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Measuring the Risks of Sinking Land with Manoochehr Shirzaei

Manoochehr Shirzaei joined Virginia Tech’s “Curious Conversations” to talk about the importance of understanding and measuring sinking land, commonly called land subsidence. He shared insights about the use of satellite data in creating high resolution maps, how land subsidence fits into the overall picture of climate change, and how he hopes the information is used by localities.

About Shirzaei

Shirzaei is an associate professor of geophysics and remote sensing in the Department of Geosciences and the director of Virginia Tech’s Earth Observation and Innovation Lab. His research uses sophisticated space-, air-, and ground-based monitoring techniques to improve our understanding of seismic and aseismic faulting processes, the evolution of crustal stresses and seismic hazard due to fluid extraction and disposal, changes in groundwater and surface water resources, and impacts of relative sea-level rise on coastal areas. 

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Travis Williams (01:50.234)

That's right. Okay. Awesome, awesome, awesome. Well, I'm kind of curious to start this off because we've talked before. I had this thought the other day. A lot of people talk, a lot of people will talk sometimes about folks that run around saying, oh, the sky is falling, but you're kind of like the person that goes around the toys like, hey, the earth is sinking. Have you caught, have you, has that happened to you yet? Have you become known as that guy yet?

Manoo (02:17.964)

Oh yeah, so we are probably the best known group for work on the land subsidence. So the sinking of the land has been known for decades and actually centuries. So we know that in many places land is sinking. But how widespread is and how consequential is land subsidence for communities, for infrastructures and for the hazards?

It was not known until the work actually came around and through research now many people, many groups, many policymakers, many scientists know how important is land subsidence for creating, for example, adaptation strategies along the coast, developing and designing cities, building infrastructures, et cetera, et cetera.

Travis Williams (03:11.226)

Yeah, and your group has, you all have done these measurements on, have you done all of the United States coasts now and maybe some other places too? Where all have you done all these measurements?

Manoo (03:21.964)

So yes, so we are the largest group at the moment globally producing high resolution map of the land subsidence. We finished the work on the coast of United States. And this is going to come out actually through different platform. For example, USGS is going to release those data to public, but also some publication. Now we are expanding our work to Africa. So we are working on the coast of Africa.

So, to provide data in a region that is data scarce.

So, in a region that data is scarce, such as Africa, or technology and knowledge has been very handy because we use satellites that are publicly available and these data have global coverage at very high resolution accuracy. And we created know -how in our lab that know -how and technology is used to process data at a very high precision and accuracy. And that is going to be used to create, for example, again, adaptation and resiliency plan for the African countries.

Travis Williams (04:37.594)

That's really fascinating. And what was the area you said that it was?

Manoo (04:41.79)

At the moment, we are working on the entire coast of Africa. So it's a whole continent.

Travis Williams (04:47.034)

Oh, okay. That's great. So Africa. Okay. Well, I'm curious. You said we've always known that the Earth is... You said that for years and decades or centuries or generations, we've known that the Earth is sinking a little bit here and there. Why has it taken until this time for us to realize how widespread it is?

Manoo (05:09.164)

Right, so probably the main reason is that land sinking is very gradual process. It has to accumulate over course of, for example, years to decades to become a significant hazard. So very often these kind of processes are overlooked. And what drive land substance is also very complex. So for that reason, lack of long -term observation, and lack of understanding of the drivers together created a vacuum, a gap, data knowledge gap that led to even scientists and the academic community to believe subsubstance is not as important as it is when it comes to the impact that it has on environments, communities, and infrastructure.

Travis Williams (06:04.73)

And so how do you all, you kind of mentioned this a second ago, but how do you all go about getting all of these measurements? You're not going out there and getting them physically.

Manoo (06:15.094)

No. So we leverage satellite data. So there are type of satellites called radar satellites that transmit a radar signal from the satellite. This signal propagates into the atmosphere and hits the ground and bounces back to the satellite. By measuring the time that this signal takes to travel to the ground and back to the satellite, over the time we can measure how land is moving up or down. And this technology is very precise. So we can measure changes smaller than one millimeter per year to that technology.

Travis Williams (06:55.066)

Okay, and so I guess you take measurements from, let's say, today and then are you able to go back in time and kind of look at measurements? How far are you able to go back and look at stuff from?

Manoo (07:04.972)

So these measurements publicly made available by European satellites that's called ERS -1. So it launched in 1992. And then that was the beginning of the era that we are in it from remote sensing perspective. So ERS -1 followed by ERS -2, Japanese launcher satellite, then Canadian a space agency launched a satellite. So now we have access together to about 13 satellites data that spans period of 1992 until 2024. And we expect that this availability increases in the time to future because hopefully next month or in one of the coming months, we will have launch of NICAR satellites, which is a...joint venture between NASA and Israel, Indian Space Agency. And that would be also a great addition. So we provide us with significant amount of data free of charge that we can leverage for our research and explorations.

Travis Williams (08:15.77)

Yeah, well, so I've heard that this is called, I've heard this referred to as kind of a missing piece of the entire climate change puzzle. How does this fit into the climate change picture?

Manoo (08:30.156)

So we believe most of the climate adaptation strategies that are built and proposed now are incorrect and don't provide the protection that we expect because they don't account the land elevation change or land subsidence in that. So for example, we know very well that sea level is rising thanks to decadal and century long observation that came from different sources. And this measurement of the sea level has been used to create resiliency and adaptation strategies for the coastal communities.

Now with our observation, we know that coastal land are subsiding some area faster than rate of the sea level rise. So it means that many of those resiliency plans are not accounting for the total picture that is posed by the hazards associated with the relative change in elevation, relative change in sea level versus the land elevation.

Travis Williams (09:35.962)

Okay, so for a long time, so it sounds like for a long time, we paid a lot of attention to the sea level going up, but not the land going down, and those two things work together.

Manoo (09:47.948)

Yes, the work in tandem. So for a person standing on the coast, whether sea goes up or land goes down, the effect is the same. So they're going to get flooded.

Travis Williams (10:00.282)

What do you hope that leaders do with this new information, this new layer of information that you and your lab are hoping to provide?

Manoo (10:39.244)

So with this new knowledge that we provide, we identify a huge gap in existing models that are used to explain impact of the climate and environment and people and they quantify the two -way relationship between the systems. So the hope is that we can develop models, new models, new approaches that can integrate land subsidence into the analysis that's into the analysis that would tell us something about the impact that climate has on people. So the problem at the moment we have is that data that we create is not still integrated in existing models because the models did not have that parameter implemented in it. So we need a whole new field of research to investigate how we can...effectively include land subsidence into our understanding of the earth system and the impact that it has on people and also the ecosystem.

Travis Williams (12:13.05)

And so some practical applications of that, or maybe a better question would be, would some practical applications of that be things like planning flood routes in a city? Or what are some practical applications of that for the average person?

Manoo (12:28.14)

So practical application of the land subsidence would be, you know, it give us an idea of what is happening where on land. So for example, a building that is subsiding is an indication of, for example, foundation that is degrading. So we can allocate resources through that, you know. The best example is that we passed this, or Congress passed the infrastructure bill. So it's a 1 .2. trillion dollar bill to maintain infrastructure, bridges, buildings, runways, airports, etc. But the problem that we have now is that we need a lot more funds to maintain or upgrade all the resources. The estimate is that we need over $27 trillion.

So the land subsidence data at this high resolution that we produce accuracy can be used as an indicator for which infrastructure is at the higher risk. And through that, we can prioritize the infrastructure that should receive the...So through this observation, we can prioritize the infrastructure that should receive the care first. So think about this as a health care system for the infrastructure, for example. So our observation provide diagnostic measurements of the health of the infrastructure, and you could pay attention to the infrastructure that is more likely to fail early on so that would reduce the cost of the maintenance significantly.

Travis Williams (14:29.304)

Yeah, so it sounds like practically speaking, it's about how we better prepare infrastructure planning, maybe even you as like the homeowner of your own home.

Manoo (14:40.908)

That's exactly true. Yeah. So for example, I have a property that is subsiding. So, and if I know that this subsidence is happening, I can very quickly get ahead of the problem by fixing the foundation of that building, not waiting for the building, for example, to fail. So, this data is very cheap, widely available and can be used by anybody for many different purposes, yes.

Travis Williams (15:08.442)

That's awesome.

Well, one thing I was going to ask you, so I know that creating the maps and doing the measurements is your expertise, but do you know why? What are some reasons? Do you know what some reasons are that the land sinks?

Manoo (15:25.832)

Exactly. So we work a lot on also to understand the driver of those subsidence. So in many places, in a large scale to speak, like a scale of the East Coast of United States, Atlantic Coast. So majority of the subsidence is driven by natural processes. So due to, for example, a glacial isostatic adjustment of the land, There was a big thick layer of ice covering North America 10 ,000, 15 ,000 years ago, and that has melted. And when it melts, land is rising in Canada, and in the perimeter of that area of the, for example, U .S. Atlantic coast, land is falling. So that creates one or two millimeter of the subsidence per year across the board. But we have many areas that are subsiding at a much faster rate, but they are local scale, you know, Chesapeake Bay, Boston. Those are places that are subject to groundwater extraction. So as we extract groundwater and fluids, poor spaces collapse and as a result of that, lands begin to subside.

Travis Williams (16:44.314)

When we talk about land subsidence and climate change, those conversations can often become a little bit grim. So I'm curious, what gives you hope?

Manoo (20:59.564)

Right. So, you know, the change in the course of climate change proven challenging. It does not mean that we cannot do that, but commitments are made and promises are broken over and over. So it's proven to be complex process. So for that reason, thinking about adaptation strategies, you know, that help us to be resilient in the face of climate change is very important. So land elevation change can actually be a positive thing, you know? So land goes down, but also land can go up. You know, if we always measure sea level rise and we use that rate as a parameter in our climate or adaptation decision making.

But what if we make the land to go up? So by rising the land, you effectively make the sea level rise to slow down. So it means that we buy time, at least along the coast, where we expect that frequency of flooding to double very soon. You know, intensity of the flooding would increase significantly very soon, within next decade or so. And already we see some of those effects. Being able to elevate the land, that would reduce many of those negative impacts. So, know, land goes down for reasons, for example, extraction of the fluid. We know very well that process, that's when you extract water, pore space collapse and land subside. At the same time, we can inject water and treated fluid under the ground and make the land to rise to compensate for the sea level rise. This is a very effective mitigation strategy that uses vertical land motion as a tool to combat climate change. And it has other effect too. So for example, the water that we inject under the ground to compensate for the elevation change can be a storm water, can be treated wastewater or sewage from the cities. And in this way,

Manoo (23:25.9)

In the long run, we also bank the water. So this water will be treated and over time purified underground and we can pump it and the next generation has water to be used. So these are the ways that we can leverage land elevation change as a mechanism that serves us in the face of climate change to combat.

Travis Williams (23:49.434)

Well, that does sound very hopeful. So it sounds like your hope comes from the fact that this is actionable information that you're helping provide people.

Manoo (23:58.986)

Exactly, exactly. So this is definitely what we are hoping to, you know, or data turned out, turned to actionable, you know, items.

Travis Williams (24:10.522)

Yeah, so I don't imagine you're going to quit running around telling people the land is sinking anytime soon.

Manoo (24:16.352)

Not really now. I think I will be sticking around for a while on this topic. Yeah, and we are very well supported thanks to taxpayers, through funding agencies are supporting us. So we feel more responsible to continue to work and bring awareness to the community.