Category Archives: Peer Reviewed Article Review

doubling of El Nino

Nature Climate Change says El Nino frequency could double due to climate change. The result: “severely disrupted global weather patterns, affecting ecosystems4, 5, agriculture6, tropical cyclones, drought, bushfires, floods and other extreme weather events worldwide3, 7, 8, 9”

El Niño events are a prominent feature of climate variability with global climatic impacts. The 1997/98 episode, often referred to as ‘the climate event of the twentieth century’1, 2, and the 1982/83 extreme El Niño3, featured a pronounced eastward extension of the west Pacific warm pool and development of atmospheric convection, and hence a huge rainfall increase, in the usually cold and dry equatorial eastern Pacific. Such a massive reorganization of atmospheric convection, which we define as an extreme El Niño, severely disrupted global weather patterns, affecting ecosystems4, 5, agriculture6, tropical cyclones, drought, bushfires, floods and other extreme weather events worldwide3, 7, 8, 9. Potential future changes in such extreme El Niño occurrences could have profound socio-economic consequences. Here we present climate modelling evidence for a doubling in the occurrences in the future in response to greenhouse warming. We estimate the change by aggregating results from climate models in the Coupled Model Intercomparison Project phases 3 (CMIP3; ref. 10) and 5 (CMIP5; ref. 11) multi-model databases, and a perturbed physics ensemble12. The increased frequency arises from a projected surface warming over the eastern equatorial Pacific that occurs faster than in the surrounding ocean waters13, 14, facilitating more occurrences of atmospheric convection in the eastern equatorial region.

growing the urban forest

This abstract in Restoration Ecology contains an interesting result: planting shrubs along with urban trees helps the trees. You might think the opposite, due to competition, but I have heard this before. One theory I’ve heard is that shrubs help establish beneficial fungi in the soil that pave the way for healthy trees. It shouldn’t be too surprising, when this is exactly the succession that will occur in an abandoned field over time, given enough rainfall and not too much fire.

Compost also helps trees, which might be surprising to some professional engineers but not to any amateur gardener (luckily, some of us are both!). Still, in urban stormwater management we engineers are often encouraged to plant trees and other vegetation, but to minimize organic matter because the same nutrients that trees need can become water pollutants if they find their way downstream. It’s a delicate balance. Civil, “environmental”, and geotechnical engineers aren’t good at finding it because it is not part of our typical training. We need the agriculture, forestry, and soil science types to help us with this.

Forests are vital components of the urban landscape because they provide ecosystem services such as carbon sequestration, storm-water mitigation, and air-quality improvement. To enhance these services, cities are investing in programs to create urban forests. A major unknown, however, is whether planted trees will grow into the mature, closed-canopied forest on which ecosystem service provision depends. We assessed the influence of biotic and abiotic land management on planted tree performance as part of urban forest restoration in New York City, U.S.A. Biotic treatments were designed to improve tree growth, with the expectation that higher tree species composition (six vs. two) and greater stand complexity (with shrubs vs. without) would facilitate tree performance. Similarly, the abiotic treatment (compost amendment vs. without) was expected to increase tree performance by improving soil conditions. Growth and survival was measured for approximately 1,300 native saplings across three growing seasons. The biotic and abiotic treatments significantly improved tree performance, where shrub presence increased tree height for five of the six tree species, and compost increased basal area and stem volume of all species. Species-specific responses, however, highlighted the difficulty of achieving rapid growth with limited mortality. Pioneer species had the highest growth in stem volume over 3 years (up to 3,500%), but also the highest mortality (up to 40%). Mid-successional species had lower mortality (<16%), but also the slowest growth in volume (approximately 500% in volume). Our results suggest that there will be trade-offs between optimizing tree growth versus survival when implementing urban tree planting initiatives.

green roofs

Everybody kind of likes the idea of green roofs, but water professionals are not always 100% confident we understand them well enough to promise they will meet water quality and flooding regulations. But the studies are gradually trickling in. Here is a new one from Ecological Engineering:

Increasing recognition is being given to the adoption of green roofs in urban areas to enhance the local ecosystem. Green roofs may bring several benefits to urban areas including flood mitigation. However, empirical evidence from full-scale roofs, especially those that have been operational for more than several years is limited. This study investigates the hydrologic performance of a full-scale extensive green roof in Leeds, UK. Monitoring of the green roof took place over a 20 month period (between 30th June 2012 and 9th February 2014). The results indicate that the green roof can effectively retain and detain rainfall from the precipitation events included in the analysis. Retention was found to correspond significantly with rainfall depth, duration, intensity and prior dry weather period. Significant differences in retention values between the summer and winter seasons were also noted. Regression analysis failed to provide an accurate model to predict green roof retention as demonstrated by a validation exercise. Further monitoring of the green roof may reveal stronger relationships between rainfall characteristics and green roof retention.

Beyond questions on performance, there is a kind of chicken and egg problem where they are not used much (in the U.S., at least) because they are expensive and they are expensive because they are not used much. That is true of many emerging technologies. Of course, this “emerging” technology has been used in Europe for centuries, not to mention it is also popular with hobbits.

aging and deflation

This study says the relationship between aging and deflation (as seen in Japan, but possibly coming to many more countries in the future) depends on whether the aging is driven by falling fertility (which shrinks the work force in absolute terms) or longevity (which shrinks it only in relative terms).

Negative correlations between inflation and demographic aging were observed across developed nations recently. To understand the phenomenon from a politico-economic perspective, we embed the fiscal theory of the price level into an overlapping-generations model. In the model, successive short-lived governments choose income tax rates and bond issues considering the political influence of existing generations and the policy response of future governments. The model sheds new light on the traditional debate about the burden of national debt. Because of price adjustments, the accumulation of government debt does not become a burden on future generations. Our analysis reveals that the effects of aging depend on its causes. Aging is deflationary when caused by an increase in longevity but inflationary when caused by a decline in birth rate. Numerical simulation shows that aging over the past 40 years in Japan generated deflation of about 0.6 percentage points annually.
Here is another study that concludes “a larger share of dependents (ie young and old) is correlated with higher inflation, while a larger share of working age cohorts is correlated with lower inflation.” So maybe it depends to what extent the aging population is dependent on the working population, and whether the working population has additional dependents in the form of children (who will become the next working population). It’s complex, dynamic stuff that is hard to puzzle out.

autonomous truck

With all the talk of self-driving cars, I figured self-driving trucks and buses wouldn’t be far behind. And here is a self-driving truck, already licensed in a few U.S. states. It sounds like there is still a human driver in it for now. But in the long term, I imagine this is bad news for human driver as an occupation. It should be good news for the safety of humans on the road in general. It seems like it could favor the economics of road freight vs. rail. Then again, it might make much narrower travel lanes practical, leaving plenty of room in the right of way for other infrastructure like high speed rail, high voltage lines, pipelines, etc. Time will tell.

meta-analysis on designing active cities

This is a great example of meta-analysis in Active Living Research. There are a few things I like about it. First, it combines academic literature, other literature, and expert opinion in a very transparent and defensible way, by giving each a score. It takes a very wide array of urban design and planning choices and relates them to a number of outcomes (physical health, mental health, environmental sustainability, health and safety, and economic growth), and draws quantitative conclusions about the importance of each. Some outcomes challenge my pre-conceived notions, for example that street connectivity is bad for safety, but the methodology is very transparent, so I can dig in if I want and try to figure out whether I disagree with a particular rating, or whether I really should rethink my preconceived notion. Those of us dealing with complex planning and engineering programs (and many other complex systems) can’t realistically expect to optimize a handful of objectives any more. Instead, we can play the odds by making sure all our small, daily decisions have a better than even chance of nudging the system in a desired direction, based on the complete body of evidence out there, even with all its contradictions and confusions.

downscaling

Here is a useful (to me, at least) Hydrology and Earth System Sciences open article on spatial and temporal downscaling of climate change model output.

Information on extreme precipitation for future climate is needed to assess the changes in the frequency and intensity of flooding. The primary source of information in climate change impact studies is climate model projections. However, due to the coarse resolution and biases of these models, they cannot be directly used in hydrological models. Hence, statistical downscaling is necessary to address climate change impacts at the catchment scale.

This study compares eight statistical downscaling methods (SDMs) often used in climate change impact studies. Four methods are based on change factors (CFs), three are bias correction (BC) methods, and one is a perfect prognosis method. The eight methods are used to downscale precipitation output from 15 regional climate models (RCMs) from the ENSEMBLES project for 11 catchments in Europe. The overall results point to an increase in extreme precipitation in most catchments in both winter and summer. For individual catchments, the downscaled time series tend to agree on the direction of the change but differ in the magnitude. Differences between the SDMs vary between the catchments and depend on the season analysed. Similarly, general conclusions cannot be drawn regarding the differences between CFs and BC methods. The performance of the BC methods during the control period also depends on the catchment, but in most cases they represent an improvement compared to RCM outputs. Analysis of the variance in the ensemble of RCMs and SDMs indicates that at least 30% and up to approximately half of the total variance is derived from the SDMs. This study illustrates the large variability in the expected changes in extreme precipitation and highlights the need for considering an ensemble of both SDMs and climate models. Recommendations are provided for the selection of the most suitable SDMs to include in the analysis.

What is potentially useful to me is that they went to a one day time scale, and they defined an “extreme precipitation index” for storms expected to happen once a year or less on average. I am interested in how or whether these concepts can be applied to “typical” hydrologic conditions that happen at the more-than-once-a-year level. Drought and flooding are probably the two most concerning conditions impacted by climate change, but there are also questions being asked about water quality, and it is the “typical” conditions that most come into play.

ecological footprint vs. planetary boundary

This article in Ecological Economics tries to link the concepts of planetary boundaries and ecological footprint.

While in recent years both environmental footprints and planetary boundaries have gained tremendous popularity throughout the ecological and environmental sciences, their relationship remains largely unexplored. By investigating the roots and developments of environmental footprints and planetary boundaries, this paper challenges the isolation of the two research fields and provides novel insights into the complementary use of them. Our analysis demonstrates that knowledge of planetary boundaries improves the policy relevance of environmental footprints by providing a set of consensus-based estimates of the regenerative and absorptive capacity at the global scale and, in reverse, that the planetary boundaries framework benefits from well-grounded footprint models which allow for more accurate and reliable estimates of human pressure on the planet’s environment. A framework for integration of environmental footprints and planetary boundaries is thus proposed. The so-called footprint–boundary environmental sustainability assessment framework lays the foundation for evolving environmental impact assessment to environmental sustainability assessment aimed at measuring the sustainability gap between current magnitudes of human activities and associated capacity thresholds. As a first attempt to take advantage of environmental footprints and planetary boundaries in a complementary way, there remain many gaps in our knowledge. We have therefore formulated a research agenda for further scientific discussions, mainly including the development of measurable boundaries in relation to footprints at multiple scales and their trade-offs, and the harmonization of the footprint and boundary metrics in terms of environmental coverage and methodological choices. All these points raised, in our view, will play an important role in setting practical and tangible policy targets for adaptation and mitigation of worldwide environmental unsustainability.

I like ecological footprint because there is no ambiguity between stocks and flows. Natural capital is the underlying stock. The ecological footprint is a proxy for natural capital, the equivalent land area required to produce the annual flow of ecosystem services. It is very intuitive that if the ecological footprint is greater than the size of the Earth, you are digging yourself a  deeper hole each year, and if it is less, you are digging yourself out of the hole. Natural capital is like a huge trust fund or endowment that we can live off of for a long time. But if we are consuming more than the interest produced each year, there will eventually come a day when the trust fund is depleted.

Planetary boundaries, on the other hand, try to measure a mish-mash of stocks and flows. Fertile farmland, for example, is clearly a stock of natural capital. But the amount of fresh water consumed each year is an annual flow of ecosystem services. Atmospheric carbon dioxide concentration is a stock – a sort of anti-ecosystem service, because it represents the opposite of the atmosphere’s ability to absorb further emissions (which are an annual flow). So it all sounds very scholarly, but it needs some cleanup before it will be a clear framework for figuring out what course of action we should be taking.

urban agriculture and carbon emissions

Here’s an article from Landscape and Urban Planning making a connection between urban agriculture and greenhouse gas emission reductions. It makes sense – any food that comes from nearby will reduce transportation energy use, air pollution, and carbon emissions. We could either decide to do this for ethical reasons, or we could build more of those external costs in the price. It probably makes sense to do some of each.

The expansion of urban agriculture assists in reducing greenhouse gas (GHG) emissions not only by producing food but also by reducing the amount of food transported from farming areas and therefore reducing the food mileage. This study seeks to estimate “the expected GHG reduction effect” in the case of a revitalization of urban agriculture. For this purpose, this study first calculated the area available for urban farming by targeting the metropolitan area of Seoul and then calculated the production per unit area by focusing on “the crops suitable for urban agriculture”. Using this estimated value, the study estimated crop production, the resultant food mileage decrement, and the reduction of carbon dioxide (CO2) emissions that could be obtained if the Seoul metropolis introduced urban agriculture. The results estimated that if the Seoul metropolis implemented urban agriculture in a 51.15 km2 area, it would be possible to reduce CO2 emissions by 11.67 million kg annually. This numerical value is the same amount of CO2 absorbed annually by 20.0 km2 of pine forests and 10.2 km2 of oak tree forests that are 20 years old. From the perspective of GHG reduction effects in the transportation sector, urban agriculture is expected to produce a considerable effect in diverse aspects such as the habituation of green growth, self-sufficiency, and food security.

saving energy by saving water

An article in Journal of Water Resources Planning and Management quantifies the energy savings that result from water conservation.

Saving water saves energy. Consequently, implementing integrated water management (IWM) measures that reduce potable water consumption, stormwater runoff, and wastewater generation can potentially translate into significant energy savings. In this paper, the energy savings associated with IWM measures of rainwater harvesting and gray-water reuse are estimated, both at national and local utility scales using published data. At the national scale, it is estimated in this paper that up to 3.8  billion kWh and $270 million can potentially be saved annually by replacing landscape irrigation and other outdoor water uses through rainwater harvesting alone, and up to 14  billion kWh and $950 million in combination with gray-water reuse. Similarly, in Charlotte, North Carolina, the local water utility can potentially save up to 31  million kWh and $1.8 million annually. However, annual energy and associated cost savings per household are low at either scale, ranging between 1 and 120 kWh with associated cost savings of less than $10. These results are discussed in terms of energy savings’ role in IWM policy considerations and promotion of sustainable water use in urban areas.