High Tide Flooding

High tide flooding often happens in low-lying areas near the coast, and can cause disruptions to communities like longer commute times, business closures, and construction delays.

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HOST: This is the NOAA Ocean Podcast. I'm Marissa Anderson. High tide flooding may be known by different names such as king tides, nuisance flooding, or sunny-day flooding. No matter what you call it, it can have big impacts to coastal communities - causing disruptions like longer commute times, business closures, and construction delays. NOAA plays an important role in helping communities prepare for and respond to these impacts. In this episode, we chat with a panel of experts from NOAA's Center for Operational Oceanographic Products and Services, also known as CO-OPS. We're joined by oceanographers Analise Keeny and Karen Kavanaugh, and chief scientist Dr. Greg Dusek. Let's dive right in as Greg tells us more about high tide flooding.

DUSEK: High tide flooding is coastal flooding. It often happens in low-lying areas near the coast, and it typically happens at high tide or is worse during high tide. And we'll often see it during the highest tides of the month or of the year, but what we're seeing is that it's happening more and more frequently due to sea level rise. So instead of just having these high tide flood days happen a couple times a year, now we're seeing them happen potentially dozens of times a year. And high tide flooding is a combination of impact of sea level rise with the tides and then sometimes caused by added by weather or storms. And so, you know, one way to think of it is as sea level rise flooding. And because of the increase in sea level rise and the role that plays in these kind of frequent flooding events, we're seeing them happen often even without storms now. And so you'll hear them call them sunny day flooding, for instance. And in many times, you know, it's not like there's a dramatic impact from a single event. The water is often not that high. You might just have a little bit of water in the streets or on sidewalks. But it's potentially enough to cause impacts where, you know, you might not be able to get to your kid's school or get to the store you're trying to get to because there's water in the streets. And then these impacts have long term consequences because once you have impacts over and over again, they can have cumulative effects and damage infrastructure. And so it's something that coastal communities are really starting to have trouble with and needing to tackle in the years to decades ahead.

HOST: That's really interesting to note that the flooding can take place even when it's not rainy conditions out. Folks may not realize that. Karen, can you share with us what locations and communities are typically impacted by high tide flooding and why is this such a problem for them?

KAVANAUGH: Coastal communities around the country and the U.S. territories are all being impacted by high tide flooding now and some more than others. But it's happening, especially in areas like Greg said, that are low lying compared to the height of the high tide. And really, regardless of where we live in the U.S., we are all being impacted by this problem with flooding because so many of the things that we buy from sneakers to cars are actually being shipped through our seaports. And those ports may be located in areas that are vulnerable to high tide flooding as well. And that high tide flooding, Greg talked about some of the impacts, but high tide flooding can result in flooded roads. That includes evacuation routes. It can temporarily close businesses because they're seeing flooding in their first floors or the sidewalks being flooded. It causes overflowing storm drains. You shouldn't be walking in that water or those puddles because they're potentially contaminated. And saltwater also causes damages to cars and buildings. And so over time, chronic flooding like this causes a lot of cumulative damage to critical infrastructure and cumulative economic losses and degraded coastal ecosystems.

HOST: And that's really powerful to think that high tide flooding affects us all and not just those that are living in those impacted areas. So now that we've talked about what high tide flooding is and how it can be such a threat to coastal areas and everybody like we were just saying, I'd like to get into the role that NOAA plays in helping to protect people and communities. Ana, I'd like to start with you. Could you give us an overview of what the annual high tide flooding product is?

KEENEY: The annual high tide flooding outlook provides users with a range of expected high tide flooding over the coming meteorological year. And we define that as May to April of the coming year. And we center our predictions and our projections around this time scale so that we can help people capture the seasonal variability and the storminess that often occurs in winter months. And so this product allows people to understand and assess what flood frequency looks like through time. We provide a little bit of historical data and sometimes for the previous few years so you can understand what different climate cycles look like with often links to more detailed historical information. But all of this is to help provide context to what we're expecting over the coming year and then what we provide to supplement this. So we accompany this data annual projections with sea level rise scenarios from interagency technical report from 2022 as well as decadal projections that we pulled from this. So people in coastal communities can understand what their risk is in the near term and also plan for what it's expected to be or potentially could be in the future based on sea level rise. And we definitely this product in particular focuses around some of those climate cycles. Right now we're in an El Nino cycle so a period of warming waters and this does tend to create increased flooding in certain areas. So we like to help our users understand what climate is actually playing in this as well as what is expected to be through the coming years based on sea level rise. We're in the midst of producing this coming year's outlook, the 2024 to 2025 outlook. Preliminary data from this year's 2024 to 2025 outlook is expecting roughly 30 stations to exceed their historical high tide flooding records. So that means that we're seeing more high tide flooding in this coming year over the previous year that is reflected in the data that we're already preliminarily seen.

HOST: In addition to the annual high tide flooding product, I'd like to touch on the monthly high tide flooding product. Karen, can you speak to that?

KAVANAUGH: Sure. With the monthly high tide flooding outlook highlights when and where above normal high tides and high tide flooding may be experienced up to a year in advance. And we show that on calendar kind of view that's easy to see like those windows of time that might be at higher risk. And during these higher risk time periods, high tides will be close to the water level height that could cause flooding and weather like a storm or onshore winds could exacerbate things and make impacts more severe. The flood likelihoods shown are derived from NOAA tide predictions, relative sea level trends at the station, and s easonal variations in water levels from our historic observations.

HOST: With both of these products, who can use them and where can users find them?

KEENEY: Most of these products are available right there on our Tides and Currents landing page. We want to make it possible for people to have access to navigation and coastal hazard support and mitigation products and services right there on our landing page.

HOST: Ana, could you briefly walk us through the process of using both of these products so our users understand how to work them?

KEENEY: Sure, I'd be happy to go into detail about the annual high tide flooding outlook. We do try to make it accessible to both users in the public community as well as more technical users by allowing people to easily navigate among the menus to be able to see where their region is and then select their station by hovering over it with their mouse. And once they select their station on the opposite side of the page, you can easily see what the projections are for the coming year's high tide flooding, as well as that brief context of historical information that we shared. And it's just a quick toggle over to another tab to be able to view the projections as well. And those are where we provide detailed information about where they're expected to experience the largest range of high tide flooding over the coming year, what's happened over the previous year, what the predictions are out into the future as well.

HOST: Karen, could you tell us about the monthly high tide flooding outlook, how users can use that tool?

KAVANAUGH: It's pretty similar navigation-wise to the annual outlook. And so there's a map, you can click on a station that you're interested in, and then on the right hand side a calendar will pop up and highlight the windows of time that are at higher risk for flooding. And then they can also click on a region tab and get sort of a summary of the reasons why high tide flooding might be occurring during that selected time period and the possible impacts they might see in their region. There's also connections to other resources on our CO-OPS page as well, like the tide predictions and coastal inundation dashboard for monitoring real-time water levels as well.

HOST: Karen, why is the monthly high tide flooding product considered to be such an advancement?

KAVANAUGH: So typically our weather forecasts are available only a few days in advance, which may be really short notice for decision makers that have to do more to prepare for a flood. And like we talked about, high tide flooding can occur during a sunny day. So people might not even know that they should be consulting a weather forecast because, you know, it's sunny. So why would you have flooding on the road? So the monthly high tide flooding outlook model is able to offer robust estimates of the likelihood of flooding up to one year in advance. And this is because at its core, it's based on the NOAA tide predictions and tides are very predictable and that's something that CO-OPS has been doing for a very long time. And the monthly outlook is more than just a tide calendar telling you when there is going to be a full moon and above normal high tide. The model also incorporates seasonal variations and that's important because ocean temperatures or regional weather patterns may make flooding more likely during certain times of year at particular stations and at different regions. The bottom line is being able to highlight when and where there will be a higher risk of flooding that far into the future helps users plan ahead lots of time. And then when they get closer to the day, they can still consult the weather forecast for the most accurate information, you know, a couple of days in advance.

HOST: So both of these products sound like such a powerful duo in helping NOAA to predict high tide flooding across a range of various timescales. Could you talk a little more about how these predictions help communities and decision makers both in the short and the long term?

KAVANAUGH: So we've been doing a lot of stakeholder engagement to hear these user stories. And so in the short term, we've heard from users that the monthly high tide flooding outlook helps local planners allocate response staff and resources when areas have the highest flood risk. It helps people at universities plan their field research trips who are studying kind of contaminated water and other impacts of high tide flooding or mitigation strategies. And it provides weather forecasters at our very own National Weather Service. It gives them an additional layer of data for making accurate flood forecasts and providing context for users. A great example that we heard is that a floodplain manager says that she shares the days on the calendar that have the highest risk of flooding with her network. And that allows her town to plan actions like possible road closures and alerts residents to, hey, you need to move your car from this particular road because we know that floods and we don't want your car to be damaged. So that's really valuable to local communities. And for long term planning, the annual high tide flooding outlook is used by civil engineers, city planners and emergency managers. And they incorporate flood frequency data into their critical infrastructure evaluations, plans for coastal development and budgeting. We've also seen it referenced in the media because the outlook is a really good illustration of how much flooding we may have, like varying from year to year because of El Nino versus La Nina cycles. And it really drives home how much flooding has increased since the year 2000 and how much is projected to increase in the decades to come because of sea level rise.

HOST: These tools, they just sound like they provide such a wealth of information to help keep people safe and to help them prepare for these type of flooding incidents in the future. So Greg, I'd like to throw this next question to you. What types of data are used to help build these predictions?

DUSEK: So really, both of these products come back to our national water level observation network. And so that's, for people who don't know, that's a network of over 200 water level stations or tide gauges across the coastal U.S. And these gauges provide water level in real time. So every six minutes, you know how high the water is in these locations. And so that's really valuable for obviously marine navigation, for understanding when there's storms and tracking floods like the ones we're talking about today with high tide flooding. But what's also critical about these data is that, you know, in many cases, we've been operating these stations for decades or even 100 years or more. And actually, in the case of San Francisco, the station we have there has been running relatively continuously since before the Civil War. And so, you know, these really long data records of water levels allow us to really understand how sea levels are changing over time. It lets us understand the tide so we can predict the tides real well. You know, we have a better understanding of month to month variability in sea level due to, you know, seasonal changes from temperatures and from winds and things like that. So by combining all these factors together, we're able to create the products that Karen and Ana talked about and really provide pretty accurate information about what's going to happen over the next few months and next few years.

HOST: Ana, this question is for you, let's talk about NOAA's Coastal Ocean Reanalysis or CORA for short. The CORA project reanalyzes past water level data to improve existing NOAA products like your high tide flooding outlooks. Can you give us a little more background on this initiative?

KEENEY: So as Greg was noting, we have the National Water Level Observation Network, and it's a series that expands across the country to our territories and as far north as Alaska, all over the country and the world. The CORA project allows us to better understand what flooding looks like between these stations. So through coupling our long term observations and these hydrodynamic models, we're able to more equitably provide historical information between our tide stations. For right now, the project focuses on the time period of 1979 to 2022. And through the methods that we've adopted with our partners at the Renaissance Computing Institute with the University of North Carolina and our validation partners at the University of Hawaii, we've come up with a very valuable data set that helps people understand how flood frequency has changed over time. And ultimately, we would like that to be the foundation of some of our products or supplement the foundation of our products moving forward.

HOST: To follow on to that, what would you say are the main goals for CORA?

KEENEY: We would love to be able to use this detailed information to provide not just the historical information between our tide stations, but to ultimately use them as a base for our projections. I think it's so powerful to be able to capture the nuance between our water level stations. And this project is allowing us to start there.

HOST: Which partners are involved in the CORA project? Do you have any other partners involved within NOAA?

KEENEY: We absolutely do. Thank you for asking. We couldn't do this work and this reanalysis without our colleagues at the Office of Coast Management that have that close connection to their communities through their regional geospatial coordinators. That information is what helps us understand that we need to more equitably expand our products and services, as well as our partners at the Integrated Ocean Observing System, IOOS. It's their technical savvy and their wide reach that allows us to have some of the more technical input into this project. It's a multi-year, multi-faceted project that is super collaborative across the board within the National Ocean Service and our academic partners. I just want to say hats off for their involvement as well.

HOST: With all the data and products we talked about so far today, the annual high tide flooding tool, the monthly high tide flooding tool, and now CORA, has your team noticed or discovered any interesting trends or findings? Greg, could you speak to this?

DUSEK: We've seen a lot of interesting results as we created these products, and I want to highlight a couple. One, from the monthly product, as we develop the model, we look back at different locations to see how well we would predict during past flood days. And one jumped out in particular, and that was in Honolulu, Hawaii, where we have a tide gauge. In 2020, they experienced 46 flood days, which was the highest number of flood days they've ever had, and actually more than twice the amount in any other previous year. So it was a really big impact for Hawaii, and to the point of even, you know, they coupled some of those flood days with large waves and had it take out a lifeguard tower in Waikiki. So they saw real impacts, and we applied our model for that year, and looking one month in advance, what we found is that we were able to predict 40 out of the 46 flood days accurately with one month lead time, which to me is just was really surprising. I didn't think we would be able to accurately predict floods that well, but I think it points to the value of our tide predictions, how well we're able to predict the tides. And when we can account for kind of elevated sea levels, we're able to predict these flood days in certain locations really well. Now, obviously, that's kind of an extreme case. We don't predict the floods that well everywhere, but I think it just kind of shows the value of this product and this information for communities. The other thing that's worth mentioning that I think popped out with all the products really is just how different it is depending on where you are in the country. And so I think often people don't realize the tides are very different depending on where you are. Sea level is very different depending on where you are in terms of what impacts sea level change from month to month and from year to year. And so what we really see is places like the Gulf, where the tides aren't that big, the weather plays a more important role when you're going to see flooding, like when you have hurricanes and tropical systems come through, you have a lot of flood days. Those are really hard to predict because it's hard to predict weather far in advance. And so for the Gulf, our model doesn't do quite as well as like the Northeast, where the tides tend to be much larger, they play a much more important role in flooding. And so we're able to predict flood days really well far in advance in locations in the Northeast. And so we see this kind of reflected throughout the country where it's really important to understand those regional differences when you're trying to provide coastal flood information. And then that goes even a step further where kind of what Ana was talking about, what happens between the gauges? So if our tide gauges are 100 miles apart, are you having floods between those gauges and where are you having them and what might impact that flooding as well? And that's what we're getting at with CORA, to be able to even dial down further and really try to provide information on a community scale to tell people as accurately as we can, when and where it's going to flood. And then hopefully understand why that's happening so we can improve predictions even further in the future.

HOST: That's such a valuable feature to be able to dig down to that more granular level, if you will. So Greg had mentioned the increased number of flood days in Hawaii. As we look towards the future, are the number of high tide flooding days expected to increase in the coming years and are particular regions more at risk? Ana, I'd like to get your thoughts on that.

KEENEY: The short answer is yes, most areas of the country are expected to experience a greater amount of high tide flooding through the coming years. And it's hard to pinpoint one location in particular. But as Greg mentioned, it's those areas that are already experiencing the impacts of sea level rise, the places that are more frequently experiencing severe storm events and climate cycles, low lying areas of the country. So even though we can't pinpoint a region in particular, we make it so that each region of the country has a chance to understand what their specific risks are and plan for what's expected to happen in the future.

HOST: Karen, I have a follow on question for you, you had previously mentioned that you had received positive feedback from a floodplain manager after they had used some of the products. How has the datasets and products been received by users overall? Also are there any plans to update or enhance products using feedback that's gathered from stakeholders since the launch of the product?

KAVANAUGH: Through this whole process, user feedback has really been guiding our product development and our team has been gathering feedback from users, like I mentioned this past year, and will continue to do so. And overall, we have received positive feedback on the products, which we're really excited about. And there's always room for improvement. So this year, we're focusing on updates that will hopefully make it easier for users to understand the information that we're providing or access the data directly. And the number one request that we've gotten has been that users want us to expand where the outlooks are available. And that is relevant to what we've been talking about, like Greg and Ana mentioned. Currently, we're only providing this data at a subset of NOAA's water level stations. And so a key research goal for the next few years is going to be hopefully leveraging CORA data to provide that information between the stations. And it's really like an ambitious goal. It's really ambitious to have accurate flood outlook information available all along the coast, serving every coastal community. But it's so important because not every community has a tide station. They may still be experiencing flooding, and we want them to have all the information they need to plan accordingly.

HOST: I'd like to touch on how the public can possibly get involved. Are there things that we can do within our communities to help prevent or prepare for flooding risks?

KAVANAUGH: Yeah, so each community is unique. So there's not a one-size-fits-all solution. And on an individual level, just learning about high tide flooding is the first step. So if you've lasted this long in the podcast, you are already on your way. And that's really exciting. I know I didn't know much about high tide flooding at all before I started at NOAA. And now my mind is just blown. And if you want to know more, you can also research if your home or your local area is vulnerable to coastal flooding and how your community is already working to mitigate flood risks. At NOAA, we hope that NOAA's high tide flooding outlooks and the coastal ocean reanalysis will provide additional information that's authoritative and accessible to communities to help with their planning and mitigation efforts. Our sister office, the Integrated Ocean Observing System, or IOOS, is helping communities install their own water level sensors so they'll be able to monitor flooding to inform their planning. And some communities are already, throughout the U.S., implementing adaptation strategies that may range from nature-based solutions like conserving wetlands, sand dunes, or mangroves. And maybe they're implementing man-made infrastructure, solutions like seawalls and pumps to redirect excess water. NOAA also provides trainings for communities to learn more about this. And it's really important, though, at the end of the day, because today's floods are tomorrow's high tides. So taking steps to minimize impacts from coastal flooding now is one of the best ways to build resilience and prepare for sea level rise.

HOST: Greg, do you have any closing thoughts to wrap up our discussion today?

DUSEK: I think it's worth kind of pulling all this together and talk about, you know, one of our products, which gives people a great jumping-off point to this information, and that's our coastal inundation dashboard. So if you go there, you see a map of all the gauges across the U.S., and it tells you where it's flooding right now and where it might flood over the next couple of days. And so it's the first thing you see, and especially if there's a tropical system or a hurricane, all that information is put on inundation dashboard. And so it's really a great spot to be able to see where flood impacts might occur in the coming days. And then you can click on those stations and dive into the historical information about when it's flooded in the past, our sea level trends, and get to the outlooks from there. So that's a great resource, and actually it's something I use all the time. If there's potential flooding, I'm going to our inundation dashboard, so I really recommend people start their journey there. In addition to coastal inundation dashboard, we're working on improving and enrolling out new sea level and coastal flood-related products. Some of those is going to be the sea level trends that people are probably familiar with and our sea level extremes, which looks at past trends and extremes, improving how people are able to interact and view those and better understand those changes in sea level over time. And that's going to be coming out in the next months to year or so. And then also NOAA is going to be rolling out something called the Sea Level Calculator, which is led by the Office of Coastal Management. And our office here at COOPS contributes to that as well. And that's going to be really providing a bunch of this information in terms of historic sea levels and future sea level and coastal flooding projections, all in one place so people can get very localized information for the places and the time periods they need. And so be on the lookout for that here in the coming months as well.

HOST: This has been the NOAA Ocean Podcast. Thanks for joining us. To learn more about NOAA's products and services related to high tide flooding, check out our show notes. And make sure to follow us on your favorite podcast player so you never miss an episode!

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