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Zhang Z, Ni W, Quegan S, Chen J, Gong P, Rodriguez LCE, Guo H, Shi J, Liu L, Li Z, He Y, Liu Q, Shimabukuro Y, Sun G. Deforestation in Latin America in the 2000s predominantly occurred outside of typical mature forests. Innovation (N Y) 2024; 5:100610. [PMID: 38586281 PMCID: PMC10998227 DOI: 10.1016/j.xinn.2024.100610] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2023] [Accepted: 03/08/2024] [Indexed: 04/09/2024] Open
Abstract
The role of tropical forests in the global carbon budget remains controversial, as carbon emissions from deforestation are highly uncertain. This high uncertainty arises from the use of either fixed forest carbon stock density or maps generated from satellite-based optical reflectance with limited sensitivity to biomass to generate accurate estimates of emissions from deforestation. New space missions aiming to accurately map the carbon stock density rely on direct measurements of the spatial structures of forests using lidar and radar. We found that lost forests are special cases, and their spatial structures can be directly measured by combining archived data acquired before and after deforestation by space missions principally aimed at measuring topography. Thus, using biomass mapping, we obtained new estimates of carbon loss from deforestation ahead of forthcoming space missions. Here, using a high-resolution map of forest loss and the synergy of radar and lidar to estimate the aboveground biomass density of forests, we found that deforestation in the 2000s in Latin America, one of the severely deforested regions, mainly occurred in forests with a significantly lower carbon stock density than typical mature forests. Deforestation areas with carbon stock densities lower than 20.0, 50.0, and 100.0 Mg C/ha accounted for 42.1%, 62.0%, and 83.3% of the entire deforested area, respectively. The average carbon stock density of lost forests was only 49.13 Mg C/ha, which challenges the current knowledge on the carbon stock density of lost forests (with a default value 100 Mg C/ha according to the Intergovernmental Panel on Climate Change Tier 1 estimates, or approximately 112 Mg C/ha used in other studies). This is demonstrated over both the entire region and the footprints of the spaceborne lidar. Consequently, our estimate of carbon loss from deforestation in Latin America in the 2000s was 253.0 ± 21.5 Tg C/year, which was considerably less than existing remote-sensing-based estimates, namely 400-600 Tg C/year. This indicates that forests in Latin America were most likely not a net carbon source in the 2000s compared to established carbon sinks. In previous studies, considerable effort has been devoted to rectify the underestimation of carbon sinks; thus, the overestimation of carbon emissions should be given sufficient consideration in global carbon budgets. Our results also provide solid evidence for the necessity of renewing knowledge on the role of tropical forests in the global carbon budget in the future using observations from new space missions.
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Affiliation(s)
- Zhiyu Zhang
- Key Laboratory of Remote Sensing and Digital Earth, Chinese Academy of Sciences, Beijing 100101, China
| | - Wenjian Ni
- Key Laboratory of Remote Sensing and Digital Earth, Chinese Academy of Sciences, Beijing 100101, China
- University of Chinese Academy of Sciences, Shijingshan District, Beijing 100049, China
| | - Shaun Quegan
- Chinal of Mathematics and Statistics, University of Sheffield, Sheffield S3 7RH, UK
| | - Jingming Chen
- Department of Geography and Program in Planning, University of Toronto, Toronto, ON M5S 3G3, Canada
| | - Peng Gong
- Department of Earth Sciences and Department of Geography, University of Hong Kong, Hong Kong, China
| | - Luiz Carlos Estraviz Rodriguez
- Forest Science Department, Luiz de Queiroz College of Agriculture, University of São Paulo, Av. Pádua Dias, 11, Piracicaba 13418-900, Brazil
| | - Huadong Guo
- Key Laboratory of Remote Sensing and Digital Earth, Chinese Academy of Sciences, Beijing 100101, China
- University of Chinese Academy of Sciences, Shijingshan District, Beijing 100049, China
| | - Jiancheng Shi
- National Space Science Center, Chinese Academy of Sciences, Beijing 100190, China
| | - Liangyun Liu
- Key Laboratory of Remote Sensing and Digital Earth, Chinese Academy of Sciences, Beijing 100101, China
- University of Chinese Academy of Sciences, Shijingshan District, Beijing 100049, China
| | - Zengyuan Li
- Institute of Forest Resource Information Techniques, Chinese Academy of Forestry, Beijing 100091, China
| | - Yating He
- Research Institute of Forest Policy and Information, Chinese Academy of Forestry, Beijing 100091, China
| | - Qinhuo Liu
- Key Laboratory of Remote Sensing and Digital Earth, Chinese Academy of Sciences, Beijing 100101, China
- University of Chinese Academy of Sciences, Shijingshan District, Beijing 100049, China
| | - Yosio Shimabukuro
- Remote Sensing Department, National Institute for Space Research (INPE), Av. dos Astronautas 1758, São José dos Campos 12227-010, Brazil
| | - Guoqing Sun
- Department of Geographical Sciences, University of Maryland, College Park, MD 20742, USA
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Ochiai O, Poulter B, Seifert FM, Ward S, Jarvis I, Whitcraft A, Sahajpal R, Gilliams S, Herold M, Carter S, Duncanson LI, Kay H, Lucas R, Wilson SN, Melo J, Post J, Briggs S, Quegan S, Dowell M, Cescatti A, Crisp D, Saatchi S, Tadono T, Steventon M, Rosenqvist A. Toward a roadmap for space-based observations of the land sector for the UNFCCC global stocktake. iScience 2023; 26:106489. [PMID: 37096039 PMCID: PMC10121458 DOI: 10.1016/j.isci.2023.106489] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/08/2023] Open
Abstract
Space-based remote sensing can make an important contribution toward monitoring greenhouse gas emissions and removals from the agriculture, forestry, and other land use (AFOLU) sector, and to understanding and addressing human-caused climate change through the UNFCCC Paris Agreement. Space agencies have begun to coordinate their efforts to identify needs, collect and harmonize available data and efforts, and plan and maintain a long-term roadmap for observations. International cooperation is crucial in developing and realizing the roadmap, and the Committee on Earth Observation Satellites (CEOS) is a key coordinating driver of this effort. Here, we first identify the data and information that will be useful to support the global stocktake (GST) of the Paris Agreement. Then, the paper explains how existing and planned space-based capabilities and products can be used and combined, particularly in the land use sector, and provides a workflow for their harmonization and contribution to greenhouse gas inventories and assessments at the national and global level.
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Labrière N, Davies SJ, Disney MI, Duncanson LI, Herold M, Lewis SL, Phillips OL, Quegan S, Saatchi SS, Schepaschenko DG, Scipal K, Sist P, Chave J. Toward a forest biomass reference measurement system for remote sensing applications. Glob Chang Biol 2023; 29:827-840. [PMID: 36270799 PMCID: PMC10099565 DOI: 10.1111/gcb.16497] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/22/2022] [Accepted: 10/14/2022] [Indexed: 05/02/2023]
Abstract
Forests contribute to climate change mitigation through carbon storage and uptake, but the extent to which this carbon pool varies in space and time is still poorly known. Several Earth Observation missions have been specifically designed to address this issue, for example, NASA's GEDI, NASA-ISRO's NISAR and ESA's BIOMASS. Yet, all these missions' products require independent and consistent validation. A permanent, global, in situ, site-based forest biomass reference measurement system relying on ground data of the highest possible quality is therefore needed. Here, we have assembled a list of almost 200 high-quality sites through an in-depth review of the literature and expert knowledge. In this study, we explore how representative these sites are in terms of their coverage of environmental conditions, geographical space and biomass-related forest structure, compared to those experienced by forests worldwide. This work also aims at identifying which sites are the most representative, and where to invest to improve the representativeness of the proposed system. We show that the environmental coverage of the system does not seem to improve after at least the 175 most representative sites are included, but geographical and structural coverages continue to improve as more sites are added. We highlight the areas of poor environmental, geographical, or structural coverage, including, but not limited to, Canada, the western half of the USA, Mexico, Patagonia, Angola, Zambia, eastern Russia, and tropical and subtropical highlands (e.g. in Colombia, the Himalayas, Borneo, Papua). For the proposed system to succeed, we stress that (1) data must be collected and processed applying the same standards across all countries and continents; (2) system establishment and management must be inclusive and equitable, with careful consideration of working conditions; and (3) training and site partner involvement in downstream activities should be mandatory.
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Affiliation(s)
- Nicolas Labrière
- Evolution and Biological Diversity (EDB)CNRS/IRD/UPSToulouseFrance
| | - Stuart J. Davies
- Forest Global Earth ObservatorySmithsonian Tropical Research InstituteWashingtonDistrict of ColumbiaUSA
| | - Mathias I. Disney
- Department of GeographyUniversity College London (UCL)LondonUK
- NERC National Centre for Earth Observation (NCEO)LondonUK
| | - Laura I. Duncanson
- Department of Geographical SciencesUniversity of MarylandCollege ParkMarylandUSA
| | - Martin Herold
- GFZ German Research Centre for GeosciencesPotsdamBrandenburgGermany
| | - Simon L. Lewis
- Department of GeographyUniversity College London (UCL)LondonUK
- School of GeographyUniversity of LeedsLeedsUK
| | | | - Shaun Quegan
- School of Mathematics and StatisticsUniversity of SheffieldSheffieldUK
| | - Sassan S. Saatchi
- Jet Propulsion Laboratory (JPL)California Institute of TechnologyPasadenaCaliforniaUSA
| | - Dmitry G. Schepaschenko
- International Institute for Applied Systems Analysis (IIASA)LaxenburgAustria
- Center for Forest Ecology and Productivity of the Russian Academy of SciencesMoscowRussia
| | | | | | - Jérôme Chave
- Evolution and Biological Diversity (EDB)CNRS/IRD/UPSToulouseFrance
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4
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Leibovici DG, Bylund H, Björkman C, Tokarevich N, Thierfelder T, Evengård B, Quegan S. Associating Land Cover Changes with Patterns of Incidences of Climate-Sensitive Infections: An Example on Tick-Borne Diseases in the Nordic Area. Int J Environ Res Public Health 2021; 18:ijerph182010963. [PMID: 34682710 PMCID: PMC8535683 DOI: 10.3390/ijerph182010963] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/26/2021] [Revised: 10/06/2021] [Accepted: 10/13/2021] [Indexed: 12/30/2022]
Abstract
Some of the climate-sensitive infections (CSIs) affecting humans are zoonotic vector-borne diseases, such as Lyme borreliosis (BOR) and tick-borne encephalitis (TBE), mostly linked to various species of ticks as vectors. Due to climate change, the geographical distribution of tick species, their hosts, and the prevalence of pathogens are likely to change. A recent increase in human incidences of these CSIs in the Nordic regions might indicate an expansion of the range of ticks and hosts, with vegetation changes acting as potential predictors linked to habitat suitability. In this paper, we study districts in Fennoscandia and Russia where incidences of BOR and TBE have steadily increased over the 1995-2015 period (defined as 'Well Increasing districts'). This selection is taken as a proxy for increasing the prevalence of tick-borne pathogens due to increased habitat suitability for ticks and hosts, thus simplifying the multiple factors that explain incidence variations. This approach allows vegetation types and strengths of correlation specific to the WI districts to be differentiated and compared with associations found over all districts. Land cover types and their changes found to be associated with increasing human disease incidence are described, indicating zones with potential future higher risk of these diseases. Combining vegetation cover and climate variables in regression models shows the interplay of biotic and abiotic factors linked to CSI incidences and identifies some differences between BOR and TBE. Regression model projections up until 2070 under different climate scenarios depict possible CSI progressions within the studied area and are consistent with the observed changes over the past 20 years.
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Affiliation(s)
- Didier G. Leibovici
- School of Mathematics and Statistics, University of Sheffield, Sheffield S10 2TN, UK;
- GeotRYcs Cie, 34000 Montpellier, France
- Correspondence: (D.G.L.); (H.B.)
| | - Helena Bylund
- Department of Ecology, Swedish University of Agricultural Sciences, 75007 Uppsala, Sweden;
- Correspondence: (D.G.L.); (H.B.)
| | - Christer Björkman
- Department of Ecology, Swedish University of Agricultural Sciences, 75007 Uppsala, Sweden;
| | - Nikolay Tokarevich
- Laboratory of Zoonoses, St. Petersburg Pasteur Institute, 197101 St. Petersburg, Russia;
| | - Tomas Thierfelder
- Department of Energy and Technology, Swedish University of Agricultural Sciences, 75007 Uppsala, Sweden;
| | - Birgitta Evengård
- Department of Clinical Microbiology, Umeå University, 90187 Umeå, Sweden;
| | - Shaun Quegan
- School of Mathematics and Statistics, University of Sheffield, Sheffield S10 2TN, UK;
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5
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Beerling DJ, Kantzas EP, Lomas MR, Wade P, Eufrasio RM, Renforth P, Sarkar B, Andrews MG, James RH, Pearce CR, Mercure JF, Pollitt H, Holden PB, Edwards NR, Khanna M, Koh L, Quegan S, Pidgeon NF, Janssens IA, Hansen J, Banwart SA. Potential for large-scale CO2 removal via enhanced rock weathering with croplands. Nature 2020; 583:242-248. [DOI: 10.1038/s41586-020-2448-9] [Citation(s) in RCA: 134] [Impact Index Per Article: 33.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2018] [Accepted: 05/07/2020] [Indexed: 11/09/2022]
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6
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Thurner M, Beer C, Ciais P, Friend AD, Ito A, Kleidon A, Lomas MR, Quegan S, Rademacher TT, Schaphoff S, Tum M, Wiltshire A, Carvalhais N. Evaluation of climate-related carbon turnover processes in global vegetation models for boreal and temperate forests. Glob Chang Biol 2017; 23:3076-3091. [PMID: 28192628 PMCID: PMC5516177 DOI: 10.1111/gcb.13660] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/26/2016] [Revised: 12/27/2016] [Accepted: 01/31/2017] [Indexed: 05/29/2023]
Abstract
Turnover concepts in state-of-the-art global vegetation models (GVMs) account for various processes, but are often highly simplified and may not include an adequate representation of the dominant processes that shape vegetation carbon turnover rates in real forest ecosystems at a large spatial scale. Here, we evaluate vegetation carbon turnover processes in GVMs participating in the Inter-Sectoral Impact Model Intercomparison Project (ISI-MIP, including HYBRID4, JeDi, JULES, LPJml, ORCHIDEE, SDGVM, and VISIT) using estimates of vegetation carbon turnover rate (k) derived from a combination of remote sensing based products of biomass and net primary production (NPP). We find that current model limitations lead to considerable biases in the simulated biomass and in k (severe underestimations by all models except JeDi and VISIT compared to observation-based average k), likely contributing to underestimation of positive feedbacks of the northern forest carbon balance to climate change caused by changes in forest mortality. A need for improved turnover concepts related to frost damage, drought, and insect outbreaks to better reproduce observation-based spatial patterns in k is identified. As direct frost damage effects on mortality are usually not accounted for in these GVMs, simulated relationships between k and winter length in boreal forests are not consistent between different regions and strongly biased compared to the observation-based relationships. Some models show a response of k to drought in temperate forests as a result of impacts of water availability on NPP, growth efficiency or carbon balance dependent mortality as well as soil or litter moisture effects on leaf turnover or fire. However, further direct drought effects such as carbon starvation (only in HYBRID4) or hydraulic failure are usually not taken into account by the investigated GVMs. While they are considered dominant large-scale mortality agents, mortality mechanisms related to insects and pathogens are not explicitly treated in these models.
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Affiliation(s)
- Martin Thurner
- Department of Environmental Science and Analytical Chemistry (ACES)Stockholm UniversityStockholmSweden
- Bolin Centre for Climate ResearchStockholm UniversityStockholmSweden
| | - Christian Beer
- Department of Environmental Science and Analytical Chemistry (ACES)Stockholm UniversityStockholmSweden
- Bolin Centre for Climate ResearchStockholm UniversityStockholmSweden
| | - Philippe Ciais
- Laboratoire des Sciences du Climat et de l'Environnement (LSCE)Gif‐sur‐YvetteFrance
| | | | - Akihiko Ito
- National Institute for Environmental StudiesTsukubaJapan
| | - Axel Kleidon
- Max Planck Institute for BiogeochemistryJenaGermany
| | - Mark R. Lomas
- School of Mathematics and StatisticsUniversity of SheffieldSheffieldUK
| | - Shaun Quegan
- School of Mathematics and StatisticsUniversity of SheffieldSheffieldUK
| | | | | | - Markus Tum
- German Aerospace Center (DLR)German Remote Sensing Data Center (DFD)WesslingGermany
| | | | - Nuno Carvalhais
- Max Planck Institute for BiogeochemistryJenaGermany
- CENSEDepartamento de Ciências e Engenharia do AmbienteFaculdade de Ciências e TecnologiaUniversidade NOVA de LisboaCaparicaPortugal
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7
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Taylor LL, Beerling DJ, Quegan S, Banwart SA. Simulating carbon capture by enhanced weathering with croplands: an overview of key processes highlighting areas of future model development. Biol Lett 2017; 13:20160868. [PMID: 28381633 PMCID: PMC5414688 DOI: 10.1098/rsbl.2016.0868] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2016] [Accepted: 01/05/2017] [Indexed: 11/12/2022] Open
Abstract
Enhanced weathering (EW) aims to amplify a natural sink for CO2 by incorporating powdered silicate rock with high reactive surface area into agricultural soils. The goal is to achieve rapid dissolution of minerals and release of alkalinity with accompanying dissolution of CO2 into soils and drainage waters. EW could counteract phosphorus limitation and greenhouse gas (GHG) emissions in tropical soils, and soil acidification, a common agricultural problem studied with numerical process models over several decades. Here, we review the processes leading to soil acidification in croplands and how the soil weathering CO2 sink is represented in models. Mathematical models capturing the dominant processes and human interventions governing cropland soil chemistry and GHG emissions neglect weathering, while most weathering models neglect agricultural processes. We discuss current approaches to modelling EW and highlight several classes of model having the potential to simulate EW in croplands. Finally, we argue for further integration of process knowledge in mathematical models to capture feedbacks affecting both longer-term CO2 consumption and crop growth and yields.
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Affiliation(s)
- Lyla L Taylor
- Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK
| | - David J Beerling
- Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK
| | - Shaun Quegan
- School of Mathematics and Statistics, University of Sheffield, Sheffield S10 2TN, UK
| | - Steven A Banwart
- School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK
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8
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Picard G, Woodward FI, Lomas MR, Pellenq J, Quegan S, Kennedy M. Constraining the Sheffield dynamic global vegetation model using stream-flow measurements in the United Kingdom. Glob Chang Biol 2005; 11:2196-2210. [PMID: 34991290 DOI: 10.1111/j.1365-2486.2005.01048.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
The biospheric water and carbon cycles are intimately coupled, so simulating carbon fluxes by vegetation also requires modelling of the water fluxes, with each component influencing the other. Observations of river streamflow integrate information at the catchment scale and are widely available over a long period; they therefore provide an important source of information for validating or calibrating vegetation models. In this paper, we analyse the performance of the Sheffield dynamic global vegetation model (SDGVM) for predicting river streamflow and quantifying how this information helps to constrain carbon flux predictions. The SDGVM is run for 29 large catchments in the United Kingdom. Annual streamflow estimates are compared with long time-series observations. In 23 out of the 29 catchments, the bias between model and observations is less than 50 mm, equivalent to less than 10% of precipitation. In the remaining catchments, larger errors are because of combinations of unpredictable causes, in particular various human activities and measurement issues and, in two cases, unidentified causes. In one of the catchments, we assess to what extent a knowledge of annual streamflow can constrain model parameters and in turn constrain estimates of gross primary production (GPP). For this purpose, we assume the model parameters are uncertain and constrain them by the streamflow observations using the generalized likelihood uncertainty estimation method. Comparing the probability density function of GPP with and without constraint shows that streamflow effectively constrains GPP, mainly by setting a low probability to GPP values below about 1100 g C-1 m2 yr-1 . In other words, streamflow observations allow the rejection of low values of GPP, so that the potential range of possible GPP values is almost halved.
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Affiliation(s)
- G Picard
- Centre for Terrestrial Carbon Dynamics, University of Sheffield, Hicks Building, S3 7RH Sheffield, UK
| | - F I Woodward
- Centre for Terrestrial Carbon Dynamics, University of Sheffield, Hicks Building, S3 7RH Sheffield, UK
| | - M R Lomas
- Centre for Terrestrial Carbon Dynamics, University of Sheffield, Hicks Building, S3 7RH Sheffield, UK
| | - J Pellenq
- Centre for Terrestrial Carbon Dynamics, University of Sheffield, Hicks Building, S3 7RH Sheffield, UK
| | - S Quegan
- Centre for Terrestrial Carbon Dynamics, University of Sheffield, Hicks Building, S3 7RH Sheffield, UK
| | - M Kennedy
- Centre for Terrestrial Carbon Dynamics, University of Sheffield, Hicks Building, S3 7RH Sheffield, UK
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9
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Picard G, Quegan S, Delbart N, Lomas MR, LE Toan T, Woodward FI. Bud-burst modelling in Siberia and its impact on quantifying the carbon budget. Glob Chang Biol 2005; 11:2164-2176. [PMID: 34991285 DOI: 10.1111/j.1365-2486.2005.01055.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Vegetation phenology is affected by climate change and in turn feeds back on climate by affecting the annual carbon uptake by vegetation. To quantify the impact of phenology on terrestrial carbon fluxes, we calibrate a bud-burst model and embed it in the Sheffield dynamic global vegetation model (SDGVM) in order to perform carbon budget calculations. Bud-burst dates derived from the VEGETATION sensor onboard the SPOT-4 satellite are used to calibrate a range of bud-burst models. This dataset has been recently developed using a new methodology based on the normalized difference water index, which is able to distinguish snowmelt from the onset of vegetation activity after winter. After calibration, a simple spring warming model was found to perform as well as more complex models accounting for a chilling requirement, and hence it was used for the carbon flux calculations. The root mean square difference (RMSD) between the calibrated model and the VEGETATION dataset was 6.5 days, and was 6.9 days between the calibrated model and independent ground observations of bud-burst available at nine locations over Siberia. The effects of bud-burst model uncertainties on the carbon budget were evaluated using the SDGVM. The 6.5 days RMSD in the bud-burst date (a 6% variation in the growing season length), treated as a random noise, translates into about 41 g cm-2 yr-1 in net primary production (NPP), which corresponds to 8% of the mean NPP. This is a moderate impact and suggests the calibrated model is accurate enough for carbon budget calculations. In addition to random differences between the calibrated model and VEGETATION data, systematic errors between the calibrated bud-burst model and true ground behaviour may occur, because of bias in the temperature dataset or because the bud-burst detected by VEGETATION is because of some other phenological indicator. A systematic error of 1 day in bud-burst translates into a 10 g cm-2 yr-1 error in NPP (about 2%). Based on the limited available ground data, any systematic error because of the use of VEGETATION data should not lead to significant errors in the calculated carbon flux. In contrast, widely used methods based on the normalized difference vegetation index from the advanced very high resolution radiometer satellite are likely to confuse snowmelt and vegetation greening, leading to errors of up to 15 days in bud-burst date, with consequent large errors in carbon flux calculations.
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Affiliation(s)
- Ghislain Picard
- Centre for Terrestrial Carbon Dynamics, University of Sheffield, Hicks Building, S3 7RH Sheffield, UK
| | - Shaun Quegan
- Centre for Terrestrial Carbon Dynamics, University of Sheffield, Hicks Building, S3 7RH Sheffield, UK
| | - Nicolas Delbart
- Centre d'Etude Spatiales de la Biosphere, 18 av Edouard Belin, BPI 2801 31401, Toulouse Cedex 9, France
| | - Mark R Lomas
- Centre for Terrestrial Carbon Dynamics, University of Sheffield, Hicks Building, S3 7RH Sheffield, UK
| | - Thuy LE Toan
- Centre d'Etude Spatiales de la Biosphere, 18 av Edouard Belin, BPI 2801 31401, Toulouse Cedex 9, France
| | - F Ian Woodward
- Centre for Terrestrial Carbon Dynamics, University of Sheffield, Hicks Building, S3 7RH Sheffield, UK
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10
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Caves R, Quegan S, White R. Quantitative comparison of the performance of SAR segmentation algorithms. IEEE Trans Image Process 1998; 7:1534-1546. [PMID: 18276219 DOI: 10.1109/83.725361] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Methods to evaluate the performance of segmentation algorithms for synthetic aperture radar (SAR) images are developed, based on known properties of coherent speckle and a scene model in which areas of constant backscatter coefficient are separated by abrupt edges. Local and global measures of segmentation homogeneity are derived and applied to the outputs of two segmentation algorithms developed for SAR data, one based on iterative edge detection and segment growing, the other based on global maximum a posteriori (MAP) estimation using simulated annealing. The quantitative statistically based measures appear consistent with visual impressions of the relative quality of the segmentations produced by the two algorithms. On simulated data meeting algorithm assumptions, both algorithms performed well but MAP methods appeared visually and measurably better. On real data, MAP estimation was markedly the better method and retained performance comparable to that on simulated data, while the performance of the other algorithm deteriorated sharply. Improvements in the performance measures will require a more realistic scene model and techniques to recognize oversegmentation.
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Affiliation(s)
- R Caves
- Centre for Earth Obs. Sci., Sheffield Univ., UK
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11
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Fuller-Rowell TJ, Codrescu MV, Rishbeth H, Moffett RJ, Quegan S. On the seasonal response of the thermosphere and ionosphere to geomagnetic storms. ACTA ACUST UNITED AC 1996. [DOI: 10.1029/95ja01614] [Citation(s) in RCA: 336] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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12
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Fuller-Rowell TJ, Codrescu MV, Moffett RJ, Quegan S. Response of the thermosphere and ionosphere to geomagnetic storms. ACTA ACUST UNITED AC 1994. [DOI: 10.1029/93ja02015] [Citation(s) in RCA: 601] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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13
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Bacon P, Stevens JC, Ruddy H, Quegan S, Kingsley SP. Optimal filtering of the auditory cortical evoked potential. Clin Phys Physiol Meas 1990; 11:135-42. [PMID: 2364638 DOI: 10.1088/0143-0815/11/2/003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The development of a linear filter to optimise the signal-to-noise ratio of the auditory cortical evoked potential is described. The filter characteristics were derived from the frequency spectra of cortical potentials taken from 40 normal and 20 hearing impaired adult ears, at two test frequencies (120 tests). The performance of the filter was compared with a typical filter used in clinical practice (1.5 Hz to 15 Hz second-order Butterworth filter). Results showed that the filter produced an average increase in the signal-to-noise ratio of approximately 38%. Further comparisons were made using 14 different Butterworth filters (all second order) and the best of these, the 5 Hz to 9 Hz filter, produced a 28% improvement in the signal-to-noise ratio. The signal-to-noise ratio was calculated by comparing the absolute integral area of the average post-stimulus data to that of the pre-stimulus data. This improvement in the signal-to-noise ratio enhances signals for objective machine scoring analysis or alternatively, allows for a reduction in the number of sweeps (and hence time) required to record the evoked potential.
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Affiliation(s)
- P Bacon
- Department of Medical Physics and Clinical Engineering, Royal Hallamshire Hospital, Sheffield, UK
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Fuller-Rowell TJ, Rees D, Quegan S, Moffett RJ, Bailey GJ. Interactions between neutral thermospheric composition and the polar ionosphere using a coupled ionosphere-thermosphere model. ACTA ACUST UNITED AC 1987. [DOI: 10.1029/ja092ia07p07744] [Citation(s) in RCA: 168] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Smith R, Winser K, Van Eyken A, Quegan S, Allen B. Observation and theoretical modelling of a region of downward field-aligned flow of O+ in the winter dayside polar cap. ACTA ACUST UNITED AC 1985. [DOI: 10.1016/0021-9169(85)90114-x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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