enabled the accurate recording of wave and storm surge magnitude, and sound numerical model guidance for storm surge and waves. This led to timely forecasts and formed the basis of successful evacuation warnings to vulnerable communities during Tropical Cyclone Harold (more than 2 000 people were evacuated), which minimized fatalities from such a devastating and life-threatening storm.” The Fijian National Disaster Management Office estimated that some 3 400 homes were impacted, and that damage was above FJ$ 10 million.

Tsunamis

Tsunamis are dangerous coastal threats. While infrequent, they have the potential to produce catastrophic impacts on coastal communities in a matter of minutes to hours. Tsunamis are not under the WMO mandate, however, many WMO Members have made their NMHSs responsible for issuing tsunami warnings. Thus, in this area, WMO collaborates closely with IOC, which leads a focused global tsunami warning and mitigation system. The WMO provides dissemination of tsunami warnings via the Global Telecommunications System (GTS) as well as transmission of data from some tide gauges via meteorological satellites.

While tsunamis have a different forcing mechanism and different predictive models, there are common requirements that are the same as for coastal inundation forecasting, including the need for better bathymetry and topography and for timely forecast dissemination 24/7 in a matter of minutes to hours. Many countries with vulnerable coastal communities also have operational tsunami warning systems. However, there are opportunities to leverage the successful international tsunami efforts in collaboration with the CIF-EWS; especially for community warning and the “last mile”.

Footnotes

1 This project was made possible through donor funds from the Korea Meteorological Administration (KMA) .