Preparing for a Future with More Flooding

Evan Banks

You're listening to Policy Currents, a weekly podcast from the RAND Corporation. I'm Evan Banks. Every Friday, we bring you new insights from RAND's latest research and commentary. It's September 8th. Flooding in the U.S. is a serious problem, causing deaths and injuries, devastating property damage, and major business disruptions. The economic costs of floods in America are staggering. A single major flood event can lead to losses of $4.6 billion on average. And in the mid-Atlantic region in particular, extreme precipitation-induced flooding has occurred nearly every season since 2018. As the effects of climate change worsen, these disasters will only increase in frequency and in severity. In fact, many parts of the Chesapeake Bay watershed are predicted to see a doubling of the number of days with extreme precipitation by the middle of the century. Stormwater planning and management is essential to mitigating current and future flood risk. Today I'm joined in the studio by Krista Romita Grocholski and we also have Michelle Miro with us joining remotely. Welcome, Krista and Michelle. Krista, could you tell me a little bit about MARISA, the Mid-Atlantic Regional Sciences and Assessments program, what it does, where it operates, what it covers?

Krista Romita Grocholski

Sure. Yeah. So we are the Mid-Atlantic Climate Adaptation Partnership, formerly Regional Integrated Sciences and Assessments Program, or CAP-RISA program. It's funded through the Climate Program Office at NOAA. We are in our second five year grant serving the mid-Atlantic region. Our job is basically to function as a boundary organization, bringing the climate science and in this case extreme precipitation information to decisionmakers and other stakeholders in the region in a form where they can use it for the decisions that they need to make. And Michelle and I have been focused on extreme rainfall and stormwater in particular for the past several years. But the MARISA team does focuses on a number of other issues as well, including extreme heat, which is something that we're seeing not just in the region but across the country this summer.

Evan Banks

I remember it was a couple of weeks ago, Washington, D.C., where I live, had one of these extreme precipitation events and it was intense. It was 80 mile per hour wind gusts. Rain coming down in just sheets. Everyone's phones were flashing alerts and people weren't able to drive. And the alerts to get inside to to seek shelter immediately. And I talked to a lot of people afterwards. And everyone that I talked to kind of reached the same conclusion or had the same consensus, which was that storms like these feel anecdotally like they're becoming more and more common and more intense in frequency. I know that that's due to the effects of climate change, but do we have data on how how much more frequently these are happening?

Michelle Miro

We do. So what we've seen in the recent historical record from meteorological stations as well as in climate projections that look at future climate, is that storms like this are occurring more frequently, as you mentioned earlier. We see nearly a doubling or more in many regions of intense precipitation events out to the middle of the century. And those trends are just going to continue as we get out to the late century.

Evan Banks

How much precipitation counts as an extreme rainfall event?

Krista Romita Grocholski

There isn't a particular definition that can make it a little bit hard to explain or pinpoint. And it also depends on over what timeframe that rain comes down.

Evan Banks

And is it like an oversaturation of like the ground and increased risk of flash floods, like that kind of thing?

Krista Romita Grocholski

Yeah. The conditions of the soil or amount of impervious surface really impacts how much you're going to get flash flooding. Like what we saw in a different recent storm where in D.C. a doggy day care was flooded and several dogs were killed. That's they've had some issues in that in that part of D.C. before with flash flooding but I think it's partially related to the fact that we've had, you know, in July, we had extreme weather events like heavy rainfall, I think in almost half the days in July. And so the initial conditions set it up that as much rainfall as you got, you were going to have it more likely to be in the streets rather than soaking through wherever there are grassy areas.

Evan Banks

Yeah. Let's talk about some of the tools that people use. There's an entire group of people out there. There's a stormwater management community in the DMV area and they include people like civil engineers and planners and policymakers on the local level. And they use a variety of tools to be able to plan for these rainwater events, correct? Yeah. What are some of those tools? And I know that this current work that you both have done is follow on from a previous tool that you released. Can you tell me about that tool?

Michelle Miro

Yeah. Well, starting with what what stormwater managers use now, generally, you know, many people have heard of the 100 year storm event or the 500 year storm event. And that's a lot of what what is used in the field of stormwater management. There is a standardized, essentially database of what those 100 year and 500 year storms are. It's developed by NOAA, the National Oceanic and Atmospheric Administration. And you know, it's free, available to access online. That is by far the most widely-used tool across the United States. It's by no means the only tool or the only way stormwater managers access data on historical precipitation that's used for planning and management. But it is again the most widely used. One of the challenges with that tool is that the data that's used to develop that 100 year or that 500 year storm event, for example, and in about 2005 to 2010, depending on the kind of version of the tool, it's called Atlas 14 that's being used. But what we've seen is that climate change is occurring and has been occurring for quite some time. And so those historical climatology based on 30 years of data or in some cases less up to 2005 don't even really represent our current climate, and they definitely don't represent the climate of the future, taking to taking into account future climate change. So when you asked about what tools we've developed, so what what Krista and I have done is with a team of researchers at Cornell and Carnegie Mellon and with partners in the Chesapeake Bay, we developed a tool that essentially would apply a numerical change factor to Atlas 14 to adjust it to account for future climate. So that's the work we've done recently and the tool we've developed for the Chesapeake Bay watershed.

Evan Banks

And then this work is a follow on work to that, where you interviewed these stormwater managers and asked them what they felt they needed to more accurately predict stormwater using this model that accounts for climate change.

Krista Romita Grocholski

One of the things that we do with MARISA is try to make sure the tools that we make are actually useful and usable. So we worked with some colleagues at the Chesapeake Stormwater Network to connect with some folks who had been early adopters of the tool to see what their experience was like and how they were using that information. And we conducted a series of interviews, I think about 9 or 10 groups of people, because they had said that they were interested in using the tool or had used the tool. And in those conversations, we found out that you need a lot more than just the tool itself or just the information or that numerical change factor that Michelle was talking about. You need a whole host of other materials or other information to try to actually use that information and operationalize it and actually make your communities more resilient to extreme precipitation.

Evan Banks

So this is ultimately about getting those people what they need to accurately plan for an uncertain future.

Krista Romita Grocholski

Yeah, I would say adequate plan rather than accurately plan, given the uncertainties involved in the amount of rainfall, because we we have a range of potential futures and we can't know which one is the right one. And that's something that people actually struggle with a lot is knowing what part of these they called intensity duration frequency curves do we choose? Which potential future models do we use? How do we make those decisions when we don't know what's going to happen? And a lot of these engineers have not been trained in thinking about future climate in that way. And that can be a big barrier in between actually using this information and not.

Evan Banks

If we know that climate change is making this problem worse. Why wouldn't you just plan for like the maximum intensity possible? Right.

Michelle Miro

I mean, the short answer is because it's expensive and it can involve big land use changes that can involve costs incurred to developers, costs incurred to local businesses. There is an enormous kind of policy and economic environment that surrounds climate adaptation that is very much non-trivial. And so picking just the worst storm possible sounds nice in theory, but in practice is often impossible or impractical to plan for.

Evan Banks

Okay. So you had talked about different climate models presenting us different scenarios in different possible futures. Can you talk a little bit more about what those different futures look like and how how they range in severity?

Michelle Miro

Yeah. So when we when we think about climate change, you'll often hear the term uncertainty paired up with it. And so what that means is that when we're looking at projections of future climate, they come from a range of different global climate models, often a suite of 30 to plus or minus a few different global climate models that all have slightly different physics, slightly different calibrations and all slightly different projections of future precipitation or future temperature for a region. On top of that, we have different scenarios of how essentially the world will or will not mitigate future emissions, and that affects the way in which our climate will change into the future. So these kind of uncertainties around our global climate system and around our global economy and society affect the directionality and magnitude of climate change. And so as researchers, we look at all of those different futures and we summarize them often into what we call like a band of uncertainty. So let's say precipitation. From one model, it's going to go up by 20%. Another model may show 22% and another model may show 18%. And so from a planning perspective, it's really useful to look at that full range of uncertainty, to understand kind of the the highest magnitude or lowest magnitude or frequency that you could see. So we look at all of that and we plan for all of that. But it is, as Krista mentioned earlier, it can be quite complicated for traditional planning approaches to incorporate that range into how they plan and how they design infrastructure systems.

Evan Banks

You somewhat answered my follow up question, which was, is averaging all of those models something that makes sense to do or something that we can do? And the answer that I was getting was sort of like sort of yes or no is that yes, we can create like a band of likely of likely scenarios, but it it doesn't make sense to average them because they are predicting like discrete futures of like depending on what the rate of climate change looks like over time and how how much we are able to adapt or mitigate it.

Michelle Miro

Yeah. Just to follow up to that point, this idea of averaging. In best practices around climate planning and adaptation, we do not average those climate models, but instead understand the sensitivity of our systems or our plans to that range. Averaging can often kind of soften the peaks in the data. So we won't see those really big changes that may create big vulnerabilities for our systems that we may want to plan for. So it's really important to look at that full range rather than averaging.

Krista Romita Grocholski

And another reason why I would say particularly for extreme precipitation, it's important not to just go with an average. It's because global climate models struggle to. Struggle to represent particularly extreme rainfall events. It's just straight up a hard thing to do with physics. At the resolution that you can feasibly run these models. And so they call it kind of a drizzle effect that has a kind of a tendency to, we think, have the right amount of rain over the course of, say, a year. But it's not necessarily concentrated in the kind of extreme events that we are seeing in the recent historical record. And so at just taking an average of the global climate models for the future, in addition to what Michele said would further wash out the potential for those extreme events. And that's really what people are struggling to plan for these cloudburst events. And so considering that upper band of uncertain uncertainty, I think is really important, particularly if you're trying to build, say, a particularly sensitive or critical piece of infrastructure.

Evan Banks

Okay. That makes a lot of sense to me, too, because you mentioned that these are all global climate models, but different areas of the country have different ecosystems and different absorption rates of rainfall and different problems that are exacerbated by climate change. Would it make sense to come up with a model that's like specific to like the the Chesapeake Bay watershed area, or?

Michelle Miro

Yeah. So I think there are two kind of distinct parts of the answer to your question. One is that well, yes, definitely. I think in general, yes. To your question, the first point is that we do have kind of North America or different kind of continental regional climate models and in some cases more specific regional climate models that we use to look at some of those regional dynamics. There's one in particular for North America that we used in the development of our tool that created those adjustment or change factors for stormwater managers. So we were able to take that into account. An advantage of those types of models, in addition to just better dealing with local climate dynamics, is that they improve that temporal and spatial resolution of the data so we basically can get precipitation data instead of daily at sub daily resolutions and instead of at low resolution grid cells, we can get pretty high resolution data, which is really useful when you look at cities. The other part of your question that I just want to emphasize is that the global climate models from like a stormwater perspective really only give us precipitation. If I'm a stormwater manager, I care a lot about how much of that precipitation runs off onto the land surface, enters my stormwater system or enters local waterways. That's a different set of models and we absolutely have a suite of local models often run and managed by stormwater managers or their consultants that are used to understand those specific dynamics.

Evan Banks

Stepping back from climate models and back towards this particular work, could we talk a little bit more about the costs of flood mitigation? I found that the part of the paper really particularly interesting because you go into talking about how not only is there like an increased development cost to mitigate stormwater, but there's also something, a few things that I hadn't considered, which is like the, the implications of like changing flood maps and how and like the costs of changing like approaches to, to planning for this. I thought that was particularly interesting.

Michelle Miro

Yes, absolutely. There is a cost associated with all sorts of aspects of adapting our stormwater systems to future climate change. When, for example, stormwater regulations are changed to account for future climate, that often means that. Developers or city departments or other parts of a community have to essentially capture more rain to account for these larger precipitation events. That is often more costly. It means more land area might need to be converted to a pervious surface. It means levees would need to be bigger. It means all sorts of different implications for size and capacity of stormwater systems. So there's a cost associated with adaptation both for public and private entities as private entities also have to comply with different types of stormwater regulations. The other part of costs that we talked about in our work is comparing the cost of these changes to the cost of inaction or really the cost of damage incurred from flood events that would occur if we don't protect our systems. And one of the points we made in our work is that it's really important to look at those two costs together. Even though it can be hard to estimate both, it's important to understand that not doing anything has a cost as well.

Evan Banks

Right.

Krista Romita Grocholski

You mentioned the average cost of from a major flood event in your intro being you on the order of $4 billion on average. And so that's, you know, not necessarily an individual community's, you know, costs, but that that cost is being felt, you know, across the region, across the country. And there really is a huge cost to doing nothing. And but because people are not used to adapting or admitting that they need to adapt, it feels like a whole new cost. But we're already paying that cost and not doing the comparison that Michele mentioned is a disservice to your community. And it's really important thing to keep in mind, but can be very difficult for stormwater managers and their consultants and others trying to make change. To make that point, it's hard for them to sit a decision maker or a policymaker down and go, "Look, we're already going to have to pay this cost," especially if it's something that hasn't happened to that community yet. So please let me make these these other charges.

Evan Banks

While we still can...

Krista Romita Grocholski

While still can make these changes. And it will cost us money, but it probably will be worth it. And that uncertainty that we were talking about makes it harder for them to communicate that this we think this will be worth it and make build that argument. And that's something that Michelle and I have been trying to provide some support for people, trying to make that argument to others with things like this report and the tools that we're building out with MARISA and and others to try to provide that independent information and support that they can point to and say, look, you know, RAND says this or MARISA says this, NOAA says this, and it helps back them up when they're trying to get people on board with these decisions and make these changes because they're big people don't like to do new things, especially if it's going to cost them a bunch of money. And getting your head around climate change, and what that really means is hard. As humans, we're not very good about thinking about the future. So it's a tough task and this is one way that we're trying to help.

Evan Banks

Yeah, climate change involves a lot of it seems to be kind of a common thread. It involves a lot of long term planning and giving up short term gains and benefits. And that is extremely difficult to do when the short term gains are on the table now. And there's politics involved.

Krista Romita Grocholski

Yeah, communities are worried about losing out development opportunities to a neighboring county say that doesn't have as strict requirements for stormwater or tax revenue and not being able to build new housing or something like that. And so there's a lot of things that these decisionmakers need to try to balance. And caring about stormwater or climate change might be one of them, but it might not rise to the top. And so it's it's hard for them to do that balancing act. And it came up again and again that sometimes it's just one stormwater manager in a community or a county that as a direct quote "has a bee in their bonnet" about this and is trying to make change. And so that's that's a steep hill to climb.

Evan Banks

Right. But if they can present a better picture of what the true cost is in the long run, then then that's a better argument.

Krista Romita Grocholski

And we think that's something that hopefully as new funding is coming in from the federal level to provide climate services that climate service providers like MARISA, like others that work with NOAA can actually provide that information. And it's not down to counties or states to try to figure that out all by themselves, especially as you're looking at counties that have one person that has to handle the stormwater and they can't afford to hire consultants to figure this out for them. It's a lot of analysis that has to go into this. And so I think that this is something that I would like to see prioritized in the coming years from the climate services as a sector.

Evan Banks

And that's also something that you've found is that stormwater managers at the local and county level, we're looking for guidance from the state and the federal level on this.

Krista Romita Grocholski

Yeah, it's a little of who no one really wants to go first. The local communities. We're looking for state or federal level guidance and the state didn't want to kind of hand down from on high these requirements that we're going to put communities in a tough spot. And so it's kind of a catch-22 when you don't really know what the full implications are of having a regulation like that that requires you to say account for 20% more rainfall. It's in our report, or in our perspective, we mentioned taking a new approach and using an adaptive regulatory approach.

Evan Banks

Can you explain?

Michelle Miro

The concept of adaptive management is that you don't plan 30 years assuming that the climate will follow the specific trajectory you plan for over those 30 years. You have essentially check in points or thresholds at which if climate changes by that amount, you'll adjust your planning or you will reassess the direction climate change is going or other planning parameters, not just climate, to to make sure the planning that you're doing still makes sense and still protects and provides the services it needs to to your communities.

Evan Banks

Does adaptive regulation have more to do with like, different rules for different localized areas?

Krista Romita Grocholski

It could.

Evan Banks

Yeah.

Krista Romita Grocholski

Or it could be linked to, like Michelle said, you know, the science as it's coming out.

Evan Banks

Okay.

Krista Romita Grocholski

So every five years or so when there's a new climate assessment, you could take a look at that and see, do our regulations currently make sense based off of that assessment? And adjust from there or just what you can adjust from there. It's one way to, I think, kind of thread the needle between let's just build for the 90%, you know, probably, you know, the worst thing that could possibly happen or and kind of balancing the cost of that. And so if you continually check in with the science or with the way that things are being implemented and if it's working, then you have the opportunity to course correct over time. That's not to say that that's an easy thing to do, but it's an approach that I haven't seen taken or has not been historically taken in stormwater management.

Evan Banks

It strikes me as just very good lawmaking to do that, kind of like something like a sunsetting provision in a bill or something to just sort of because the world changes over time and technology changes over time and the laws and regulations that we have don't. So it's an that's an interesting provision. I would be interested to learn more about it.

Krista Romita Grocholski

We would probably be interested to spend more time thinking about it.

Evan Banks

Yeah.

Krista Romita Grocholski

And having more reports on things like that and how that would work in real life.

Evan Banks

My very last question is just what comes next for MARISA, for stormwater management, for this kind of series of studies that you've been working on?

Michelle Miro

Our first steps are really trying to address the recommendations we lay out in our work that's providing tangible, practical guidance to stormwater utilities on how to estimate costs of adaptation versus inaction, on how to communicate climate change to their policymakers and their communities, and how to pick between that uncertainty band that we talked about. So there's a large need for information and guidance and support in those areas that places like MARISA and as researchers, we can really provide, so that that would be the first step. There are kind of larger next steps for the climate services or the federal funding community to provide funding and resources for this type of work more broadly, we certainly shouldn't be the only ones doing this. And the mid-Atlantic isn't the only region in need of this type of information.

Evan Banks

That's it for this episode. Thank you both so much for joining me.

Michelle Miro

Yeah, thanks for having us.

Evan Banks

You can learn more about MARISA and Michelle and Krista's work and stormwater management in the show notes at rand.org/podcast. We'll see you next week. RAND is a nonprofit institution that helps improve policy and decisionmaking through research and analysis.