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Tag Archive: soil

  1. Review of research and future priorities to inform CA’s GHG emissions reductions plan: Agriculture and working lands

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    Byrnes R, Eviner V, Kebreab E, Horwath W, Jackson L, Jenkins B, Kaffka S, Kerr A, Lewis J, Mitloehner F, Mitchell J, Scow K, Steenwerth K, Wheeler S. 2017. Review of research to inform California’s climate scoping plan: Agriculture and working lands. California Agriculture 71(3):160-168. https://doi.org/10.3733/ca.2017a0031.

    This article grew out of conversations with state agencies concerning the need for a review of the current evidence base to inform emissions-reduction modeling and revisions to the state Climate Change Scoping Plan (CARB 2017b), which specifies net emissions reduction targets for each major sector of the California economy (table 1). It is important to note that the Scoping Plan states that work will continue through 2017 to estimate the range of potential sequestration benefits from natural and working lands (including agriculture and rangelands).

    Abstract: Agriculture in California contributes 8% of the state’s greenhouse gas (GHG) emissions. To inform the state’s policy and program strategy to meet climate targets, we review recent research on practices that can reduce emissions, sequester carbon and provide other co-benefits to producers and the environment across agriculture and rangeland systems. Importantly, the research reviewed here was conducted in California and addresses practices in our specific agricultural, socioeconomic and biophysical environment. Farmland conversion and the dairy and intensive livestock sector are the largest contributors to GHG emissions and offer the greatest opportunities for avoided emissions. We also identify a range of other opportunities including soil and nutrient management, integrated and diversified farming systems, rangeland management, and biomass-based energy generation. Additional research to replicate and quantify the emissions reduction or carbon sequestration potential of these practices will strengthen the evidence base for California climate policy.

    A no-till field with residue from a winter crop of triticale. Management practices can increase total soil carbon, but the magnitude and persistence of sequestration is dependent on inputs and time.A no-till field with residue from a winter crop of triticale. Management practices can increase total soil carbon, but the magnitude and persistence of sequestration is dependent on inputs and time.

    …soil carbon sequestration is highly dependent on annual carbon inputs and if management changes, soil carbon is prone to return to the atmosphere.Given the reality of inconsistent management, rates of soil carbon sequestration that can be expected in row crop systems practice are perhaps 10% of the values seen in these long-term research trials, namely in the range of 0.014 to 0.03 tons per acre per year (unpublished data). If soil carbon sequestration and storage are priorities, management plans and incentive structures should account for the wide variability of California soils and the need for consistent management over time.

    While any single soil and nutrient management practice may have limited impact on GHG emissions, many have well-documented co-benefits, including reductions in erosion, improved air quality (Madden et al. 2008), reduced farm machinery fossil fuel use (West et al. 2002), reduced nitrogen leaching (Poudel et al. 2002), enhanced water infiltration and reduced soil water evaporation (Mitchell 2012), and increased carbon stocks below the root zone to improve carbon sequestration (Suddick et al. 2013)

    The research above points to the magnitude of opportunity from alternative rangeland practices and the need to identify socioeconomic opportunities and barriers to greater participation in range management incentive programs

    Priorities for future research

    Here we identify cross-cutting priorities that will enable scaling and, equally important, the integration of multiple practices to achieve more substantial progress toward both climate change mitigation and adaption in agriculture. Among the priorities we identify are:

    • Replication and longer-term studies to quantify the GHG mitigation or carbon sequestration associated with specific practices.
    • Quantification of synergies from stacking multiple practices over time and scale (e.g., field to region) to address efficacies for carbon sequestration, emissions reductions and nitrogen use.
    • Characterization and, where possible, quantification of co-benefits (water, economic, air quality) from soil management practices, livestock grazing and manure management, and biomass-based fuels.
    • Using social and political science research to identify socioeconomic factors that either create barriers or promote adoption of practices (e.g., social networks, gender, social norms, and values).
    • Validation of metrics for soil health parameters, including calibration of models for California conditions that may be used to estimate metrics, such as:
    • Potential use of remote sensing to measure adoption of specific practices outlined above.
    • Validation and/or calibration of models for estimating GHG emissions, including the crop and soil process model, DAYCENT (Del Grosso et al. 2005), and the USDA’s whole farm and ranch carbon and GHG accounting system, which uses the DAYCENT model (COMET-Farm; http://cometfarm.nrel.colostate.edu/ ).
    • Research into the design of incentives (such as payments, tax credits, low interest loans, etc.) to leverage private investment and promote adoption of emissions-reduction practices in agriculture.
    • Development of metrics and sampling or survey tools to assess adoption of emissions-reduction practices.
    • Development of farmer demonstration and evaluation networks for scaling up the adoption of improved performance systems.
  2. Diversity of large animals plays an important role in carbon cycle

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    • We have to maintain the diversity and abundance of animals, especially mammals, in order to ensure a well-functioning carbon cycle and the retention of carbon in soils
    • To increase carbon sequestration, we have to preserve not only high numbers of animals but also many different species

    October 10, 2017 Stanford University read full ScienceDaily article here

    With abundant data on plants, large animals and their activity, and carbon soil levels in the Amazon, research suggests that large animal diversity influences carbon stocks and contributes to climate change mitigation….

    …”It’s not enough to worry about the trees in the world holding carbon. That’s really important but it’s not the whole story,” said Fragoso. “We also have to worry about maintaining the diversity and abundance of animals, especially mammals at this point, in order to ensure a well-functioning carbon cycle and the retention of carbon in soils.”

    Although scientists have long understood that animals — through ingestion, digestion, breathing and decomposition — are part of the carbon cycle, the work, published Oct. 9 in Nature Ecology and Evolution is the first to suggest the importance of animal biodiversity rather than just animal numbers in the carbon cycle.

    If we want to increase carbon sequestration, we have to preserve not only high numbers of animals but also many different species, the authors said.

    …The researchers found that soil had the highest carbon concentrations where they saw the most vertebrate species. When they looked for a mechanism that could explain this relationship, it turned out that the areas with highest animal diversity had the highest frequency of feeding interactions, such as animals preying on other animals or eating fruit, which results in organic material on and in the ground. The researchers suggest that these meal remnants bump up diversity and abundance of soil microbes, which convert the remains into stored carbon

    Mar Sobral, Kirsten M. Silvius, Han Overman, Luiz F. B. Oliveira, Ted K. Rabb, José M. V. Fragoso. Mammal diversity influences the carbon cycle through trophic interactions in the Amazon. Nature Ecology & Evolution, 2017; DOI: 10.1038/s41559-017-0334-0

  3. Carbon feedback from forest soils accelerates global warming

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    • Soil warming stimulates periods of abundant carbon release from the soil to the atmosphere alternating with periods of no detectable loss in soil carbon stores
    • Humans release about 10 billion metric tons (Gt) of carbon into the atmosphere each year and Earth’s soils contain about 3500 billion metric tons (Gt) of carbon which if added to atmosphere could accelerate global warming
    • Over the course of the 26-year experiment (which still continues), the warmed plots lost 17 percent of the carbon that had been stored in organic matter in the top 60 centimeters of soil
    • Study demonstrates value of long term data sets

    October 5, 2017  Marine Biological Laboratory  read full ScienceDaily article here

    After 26 years, the world’s longest-running experiment to discover how warming temperatures affect forest soils has revealed a surprising, cyclical response: Soil warming stimulates periods of abundant carbon release from the soil to the atmosphere alternating with periods of no detectable loss in soil carbon stores. The study indicates that in a warming world, a self-reinforcing and perhaps uncontrollable carbon feedback will occur between forest soils and the climate system, accelerating global warming.

    ….each year, mostly from fossil fuel burning, we are releasing about 10 billion metric tons of carbon into the atmosphere. That’s what’s causing the increase in atmospheric carbon dioxide concentration and global warming. The world’s soils contain about 3,500 billion metric tons of carbon. If a significant amount of that soil carbon is added to the atmosphere, due to microbial activity in warmer soils, that will accelerate the global warming process. And once this self-reinforcing feedback begins, there is no easy way to turn it off. There is no switch to flip.”…

    ….”if the microbes in all landscapes respond to warming in the same way as we’ve observed in mid-latitude forest soils, this self-reinforcing feedback phenomenon will go on for a while and we are not going to be able to turn those microbes off. Of special concern is the big pool of easily decomposed carbon that is frozen in Arctic soils. As those [Arctic] soils thaw out, this feedback phenomenon would be an important component of the climate system, with climate change feeding itself in a warming world….”

    Heated and control plots in a long-term soil warming study at Harvard Forest, Petersham, Mass. Jerry Melillo of the Marine Biological Laboratory, Woods Hole, Mass., and colleagues began the study in 1991.
    Credit: Audrey Barker-Plotkin
    …Melillo and colleagues began this pioneering experiment in 1991 in a deciduous forest stand at the Harvard Forest in Massachusetts. They buried electrical cables in a set of plots and heated the soil 5° C above the ambient temperature of control plots. Over the course of the 26-year experiment (which still continues), the warmed plots lost 17 percent of the carbon that had been stored in organic matter in the top 60 centimeters of soil….
    J. M. Melillo, S. D. Frey, K. M. DeAngelis, W. J. Werner, M. J. Bernard, F. P. Bowles, G. Pold, M. A. Knorr, A. S. Grandy. Long-term pattern and magnitude of soil carbon feedback to the climate system in a warming world. Science, 2017; 358 (6359): 101 DOI: 10.1126/science.aan2874
  4. Strips of prairie plants slow loss of soil, nutrients and water from ag fields, double biodiversit

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    • Converting as little as 10 percent of the cropped area to prairie strips reduced soil loss by 95 percent, phosphorus losses in surface runoff by 77 percent, nitrate concentrations in groundwater by 72 percent and total nitrogen losses in surface runoff by 70 percent, compared with all-crop watersheds. Pollinator and bird abundance more than doubled

    October 2, 2017 USDA Forest Service – Northern Research Station read full ScienceDaily article here

    Prairie strips integrated in row crops reduce soil and nutrient loss from steep ground, provide habitat for wildlife, and improve water infiltration, a decade of research is demonstrating….

    ….Research suggests that prairie strips reduce soil and nutrient loss from steep ground, provide habitat for wildlife and improve water infiltration. According to the study published by PNAS, converting as little as 10 percent of the cropped area to prairie strips reduced soil loss by 95 percent, phosphorus losses in surface runoff by 77 percent, nitrate concentrations in groundwater by 72 percent and total nitrogen losses in surface runoff by 70 percent, compared with all-crop watersheds. Pollinator and bird abundance more than doubled….

    …”The strips are designed to act as a speed bump to slow water down and give it time to infiltrate the soil,” said Lisa Schulte Moore, the study’s lead author and a professor at Iowa State University. Researchers estimate that prairie strips could be used to improve biodiversity and ecosystem services across 3.9 million hectares of cropland in Iowa and a large portion of the 69 million hectares planted in rowcrops in the United States, much of it in the Midwest.

    Lisa A. Schulte, Jarad Niemi, Matthew J. Helmers, Matt Liebman, J. Gordon Arbuckle, David E. James, Randall K. Kolka, Matthew E. O’Neal, Mark D. Tomer, John C. Tyndall, Heidi Asbjornsen, Pauline Drobney, Jeri Neal, Gary Van Ryswyk, Chris Witte. Prairie strips improve biodiversity and the delivery of multiple ecosystem services from corn–soybean croplands. Proceedings of the National Academy of Sciences, 2017; 201620229 DOI: 10.1073/pnas.1620229114

  5. Maximizing successful forest restoration in tropical dry forests

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    • tests maximizing success of tree replanting efforts in degraded soils in tropics
    • tree species that were drought tolerant did better
    • soil amendments only helped to get seedlings off to good start

    September 21, 2017 University of Minnesota read full ScienceDaily article here

    A new study has uncovered some valuable information on ways to maximize the success of replanting efforts [in tropical dry forests], bringing new hope for restoring these threatened ecosystems.

    …Over the past century most of these forests, which help keep water clean and provide valuable habitat for wildlife, were replaced by farms and cattle pastures. Now, as conservationists work to replant deforested areas, they’re finding that the already challenging, high-clay soils underlying them have been degraded to an extent that makes it hard for tree seedlings to sink their roots.

    …To find out what works best for reestablishing tropical dry forests, the researchers planted seedlings of 32 native tree species in degraded soil or degraded soil amended with sand, rice hulls, rice hull ash or hydrogel (an artificial water-holding material). After two years, they found that tree species known for traits that make them drought tolerant, such as enhanced ability to use water and capture sunlight, survived better than other species. Some of the soil amendments helped get seedlings off to a good start, but by the end of the experiment there was no difference in survival with respect to soil condition

    Leland K. Werden, Pedro Alvarado J., Sebastian Zarges, Erick Calderón M., Erik M. Schilling, Milena Gutiérrez L., Jennifer S. Powers. Using soil amendments and plant functional traits to select native tropical dry forest species for the restoration of degraded Vertisols. Journal of Applied Ecology, 2017; DOI: 10.1111/1365-2664.12998

  6. Quantifying soil carbon measurement for agricultural soils management: 11 white papers

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    • Regardless of what approach is pursued, reliable and cost effective quantification methods are critical to designing and implementing improved management of soil organic matter including soil organic carbon, and C sequestration policies in the land use sector.
    Together the group, including Point Blue, produced a set of 11 white papers related to soil organic carbon quantification– see here and below.

    Quantifying soil carbon measurement for agricultural soils management: A consensus view from science

    Building a 21st-century soil information platform for US and world soils

    Soil Carbon Accounting – the Australian example

    Integrating soil carbon stocks across point to continental scales

    How do we get the most out of soil data? The opportunities and challenges of developing open soil data

    Measurement of Soil Carbon Stocks

    Meeting local/state/national/international climate change mitigation goals

    Case Study of Soil C Quantification: Alberta GHG Offset System

    EPIC model based search of agronomic strategies for increasing SOC

    Gridded agroecosystem and SOC modeling with EPIC model

    Land Management

    • There is heightened interest in increasing soil organic carbon (SOC) stocks to improve
    performance of working soils especially under drought or other stressors, to increase
    agricultural resilience, fertility and reduce greenhouse gas emissions from agriculture.
    • There are many improved management practices that can be and are currently being
    applied to cropland and grazing lands to increase SOC.
    • Farmers and ranchers are decisionmakers who operate in larger contexts that often
    determine or at least bound their agricultural and financial decisions (e.g., crop insurance, input subsidies, etc.). Any effort to value improvements in the performance of agricultural soils through enhanced levels of SOC will require feasible, credible and
    creditable assessment of SOC stocks, which are governed by dynamic and complex soil
    processes and properties.
    • This paper provides expert consensus evaluation of currently accepted methods of
    quantifying SOC that could provide the basis for a modern soil information system.
  7. Plastics in soil: municipal compost possible major entry path

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    • At least 300 million tons of plastic are produced annually, from which large parts end up in the environment, where it persists over decades, harms biota and enters the food chain. Yet, almost nothing is known about plastic pollution of soil.
    • Soils may receive plastic inputs via plastic mulching or the application of plastic containing soil amendments.
    • In compost up to 2.38–1200 mg plastic kg−1 have been found so far. Compost, especially of municipal origin, must be considered as a serious entry path of plastic in soil.

    Highlights

    •Analytical methods and possible input pathways of plastic in soil were discussed.
    •Organic matter challenges plastic quantification in soil.
    •Soil amendments and irrigation are likely major plastic sources in agricultural soils.
    •Flooding, atmospheric input and littering can potentially pollute even remote soil.
    •Leaching of small plastics from soil into groundwater cannot be excluded

    Abstract

    At least 300 Mio t of plastic are produced annually, from which large parts end up in the environment, where it persists over decades, harms biota and enters the food chain. Yet, almost nothing is known about plastic pollution of soil; hence, the aims of this work are to review current knowledge on i) available methods for the quantification and identification of plastic in soil, ii) the quantity and possible input pathways of plastic into soil, (including first preliminary screening of plastic in compost), and iii) its fate in soil. Methods for plastic analyses in sediments can potentially be adjusted for application to soil; yet, the applicability of these methods for soil needs to be tested. Consequently, the current data base on soil pollution with plastic is still poor. Soils may receive plastic inputs via plastic mulching or the application of plastic containing soil amendments. In compost up to 2.38–1200 mg plastic kg− 1 have been found so far; the plastic concentration of sewage sludge varies between 1000 and 24,000 plastic items kg− 1. Also irrigation with untreated and treated wastewater (1000–627,000 and 0–125,000 plastic items m− 3, respectively) as well as flooding with lake water (0.82–4.42 plastic items m− 3) or river water (0–13,751 items km− 2) can provide major input pathways for plastic into soil. Additional sources comprise littering along roads and trails, illegal waste dumping, road runoff as well as atmospheric input. With these input pathways, plastic concentrations in soil might reach the per mill range of soil organic carbon. Most of plastic (especially > 1 μm) will presumably be retained in soil, where it persists for decades or longer. Accordingly, further research on the prevalence and fate of such synthetic polymers in soils is urgently warranted.

    Melanie Bläsing and Wulf Amelung. Plastics in soil: Analytical methods and possible sources. Science of The Total Environment Volume 612, 15 January 2018, Pages 422-435

  8. Soil carbon debt from 12,000 years of human land use

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    • global carbon debt due to agriculture of 133 Pg C [133 Gt (billion metric tons of C) or 488 Gt CO2e] for the top 2 m of soil, with the rate of loss increasing dramatically in the past 200 years
    • assuming soil organic carbon (SOM) reaches a new steady state in 20 y (35, 44), this calculation suggests that 8 Pg C to 28 Pg C [up to 28 Gt (billion metric tons of C) or 103 Gt CO2e] or can be recaptured
    • there are identifiable regions which can be targeted for SOC (soil organic carbon) restoration efforts
    • [Note: Hansen et al 2017 calls for 150 Pg C or ~550 Gt CO2e extraction from atmosphere globally with massive greenhouse emissions reductions of 6%/year starting in 2021 to return to 350 PPM CO2 in atmosphere and to secure a safe climate (Holocene) for human civilization by 2100]
      • [Sanderman high end scenario would be 19% of CO2e extraction needed to secure safe climate by 2100 per Hansen above]

    Jonathan Sanderman, Tomislav Hengl and Gregory J. Fiske. Soil carbon debt of 12,000 years of human land use. PNAS September 5, 2017 vol. 114 no. 36 9575-9580

    Abstract: Human appropriation of land for agriculture has greatly altered the terrestrial carbon balance, creating a large but uncertain carbon debt in soils. Estimating the size and spatial distribution of soil organic carbon (SOC) loss due to land use and land cover change has been difficult but is a critical step in understanding whether SOC sequestration can be an effective climate mitigation strategy. In this study, a machine learning-based model was fitted using a global compilation of SOC data and the History Database of the Global Environment (HYDE) land use data in combination with climatic, landform and lithology covariates. Model results compared favorably with a global compilation of paired plot studies. Projection of this model onto a world without agriculture indicated a global carbon debt due to agriculture of 133 Pg C for the top 2 m of soil, with the rate of loss increasing dramatically in the past 200 years. The HYDE classes “grazing” and “cropland” contributed nearly equally to the loss of SOC. There were higher percent SOC losses on cropland but since more than twice as much land is grazed, slightly higher total losses were found from grazing land. Important spatial patterns of SOC loss were found: Hotspots of SOC loss coincided
    with some major cropping regions as well as semiarid grazing regions, while other major agricultural zones showed small losses and even net gains in SOC. This analysis has demonstrated that there are identifiable regions which can be targeted for SOC restoration efforts.

    Implications: This analysis indicates that the majority of the used portions of planet Earth have lost SOC, resulting in a cumulative loss of ∼133 Pg C due to agricultural land use. These SOC losses are on par with estimates of carbon lost from living vegetation primarily due to deforestation (40) and are nearly 100 Pg C higher than earlier estimates of land use and land use change-driven losses of SOC (41). Importantly, as Fig. 1 demonstrates, there are hotspots of SOC loss, associated with extensive cropping regions but also with highly degraded grazing land (SI Appendix, Fig. S9), suggesting that there are identifiable regions which should be targets for SOC restoration efforts.

    The potential to recover lost SOC may be more limited than is often assumed. The amount of SOC that has been lost historically can be thought of as the carbon sink potential of the soil (42). Our analysis has found that this sink potential is ∼133 Pg C (SI Appendix, Table S3). A widely repeated figure is that, with adoption of best management practices, two thirds of lost SOC can be recovered (42). If the two-thirds figure is accurate, then SOC sequestration has the potential to offset 88 Pg C (322 Pg CO2) of emissions. However, bottom-up estimates of the maximum biophysical potential for carbon sequestration on cropping and grazing land range from 0.4 Pg Cy−1 to 1.4 Pg Cy−1 (20, 43). Assuming SOC reaches a new steady state in 20 y (35, 44), this calculation suggests that 8 Pg C to 28 Pg C can be recaptured. Even the range of 8 Pg C to 28 Pg C is likely overly ambitious given the various social, economic, and technical constraints on universal adoption of best management practices (45), suggesting that the amount of the carbon sink that can be filled is on the order of, at best, 10 to 30% globally and may well be <10%.

    Conclusions: Our data-driven statistical analysis confirms that agricultural land use is a significant driver of SOC levels. ….This analysis also demonstrated that not all land use is associated with large losses in SOC, particularly in regions with naturally infertile soils. These results provide a basis for national and international policies to target SOC restoration efforts but also suggest that more effort needs to be put into collecting, integrating, and using legacy soil profile data, especially historic data 50+ y old, so that even more reliable models of SOC dynamics can be produced.

     

  9. The significant role of microbes in soil carbon

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    • Soil is important to life on Earth as we know it…. soil organic matter is key to many of the essential services and functions that soils provide.
    • … long believed that remnants of decayed plant matter were the principal components of stabilized soil carbon…But evolving analytical approaches have led toward view that dead microbial biomass and other microbial residues could contribute even more significantly to stable carbon pools.
    • The scientists suggest adopting an approach based on a concept called the soil microbial carbon pump to help stimulate fruitful new research in this area.

    August 29 2017 read full ScienceDaily article here

    …In the carbon cycle, carbon moves among plants, animals, soils, Earth’s crust, fresh water, the oceans and the atmosphere. Sequestered carbon is carbon that stays in long-term storage. Soil carbon waxes and wanes, depending on the balance between inputs of new organic materials and outputs. Losses occur mostly through decomposition, but also through leaching into groundwater or surface erosion.

    Studies have long focused on how plant litter — mostly dead leaves, stems and roots — decomposes and transforms into soil organic matter. The contribution of the living biomass of microbes to soil carbon, which accounts for only 1 to 5 percent of total soil carbon, has received much less attention, however

    …Even though the living biomass of microbes is small, these organisms grow, live and die at a rapid pace. This means that microbial inputs to soil organic matter can be much larger than previously thought, particularly when a significant portion of those inputs are stabilized rather than decomposed. But even with new insights and improvements in the tools used to study soil organic matter, many questions and unknowns persist.

    …Through catabolic activity, microbes break down complex molecules to form simpler ones, which releases carbon as carbon dioxide. Through anabolic activity, microbes synthesize complex molecules from simpler ones, which contributes to carbon storage.

    The scientists suggest adopting an approach based on a concept called the soil microbial carbon pump to help stimulate fruitful new research in this area. Marine researchers first raised the microbial carbon pump concept. The marine microbial carbon pump sequesters carbon by transferring it deep into the oceans. Through this process, bacteria contribute significantly to long-term carbon storage and the regulation of atmospheric carbon dioxide.

    ….addition of new, externally produced carbon can increase the production of carbon dioxide by priming microbial decomposition of existing soil organic matter, and at the same time it can lead to greater entombment of microbial residues.

    “But, researchers will need better analytical tools to more accurately quantify the mass of dead microbial material and residues in soils, and to understand the factors controlling the balance between the entombing and priming effects,” Liang noted….

    Chao Liang, Joshua P. Schimel, Julie D. Jastrow. The importance of anabolism in microbial control over soil carbon storage. Nature Microbiology, 2017; 2 (8): 17105 DOI: 10.1038/nmicrobiol.2017.105

     

  10. Urban floods intensifying, countryside drying up

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    • An exhaustive global analysis of rainfall and rivers shows signs of a radical shift in streamflow patterns, with more intense flooding in cities and smaller catchments coupled with a drier countryside

    August 14, 2017 University of New South Wales  read full ScienceDaily article here

    Drier soils and reduced water flow in rural areas — but more intense rainfall that overwhelms infrastructure and causes flooding and stormwater overflow in urban centers. That’s the finding of an exhaustive study of the world’s river systems, based on data collected from more than 43,000 rainfall stations and 5,300 river monitoring sites across 160 countries…

    …”The [study] relied on observed flow and rainfall data from across the world, instead of uncertain model simulations, means we are seeing a real-world effect — one that was not at all apparent before.”

    “It’s a double whammy,” said Conrad Wasko, lead author of the paper and postdoctoral fellow at UNSW’s Water Research Centre. “People are increasingly migrating to cities, where flooding is getting worse. At the same time, we need adequate flows in rural areas to sustain the agriculture to supply these burgeoning urban populations.”

    …[the study] found warmer temperatures lead to more intense storms, which makes sense: a warming atmosphere means warmer air, and warmer air can store more moisture…But…why is flooding not increasing at the same rate as the higher rainfall?

    The answer turned out to be the other facet of rising temperatures: more evaporation from moist soils is causing them to become drier before any new rain occurs — moist soils that are needed in rural areas to sustain vegetation and livestock. Meanwhile, small catchments and urban areas, where there are limited expanses of soil to capture and retain moisture, the same intense downpours become equally intense floods, overwhelming stormwater infrastructure and disrupting life.

    Global flood damage cost more than US$50 billion in 2013; this is expected to more than double in the next 20 years as extreme storms and rainfall intensify and growing numbers of people move into urban centres. Meanwhile, global population over the next 20 years is forecast to rise another 23% from today’s 7.3 billion to 9 billion — requiring added productivity and hence greater water security….

    “We need to adapt to this emerging reality,” said Sharma. “We may need to do what was done to make previously uninhabitable places liveable: engineer catchments to ensure stable and controlled access to water. Places such as California, or much of the Netherlands, thrive due to extensive civil engineering. Perhaps a similar effort is needed to deal with the consequences of a changing climate as we enter an era where water availability is not as reliable as before.”…

    Conrad Wasko, Ashish Sharma. Global assessment of flood and storm extremes with increased temperatures. Scientific Reports, 2017; 7 (1) DOI: 10.1038/s41598-017-08481-1