When Hurricane Ida made landfall in Louisiana in August 2021, it was classified as a Category 4 storm with winds of 150 mph, a storm surge measuring over five feet in New Orleans and 10 feet in Grand Isle. , and precipitation of more than 15 inches. Inland flooding from rain, combined with overflowing streams and flooding from storm surges, resulted in compound flooding.
In 2021, extreme rain flooding affected residents across the United States, causing property damage and loss of life. These extreme weather events are more and more frequent. In fact, a recent United Nations report—Climate change 2021– found that heavy rains are likely to become more intense and more frequent, leading to an increase in severe flooding around the world.
Climate change preparedness and response is a priority for the Department of Homeland Security (DHS), with Secretary Alejandro Mayorkas announcing earlier this year the creation of a Climate Change Action Group to steer the cross-functional efforts of the department. And as a research and development arm of DHS, the Science and Technology Directorate (S&T) develops resilience tools and resources to help communities and first responders prepare for the effects of climate change.
Community planning for flood risks in coastal communities
South Carolina has seen its share of historic weather events that have caused severe flooding. In October 2016, Hurricane Matthew was a Category 1 storm when it hit the state and left in its wake crushing flooding caused by storm surges, heavy rains and overflowing rivers. In September 2017, Hurricane Irma, one of the strongest hurricanes on record in the Atlantic Ocean, caused extensive destruction in the Caribbean and the southeastern United States. over Georgia and South Carolina, it caused extensive flooding caused by storm surges and gusts of wind, tornadoes, torrential rains and river floods. When an area is submerged by more than one flood source at the same time, it becomes a compound flood event.
S&T has partnered with Deltares USA to manage the risks associated with this type of event, developing a community-driven flood risk modeling and impact assessment decision support tool using open source data, models and software. S&T and Deltares are integrating a suite of open source tools the company has developed into a Community Flood Resilience Support System (CFRSS) that can help communities make more informed decisions about flood risks and l mitigation of climate change. The CFRSS models flooding and damage from the combined effects of tides, storm surges, heavy precipitation, and river flows to improve understanding and ability to cope with vulnerability to compound events.
S&T works with Deltares because of its robust open source software and scientifically validated models, and the practitioner’s focus on the company will ensure that the tools are useful to end users. Training materials are also being developed so that other communities can also learn how to take advantage of the technology.
“Our partnership with Deltares provides technology that connects multiple types of flooding and the expertise of local stakeholders has helped perfect the software into an effective community planning tool,” said Dr. David Alexander, Senior Science Advisor in S&T for resilience. “Additionally, users can play around with flood mitigation parameters, such as adding flood walls or pumps or elevated structures, to see how these would impact potential flood areas. “
Work with local experts
S&T and Deltares chose Charleston, SC as the CFRSS test bed because it had ideal conditions and had experienced flooding in the compound. The city has had to contend with coastal flooding caused by surges and tides, as well as hurricanes; it suffered from inland flooding due to heavy rainfall and river flooding; and it has faced flash floods caused by the changing landscape of a developing area. With all of these flood risk factors, Charleston was an optimal place to test and apply the CFRSS system.
In addition, S&T and Deltares are leveraging existing research relationships in Charleston, including with the National Oceanographic and Atmospheric Administration (NOAA) Coastal Management Office and the US Army Corps of Engineers, which already has a marine management study. risk of an ongoing coastal storm with the city. The CFRSS pilot project with Charleston will include a hands-on training demonstration, with the participation of community partners. This training is also an opportunity to test the latest version of CFRSS. The results will be shared with the Association of State Floodplain Management (ASFPM) 46e Annual conference in May.
While Charleston is blessed with high-quality model input data, CFRSS is designed to enable user communities to take advantage of national open data sources. Communities without site-specific or high-precision data can use general data from sources such as NOAA to produce a risk assessment that is useful and insightful.
“Charleston, like many coastal communities, has experienced a rapid increase in tidal flooding and extreme weather events over the past 20 years,” said Dale Morris, Charleston Director of Resilience. “With sea level rise of two to four feet expected over the next 50 years and the growing and worsening threat of rain and storm surges, the city needs a planning tool to help policymakers and stakeholders to explore vulnerabilities, risks and opportunities in different scenarios. , as well as the comparative advantages of mitigation measures. This modeling tool will allow us to quickly analyze specific threats and identify the different adaptation paths that the City must explore.
One of the main goals of the project is to engage multiple stakeholders and strengthen Charleston’s collaborations with other communities across the country. By sharing software, risk data and program outcomes, CFRSS will help Charleston and other community stakeholders move forward in their larger resilience planning efforts.
Building resilience in flood and infrastructure planning
The CFRSS will allow communities to explore how their specific flood risks change as future conditions, such as sea level, frequency of storms, and population growth, change. It will also allow users to test different measures and visualize the effectiveness of these measures on flooding and impacts. CFRSS allows users to easily explore scenarios, such as the impact of a proposed infrastructure project, against a predicted sea level rise, without having to modify model data. CFRSS does this work for the user automatically. After running a scenario, the results can be automatically imported into a preformatted ArcGIS project for viewing or uploaded to an online viewer for easy sharing and communication.
CFRSS was designed to be transparent with base model input data, such as bathymetry, building replacement values, or depth damage functions, to make it accessible and flexible. A user can explore the basic data used in flood and damage models and if a community has new or more accurate model input data, this information can be easily updated in the system. Additionally, when CFRSS simulates a scenario by automatically modifying the model input data, the modified model input data is also accessible so that a user can explore how a change, such as a projection of population growth, is represented. in the model.
Understanding and planning for flood events combined with tools such as CFRSS will help communities mitigate risk and improve climate resilience, saving lives and property. The actual results obtained from the Charleston testing program will serve as a guide for other CFRSS users to better understand and prepare for compound flood events. The project team will use the results of the pilot to update the modeling software and look forward to promoting the tool at the ASFPM conference, where links to resources will also be available to share.