Coastal inundation occurs along vulnerable coastlines. The combination of storm surges – typically from tropical cyclones or extratropical storms – and waves, with riverine flooding at various tidal states regularly leads to major loss of life. At least 2.6 million people are estimated to have drowned due to coastal inundation caused by storm surges over the last 200 years (Dilley et al., 2005). Yet, most countries with vulnerable coastlines are experiencing increases in human settlement and levels of development for fishing, tourism and other infrastructure in coastal areas, leaving more people at risk. This has led to even greater concern for coastal flooding and inundation.
Changes are also occurring in catchment areas through encroachment on floodplains, land use and resulting modifications to runoff that can be exacerbated by ocean-related storm surges, extreme waves and so forth. Heavy rainfall often accompanies storm surges, resulting in rivers overtopping their banks, further worsening local flooding. Rising global sea levels also contribute to increased vulnerability.
These and other statistics highlight the increasing threat to populations, especially those in coastal areas, pointing to the need for coastal inundation warning systems that adequately reflect the various hazards and their interactions. The WMO/IOC (Intergovernmental Oceanographic Commission of UNESCO) Joint Technical Commission for Oceanography and Marine Meteorology (JCOMM) and the WMO Commission for Hydrology (CHy) decided to work together to address this threat. In 2009, they initiated the Coastal Inundation Forecasting Demonstration Project (CIFDP) to meet the challenges of coastal community safety and to support resilience building by enhancing coastal inundation forecasting and warning systems at national and regional scales.
Coastal Inundation Forecasting Demonstration Project
CIFDP was unique in facilitating the design and development of a comprehensive alert and warning system for coastal flooding caused by multiple sources. It focused on early warning in coastal zones and basins subject to tropical cyclones and storm surges, strong wave action from distant sources, tidal considerations and riverine flood events.
This initiative and its subprojects were designed to improve safety in communities at risk, which is a fundamental priority of WMO. JCOMM and CHy, in cooperation with numerous experts and related institutions, have primarily facilitated the accurate and timely forecast of coastal inundation from the viewpoint of the total water level envelope and its interactions with riverine environments and vulnerable communities. The modelling framework illustrating the complexities that are needed to reflect local hazards and their interactions is described in the CIFDP Implementation Plan (WMO, 2017a).
Only a limited number of national agencies concurrently operate storm surge, wave and hydrological models, and coupled coastal forecasting systems, and virtually none are in developing countries. Hence, CIFDP was designed to support national agencies in developing and using forecast products operationally and in creating links between them and coastal flood management programmes and other related user communities. This required extensive training in the use of these products under different hydrometeorological and risk situations.
CIFDP facilitated development and implementation of warning services for coastal inundation from oceanographic and hydrological phenomena, resulting from severe hydrometeorological events. The goal was to operate and maintain a reliable forecasting system that informs national decision-making for coastal inundation management by:
- Identifying national and regional requirements, particularly end-user needs
- Encouraging full engagement of all stakeholders
- Implementing coastal inundation end-to-end operational forecasting and warning systems
- Developing cross-cutting cooperation among different scientific disciplines and user communities
- Building communication platforms among researchers, forecasters and disaster managers involved in coastal inundation management
- Transferring technology to participating countries
- Providing specialized training for operators, forecasters and disaster managers
Four separate and disparate subprojects were undertaken in Bangladesh (completed 2017), the Caribbean (completed 2018), Indonesia (completed 2019) and Fiji (expected completion end of 2019). 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). The final reports of the subprojects provide implementation details (WMO, 2017b, 2018, 2019).
Figure 1. Coastal inundation predicted extent during Cyclone Fani, 1 May 2019, using the coastal inundation forecasting system developed by CIFDP-Bangladesh Source: Courtesy of Qamral Hassan (BMD) and Bapon Fakhruddin (Tonkin Taylor)
The coast of Bangladesh is subject to major storm surges, rivers overtopping banks and tidal impacts. The long continental shelf, shallow bathymetry, complex coastal morphology and long tidal range between east and west coasts are known features for generating high storm surges of long durations. On average, five to six tropical cyclones are formed in this region every year.
The United Nations Development Programme (UNDP) identified Bangladesh as the most vulnerable country in the world to tropical cyclones and resulting storm surges. Furthermore, the country has three large river systems flowing through it: the Brahmaputra, Ganges, and Meghna. The combination of the discharge of these major river systems and storm surge heights, which can exceed 10 metres (m) above mean sea level, can create catastrophic coastal inundation. Bangladesh was therefore selected as the first CIFDP subproject in 2009, in agreement with the Bangladesh Meteorological Department (BMD). Funding was provided by the United States Agency for International Development (USAID) Office of Foreign Disaster Assistance.
The storm surge model of the Japan Meteorological Agency (JMA) was upgraded to incorporate wave and tidal input into forecasting total water level estimates. Hydrological and hydrodynamic inputs from stream discharge were parametrized for input to the forecasting system. Cyclone information was ingested from the Regional Specialized Meteorological Centre, the Joint Typhoon Warning Centre and the Regional Integrated Multi-Hazard Early Warning System for Africa and Asia. The Delft Flood Early Warning System (FEWS) integration system was used. Bathymetry data, as major input to the warning system, were available from various sources with the best being that of the Bangladesh Navy. Digital elevation model data are critical for coastal inundation modelling, and those of the Survey of Bangladesh were used for this purpose. This illustrates some of the types of collaboration needed from data to model and establish a successful coastal inundation forecasting system.
A range of integration and operational requirements were considered before settling on an end-to-end impact-based early warning system design. This included adopting simplified modelling in some cases (such as the riverine discharge modelling), to keep the computer run time reasonable for provision of forecasts with adequate lead times to enable effective response, with at least 12–24-hour advance warning. The goal was not to change any procedures for disaster management in the country nor to change mandates, but rather to improve and assist the decision-making process for procedures already in place. The intent was to provide a system that better responds to the needs of Bangladesh and local stakeholders.
Since the system has been in place, fewer lives have been lost – 26 in 2016 and 2 in 2017 – compared with the thousands lost in the events of 1998 and 2007. Improved early warnings have helped to inform local decision-making, thereby contributing to the overall success of Bangladesh in this area of disaster risk reduction from coastal inundation. Future events could still overwhelm the country, but the evidence is extremely positive that this CIFDP subproject has been a success. The system is already being used by BMD, with a recent example, during Cyclone Fani in May 2019, shown in Figure 1.
Coastal inundation in Semarang, Indonesia disrupting traffic and flooding buildings in the city.
In terms of coastal flooding, Indonesia is unique in its vulnerability of coastal communities. An archipelago, it has almost 100 000 kilometres (km) of coastline subject to catastrophic flooding caused by a number of hazards, either individually or in parallel. These include high tides, heavy rainfall, river flooding, sea surface height anomalies and ocean waves. Even subtle pressure and wind variations can cause 0.5 m surges, which can affect low-lying land. Another unique and complicating aspect for the coastal flooding in Indonesia is large subsidence in urban areas, often more than 25 centimetres (cm) per year, coupled with ever-increasing coastal land development. Such issues can increase vulnerabilities over time.
Many agencies have collaborated in establishing a successful coastal inundation forecasting system in Indonesia. The Indonesian subproject agreement signed in 2017 included five ministries/institutions: the Meteorology, Climatology, and Geophysical Agency (BMKG) Maritime Meteorology Centre, Research Centre and Development of Water Resources of the Ministry of Pupera, Directorate of Coastal and Small Island Utilization, BIG Geodetic Control and Geodynamics Control Centre, and Directorate of Preparedness.
Outputs from the various coastal forecast systems were integrated under the Delft FEWS, including the Delft 3D (hydrodynamic) model for storm surge, the U.S. National Oceanic and Atmospheric Administration (NOAA) WAVEWATCH III® wave model, operated by BMKG for Indonesian coastal waters, and several other national and international models, including the Australian Bureau of Meteorology operational forecasts of sea surface anomaly and global tidal models.
It is important to note that BMKG has strong forecasting capability and well-trained staff and procedures. This allowed further advancement of the system as well as greater sustainability. The major funding for the project also came from BMKG, whose capability and capacity improved dramatically with CIFDP. The subproject was completed in January 2019, and a new national operational programme for coastal inundation forecasting for Indonesia was launched in April 2019.
Each year tropical cyclones pose a threat to Hispaniola – an island comprising two countries: the Dominican Republic and Haiti – during the hurricane season from 1 June to 30 November. Since 1851, more than 150 tropical cyclones have come within a radius of 300 km of the island, generating strong winds, high storm surges, large waves, heavy rainfall and riverine flooding. Prior to this CIFDP subproject, the Dominican Republic and Haiti did not have storm surge and coastal inundation planning and preparedness products available to aid in emergency management. This is also true for many other Caribbean countries.
With regard to project design and implementation, the WMO Regional Specialized Meteorological Centre for Tropical Cyclone and NOAA’s National Hurricane Center (NHC) provided the leading technical contributions in collaboration with the CIFDP Project Steering Group and other partners. Funding was provided by USAID. The National Coordination Team included experts, forecasters and disaster managers from various agencies of the Dominican Republic. Haiti was included in the efforts and various meetings, so its experts could also make informed use of products to issue warnings and influence emergency response.
The coastal modelling approach of the Caribbean CIFDP subproject was different from that used in the other subprojects. Rather than running a computationally time-consuming real-time full storm surge model coupled with a wave model, the subproject used the approach of the NHC in Miami, which can be run on a regular desktop computer. It involved making runs of various categories of hurricanes and the different pathways that could make landfall in Hispaniola using the Sea, Lake, and Overland Surges from Hurricanes (SLOSH) model. All possible scenarios of intensity, speed and direction of propagation, totalling about 10 000 possibilities, were run using a supercomputer. A wave model was run superimposed on the storm surge model output to account for wave action and raising the water level reached.
These SLOSH runs created a set of maximum envelope of water (MEOW) and maximum of MEOWS estimates. A critical element was the use of a Digital Terrain Model provided by a German Satellite (TanDEM-X) on a 12 m grid resolution. This fine resolution was needed as only coarse-resolution grid data were otherwise available and unacceptable for use in storm surge model runs. The bathymetry data were single-beam data used for tsunami models.
The resulting forecasts are available almost instantaneously, allowing more time for preparation of warnings and communications with emergency responders. Such a responsive system also allows the updating of guidance and warnings should the storm parameters change.
The demonstration project was completed in December 2018 and has been operational during the 2019 Atlantic hurricane season. Work is continuing in the post-demonstration phase to develop linkages between the storm surge forecasts and the riverine flood forecasts, the latter of which will be produced by the National Institute for Hydrological Resources. This effort will also consider the effect of forecast storm surges on riverine flood conditions, which may be predominately influenced by the heavy rain that accompanies tropical storms.
Flooding of resorts along the Coral Coast of Viti Levu, Fiji, caused by swell waves approaching from the south. (Photo: Pacific Community (SPC) 2011)
Fiji comprises more than 330 Pacific islands, only 110 permanently inhabited. The two major islands, Viti Levu and Vanua Levu, account for 87% of the population of almost 850 000. Approximately 75% of the Fijian population live on Viti Levu’s coasts.
Fiji’s location makes it vulnerable to tropical cyclones. These can cause dangerous and damaging storm surges in areas that have significant shallow coastal areas (shelves), particularly the NW coast of Viti Levu, which contributes to storm surges in the towns of Nadi and Lautoka. The south coast of Viti Levu does not have such a shelf area and is not subject to wind-driven storm surges, but is affected by long-distance swell travelling from as far south as Australia and New Zealand.
Tropical cyclones may bring extended periods of heavy rain to Fiji, causing inundation in the form of flash flooding or riverine flooding. When riverine flooding occurs in conjunction with storm surges, the resulting inundation may be much more severe than would have otherwise occurred from either the surge or riverine runoff occurring separately. This underscores the importance of surge and riverine modelling in combination. For example, this is the case for Nadi, which is a coastal urban city that can experience extensive and damaging flooding, resulting in loss of life.
This CIFDP subproject concentrated on the main island Viti Levu, in particular two major areas of population and economic activity: the Coral Coast on the southern edge of the island and the NW coast around Nadi. It was funded by the Korean International Cooperation Agency and the Korean Meteorological Administration. The Fiji implementation is a system of systems, with three distinct components:
(a) The south coast subject to inundation from distant swell waves
(b) The NW and NE coasts predominantly subject to storm surges (including from tropical cyclones)
(c) Riverine flooding, initially focused on the Nadi river basin.
Flooding caused by swell approaching Fiji from the south, coupled with high tides, can lead to serious and disruptive inundation. In terms of impacts, on the coral coast, there is a major transport road plus tourist hotels. Rather than running a complex, high-resolution wave model in real time, the forecast system accesses the results of hundreds of possible scenarios of swell height, period and direction. This allows for rapid results, and runs on a standard desktop computer. Alerts are broadcast 48 hours ahead of time and warnings given with a 24-hour lead time. The pre-operational phase has successfully provided early and comprehensive warnings for the south coast in a few major events.
To address the storm surges on the coastal slopes of the NW and NE portions of Viti Levu, JMA has implemented a storm surge model concentrating particularly on this island, but also encompassing all of the Fijian islands. This has been operating in trial mode since 2018, and is expected to be fully operational by the 2019–2020 cyclone season.
The Nadi river can overtop its banks relatively quickly, within 2–4 hours, following the occurrence of heavy rainfall that can accompany tropical cyclones and storms. To help address the need for riverine flood early warnings, the subproject has implemented a Nadi floodplain inundation warning system. The system uses a decision tree logic with inputs of observed and forecasted rainfall, storm surge levels and upstream hydrological conditions, based on expert knowledge, to provide guidance to forecasters. Implementation allows issuance of alerts and potential warnings of possible flooding in a complicated surge-riverine environment.
All components of the Fiji CIFDP have been implemented in pre-operational mode. It is anticipated that the demonstration phase, including transference to full operational capability, will be completed by the end of 2019.
WMO commissioned an independent review (Barrett and Canterford, 2018) of CIFDP that provided a thorough assessment of the innovative concept of the demonstration project with various conclusions and recommendations. The review confirmed that the subprojects have been successful in demonstrating the ability to make impact-based forecasts and warnings for coastal inundation when there are complex combinations of forcing mechanisms. The review found that there would be benefits to extending and enhancing CIFDP approaches in other vulnerable developing countries.
For example, the Fiji subproject has provided an excellent model for application to other small island environments in the South Pacific, while the Hispaniola case can be readily adapted to other Caribbean islands. The implementation in Bangladesh could be applied to other countries around the Bay of Bengal, and the Indonesia study, which focused on the cities of Jakarta and Semarang, could be implemented for other locations in Indonesia or neighbouring countries.
The Eighteenth Session of the World Meteorological Congress endorsed the main findings and recommendations of the review and removed the “demonstration” tag to create a new programme: Coastal Inundation Forecasting Initiative (CIFI). CIFI fits the concept of a Multi-Hazard Early Warning System (MHEWS) advocated in the Sendai Framework for Disaster Risk Reduction. Thus, it will seek out synergies where possible, including with tsunami early warning processes.
The successful completion of CIFDP has demonstrated the value of designing early warning systems with flexibility to account for inundation from multiple sources. Over the past decade, the dedicated efforts of Members working together with their partners in the participating countries as well as of JCOMM, CHy and many other experts has demonstrated the value of an innovative early warning system and the value of interdisciplinary collaboration at an international scale for the greater good of public safety.
Barrett, C. and R. Canterford, 2018: Assessment Report, Coastal Inundation Forecasting Demonstration Project (CIFDP). Geneva, World Meteorological Organization.
Dilley, M., R.S. Chen, U. Deichmann, A.L. Lerner-Lam, M. Arnold, J. Agwe, P. Buys, O. Kjevstad, B. Lyon and G. Yetman, 2005: Natural Disaster Hotspots: A Global Risk Analysis. Disaster Risk Management Series No. 5. Washington, DC, World Bank.
World Meteorological Organization, 2017a: Coastal Inundation Forecasting Demonstration Project Implementation Plan. Joint Technical Commission for Oceanography and Marine Meteorology Technical Report No. 64. Geneva.
———, 2017b: Final Report of the Coastal Inundation Forecasting Demonstration Project (CIFDP) for Bangladesh. Joint Technical Commission for Oceanography and Marine Meteorology Technical Report No. 95. Geneva.
———, 2018: Final Report of the Coastal Inundation Forecasting Demonstration Project (CIFDP) for Caribbean. Joint Technical Commission for Oceanography and Marine Meteorology Technical Report No. 96. Geneva.
———, 2019: Final Report of the Coastal Inundation Forecasting Demonstration Project (CIFDP) for Indonesia. Joint Technical Commission for Oceanography and Marine Meteorology Technical Report No. 97. Geneva.
Val Swail, Environment and Climate Change Canada
Sarah Grimes, WMO Secretariat
Paul Pilon, WMO Secretariat
Ray Canterford, Natural Hazard Specialist, Australia
Curtis Barrett, United States Agency for International Development
Yuri Simonov, RosHydromet