– Profile written by Bart Hawkins Kreps –
Imagine you’re looking at a one-hectare parking lot surrounded by fertile farmland. And imagine that there are two rows of trees growing in narrow green strips built through this parking lot. How would you estimate the Biocapacity of this hectare? Since it was taken from farmland, would you assign it the same per-hectare Biocapacity as the surrounding lands? In that case your estimate reflects the former productivity, but not the current productivity. Or you might see that the current Biocapacity of that parking lot is low, but it is greater than 0 – particularly if the trees are healthy and flourishing. University of Iceland masters student Anne van Berkum’s research is focused on just this issue.
The approved methodology now used to assess Biocapacity of built-up lands assigns these lands the same Biocapacity as area farmland, starting from the not unreasonable assumption that most cities were begun in areas that provided people with crops. This assumption is built into the methodology of the National Ecological Footprint and Biocapacity Accounts. Anne is a co-author of a forthcoming edition of the accounts. Ideally, however, we would have a method of estimating the actual current Biocapacity of our one-hectare parking lot – and of every other hectare of built-up land in cities around the world.
Anne van Berkum’s research is aimed at estimating the actual Biocapacity of built-up land in cities, in a way that can also reflect future improvements in green urbanism. “Cities can become so much greener,” Anne says. Looking at the flat roofs of dozens of other buildings from the window of her apartment in The Hague, Netherlands, she says “I see a lot of real estate for greenery.”
Anne believes a green-roofs programme could add significant Biocapacity in The Hague. And she believes the Ecological Footprint framework could and should account for such changes and gradations of bioproductivity within built-up areas.
Anne’s journey to this project started when she enrolled in a liberal arts program named “Earth, Energy and Sustainability.” During a study exchange, when most classmates went south to warm places like the coast of Spain, she bought a cheap ticket to Iceland and went north instead. That first weekend in Iceland was enough to kindle an interest. And once she applied to and was admitted to the University of Iceland, it was just one more short step to the International Ecological Footprint Learning Lab (IEFLL).
“During the first day of orientation I met Dr. Brynhildur Davíðsdóttir” – coordinator of IEFLL in Iceland. “The funding for the project had just been approved a few days earlier, and the courses weren’t yet showing in the course calendar. But the work that Brynhildur described was really interesting, so I signed up.”
She found the Ecological Footprint Informatics course especially valuable, as it gave her the knowledge for the internship working on biocapacity for the next edition of the national ecological footprint and biocapacity accounts. In combination with her skills in using remote sensing data, this knowledge has become an essential part of her research. She is finishing a literature review on issues of accounting for biocapacity in cities, while her GIS work is in progress. Ideally, she says, she will be able to demonstrate a “proof of concept” which others can build on.
She began the project by acquiring remote sensing for a portion of the area of The Hague. With a population of 550,000, the city is 98 sq km (9800 hectares) in area. Farmland in The Netherlands, being significantly more productive than the global average, has an Equivalence Factor of 2.52 – so a hectare of Dutch farmland becomes 2.52 Global Hectares in the Ecological Footprint and Biocapacity calculations. The same Equivalence Factor is applied to “built-up land”. As a result the 9800 hectares of land in The Hague have a calculated Biocapacity of 24,696 Global Hectares.
In her initial work with remote sensing data, Anne used free data from the European Space Agency’s Sentinel-2 satellite. With 10-meter resolution, that data isn’t always adequate to reflect urban Biocapacity. Small gardens, even if they are numerous, may not show up in 10-meter data, and a row of trees beside a wide paved street might also escape the analysis.
For her research Anne was also able to purchase a block of 1.2-meter data from the Pleiades satellite system. The 2800 hectares covered by this Pleiades data became her study area. Part of the project involves an assessment of whether the finer but costly data provides a significant improvement in the analysis. There were complications comparing the data sets. Though both data sets were captured in the spring, last spring was very cloudy and there was a three-week gap in acquisition dates. There was a lot of shadow in the Pleiades imagery, meaning that, for example, “I had to train the algorithm on the land covers in shade and then combine the shaded grassland with unshaded grassland.” Still, Anne says, “the Pleiades has so much more information. I can see individual green roofs, trees on streets between skyscrapers, etcetera, which are just invisible to Sentinel 2.”
Analysis using the Pleiades data analysis shows almost three times as much forest cover as shown in the Sentinel-2 data. On the other hand, the Sentinel-2 analysis indicates the study area is about 14% cropland, which Anne says does not match the reality on the ground; analysis of the Pleiades data shows about 7% cropland. In spite of such differences in individual land cover types, the Biocapacity Equivalence Factors indicated by the two satellite data analyses are quite close: the Sentinel-2 data analysis shows an EQF of .514, while the analysis of the Pleiades shows an EQF of .558. But they both differ dramatically from the EQF of 2.52 used for the area of The Hague in the currently accepted Ecological Footprint and Biocapacity framework.
Using the EQF of .558 derived from the Pleiades data would yield a Biocapacity for the study area of 1562 Global Hectares. Using the Dutch farmland EQF of 2.52 would show the study area’s Biocapacity as 7056 Global Hectares.
For this urban area, the satellite data-derived Biocapacity is only about 20% as high as the Biocapacity indicated in the currently used framework – but significantly higher than 0. And whereas the satellite-data derived Biocapacity would reflect any future expansions in programs such as green roofs, the currently used framework has no way of reflecting such increases in urban biocapacity. In addition to refining her work with the data for The Hague, Anne is hoping to apply this method to another, significantly different city. She hopes to complete this project within about six months. At that point, she says, she will switch her focus to different subjects – while hoping that her work will be taken up by others in the Ecological Footprint family as an improvement in the accepted methodology.