Tag Archives: green infrastructure

May 2016 in Review

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3 most frightening stories

  • There are scary and seemingly reckless confrontations going on between U.S. and Russian planes and ships in the Indian Ocean. And yet, it is bizarrely humorous when real life imitates Top Gun.
  • The situation in Venezuela may be a preview of what the collapse of a modern country looks like.
  • Obama went to Hiroshima, where he said we can “chart a course that leads to the destruction” of nuclear weapons, only not in his lifetime. Obama out.

3 most hopeful stories

3 most interesting stories

  • I try not to let this blog get too political, really I do. But in an election season I just can’t help myself. This is a blog about the future of civilization, and the behavior of U.S. political, bureaucratic, and military elites obviously has some bearing on that. In May I mused on whether the U.S. could possibly be suffering from “too much democracy“, Dick Cheney, equality and equal opportunity, and what’s wrong with Pennsylvania. And yes, I’ve said it before and I’ll say it again, TRUMP IS A FASCIST!
  • The world has about a billion dogs.
  • It turns out coffee grounds may not make good compost.

urban vegetation design for heat

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When you see completely mangled English in a paper that has supposedly passed peer review, you have to wonder about the quality of the peer review. Nonetheless, I was interested in the results of this study that looked at trees, shrubs, and lawn to see which had the most effect on urban heat.

Numerical simulation of the impact of different vegetation species on the outdoor thermal environment

For air temperature at 1.5 m and thermal comfort and safety (PET and WBGT), the sequence is trees> lawn> shrubs, but for surface temperature, the sequence is lawn> shrubs> trees

I’m always interested in the idea of designing urban areas to maximize hydrologic function, ecological function, and human comfort simultaneously. There is so much that could be done, and so much closed-mindedness and poor communication among the various professions and disciplines that could be doing it.

I’ve always assumed trees are the gold standard, because you get both the evapotranspiration function and the shading function, whereas with lawn and shrubs you only get the former. Also, you only need a small area of soil to plant the tree (although often more than we allow in urban areas), and then its leaves can cover a large area of concrete or asphalt, which would otherwise be generating a lot of heat and polluted runoff. Also, grass provides very little ecological function (unless you let it grow taller and/or take a lenient approach to what some of your neighbors choose to define as “weeds”, which can be socially unacceptable), where trees and bushes provide ecological function. Bushes take up a lot of space, either in a sidewalk context or a small urban yard – paradoxically, once trees mature a little bit they take up less space because there is space under them. On the other hand, I’ve argued with purists that if people really want lawn in urban areas, it is a lot better than concrete in terms of hydrology, heat, and aesthetics. Although if you’re in a water-stressed area, that adds another factor to the hydrology equation that those of us in wetter areas have the luxury of not worrying about too much.

no coffee grounds in compost?

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This article is a bit disturbing, because I have been composting coffee grounds for years with seemingly good results. Then again, I wasn’t doing an actual controlled experiment.

Applying spent coffee grounds directly to urban agriculture soils greatly reduces plant growth

There are frequent anecdotal recommendations for the use of locally produced spent coffee grounds in urban agriculture and gardens, either through direct soil application or after composting with other urban organic wastes. This study investigates the scientific basis for direct application of spent coffee grounds (SCG) and the influence of different: i) plant pH and nitrogen preferences, ii) soil types, and iii) application rates. We specifically consider impacts upon plant growth, soil hydrology and nitrogen transformation processes.

We grew five horticultural plants (broccoli, leek, radish, viola and sunflower) in sandy, sandy clay loam and loam soils, with and without SCG and fertilizer amendments. The same horticultural plants were grown in the field with 0, 2.5, 5, 10 and 25% SCG amendment rates. Plant biomass growth was related to soil pH, soil moisture, nitrogen concentration and net mineralization, as was weed growth after harvesting.

All horticultural plants grew poorly in response to SCG, regardless of soil type and fertiliser addition. Increasing SCG amendment significantly increased soil water holding capacity, but also decreased horticultural plant growth and subsequent weed growth. There was evidence of nitrate immobilization with SCG amendment. Growth suppression was not explained by soil pH change, or nitrogen availability, so is more likely due to phytotoxic effects.

Fresh SCG should not be used as a soil amendment in ‘closed loop’ urban food production systems without consideration of potential growth suppression. Further research is required to determine the optimal composting conditions for SCG and blends with other organic wastes.

I’m not a very scientific composter. I just throw stuff together in an old recycling bin, then when it fills up I move it to another bin, and then a third (despite a few raised eyebrows from neighbors, I rescued all these bins on my old street after they were abandoned for at least a week, and filled with litter and dog crap). At that point it’s usually a nice crumbly organic mix that I can use. I don’t follow any of the rules. I don’t mix green and brown items in the right proportions, I let it get wet and dry according to the rain, I compost perennial weeds, and my pile almost certainly doesn’t get hot enough. I probably wouldn’t give the stuff away because there are weeds in there, but I don’t worry about putting it back on my garden, which is where the weeds came from. If they want to keep pulling carbon dioxide out of the air and turning it into organic matter for me, I am fine with that. I would rather be outside pulling weeds than doing almost anything inside.

“hybrid” infrastructure

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I like a couple things in this abstract from the journal Cities.

One is a definition of hybrid infrastructure as “infrastructure systems that are integrated within buildings and landscapes that also provide non-infrastructure uses”. In other words, you are trying to kill two birds with one stone. This should be efficient and cost-effective compared to killing two birds with two stones, but the reason it often doesn’t happen (at least in the U.S. cities I am familiar with) is that there are typically two entities responsible for killing one bird each, and if their stone happens to kill the other bird they will ignore that and not count it as a benefit. Each agency calculates the cost as one stone, while the actual cost to society was two stones. (The only problem with this analogy, obviously, is that we are talking about ecological benefits and killing birds would actually be bad.)

The second thing I like is that the question asked is about the “maximum ecological performance potential of buildings and landscapes”. This is a nice question to ask – not just how can one type of infrastructure perform one function cost-effectively, but how can it fit into the landscape and perform many functions at the same time. If those two agencies (or in real life, 10 or 20 agencies) were all asking this question together, maybe you could achieve much better outcomes in cities.

value of trees

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There have been a lot of studies on the value of urban trees. Well, here’s another. This one is notable for giving a canopy target at which value is maximized (30% at the property level, 38% at the county level).

The implicit value of tree cover in the U.S.: A meta-analysis of hedonic property value studies

Trees in residential neighborhoods and communities provide benefits for homeowners that are capitalized into residential property values. In this paper, we collected data from hedonic property value studies and merged these data with ancillary spatial data describing forest and socio-economic characteristics surrounding each study area to conduct a meta-analysis of the impact of tree canopy cover on the value of residential properties. The meta-analysis suggests that property-level tree cover of about 30% and county-level tree cover of about 38% maximize the implicit price of tree cover in property values. Currently, tree cover in the original study areas was about 14%, on average, around or near study properties. The empirical results, therefore suggest under investment of tree cover on private property from the perspective of individual property owners and from a societal perspective. The findings also have implications for community forest programs regarding planting trees and protection of mature trees to address potential changes in tree abundance, species diversity and stand age due to development and climate change.

green space and mental health

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Here’s a new study on green space and health, based on the large-scale nurses’s study. One interesting finding is that mental health explains around 30% of the total benefit.

Exposure to Greenness and Mortality in a Nationwide Prospective Cohort Study of Women

In models adjusted for mortality risk factors (age, race/ethnicity, smoking, and individual- and area-level socioeconomic status), women living in the highest quintile of cumulative average greenness (accounting for changes in residence during follow-up) in the 250m area around their home had a 12% lower rate of all-cause non-accidental mortality (95% CI 0.82, 0.94) compared to those in the lowest quintile. Results were consistent for the 1,250m area, although the relationship was slightly attenuated. These associations were strongest for respiratory and cancer mortality. Findings from a mediation analysis suggest that the association between greenness and mortality may be at least partly mediated by physical activity, particulate matter less than 2.5 micrometers, social engagement, and depression.

soil and carbon sequestration

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This open-access article in Nature makes a surprising claim – that much better management of agricultural soil could offset a significant portion of annual carbon emissions from all sources (not just agriculture), while also being good for ecosystems and food security.

How important, in total, is this large, varied set of land-use and management practices as a GHG mitigation strategy? One of the challenges in answering this question is to distinguish between what is technically feasible and what might be achieved given economic, social and policy constraints. A comprehensive global analysis of agricultural practices combined climate-stratified modelling of emission reductions and soil C sequestration with economic and land-use change models to estimate mitigation potential as a function of varying ‘C prices’ (reflecting a social incentive to pay for mitigation). They estimated total soil GHG mitigation potential ranging from 5.3 Pg CO2(eq) yr−1 (without economic constraints) to 1.5 Pg CO2(eq) yr−1 at the lowest specified C price (US$20 per Mg of CO2(eq)). Average rates for the majority of management interventions are modest, <1 Mg CO2(eq) ha−1 yr−1. Thus, achieving large global GHG reductions requires a substantial proportion of the agricultural land base (Fig. 2). Although the economic and management constraints on biochar additions (not assessed by ref. 19) are less well known, ref. 67 estimated a global technical potential of 1–1.8 Pg CO2(eq) yr−1 (Fig. 2).

A more unconventional intervention that has been proposed is the development of crops with larger, deeper root systems, hence increasing plant C inputs and soil C sinks. Increasing root biomass and selecting for root architectures that store more C in soils has not previously been an objective for crop breeders, although most crops have sufficient genetic plasticity to alter root characteristics substantially and selection aimed at improved root adaptation to soil acidity, hypoxia and nutrient limitations could yield greater root C inputs as well as increased crop yields. Greater root C input is well recognized as a main reason for the higher soil C stocks maintained under perennial grasses compared to annual crops. Although there are no published estimates of the global C sink potential for ‘root enhancement’ of annual crop species, as a first-order estimate, a sustained increase in root C inputs might add ~1 Pg CO2(eq) yr−1 or more if applied over a large portion of global cropland area (Fig. 2).

Thus, the overall mitigation potential of existing (and potential future) soil management practices could be as high as ~8 Pg CO2(eq) yr−1. How much is achievable will depend heavily on the effectiveness of implementation strategies and socioeconomic and policy constraints.

I tried to get a quick answer on global annual emissions in Pg CO2(eq), and failed. Now I’m out of time. I’ll figure it out some other time.

green roofs

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Here’s a green roof modeling study from Singapore. Green roofs reduce peak flows enough to help with flooding. They reduce the volume of runoff a little bit through increased evapotranspiration, which would have an effect on the water supply in Singapore where urban runoff is used as a water source.

Effect of Catchment-Scale Green Roof Deployment on Stormwater Generation and Reuse in a Tropical City

Low-impact development (LID) comprises a broad spectrum of stormwater management technologies for mitigating the impacts of urbanization on hydrological processes. Among these technologies, green roofs are one of the most adopted solutions, especially in densely populated metropolitan areas, where roofs take up a significant portion of the impervious surfaces and land areas are scarce. While the in situ hydrological performance of green roofs—i.e., reduction of runoff volume and peak discharge—is well addressed in literature, less is known about their impact on stormwater management and reuse activities at a catchment or city scale. This study developed an integrated urban water cycle model (IUWCM) to quantitatively assess the effect of uniform green roof deployment (i.e., 25, 50, and 100% conversion of traditional roofs) over the period 2009–2011 in the Marina Reservoir catchment, a 100-km2100-km2, highly urbanized area located in the heart of Singapore. The IUWCM consists of two components: (1) a physically based model for extensive green roofs integrated within a one-dimensional numerical hydrological-hydraulic catchment model linked with (2) an optimization-based model describing the operation of the downstream, stormwater-fed reservoir. The event-based hydrological performance of green roofs varied significantly throughout the simulation period with a median of about 5% and 12% for the catchment scale reduction of runoff volume and peak discharge (100% conversion of traditional roofs). The high variability and lower performance (with respect to temperate climates) are strongly related to the tropical weather and climatic conditions—e.g., antecedent dry weather period and maximum rainfall intensity. Average annual volume reductions were 0.6, 1.2, and 2.4% for the 25, 50, and 100% green roof scenarios, respectively. The reduction of the stormwater generated at the catchment level through green roof implementation had a positive impact on flood protection along Marina Reservoir shores and the energy costs encountered when operating the reservoir. Vice versa, the drinking water supply, which depends on the amount of available stormwater, decreased due to the evapotranspiration losses from green roofs. Better performance in terms of stormwater reuse could only be obtained by increasing the time of concentration of the catchment. This may be achieved through the combination of green roofs with other LID structures.

“transitioned” infiltration basins

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Here’s an interesting article about an infiltration basin that has failed in its infiltration function and “transitioned” into a wetland. Interestingly, the researchers determined that it still performs a stormwater management function, while also performing ecological functions.

Ecological assessment of a transitioned stormwater infiltration basin

Infiltration basins are stormwater control measures (SCMs) widely employed for urban stormwater management. A transitioned infiltration basin is a failed infiltration basin that has gradually transformed into a wetland- or wetpond-like practice. The transitioned basin was found to effectively control the storm runoff flows and volumes, and improve the discharge water quality, thereby reducing the downstream hydrologic and pollutant loads on most occasions. Qualitative assessment of the site showed presence of wetland and non-wetland vegetation, small animals, and some potential for cultural benefit. The ecological evaluation demonstrated that runoff management and habitat provision in a sub-urban setting enhance the overall functionality of this new type of SCM ecosystem. A functionality assessment guide was developed for assessing infiltration basins considered to have failed. The Level-1 assessment includes visual criteria such as hydrophytic vegetation, hydric soils, hydrologic regime modification, and design check. The rapid assessment plans developed in this study can be applied to determine the ecological and stormwater management functions and benefits of failed/transitioning/transitioned basins, and may be adapted for other similar SCMs.

A lot of us engineers assume that green infrastructure will have a useful service life and then eventually fail. This is in keeping with the idea of infrastructure, which needs constant maintenance to keep it from wearing out, or else eventually wears out and has to be replaced. But green infrastructure is supposed to be a designed ecosystem. Ecosystems can change over time but they don’t exactly wear out, in fact their functions tend to stay stabilize or increase over time. So if we really understand an ecosystem thoroughly and are able to design it, we should be able to anticipate and even control these changes. An example would be planting deep rooted, self-mulching plants that keep the soil of the infiltration basin loose and permeable for the long term. But even if there is a limit to that, you could let it gradually transition to a forested and/or wetland condition in a controlled way over time.

So here’s an idea I have to build streetside rain gardens on the cheap. Take a typical sad, compacted tree pit where a tree recently died or was removed (sadly, very, very common here in Philadelphia). Remove a foot or so of soil, or at least down to a few inches below street level. Throw in a handful of seeds like clover, daikon radish, prairie grasses, horseradish, or anything else aggressive, deep-rooted, perennial or self-seeding. Throw in an acorn or other tree seed (why not pick something edible). Now wait a year or two for all this to grow and begin to loosen up the soil and create some organic matter. When the plants have established themselves, go back and cut a hole in the curb to let water in. Gradually, the tree will grow and shade out the smaller plants. With this system, you get a functioning ecosystem in a few years with maybe $5 worth of seeds, and a lot of patience. If it doesn’t grow, you can afford to throw in another $5 worth of seeds.

tree canopy volume

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I had never thought about modeling tree canopy volume in 3D before. I’ve played around with simple algorithms to place trees on a map, assume a mature canopy area per tree, and estimate the total canopy area. This is useful because cities sometimes set targets and metrics in terms of number of trees, and sometimes in terms of tree canopy. The latter is better because it is more relatable to other goals a city might have related to the hydrologic cycle, carbon, heat, air quality, aesthetics and property values, biodiversity and habitat, and the financial cost to public offers of achieving these goals. Once you have an algorithm relating number of trees to canopy area, you can add more variables like type of tree, growth over time, and some assumed attrition rate or half life. Come to think of it, I have played around with leaf area index which is a quasi-3D concept. Anyway, without further ado here is the article that prompted my line of thought:

Local Impact of Tree Volume on Nocturnal Urban Heat Island: A Case Study in Amsterdam

The aim of this research is to quantify the local impacts of tree volumes on the nocturnal urban heat island intensity (UHI). Volume of each individual tree is estimated through a 3D tree model dataset derived from LIDAR data and modelled with geospatial technology. Air temperature is measured on 103 different locations of the city on a relatively warm summer night. We tested an empirical model, using multi-linear regression analysis, to explain the contribution of tree volume to UHI while also taking into account urbanization degree and sky view factor at each location. We also explored the scale effect by testing variant radii for the aggregated tree volume to uncover the highest impact on UHI. The results of this study indicate that, in our case study area, tree volume has the highest impact on UHI within 40 meters and that a one degree temperature reduction is predicted for an increase of 60,000 m3 tree canopy volume in this 40 meter buffer. In addition, we present how geospatial technology is used in automating data extraction procedures to enable scalability (data availability for large extents) for efficient analysis of the UHI relation with urban elements.