For Professor Anthony
cayeki
Lecture5-UrbanMetabolism.pdf
Urban Metabolism ECI 123
Urban metabolism
• “The study of material and energy flows arising from urban socioeconomic activities and regional and global biogeochemical processes.”
– John Fernandez
Why Urban Metabolism?
• Consider resource efficiency and compare across cities to infer resource-efficient planning and design
• Facilitate the use of “system dynamics modeling to examine complex, dynamic interrelationships that exist in physical and social processes of the urban metabolism” https://resourceefficientcities.org/wp-content/uploads/2017/09/Urban- Metabolism-for-Resource-Efficient-Cities.pdf
Recall: Flows and Indicators of Material Balance across an Urban System
4
Material Accumulation
Material Throughput
Recycling
(local +
external)
Imports -Fuels
-Raw Materials
-Unfinished products
-Finished products
-Wastes
Local Extraction -Minerals/fossil fuels
-Biomass
Balancing Inputs
Indirect Flows
To Nature (local) e.g. air emissions
Balancing Outputs
To Nature (exported) e.g. waste to landfill
Non-waste exports
Indirect Flows
Different ways to think about cities
Reproduced from: https://resourceefficientcities.org/wp-
content/uploads/2017/09/Urban-Metabolism-for-Resource-Efficient-Cities.pdf
Let’s start by talking about the critical flows
• Water
• Energy
• Materials (minerals, building materials, etc.)
• Finished and unfinished products
• Nutrients
• Food
Let’s work through some real studies
• Ngo, N. S., Pataki, D. E. (2008) The energy and mass balance of Los Angeles County Urban Ecosystems. 11(2): 121–139
• Reduced scope – not everything is modeled and tracked
– Energy
– Water
– Food
• Compared results for
1990 and 2000
UM of Los Angeles
Imports Local Sources Outputs
Fuel, Electricity
Local Energy
Generation
and Use
Air pollutants
Greenhouse Gases
Waste Heat
Water Pollution
Surface H2O
Ground H2O
Precipitation
Groundwater
Evapotranspiration
Stormwater run-off
Wastewater Discharge
Food (finished
and unfinished)
Local food
production
Solid waste
Water production
Scope is urban areas of LA county
Comparative study between 1990 and 2000
Population
growth = 7%
Population
density growth
= 7%
Farms and
livestock
decreased
Food inputs
Used national data on average per capita food consumption to estimate total
demand
- Found that between 1990 and 2000 some small amount of food within the city
limits started being produced – no more than 1% of vegetables, and 2-3% of
fruit
Residential and Commercial Energy Use
Electricity: 2.3
kWh losses per
1 kWh
delivered (sold)
Electricity: 2.3
kWh losses per
1 kWh
delivered (sold)
Electricity: 2.3
kWh losses per
1 kWh
delivered (sold)
Electricity
consumption
up, Natural Gas
consumption
down
Industrial and Transportation Energy Use
Petroleum up a
little, electricity
up by 80% and
natural gas
down by 48%
• What do you think about counting net solar radiation as an input?
– Helpful, confusing….
• What about electricity “losses”? The authors picked one input and one metric to consider the upstream impacts for…
– For example, electricity generation is very water- use intensive
What matters for transport energy?
• Density of population matters
Kennedy et al. 2007. The
changing metabolism of cities.
Journal of Industrial Ecology
11(2)
But density isn’t
everything. What
else might matter?
CO2 emissions
48 51.1
19.7 21.4
10.9 14.6
12.9 11.4
0
20
40
60
80
100
120
1990 2000
Total CO₂e
Metric tons CO₂ Emissions
Residential Commercial Industrial
Transportation Electricity (in state) Electricity (imported)
Unknown end use
Methane Emissions
0 0.5
1 1.5
2 2.5
3 3.5
4 4.5
5
1990 2000
Total CO₂e
CH₄ as CO₂e
Stationary Source Combustion Mobile Source Combustion
Wastewater Treatment Landfills
Decrease
Petro and natural gas
supply & NG
distribution
Wastewater
Treatment
Increase
Nitrous Oxide and High GWP gases
0
1
2
3
4
5
1990 2000
Total CO₂e
Nitrous Oxide (N2O)
Stationary Source Combustion
Mobile Source Combustion
Nitric Acid
0
1
2
3
4
1990 2000
Total CO₂e
High GWP Gases
Electricity transmissionand distribtion (SF6)
Semiconductor manufacture
Substitution of Ozone depleting gases
Which types of gases are most important?
95
100
105
110
115
120
125
130
1990 2000
Total CO₂e
Total CO2e Emissions from LA County
CO2 CH4 N2O High GWP Gases
Freshwater Consumption Wells
Wells &
surface
Wastewater Discharge
-Increase in total effluent, and quality is less suspended solids and more BOD
-Even with population growth, still a surprising amount of increase in wastewater
What are the ramifications of urban water use?
• We saw that well water use increased substantially (and the public system also depends on groundwater)
Chicago has been using groundwater since at least 1864 and groundwater has been the sole source of drinking water for about 8.2 million people in the Great Lakes watershed. This long-term pumping has lowered groundwater levels by as much as 900 feet.
What happens when there are lots of wells and they compete for water?
http://www.scienceforthepeople.net/EHS/Water_Survey/ws.htm
National Map (1900-2008) on groundwater decline
-Much of the yellow
and red areas are
actually agricultural
areas
-But some are
not…some are high
density urban
areas.
But if you pump enough out…something else happens
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Local effects of groundwater depletion
Mexico City
• Has depended on groundwater for centuries and has suffered subsidence for centuries as well
RATE of subsidence in Mexico City
https://phys.org/news/2014-12-esa-image-mexico-city-subsidence.html
Other effects (relevant to coastal cities)
https://water.usgs.gov/edu/gwdepletion.html
Some cities start importing from outside…
Kennedy et al. 2007. The
changing metabolism of cities.
Journal of Industrial Ecology
11(2)
Modeling Approaches
• How would we actually go about conducting an Urban Metabolism?
• Where do we go for data? For example.
What is top-down and bottom-up?
• This refers to how you approach understanding/collecting data for your modeling activity.
• Let’s imagine that you have data on the total amount of Energy Use broken down fuel type and electricity (based on data collected by say tax receipts). This is top-down data – you have information on the system-wide consumption of energy.
What is top-down and bottom-up?
• On the other hand, you could try to actually model energy use bottom up by modeling all the energy uses (e.g. based on counting homes, business, vehicle miles traveled, etc.) and doing some kind of measurement of expected energy use for each contributing process/technology.
A tangible example
• My research team is doing an LCA of almond milk production. We have one participating company who is providing data. We collected facility wide data on fuels, electricity, water use and waste water generation, solid waste, and chemical inputs.
– This is top down data
• We also collected process level data for each step in the almond milk production process (where possible, since much equipment doesn’t track data on specific energy use).
Why collect both
• Process data means we can come up with ideas for improvement
• In many cases the difference between process level and facility wide is enormous…especially for things like electricity and water. Why?
– Overhead – lights, HVAC, etc.
– Leaks! Restrooms and cafeterias…factories often have people in them…
So…what are sources of top down data for doing urban metabolism
• Some kinds of material flows are tracked (e.g. public water supply, wastewater treatment, total electricity imports, travel behavior, maybe total fuel use, etc.)
• Other data is tracked at a national or statewide scale and might be downsized to represent a city
Bottom up data collection
• Takes a long time, and very data-intensive but gives lots of granularity and can include spatial information (i.e. where a stock or flow occurs)
• Data sources = you? Or at least you plus a bunch of research and data collection efforts
• Most of the time we have to combine both approaches to complete a study.
