The place of nature in the city
By: Guilherme M. Iablonovski
Tags: Ian Mcharg, Environment, GIS, Nature, Design

The place of nature in the city

A practical take on Ian McHarg's suitability analysis method.

The year of 2019 marked the 50 year anniversary of Ian McHarg's influential book, Design with Nature. I was first introduced to this book back in 2013, and no book has made a deeper impression in me since.

Back in 1969 when it was first published, the environmental movement was popping all over the world. The 1970s and ’80s were the time of landmark legislation surrounding ecological concerns, and McHarg argued that landscape architecture alone was able to integrate all the fields involved. The book's techno-utopian ideas of fitness, suitability, and the ability of data to reveal the “right” answers pulled landscape architects out of gardens and parks and into larger territories of action. McHarg viewed landscape architecture as an exercise in problem-solving, based on the notion that ecological concepts and rational planning could provide designers with a ticket to relevance in an ever-more-technocratic world.

Sir Ian McHarg’s in 1969 promoting his book on The Mike Douglas Show. Courtesy the Architectural Archives, University of Pennsylvania.

My first contact with the book came a mere year after having been introduced to Geographic Information Systems (GIS). What stroke me the most was how much of the book was in tune with what I had been hearing as "cutting-edge" subjects in spatial planning. The power of data to evidence planning choices and the problem-solving approach are what the 2010s have been about, with the explosion of data science and design thinking.

So, back in 2013 when I was still an Architecture & Urbanism undergrad student, I simply had to give a try to McHarg's methods. This is the story of how I implemented McHarg’s “layer-cake” method, otherwise termed “suitability analysis” — which predated the invention of today’s GIS — , and what I found when I took Design with Nature into the context of my home town, Porto Alegre.

The Porto Alegre case study

Porto Alegre, Brazil’s southernmost capital, had, throughout the last 50 years, a tradition in environmental management to be proud of. The city published an Urban Environment Atlas, created the Participatory Budget policy — the same one that is nowadays adopted in the city of Paris — , and destined up to 24% of its territory to specially protected areas. In the last 10 years, however, the municipality grew to neglect environmental matters, and we watched the slow dismantlement of the ideas that molded the city once recognized as Brazil’s greenest capital.

The evolution of human occupation in Porto Alegre. The first map shows the incremental occupation year by year, color coded. The second one shows where we stood by the year of 2010. The third map show the municipalitie's plan of expansion. And the fourth is a computer generated simmulation of human expansion given the land traits.

Porto Alegre’s form and development were, from the start, deeply connected with the landscapes and scenic beauties available, from the beaches to the hills and now towards the bucolic landscapes currently occupied by rural plots. This occupation would be initially lead by the rich, which in time ended up bringing the infrastructure that would allow the latter occupation of not-as-wealthy populations. This effect can be observed today in the southernmost portion of the city — once known as the rural zone of Porto Alegre — by luxury condos that carry along with them major urban equipments and mega-infrastructures.

The current landscape gradient, from most urban, to nearly rural luxury condos, present in today's Porto Alegre.

The layer-cake method applied

To completely understand what this occupation pattern means, McHarg’s suitability analysis method provides with a fairly simple and effective way to assess if the current expansion of human occupation makes sense or not.

The superposition of all the features that provide most value to humans makes for a very colorful map.

The method consists in mapping main territorial atributes that promote the most value to humans when left untouched, and superpose those on a single map.

These are land features such as flood areas, wetlands, aquifer recharge zones, steep vegetated slopes, protected areas, forest patches and nutrient rich soils.

In this exercise, one must assume that ecosystem services represent an impossible-to-calculate value. Secondly, if something represents value, by logical deduction, it must also represent a cost to its users if it were to be destroyed.

The human occupation cost map, superposed with the existing and planned urban occupation we had seen at the beggining of this article.

Using that logic, McHarg proposes that to assess the real cost of losing these land features, we must not use numbers, but rather maps.

So, if we take the previous map and assign the same color (grey) and opacity (50%) to each land atribute, we actually produce a Human Occupation Cost Map.

In this new map, the darkest areas represent those that probably provide more ecosystem services (provision, regulation, culture and support).

When this information is confronted with the roads planned by the city hall and future allotments, one must come to the conclusion that the urban expansion is taking place precisely on the city’s most environmentally relevant areas.

Do we need to be occupying that land?

The suitability analysis method produced evidence for what I already had a feeling was happening in Porto Alegre. The city was expanding into the ecologically rich southernmost parts of the municipality — currently occupied by rural properties — with a very particular kind of real estate product, the green luxury condos. But is that argument compelling enough to put a halt to that expansion? Probably not. So perhaps we should take a look at the city itself: do we actually need to claim more land to accomodate new inhabitants?

It didn’t take me long to discover that it wasn’t the case. In 2014, Porto Alegre had 38 thousand families living in extreme poverty conditions, with nowhere to live.

On the left, the demographic density allowed by the city's masterplan. On the right, the actual demographic density produced by the city as it is. Talk about wasted potential!

At the same time, 48 thousand apartments and houses lied vacant in the inner city alone, a courtesy of real state speculation.

It becomes even clearer if we compared the demographic densities allowed by the city’s masterplan — already quite low, no more than 250 hab/ha — to the actual densitites produced by the city — 90 hab/ha at the most — .

It becomes clear that the luxury condos are not by necessity, but by choice. Wealthy populations are looking for a place to spend the weekend or to live a more relaxed way of life, to the expense of everyone's proximity market and ecosystem services. Taking all this into account, it goes without saying that a more compact occupation model is urgent in Porto Alegre. That is to say we need to find a way to fill in the gaps in the city, instead of make it even more sprawled.

How can we tackle this issue?

This compacity, however, has its advantages and disadvantages. On one hand, economies of scale can be obtained — concentration of jobs, greater competition, better quality of services — , on the other hand, already existing negative externalities might be enhanced.

And we do have plenty of negative externalities! During the last 5 years, the city was included in the list of municipalities in critical situation regarding the Industry Potencial Pollution Index. The water from its main drinking water source, the Guaíba Lake, is found heavily polluted by domestic and industrial wastewater, and high temperature records are beaten every year. Last but not least, in 2007, the city had doubled the pollution level recommended by the World Health Organization, obtaining, with this, the title of Brazil’s second most polluted capital.

This means that as the degree of compacity grows, both the economies of scale and the negative externalities curves go up. This suggests that, at some point, one should find an optimal threshold of compacity; everything beyond this point causes more prejudice than earnings for the city.

According to some of today's most influential urban economists, the “antidote” for raising compacity without extrapolating the negative externalities are innovative technologies, or game changing tools that cancel the holdbacks that exist under current sociotechnical systems.

Bringing McHarg’s legacy into the 21st century

So what might those innovative technologies be? The term never existed while McHarg lived, but I'm sure many will suggest that we have a very clear answer for addressing those issues: Nature Based Solutions, or Green Infrastructures.

By “design with nature” McHarg meant that the way we occupy and modify the earth is best when it is planned and designed with careful regard to both the ecology and the character of the landscape. In this way, he argued that our cities, industries and farms could avoid major natural hazards and become truly regenerative. More deeply, McHarg believed that by living with rather than against the more powerful forces and flows of the landscape, communities would gain a stronger sense of place and identity.

In face of the now trending Nature Based Solutions, the meaning of "Design with Nature" has somewhat shifted from a philosophy for problem solving into a delimited toolbox of solutions that make use of natural processes for developping better sociotechnical systems. That is good news for us, and certainly honours McHarg's legacy by showing just how much his book is still relevant in the 21st Century. One can only hope it's taken seriously. And as for Porto Alegre, you can check my own idea of what this new sociotechnical system should look like here.