Eyes on Earth Episode 77 – ECOSTRESS and Urban Heat

GREG SPOTTS:

He showed me an ECOSTRESS image of L.A. at midnight and then at 4 a.m., and in both cases, in the middle of the summer, you can see our entire road system: the freeways, the ports and the airports, because they're emitting heat. There's no base map on this image. The only reason why you can see the roads is because the roads are hot. 

JOHN HULT:

Hello everyone, and welcome to another episode of Eyes on Earth. We're a podcast that focuses on our ever-changing planet and on the people here at EROS and across the globe, we use remote sensing to monitor and study the health of Earth. I'm your host for today, John Hult. We don't need a scientist to tell us that city streets catch and hold heat. Anyone who's walked barefoot from a parking lot to a beach can tell you that. What scientists can help us understand, particularly scientists who work with spaceborne, remotely sensed data, is just how big a difference there is between cities and the countryside. That gap is sometimes referred to as the urban heat island effect. At the height of summer, heat disparities can have a large impact on at risk human populations. Extreme heat events like those seen across the Pacific Northwest in 2021 can magnify those concerns. And extreme heat events are growing more common because of climate change. Today's guests know a thing or two about that. We have Dr. Glynn Hulley of NASA's Jet Propulsion Laboratory. He helps to produce land surface temperature products from sensors onboard satellites like Landsat, Terra, and Aqua. He's also the level-2 thermal lead for the Ecosystem Spaceborne Thermal Radiometer Experiment on Space Station mission, which is known as ECOSTRESS, because it's way easier to say. That data is available through NASA's Land Processes Distributed Active Archive Center or LP DAAC, which is located on site here at EROS. Glynn used data from ECOSTRESS and a sensor known as MODIS, that's short for Moderate Resolution Imaging Spectroradiometer, to produce a new way of mapping a community's heat vulnerability. His team investigated this approach by mapping vulnerability in Los Angeles, California, one of the hottest and most densely populated cities in the United States. Which is why we're joined by Greg Spotts, who is the chief sustainability officer for the Bureau of Street Services in the city of Los Angeles. Glynn, Greg, so glad to have you with us. Welcome to Eyes on Earth. 

GLYNN HULLEY:

Thank you. Glad to be here. 

SPOTTS:

Thank you. Good morning. 

HULT:

All right. Let's start off just talking in general terms about urban heat and how satellites are used to study the urban heat island effect. Why can't we just rely on ground temperature readings?

HULLEY:

From the ground, we can measure the actual air temperature, which we call the urban heat island. And then from space, we actually have a different term, the surface urban heat island effect, so ... 

HULT:

Because it's different, isn't it? It's not, it doesn't match up the surface and the air temperature. One is higher than the other, is that right? 

HULLEY:

Yes. So during the daytime, typically the actual surfaces heat up quite a bit faster than the actual air above it. The air above it has a very low heat capacity, so that, there's kind of a lag, temperature lag, that we get in the afternoon where if you feel the air temperature starts getting warmer later in the afternoon, but the actual surfaces are much hotter earlier in the day, from about noon till 3 p.m. And then what happens at nighttime due to radiative cooling and other effects, those two temperatures actually thermalize and we get almost similar temperatures between the surface and the air. So they're a little bit different, and they also vary by wind speed and solar radiation, things like that. But generally from space, what we refer to is the surface urban heat island. 

HULT:

Sure. And why do we need to get that from space? Why can't we just rely on sensors on the ground?

HULLEY:

For a couple of reasons. One is that it's very difficult to make these measurements on the ground autonomously and collect that data and do it over large, widespread areas. There are sensors in different cities around the world, operated by NOAA and NASA and other agencies, but they're pretty sparse. And so they measure general air temperature of a neighborhood level. For example, there's about three or four sensors in the San Fernando Valley in Los Angeles. The real benefit of the spaceborne data is that we can measure that routinely, almost every day, but also at very high spatial resolution. So with ECOSTRESS, as you mentioned, the resolution there is about 70-by-70 meters for each pixel. That's roughly the size of a football field. And we can measure that almost every day. 

HULT:

You don't have to worry about missing spots because you're covering everything. And at least with some of the sensors, you have pretty high resolution, as you say, football field scale pixels. Stepping back just a second, kind of a general question, not a remote sensing one. Why is it so important to study urban heat at all? Why are we looking at this? And I guess I'd kick that to both of you. I'd like to hear your thoughts on that.

SPOTTS:

It's really a public health issue. Cities are facing a significant future increase in heat-related emergency room visits and deaths. We have neighborhoods in Los Angeles today where there's about 40 to 50 days a year where the high temperature is at least 95 degrees Fahrenheit. In some of those neighborhoods, that's going to double in the next 20 to 40 years. And that's very worrisome. And then we have neighborhoods today that only have, you know, 15 such high heat days, and they're going to have the same 40 to 50 that our hottest neighborhoods have today. We urgently need to kind of rethink our urban design if we want to get ahead of this great risk. 

HULLEY:

There's been a number of studies now over the last decade or so that have showed that not only are these extremes increasing, as Greg mentioned, but heat waves are getting more humid over time due to a bunch of factors such as sea surface temperature warming. The nighttime humidity of these extreme heat events are also increasing, which is further exacerbating the human health effects. From the climate perspective, when we look at these long term trends, it really is quite dire. 

HULT:

Greg, you are one of many sustainability officers in the city of Los Angeles. You're one of 41. Talk to us a little bit about the city's sustainability efforts. And then I'd like to get into, if possible, a little more depth into how you connected with Glynn and that work. But first off, let's tell us where the city's at and what you've done so far.

SPOTTS:

Two years after Mayor Garcetti was sworn in, in the summer of 2015, he published his first Sustainable City Plan for Los Angeles. And one of the components in that plan was that each one of the 40 city departments should designate someone as the departmental Chief Sustainability Officer. And that wasn't going to be a standalone position. It was going to be sort of a second hat that you would wear that very day, I walked into my Director's office and said, I would like to be the Chief Sustainability Officer for Streets L.A. And it turns out raising my hand on that day has really changed the whole arc of my career. And although I have a whole lot of operating responsibilities as Executive Officer of Streets L.A., I get my greatest satisfaction out of this additional role as Chief Sustainability Officer. 

HULT:

So it sounds like about seven year or so, the city has had this sustainability plan, and you're working through this. Tell me how you connected with Glynn and how you decided that this would work into what you've been looking at with urban heat.

SPOTTS:

That same year I volunteered to be Chief Sustainability Officer, we did our first pilot with a cool pavement coating. We had a manufacturer install 7,500 square feet of that coating on a newly resurfaced parking lot at one of our parks. And we kind of coated half the parking lot, and then we compared it with the other black asphalt across the median. And we found that on warm summer afternoons, there would be a growing temperature differential between the coated and uncoated sections, until the coated sections were about ten degrees Fahrenheit cooler or more. We thought that was really intriguing, so we put together a funding package. We got a small amount of money for 2017, and that's when we installed one city block of cool pavement coating in each of the 15 council districts. Very shortly after that, I was at a conference and I met, um, an engineer from the Facilities Group at NASA's Jet Propulsion Laboratory, and we were talking about this, and she said, "I'd love to come have you present, because we have a big parking lot at JPL that we're thinking about putting cool pavement coating on, and using our sensors to understand how it works." And, you know, I was just really excited to have like a chance to set foot at JPL. I'm like a space dork, like a bunch of other people, you know, love the Mars Rovers, and I was really excited about going there. And when we sat down in the conference room, it turned out Glynn was the other presenter. He presented first, and I presented second. And it was a little bit like one of these moments where, you know, you meet your brother from another mother. 

HULT:

So, Glynn, what are your memories of that meet up? And was it kind of instant like, all right, we're going to work together? Like Greg says? 

HULLEY:

Uh, yeah, pretty much, you know. Immediately there was this synergy that I found that we could really work together and show some real applications, examples, of using the data to try and quantify these cooling effects on the streets. And so, what year was that, Greg? That was 2018? 

SPOTTS:

I think that was 2018, because in 2019 we did our first neighborhood cooling projects in the spring and one of them is this neighborhood in the west San Fernando Valley called Winnetka. And we told you these locations, and then Glynn went and observed this 12-block cool pavement coating project from space. It just so happened that the street we picked was like this crescent-shaped street, and we coated the street and the five cul de sacs that come off that crescent. It was very recognizable from space. That cool crescent was a cooler color than the reds and oranges of the whole rest of Winnetka. And we had a sort of eureka moment about that. 

HULT:

Glynn, talk to us a little bit about why ECOSTRESS is so well-suited for this particular job.

HULLEY:

So it was a really hot heat wave, you know, after launch in early July of 2018. And I showed Greg this image of all the streets and road networks and parking lots just lighting up at 4 a.m. You know, all these services are still really, really hot. And there is a one-of-a-kind image, because the ISS has this very strange precessing orbit which allows us to come over at different times of the day, every other day. On one day, we may come over at noon, and then two days later it may be three or four in the morning. That enables us to build up this sort of history of the diurnal cycle of the temperature change in the urban areas. And that's a very powerful tool. And there's no other sensor right now that is able to achieve that high frequency. 

HULT:

And again, just by contrast, you're talking about getting a couple images a day and having this precessing orbit. Most of the other sensors that you have access to, it's 10 a.m. every day or so. It's the same time every day. So you don't get that overnight, and you don't get that middle of the day, hottest part of the day from what is available or what was available before ECOSTRESS. Is that right? 

HULLEY:

Exactly right. So while MODIS and VIIRS come over every day, their spatial resolution as a thousand meters, it's just not sufficient to resolve those finer scale urban temperatures. Now there is Landsat, and Landsat 8 and 9, but as you say, they only come over at 10 a.m. every day, they only get that sort of morning temperature and not the more extremes in the afternoon. And they don't reveal the nighttime urban heat island effects. 

HULT:

Sure. So maybe the resolution is a little better on Landsat, but there are disadvantages there as well. Let's dig into the study, now, if that's okay. Talk to us about that. How did this study come together and what was the collaboration like and what did you find? I suppose I should ask you that. What did you find out? 

HULLEY:

In general, we've used ECOSTRESS in different ways. One is to actually quantify the cooling effect of the cool painted streets and not only of the direct cooling effect of the street itself, but what were finding is that within about a pixel or two of the street itself, we're seeing a cooling of the neighborhood, which is very encouraging to see. Secondly, with ECOSTRESS we can actually combine the data with other data sources that tell us something about the demographics of the areas within cities such as L.A.. Where do the more vulnerable people live? And we can combine that data together in what we call a heat vulnerability model, where we quantify the actual societal heat vulnerability that people are feeling in different regions of the city. You can imagine some areas may be still very hot, but there's maybe a lot of trees and people are, have air conditioning and they can be okay and survived that kind of heat. But in other areas, people are more vulnerable. 

SPOTTS:

It really played into the development of our work in L.A. from a series of pilots to a program. We got to the point in 2019, we'd done five different neighborhood cooling projects and we wanted to take it to a program. And yet the pandemic dramatically reduced city tax revenue. I had these findings from ECOSTRESS that really showed that there's a neighborhood cooling effect. That was the critical finding we needed to go big, but now we're trying to go big in a very difficult fiscal environment. And I went to my Director at the time.  I told him that Phoenix had just done a couple million square feet of cool pavement coating. And even though we helped them, now they're Hertz and we're Avis, we're number two. And I said, "Boss, what do you want to do?" And he said, "Come up with something so big and bold that I can't say no." So we developed ... 

HULT: 

I like that

SPOTTS: 

It was the best ... it's like one of the best pieces of direction I've ever gotten from a leader. And so we used all these different mapping sources, and we identified eight underserved neighborhoods where we could do a program of 200 city blocks of cool pavement across those eight neighborhoods and planting up to 2000 trees. And we built this really extensive Power Point. We created visualizations of how the streets would change. The slide that got us the funding was that slide of the cool crescent from Winnetka. It was visceral. The policymakers intuitively grasped it. I call that the $4 million slide, because we were able to get $4 million of cool pavement funding. But it continues. We got $2 million for the tree planting for next year. We have another $4 million for cool pavement coating, and two members of Congress from L.A. got $1 million earmarks for urban cooling projects in the U.S. federal budget. And certainly the collaboration with NASA really helped get the attention of those federal members of Congress. So that slide has brought a whole lot of funding, and therefore cooling to Angelinos. 

HULT:

You call it the $4 million slide, which is kind of interesting, at least sitting where I'm sitting at EROS, because it's a $4 million slide that's free. This is public data. Any city could get this, any remote sensing scientist could use this information in the way that you used it. 

SPOTTS:

You're right. And something I didn't understand until later ... The goal is to have on the ground civilians utilize this data to support smart climate related decisions. And that's been really wonderful to know that it isn't just a one-way benefit for us. 

HULT:

Let's talk about that, Glynn. Tell us about how that helps out. And I want to talk a little bit more about the future. What does building resilient communities look like? Obviously, we're talking about street cooling projects and planting trees, but where else could this go if this data is widely utilized, available, etc., etc., like Greg was talking about?

HULLEY:

Firstly talking about ECOSTRESS. Again, there's been this paradigm shift almost in NASA, where initially the data we'd only mostly get funding and be able to use the data just for fundamental science research. But there's been this shift to including more societal applications of the data itself. And this is a great example. And I just got an email this morning from the American Astronomical Society where Greg and I actually were the recipient of the 2022 International Space Station Research Awards Innovation Award, based on our urban cooling impacts with ECOSTRESS. And so we're going to apparently receive this award at the end of July, and we won out against a number of other sensors on the ISS. So that was great to see for ECOSTRESS, and again our cooling crescent image over Winnetka has sort of reaped some more rewards.

HULT:

Congratulations.

SPOTTS:

The $4 million slide keeps paying!

HULLEY:

Yeah, right. But you know, I think that speaking to your question there about the future. At the end of 2020, I believe, I was actually able to help host this hackathon where you get a number of just civilians joining on and learning how to use different types of NASA data. And in this case, the tutorial was on how to use ECOSTRESS data to map urban heat islands. We had almost 200 people joined from around the world, learning how to get their hands on ECOSTRESS data and make some of the images that I made. I think that is the future. Getting more citizen scientists involved to actually understand where temperatures are warmer in their neighborhoods. And I think that's really because people are actually feeling the consequences of urban heating even more and they're trying to understand how they can help and map out different hot regions of the city. 

SPOTTS:

One thing I wanted to mention, as I was listening to you, Glynn, is when we apply this cool pavement coating, right, people come out of their homes and they ask what we're doing. Every single person from every walk of life that I've spoken to at that moment says "this neighborhood's been getting hotter recently." It's so interesting if you talk about climate change, people talk about politics with you. But if you talk about their neighborhood, every single Angelino thinks their neighborhood is getting hotter and more humid. 

HULT:

So the people on the ground, they know what's going on and they're thankful for what you're doing, and you can measure what you're doing and do what you're doing better from space, as far away as possible from that person's doorstep. You sort of make the connection and help them out. 

SPOTTS:

In some ways, space is the great equalizer, right? Because I can't put sensors in people's backyards. That's private property. I can't put sensors on the Walmart parking lot. You can look at the whole city and all the different land uses and activities and the roofs of all of the buildings and see what's contributing to warming and what's reflecting some of that solar radiation back into space. 

HULLEY:

Very true. You know, we've talked about the uniqueness of this ECOSTRESS data record and measurement from space. And the instruments on the ISS typically have a pretty short life time, just because there's a lot of competition with people proposing new measurements on the ISS. And so ECOSTRESS is slated to end its commission on the ISS at the end of 2023. And the next type of measurement such as ECOSTRESS, will only start in 2025, 2026 from the actual European Space Agency. And so at the moment, we're really trying to campaign and trying to just show how valuable the ECOSTRESS data record is, and trying to extend past the 2023 timeframe, especially in this critical time, where if we lose that data with the increase in the number of mitigation efforts in cities, we'll lose that ability to quantify those changes. 

HULT:

Greg, anything you want to make sure you tack on here? 

SPOTTS:

Yeah. I mean, I'd just like to make a call to the young people out there, the early tenure professionals. There's never been a time like this where very complex government data is publicly accessible. You can learn how to download it and manipulate it and make your own uses of it. The opportunities in sustainability and technology and data are just unlimited and wide open. And it's going to be the younger people and the emerging professionals who take us where we need to go.

HULT:

Yeah, anybody can just go to the LP DAAC page. There are training modules on there, you can learn how to use this stuff and as we've talked about, it's free, you can get the ECOSTRESS data you want with the click of a button. It's an amazing place to be. 

We've been talking with Glynn Hulley and Greg Spotts about urban heat and how combining satellite datasets can help us to understand and respond to heat waves and climate change. Glynn, Greg, thank you so much for joining us. 

HULLEY:

Thank you.

SPOTTS:

Thank you. 

HULT:

And a big thank you to the listeners for joining us as well. You can find all our shows on our Web site at USGS dot gov slash EROS, that's U-S-G-S-dot-G-O-V, forward slash E-R-O-S. You can also follow EROS on Facebook or Twitter to find the latest episodes, or to subscribe on Apple or Google podcasts. This podcast, this podcast, this podcast, this podcast is a product of the U.S. Geological Survey, Department of Interior.