March 29, 2022
RIDING OUT A HURRICANE AT A MAYAN ARCHAEOLOGICAL SITE
Hurricane Grace blasted Mexico’s Yucatán Peninsula with ferocious wind and lashing rain in the pre-dawn hours of Thursday, August 19, 2021. I was in the city of Tulum, where we took a direct hit from this small but powerful storm.
As I endured Grace’s fury, I thought of the Mayan archaeological treasures I had just explored hours before. Tulum was an important spiritual and religious center to the Mayans, and the walled city contained temples to their god of the sun and god of the wind, perched on a plateau ending abruptly as a beach cliff. These artifacts have been preserved, drawing millions of visitors to the area annually.
As Grace approached, the roar of the pounding waves on the cliffs grew louder. My plan was to ride out Grace in the comfort and protection of my rental car, which I could position far from falling trees, yet still video the extreme wind and rain with my lights on high beam. I was located on the edge of the archaeological site, where I befriended several security guards in the previous hours. A new friend joined me in my vehicle, as it provided superior protection than the security guard shack where he worked the night shift, under an overhanging tree.
Through the storm, I reflected on the fact that this site has certainly endured dozens of hurricanes in the ~1500 years since it was constructed. I trusted that these fortified walls would stand up against yet another vicious storm on the night of my visit. However, against a backdrop of rising sea levels, increasing oceanic heat content and rapidly intensifying hurricanes in recent years, I wondered what the future looks like for this and other coastal sites that preserve our past in precarious areas prone to hurricanes and other weather extremes.
PROTECTING LARGE HISTORIC SITES
Stateside, Miami’s Deering Estate shares some things in common with Tulum, as the 1920s-era national landmark covers a large area and is prone to major hurricane strikes. Hurricane Andrew’s (1992) category-5 winds peaked in this area, south of Miami’s core, and a tree on the graceful estate still shows the scar where Andrew’s storm surge washed off the tree bark.
Jennifer Tisthammer, Director of the Deering Estate, recently reflected on the challenges of protecting such a valuable cultural site that sits in a precarious position along the western shore of Biscayne Bay. Tisthammer’s team calculated that implementing complete protective measures for a category-5 hurricane would take 14 days of labor, if starting from scratch. So much time is required because The Deering Estate is a 450-acre cultural and ecological field station, containing 26 archaeological sites, 17 terrestrial caves, and 11 historic structures listed on the National Register of Historic Places.
Preparing for hurricanes at this site involves the installation of special hurricane shutters and storm surge panels, especially designed to protect the site from the worst possible conditions. Unfortunately, the best science cannot give us accurate 14-day hurricane forecasts, so The Deering Estate team has found a creative way to protect the site, while remaining open to the public throughout hurricane season.
Every spring they prepare the site for a strike from a category 1 or 2 hurricane, completing tasks such as ordering supplies, trimming trees and servicing equipment, which are the most time-intensive tasks, requiring around 80% of the time to prepare for a category-5 hurricane from scratch. This leaves around 48-72 hours to ramp up to cat-5 protection, should a major hurricane threaten with a direct strike.
[Check out this GeoTrek podcast that features Jennifer Tisthammer discussing hurricane preparation in more detail, as well as the broader topic of improving resiliency] (LINK: https://geo-trek.com/podcasts/trekking-through-the-south-florida-landscape)
Efficient hurricane preparations have never been more important, as recent years have observed numerous hurricanes undergo rapid intensification in the 24 hours before landfall. Just last week, Hurricane Ida exploded from a category-1 hurricane with 95 mph winds to a category-4 hurricane with 150 mph winds in the 24 hours before making landfall in South Louisiana.
The graphic above shows that five hurricanes have intensified by at least 40 mph in the 24 hours before landfall over the past five years, or one per year. Since 1950 this has only happened 10 times, and the frequency of rapid intensification from 1950-1999 averaged once every 17 years.
While coastal sites are a major focus of the increasing dialogue on the impact of extreme weather events on historic preservation, inland locations are also addressing this topic. Petroglyph National Monument in Albuquerque, New Mexico, is an example of an inland historic site that faces threats from erosion, which is often enhanced during heavy downpours.
The 7,244-acre monument protects one of the largest petroglyph sites in North America, where Native Americans and Spanish settlers carved designs into volcanic rocks from 400 to 700 years ago. The site is managed through a unique partnership between the National Park Service and City of Albuquerque.
On a phone interview, Ranger David explained that unauthorized human activity exacerbates the rate of erosion at this site, as off-trail foot traffic kills desert plants and loosens rock that can be more easily eroded during future flood events. Establishing appropriate and safe human use of the monument is a challenge because the boundaries of this urban park approach several communities. Park staff frequently initiate education and outreach activities with the local community to increase local understanding about the fragile nature of this environment.
Whereas coastal sites in hurricane-prone areas need to ramp up to protect a historic site against severe wind and flood damage that will strike in a small window of time, protection of an inland site like Petroglyph National Monument appears to take on a longer time frame. Their biggest threat to the petroglyphs is enhanced erosion from the combination of unauthorized foot traffic followed by heavy rain, and the component of that equation that park rangers can influence- encouraging compliant behavior from park visitors, is an ongoing engagement that happens every day of the year.
Climate models suggest that the potential for heavy rainfall will increase as the climate warms, as warm air holds more water vapor than cooler air. The maps below show the greatest potential for heavier rain is predicted in the northeast and northwest United States, including the Great Lakes. Fortunately for Petroglyph National Monument, increased precipitation rates are forecast to be lower in New Mexico.
PROTECTING INDIVIDUAL HISTORIC PROPERTIES
While large cultural and historic sites like Tulum’s Mayan ruins, Miami’s Deering Estate and Albuquerque’s Petroglyph National Monument, benefit from strategic management plans, much attention has been given in recent years to the necessity of protecting individual historic buildings from high-risk areas that are prone to flood, fire, or other hazards.
Roderick Scott, Board Chair of The Flood Mitigation Industry Association, points to the town of Mandeville, Louisiana, on the north shore of Lake Pontchartrain, as a proactive example of a town that has embraced elevating historic buildings. According to Scott, the four blocks closest to Lake Pontchartrain have historically observed the most frequent flood impacts, but 60% of the historic buildings in this area have been elevated. New FEMA-compliant construction makes up the balance in that community, bringing the proportion of elevated homes in the area to 80%.
Non-elevated buildings in the most susceptible zones are facing rapid increases of insurance premiums, and Scott predicts that, “The National Flood Insurance Program (NFIP) rates are going to get them long before the sea does.” He provides an example of The Lake House on Lakeshore Drive in Mandeville, a FEMA-designated severe repetitive loss property in the VE- flood zone, where FEMA predicts wave action will impact buildings in storm surge floods. Scott notes that 10 years ago the tenant paid $2500 per year for flood insurance, but the premium today is $25,000, a 10-fold increase. Once all subsidies are removed, in five years, the estimated annual premium for this site will reach around $45,000/ year.
Changes to insurance premiums will be accelerated in the near future, as FEMA’s Risk Rating 2.0, a new risk-rating methodology, goes into effect on October 1, 2021. Independent insurance agent Carl Schneider, of Mobile, Alabama, reflected, “This is the first major change in how rates are calculated since the start of FEMA’s National Flood Insurance Program,” often referred to as NFIP. This program was created in 1968 when Congress enacted the National Flood Insurance Act.
FEMA states, “Risk Rating 2.0 is not just a minor improvement but a transformational leap forward.” While the old system relied on a homeowner’s elevation within a flood zone to determine premiums, the new system includes more robust metrics, including flood frequency, distance to water, elevation, cost to rebuild and flood type that threatens an area (https://www.fema.gov/flood-insurance/risk-rating/)
Risk Rating 2.0 contains a few changes that will greatly impact people in historic communities. The most important change may be that grandfathering, the practice of subsidizing insurance premiums of homes previously built below today’s required elevation of new construction, will be done away with under the new system.
The practice of grandfathering explains why we see so many non-elevated historic homes on low-lying ground in places like Galveston, Biloxi and Charleston. Those homes were built before FEMA’s flood insurance program placed elevation regulations on new construction. As long as people kept existing flood insurance on such low-elevated homes, they paid a highly subsidized premium after elevation regulations were established for new construction.
Risk Rating 2.0 removes such subsidies, increasing premiums by 6-15% annually for high-risk homes, according to Schneider. As new rates go into effect, homeowners with a gap in coverage will pay full, non-subsidized rates. Policies purchased before October 1 will be at least partially subsidized, but increase regularly until homeowners are paying the full rate.
The new program will also count all previous flood losses against homeowners. This is stricter than the previous program, which did not count the first loss against a homeowner.
ALTERNATIVE METHODS OF FLOOD MITIGATION
While widespread building elevation initiatives have worked well in Mandeville, communities may find it optimal to investigate additional mitigation strategies, like dry and wet floodproofing, first floor abandonment, and buoyant foundations, a concept that has gained traction internationally in recent years.
A buoyant foundation allows the home on the left in this image to float, while the home on the right is inundated with flood water. Photo: www.buoyantfoundation.org/.
Galveston, Texas, is an ideal place to consider such adaptations, because a 10-mile-long seawall protects the flood-prone city from incoming waves during coastal storms. Yet, the city contains thousands of historic buildings that are situated on low ground and flood prone. In 2016, Galveston Historical Foundation hosted a workshop called Approaching Water, which featured the creation of a model buoyant foundation house built in a tank. Precise engineering and mathematics were employed to ensure the model home had the correct center of mass, so it would not tip over when the tank was filled with water.
Learn more about this innovative concept by visiting the Buoyant Foundation Project (www.buoyantfoundation.org).
If a building is not elevated above flood water and it is not buoyant, wet and dry floodproofing can minimize the flood impacts. Wet floodproofing is a practice whereby flood-damage-resistant materials minimize the impact of water that enters a building. Dry floodproofing is the practice of using flood barriers, panels or other obstructions to prevent water from entering the building in the first place.
FEMA has created a 184-page manual called Floodproofing Non-Residential Buildings. Link: https://www.fema.gov/sites/default/files/2020-07/fema_p-936_floodproofing_non-residential_buildings_110618pdf.pdf. They recommend focusing dry floodproofing on commercial or industrial buildings because the practice creates tremendous pressure on the walls of buildings and this pressure generally exceeds design capabilities of most residential buildings.
CONCLUSION AND ACTION ITEM
Part 1 of this article introduced the topic of extreme weather and climate change impacts on large historic and heritage sites. This article opened with the story of a hurricane strike at a Mayan archaeological site, and then discussed some proactive measures undertaken by Miami’s Deering Estate and Petroglyph National Monument to minimize the impacts of extreme weather events. Although these sites face different threats, a common theme found between them is that site managers must be proactive and intentional to employ best practices that minimize damage from storms.
The article then discussed some challenges faced by homeowners of individual historic buildings, focusing heavily on changes to FEMA’s National Flood Insurance Program (NFIP) practices and rates. Part 1 of this article concluded with the introduction of various flood mitigation strategies, including home elevation, buoyant foundations, wet- and dry-proofing.
Part 2 will focus on conceptual topics related to extreme weather, climate change and historic/ heritage preservation. As the world changes, we must change with it, and we will take a look at insights from several experts who have extensive experience with the topic of extreme weather, climate change and historic/ heritage preservation. Part 2 is scheduled to post on Monday, September 13.
We close Part 1 of this article with an action item. Keeping History Above Water has emerged a global public-engagement platform for connecting cultural heritage sites, climate change experts, and heritage professionals to create solutions for climate impacts on historic communities. The next workshop in this series will be held September 13-14 in Salem, Massachusetts. The event is sponsored by the City of Salem, Salem Preservation Partners and Keeping History Above Water.
Here is a link to the workshop site: https://www.salem.com/home/news/keeping-salem-history-above water?fbclid=IwAR1BjfkTMyCtarmS5ixwNsKkKrZq_cwSIvDyU6rpmxcRH4_exlGH92DkSxo