In Part 1 of Urbanizing the world's deserts we looked into how much land would need to be repurposed to allow for relatively high density cities. To move about 20% of the world's current population into cities with a density of 6300 residents per square kilometer. The total area of these new cities would be about 245,000 sq km or a bit smaller than the state of Oregon. Building said cities in just the Sahara, would require that about 3% of the Sahara's 9.2 million sq kilometers.
No matter how you approach the problem converting 3-15*% of the Saharah Desert in relatively high density cities would be a massive undertaking. Building these cities in such a way that the impact of building and maintaining them is done as sustainably as possible will be even more complicated. This article will attempt to highlight some of the challenges and sollutions for developing sustainable cities in water poor regions of the world.
The two most abundant materials in building modern cities are also some of the largest sources of carbon dioxide emissions on the planet. Concrete and steel production are responsible for between 15 and 17% of humanities carbon emmissions. Making concrete produces roughly 8% of the world's CO2 emissions, due in large part to the heat and chemistry involved in the concrete fabrication process. Steel similarly produces 7-9% of global green house gas emissions, where the average tonne of steel requires 1.83 tonnes of carbon dioxide to be emitted. Efforts to find lower carbon alternatives to concrete and steel will be critical in helping to offset the impact of creating a new city. A relative new comer to the construction industry is cross laminated timber, similar to plywood sheets but way thicker. Cross laminated timber has already been used to build structures over 10 floors in height, more than tall enough to achieve a target population density of 6300 people per square kilometer.
Reducing the carbon impact of concrete on urban development is more complicated, concrete is one of the most commonly used materials by human civilization, only water is consumed in greater volumes. Each year humans consume over 4 billion tonnes of concrete, emitting 1.5 billion tonnes of carbon dioxide. Research is ongoing into ways to make types of concrete that produce fewer carbon emissions but the easiest way to reduce these emissions is to simply not use the concrete in the first place. Some of the lowest hanging fruit for city planners to eliminate concrete from their cities is to drastically reduce private car ownership. Estimates for the volume of parking spaces around the world vary, for the United States it is estimated that for our 327 million residents there are 27 thousand square kilometers of parking spaces. To put that in perspective the US has roughly 1/5th the population of our future mega cities, and consumes over 10% of the land that our 1.5 billion city dwellers would need, just for parking. Reducing private car ownership and promoting various forms of mass transit could drastically reduce concrete useage.**
Low carbon construction and design are important, but making buildings truly efficient will be critical to the long term sustainability of our desert cities. As we are building in arid and semi-arid regions of the planet, one primary concern will be water conservation. In 2018 Cape Town, South Africa was fast approaching "Day Zero" a cut off point where the city's water reserves would effectively run out. At the height of the crysis Cape Town residents were limited to 13 gallons of water per person in each household, the average American directly consumes between 80-100 gallons per day. According to the United Nations humans require around 2000 cubic meters of water (520,000 gallons) per year. The Sahara, on average recieves between 1 and 4 inches of rain fall. If we assume that our cities are built in the drier regions of the Sahara, so 2 inches of rain fall on an average year, it becomes obvious that the Sahara cannot support 1.5 billion humans from natural percipitation***. Our future cities will most likely agressively capture and recycle as much water as they possibly can, but realistically some percentage of water used will need to be imported, thankfully enough our cities have a commodity to trade for their water, heat and electricity produced from the 3000+ hours of sulight they recieve each year.
Importing enough water for 1.5 billion people would be an incredible undertaking, so much so that it is likely to be unrealistic. To provide 2000 cubic meters of water for 1.5 billion people, you would need 3,000 cubic kilometers of water. For perspective so called super-tankers in the world can transport 320,000 cubic meters of water, which is only enough to provide enough water for 160 people for a year.**** For sake of continuing this series I'm going to act as if the complexities of water use are reasonably solved.
Thanks for reading, if you have any questions please ask, Part 3 will provide a narrative of what life in our cities might look like.
*15% was for the estimation that you were moving all of humanity into the Sahara.
** this article isn't saying that private car ownership within these future cities is an absolute no, I'm just suggesting that reducing private car ownership and promoting mass transit could free up a lot of land for other uses, and ideally be done without requiring as much concrete.
According to UN statistics the Earth is covered in 25.5 million square kilometers of Arid and Semi Arid terrain
https://www.un.org/en/events/desertification_decade/whynow.shtml
*** for those who want to see the math, 2 inches of water is about 5 cm (I'm rounding down but it gets us close enough considering the scope)
that means that to collect 1 cubic meter of water of rainfall, we need to collect all of the water that falls over a year for an area of 20 square meters
0.05cm water/year/sq meter/year *X = 1 cubic meter of water and X = 20 square meters (ok I'm not showing the right units but I'm like 90% sure the math is good, corrections welcome)
to meet one person's water needs according to the UN we are going to need 2,000 cubic meters, that works out to 40,000 square meters per person
that means that 1 sq kilometer (1,000,000 sq meters) can, at best, with no recycling but perfect water capture, 1 sq kilometer can support 250 people, less than 1/25th of the population density we require.
**** so it wasn't until I started to write this section that I began to appreciate how difficult it would be to transport enough water into our hypothetical collection of cities, that being said this assumes you're making your megacities all at once and they need all of their water all at once, the more realistic/gradual approach, is that you build smart sustainable cities gradually, building up sufficient water reserves before building new cities would make a huge difference. Also I'm going to spend some time looking into the 2000 cubic meters per person stat, because when I compared the stat vs American personal water consumption there was quite a gap, ex. Americans consume 80-100 gallons of water per year, ok so that means that every 2.5 days we consume about a cubic meter of water that means in a given year Americans directly consume about 146 cubic meters of water, for things like drinking, bathing etc....
OK so I spent a few minutes looking into this and it looks like the water volume value comes from things like agricultural water requirements, for example, when you eat a donut, it took some amount of water to grow the crops that were used to make the ingredients for our donut, that is where the 2000 cubic meters comes from https://www.theworldcounts.com/stories/average-daily-water-usage
alright, I will probably talk about updated numbers in part 3
No matter how you approach the problem converting 3-15*% of the Saharah Desert in relatively high density cities would be a massive undertaking. Building these cities in such a way that the impact of building and maintaining them is done as sustainably as possible will be even more complicated. This article will attempt to highlight some of the challenges and sollutions for developing sustainable cities in water poor regions of the world.
The two most abundant materials in building modern cities are also some of the largest sources of carbon dioxide emissions on the planet. Concrete and steel production are responsible for between 15 and 17% of humanities carbon emmissions. Making concrete produces roughly 8% of the world's CO2 emissions, due in large part to the heat and chemistry involved in the concrete fabrication process. Steel similarly produces 7-9% of global green house gas emissions, where the average tonne of steel requires 1.83 tonnes of carbon dioxide to be emitted. Efforts to find lower carbon alternatives to concrete and steel will be critical in helping to offset the impact of creating a new city. A relative new comer to the construction industry is cross laminated timber, similar to plywood sheets but way thicker. Cross laminated timber has already been used to build structures over 10 floors in height, more than tall enough to achieve a target population density of 6300 people per square kilometer.
Reducing the carbon impact of concrete on urban development is more complicated, concrete is one of the most commonly used materials by human civilization, only water is consumed in greater volumes. Each year humans consume over 4 billion tonnes of concrete, emitting 1.5 billion tonnes of carbon dioxide. Research is ongoing into ways to make types of concrete that produce fewer carbon emissions but the easiest way to reduce these emissions is to simply not use the concrete in the first place. Some of the lowest hanging fruit for city planners to eliminate concrete from their cities is to drastically reduce private car ownership. Estimates for the volume of parking spaces around the world vary, for the United States it is estimated that for our 327 million residents there are 27 thousand square kilometers of parking spaces. To put that in perspective the US has roughly 1/5th the population of our future mega cities, and consumes over 10% of the land that our 1.5 billion city dwellers would need, just for parking. Reducing private car ownership and promoting various forms of mass transit could drastically reduce concrete useage.**
Low carbon construction and design are important, but making buildings truly efficient will be critical to the long term sustainability of our desert cities. As we are building in arid and semi-arid regions of the planet, one primary concern will be water conservation. In 2018 Cape Town, South Africa was fast approaching "Day Zero" a cut off point where the city's water reserves would effectively run out. At the height of the crysis Cape Town residents were limited to 13 gallons of water per person in each household, the average American directly consumes between 80-100 gallons per day. According to the United Nations humans require around 2000 cubic meters of water (520,000 gallons) per year. The Sahara, on average recieves between 1 and 4 inches of rain fall. If we assume that our cities are built in the drier regions of the Sahara, so 2 inches of rain fall on an average year, it becomes obvious that the Sahara cannot support 1.5 billion humans from natural percipitation***. Our future cities will most likely agressively capture and recycle as much water as they possibly can, but realistically some percentage of water used will need to be imported, thankfully enough our cities have a commodity to trade for their water, heat and electricity produced from the 3000+ hours of sulight they recieve each year.
Importing enough water for 1.5 billion people would be an incredible undertaking, so much so that it is likely to be unrealistic. To provide 2000 cubic meters of water for 1.5 billion people, you would need 3,000 cubic kilometers of water. For perspective so called super-tankers in the world can transport 320,000 cubic meters of water, which is only enough to provide enough water for 160 people for a year.**** For sake of continuing this series I'm going to act as if the complexities of water use are reasonably solved.
Thanks for reading, if you have any questions please ask, Part 3 will provide a narrative of what life in our cities might look like.
*15% was for the estimation that you were moving all of humanity into the Sahara.
** this article isn't saying that private car ownership within these future cities is an absolute no, I'm just suggesting that reducing private car ownership and promoting mass transit could free up a lot of land for other uses, and ideally be done without requiring as much concrete.
According to UN statistics the Earth is covered in 25.5 million square kilometers of Arid and Semi Arid terrain
https://www.un.org/en/events/desertification_decade/whynow.shtml
*** for those who want to see the math, 2 inches of water is about 5 cm (I'm rounding down but it gets us close enough considering the scope)
that means that to collect 1 cubic meter of water of rainfall, we need to collect all of the water that falls over a year for an area of 20 square meters
0.05cm water/year/sq meter/year *X = 1 cubic meter of water and X = 20 square meters (ok I'm not showing the right units but I'm like 90% sure the math is good, corrections welcome)
to meet one person's water needs according to the UN we are going to need 2,000 cubic meters, that works out to 40,000 square meters per person
that means that 1 sq kilometer (1,000,000 sq meters) can, at best, with no recycling but perfect water capture, 1 sq kilometer can support 250 people, less than 1/25th of the population density we require.
**** so it wasn't until I started to write this section that I began to appreciate how difficult it would be to transport enough water into our hypothetical collection of cities, that being said this assumes you're making your megacities all at once and they need all of their water all at once, the more realistic/gradual approach, is that you build smart sustainable cities gradually, building up sufficient water reserves before building new cities would make a huge difference. Also I'm going to spend some time looking into the 2000 cubic meters per person stat, because when I compared the stat vs American personal water consumption there was quite a gap, ex. Americans consume 80-100 gallons of water per year, ok so that means that every 2.5 days we consume about a cubic meter of water that means in a given year Americans directly consume about 146 cubic meters of water, for things like drinking, bathing etc....
OK so I spent a few minutes looking into this and it looks like the water volume value comes from things like agricultural water requirements, for example, when you eat a donut, it took some amount of water to grow the crops that were used to make the ingredients for our donut, that is where the 2000 cubic meters comes from https://www.theworldcounts.com/stories/average-daily-water-usage
alright, I will probably talk about updated numbers in part 3
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