Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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    Global carbon budget 2014
    Quéré, C. Le; Peters, W. ; Moriarty, R. ; Friedlingstein, P. - \ 2015
    Earth System Science Data 7 (2015)1. - ISSN 1866-3508 - p. 47 - 85.
    land-use change - environment simulator jules - co2 flux variability - mixed-layer scheme - earth system model - atmospheric co2 - dioxide emissions - interannual variability - terrestrial ecosystems - international-trade
    Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere is important to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe data sets and a methodology to quantify all major components of the global carbon budget, including their uncertainties, based on the combination of a range of data, algorithms, statistics, and model estimates and their interpretation by a broad scientific community. We discuss changes compared to previous estimates, consistency within and among components, alongside methodology and data limitations. CO2 emissions from fossil fuel combustion and cement production (EFF) are based on energy statistics and cement production data, respectively, while emissions from land-use change (ELUC), mainly deforestation, are based on combined evidence from land-cover-change data, fire activity associated with deforestation, and models. The global atmospheric CO2 concentration is measured directly and its rate of growth (GATM) is computed from the annual changes in concentration. The mean ocean CO2 sink (SOCEAN) is based on observations from the 1990s, while the annual anomalies and trends are estimated with ocean models. The variability in SOCEAN is evaluated with data products based on surveys of ocean CO2 measurements. The global residual terrestrial CO2 sink (SLAND) is estimated by the difference of the other terms of the global carbon budget and compared to results of independent dynamic global vegetation models forced by observed climate, CO2, and land-cover-change (some including nitrogen–carbon interactions). We compare the mean land and ocean fluxes and their variability to estimates from three atmospheric inverse methods for three broad latitude bands. All uncertainties are reported as ±1s, reflecting the current capacity to characterise the annual estimates of each component of the global carbon budget. For the last decade available (2004–2013), EFF was 8.9 ± 0.4 GtC yr-1, ELUC 0.9 ± 0.5 GtC yr-1, GATM 4.3 ± 0.1 GtC yr-1, SOCEAN 2.6 ± 0.5 GtC yr-1, and SLAND 2.9 ± 0.8 GtC yr-1. For year 2013 alone, EFF grew to 9.9 ± 0.5 GtC yr-1, 2.3% above 2012, continuing the growth trend in these emissions, ELUC was 0.9 ± 0.5 GtC yr-1, GATM was 5.4 ± 0.2 GtC yr-1, SOCEAN was 2.9 ± 0.5 GtC yr-1, and SLAND was 2.5 ± 0.9 GtC yr-1. GATM was high in 2013, reflecting a steady increase in EFF and smaller and opposite changes between SOCEAN and SLAND compared to the past decade (2004–2013). The global atmospheric CO2 concentration reached 395.31 ± 0.10 ppm averaged over 2013. We estimate that EFF will increase by 2.5% (1.3–3.5%) to 10.1 ± 0.6 GtC in 2014 (37.0 ± 2.2 GtCO2 yr-1), 65% above emissions in 1990, based on projections of world gross domestic product and recent changes in the carbon intensity of the global economy. From this projection of EFF and assumed constant ELUC for 2014, cumulative emissions of CO2 will reach about 545 ± 55 GtC (2000 ± 200 GtCO2) for 1870–2014, about 75% from EFF and 25% from ELUC. This paper documents changes in the methods and data sets used in this new carbon budget compared with previous publications of this living data set (Le Quéré et al., 2013, 2014). All observations presented here can be downloaded from the Carbon Dioxide Information Analysis
    Causal feedbacks in climate change
    Nes, E.H. van; Scheffer, M. ; Brovkin, V. ; Lenton, T.M. ; Ye, H. ; Deyle, E. ; Sugihara, G. - \ 2015
    Nature Climate Change 5 (2015). - ISSN 1758-678X - p. 445 - 448.
    carbon-cycle - ice core - antarctic temperature - last deglaciation - atmospheric co2 - global climate - dioxide - record - model - lag
    The statistical association between temperature and greenhouse gases over glacial cycles is well documented1, but causality behind this correlation remains difficult to extract directly from the data. A time lag of CO2 behind Antarctic temperature—originally thought to hint at a driving role for temperature2, 3—is absent4, 5 at the last deglaciation, but recently confirmed at the last ice age inception6 and the end of the earlier termination II (ref. 7). We show that such variable time lags are typical for complex nonlinear systems such as the climate, prohibiting straightforward use of correlation lags to infer causation. However, an insight from dynamical systems theory8 now allows us to circumvent the classical challenges of unravelling causation from multivariate time series. We build on this insight to demonstrate directly from ice-core data that, over glacial–interglacial timescales, climate dynamics are largely driven by internal Earth system mechanisms, including a marked positive feedback effect from temperature variability on greenhouse-gas concentrations.
    Estimating Asian terrestrial carbon fluxes from CONTRAIL aircraft and surface CO2 observations for the period 2006 to 2010
    Zhang, H.F. ; Chen, B.Z. ; Laan-Luijkx, I.T. van der; Machida, T. ; Matsueda, H. ; Sawa, Y. ; Peters, W. - \ 2014
    Atmospheric Chemistry and Physics 14 (2014)11. - ISSN 1680-7316 - p. 5807 - 5824.
    atmospheric co2 - interannual variability - parameterization sib2 - model formulation - transport models - dioxide exchange - north-america - south-asia - east-asia - china
    Current estimates of the terrestrial carbon fluxes in Asia show large uncertainties particularly in the boreal and mid-latitudes and in China. In this paper, we present an updated carbon flux estimate for Asia ("Asia" refers to lands as far west as the Urals and is divided into boreal Eurasia, temperate Eurasia and tropical Asia based on TransCom regions) by introducing aircraft CO2 measurements from the CONTRAIL (Comprehensive Observation Network for Trace gases by Airline) program into an inversion modeling system based on the CarbonTracker framework. We estimated the averaged annual total Asian terrestrial land CO2 sink was about -1.56 Pg C yr-1 over the period 2006–2010, which offsets about one-third of the fossil fuel emission from Asia (+4.15 Pg C yr-1). The uncertainty of the terrestrial uptake estimate was derived from a set of sensitivity tests and ranged from -1.07 to -1.80 Pg C yr-1, comparable to the formal Gaussian error of ±1.18 Pg C yr-1 (1-sigma). The largest sink was found in forests, predominantly in coniferous forests (-0.64 ± 0.70 Pg C yr-1) and mixed forests (-0.14 ± 0.27 Pg C yr-1); and the second and third large carbon sinks were found in grass/shrub lands and croplands, accounting for -0.44 ± 0.48 Pg C yr-1 and -0.20 ± 0.48 Pg C yr-1, respectively. The carbon fluxes per ecosystem type have large a priori Gaussian uncertainties, and the reduction of uncertainty based on assimilation of sparse observations over Asia is modest (8.7–25.5%) for most individual ecosystems. The ecosystem flux adjustments follow the detailed a priori spatial patterns by design, which further increases the reliance on the a priori biosphere exchange model. The peak-to-peak amplitude of inter-annual variability (IAV) was 0.57 Pg C yr-1 ranging from -1.71 Pg C yr-1 to -2.28 Pg C yr-1. The IAV analysis reveals that the Asian CO2 sink was sensitive to climate variations, with the lowest uptake in 2010 concurrent with a summer flood and autumn drought and the largest CO2 sink in 2009 owing to favorable temperature and plentiful precipitation conditions. We also found the inclusion of the CONTRAIL data in the inversion modeling system reduced the uncertainty by 11% over the whole Asian region, with a large reduction in the southeast of boreal Eurasia, southeast of temperate Eurasia and most tropical Asian areas.
    The seasonal variation of the CO2 flux over Tropical Asia estimated from GOSAT, CONTRAIL, and IASI
    Basu, S. ; Krol, M.C. ; Butz, A. ; Clerbaux, C. ; Sawa, Y. ; Machida, T. ; Matsueda, H. ; Frankenberg, C. ; Hasekamp, O.P. ; Aben, I. - \ 2014
    Geophysical Research Letters 41 (2014)5. - ISSN 0094-8276 - p. 1809 - 1815.
    atmospheric co2 - carbon balance - emissions - gosat - retrievals - aerosol - fires
    We estimate the CO2 flux over Tropical Asia in 2009, 2010, and 2011 using Greenhouse Gases Observing Satellite (GOSAT) total column CO2(XCO2) and in situ measurements of CO2. Compared to flux estimates from assimilating surface measurements of CO2, GOSAT XCO2 estimates a more dynamic seasonal cycle and a large source in March–May 2010. The more dynamic seasonal cycle is consistent with earlier work by Patra et al. (2011), and the enhanced 2010 source is supported by independent upper air CO2 measurements from the Comprehensive Observation Network for Trace gases by Airliner (CONTRAIL) project. Using Infrared Atmospheric Sounding Interferometer (IASI) measurements of total column CO (XCO), we show that biomass burning CO2 can explain neither the dynamic seasonal cycle nor the 2010 source. We conclude that both features must come from the terrestrial biosphere. In particular, the 2010 source points to biosphere response to above-average temperatures that year.
    Simulating the integrated summertime d14CO2 signature from anthropogenic emissions over Western Europe
    Bozhinova, D.N. ; Molen, M.K. van der; Velde, I.R. van der; Krol, M.C. ; Laan, S. van der; Meijer, H.A.J. ; Peters, W. - \ 2014
    Atmospheric Chemistry and Physics 14 (2014)14. - ISSN 1680-7316 - p. 7273 - 7290.
    fossil-fuel co2 - carbon-dioxide - atmospheric co2 - field campaign - (co2)-c-14 observations - transport models - c-14 discharges - mixing ratios - radiocarbon - cycle
    Radiocarbon dioxide (14CO2, reported in d14CO2) can be used to determine the fossil fuel CO2 addition to the atmosphere, since fossil fuel CO2 no longer contains any 14C. After the release of CO2 at the source, atmospheric transport causes dilution of strong local signals into the background and detectable gradients of d14CO2 only remain in areas with high fossil fuel emissions. This fossil fuel signal can moreover be partially masked by the enriching effect that anthropogenic emissions of 14CO2 from the nuclear industry have on the atmospheric d14CO2 signature. In this paper, we investigate the regional gradients in 14CO2 over the European continent and quantify the effect of the emissions from nuclear industry. We simulate the emissions and transport of fossil fuel CO2 and nuclear 14CO2 for Western Europe using the Weather Research and Forecast model (WRF-Chem) for a period covering 6 summer months in 2008. We evaluate the expected CO2 gradients and the resulting d14CO2 in simulated integrated air samples over this period, as well as in simulated plant samples. We find that the average gradients of fossil fuel CO2 in the lower 1200 m of the atmosphere are close to 15 ppm at a 12 km × 12 km horizontal resolution. The nuclear influence on d14CO2 signatures varies considerably over the domain and for large areas in France and the UK it can range from 20 to more than 500% of the influence of fossil fuel emissions. Our simulations suggest that the resulting gradients in d14CO2 are well captured in plant samples, but due to their time-varying uptake of CO 2, their signature can be different with over 3‰ from the atmospheric samples in some regions. We conclude that the framework presented will be well-suited for the interpretation of actual air and plant 14CO2 samples. © Author(s) 2014. CC Attribution 3.0 License.
    Increased water-use efficiency does not lead to enhanced tree growth under xeric and mesic conditions
    Lévesque, M. ; Siegwolf, R. ; Saurer, M. ; Eilmann, B. ; Rigling, A. - \ 2014
    New Phytologist 203 (2014)1. - ISSN 0028-646X - p. 94 - 109.
    carbon-isotope discrimination - scots pine - atmospheric co2 - climate-change - conceptual-model - stomatal conductance - c-13/c-12 variations - forest ecosystems - drought response - oxygen isotopes
    Higher atmospheric CO2 concentrations (ca ) can under certain conditions increase tree growth by enhancing photosynthesis, resulting in an increase of intrinsic water-use efficiency (i WUE) in trees. However, the magnitude of these effects and their interactions with changing climatic conditions are still poorly understood under xeric and mesic conditions. We combined radial growth analysis with intra- and interannual d(13) C and d(18) O measurements to investigate growth and physiological responses of Larix decidua, Picea abies, Pinus sylvestris, Pinus nigra and Pseudotsuga menziesii in relation to rising ca and changing climate at a xeric site in the dry inner Alps and at a mesic site in the Swiss lowlands. i WUE increased significantly over the last 50 yr by 8-29% and varied depending on species, site water availability, and seasons. Regardless of species and increased i WUE, radial growth has significantly declined under xeric conditions, whereas growth has not increased as expected under mesic conditions. Overall, drought-induced stomatal closure has reduced transpiration at the cost of reduced carbon uptake and growth. Our results indicate that, even under mesic conditions, the temperature-induced drought stress has overridden the potential CO2 'fertilization' on tree growth, hence challenging today's predictions of improved forest productivity of temperate forests
    How light competition between plants affects their response to climate change
    Loon, M.P. van; Schieving, F. ; Rietkerk, M. ; Dekker, S.C. ; Sterck, F.J. ; Anten, N.P.R. - \ 2014
    New Phytologist 203 (2014)4. - ISSN 0028-646X - p. 1253 - 1265.
    leaf-area index - co2 enrichment face - canopy carbon gain - elevated co2 - atmospheric co2 - stomatal conductance - terrestrial ecosystems - nitrogen availability - global change - gas-exchange
    How plants respond to climate change is of major concern, as plants will strongly impact future ecosystem functioning, food production and climate. Here, we investigated how vegetation structure and functioning may be influenced by predicted increases in annual temperatures and atmospheric CO2 concentration, and modeled the extent to which local plant–plant interactions may modify these effects. A canopy model was developed, which calculates photosynthesis as a function of light, nitrogen, temperature, CO2 and water availability, and considers different degrees of light competition between neighboring plants through canopy mixing; soybean (Glycine max) was used as a reference system. The model predicts increased net photosynthesis and reduced stomatal conductance and transpiration under atmospheric CO2 increase. When CO2 elevation is combined with warming, photosynthesis is increased more, but transpiration is reduced less. Intriguingly, when competition is considered, the optimal response shifts to producing larger leaf areas, but with lower stomatal conductance and associated vegetation transpiration than when competition is not considered. Furthermore, only when competition is considered are the predicted effects of elevated CO2 on leaf area index (LAI) well within the range of observed effects obtained by Free air CO2 enrichment (FACE) experiments. Together, our results illustrate how competition between plants may modify vegetation responses to climate change.
    TransCom model simulations of methane: Comparison of vertical profiles with aircraft measurements
    Saito, R. ; Patra, P.K. ; Sweeney, C. ; Machida, T. ; Krol, M.C. ; Houweling, S. ; Bousquet, P. ; Agusti-Panareda, A. ; Belikov, D. ; Bergmann, D. ; Bian, H.S. ; Cameron-Smith, P. ; Chipperfield, M.P. ; Fortems-Cheiney, A. ; Fraser, A. ; Gatti, L.V. ; Gloor, E. ; Hess, P. ; Kawa, S.R. ; Law, R.M. ; Locatelli, R. ; Loh, Z. ; Maksyutov, S. ; Meng, L. ; Miller, J.B. ; Palmer, P.I. ; Prinn, R.G. ; Rigby, M. ; Wilson, C. - \ 2013
    Journal of Geophysical Research: Atmospheres 118 (2013)9. - ISSN 2169-897X - p. 3891 - 3904.
    chemical-transport model - atmospheric co2 - troposphere - stratosphere - variability - sensitivity - version - ozone - flux - air
    To assess horizontal and vertical transports of methane (CH4) concentrations at different heights within the troposphere, we analyzed simulations by 12 chemistry transport models (CTMs) that participated in the TransCom-CH4 intercomparison experiment. Model results are compared with aircraft measurements at 13 sites in Amazon/Brazil, Mongolia, Pacific Ocean, Siberia/Russia, and United States during the period of 2001-2007. The simulations generally show good agreement with observations for seasonal cycles and vertical gradients. The correlation coefficients of the daily averaged model and observed CH4 time series for the analyzed years are generally larger than 0.5, and the observed seasonal cycle amplitudes are simulated well at most sites, considering the between-model variances. However, larger deviations show up below 2 km for the model-observation differences in vertical profiles at some locations, e.g., at Santarem, Brazil, and in the upper troposphere, e.g., at Surgut, Russia. Vertical gradients and concentrations are underestimated at Southern Great Planes, United States, and Santarem and overestimated at Surgut. Systematic overestimation and underestimation of vertical gradients are mainly attributed to inaccurate emission and only partly to the transport uncertainties. However, large differences in model simulations are found over the regions/seasons of strong convection, which is poorly represented in the models. Overall, the zonal and latitudinal variations in CH4 are controlled by surface emissions below 2.5 km and transport patterns in the middle and upper troposphere. We show that the models with larger vertical gradients, coupled with slower horizontal transport, exhibit greater CH4 interhemispheric gradients in the lower troposphere. These findings have significant implications for the future development of more accurate CTMs with the possibility of reducing biases in estimated surface fluxes by inverse modeling.
    Tropical forests and global change: filling knowledge gaps
    Zuidema, P.A. ; Baker, P.J. ; Groenendijk, P. ; Schippers, P. ; Sleen, J.P. van der; Vlam, M. ; Sterck, F.J. - \ 2013
    Trends in Plant Science 18 (2013)8. - ISSN 1360-1385 - p. 413 - 419.
    water-use efficiency - climate-change - rain-forest - tree-rings - elevated co2 - pervasive alteration - western thailand - traits determine - growth-patterns - atmospheric co2
    Tropical forests will experience major changes in environmental conditions this century. Understanding their responses to such changes is crucial to predicting global carbon cycling. Important knowledge gaps exist: the causes of recent changes in tropical forest dynamics remain unclear and the responses of entire tropical trees to environmental changes are poorly understood. In this Opinion article, we argue that filling these knowledge gaps requires a new research strategy, one that focuses on trees instead of leaves or communities, on long-term instead of short-term changes, and on understanding mechanisms instead of documenting changes. We propose the use of tree-ring analyses, stable-isotope analyses, manipulative field experiments, and well-validated simulation models to improve predictions of forest responses to global change.
    Biosphere model simulations of interannual variability in terrestrial 13C/12C exchange.
    Velde, I.R. van der; Miller, J.B. ; Schaefer, K. ; Masarie, K.A. ; Denning, S. ; White, J.W.C. ; Krol, M.C. ; Peters, W. ; Tans, P.P. - \ 2013
    Global Biogeochemical Cycles 27 (2013)3. - ISSN 0886-6236 - p. 637 - 649.
    carbon-isotope discrimination - ocean co2 sink - stomatal conductance - c-13 discrimination - atmospheric co2 - cycle - climate - fires - photosynthesis - assimilation
    Previous studies suggest that a large part of the variability in the atmospheric ratio of (CO2)-C-13/(12)CO(2)originates from carbon exchange with the terrestrial biosphere rather than with the oceans. Since this variability is used to quantitatively partition the total carbon sink, we here investigate the contribution of interannual variability (IAV) in biospheric exchange to the observed atmospheric C-13 variations. We use the Simple Biosphere - Carnegie-Ames-Stanford Approach biogeochemical model, including a detailed isotopic fractionation scheme, separate C-12 and C-13 biogeochemical pools, and satellite-observed fire disturbances. This model of (CO2)-C-12 and (CO2)-C-13 thus also produces return fluxes of (13)CO(2)from its differently aged pools, contributing to the so-called disequilibrium flux. Our simulated terrestrial C-13 budget closely resembles previously published model results for plant discrimination and disequilibrium fluxes and similarly suggests that variations in C-3 discrimination and year-to-year variations in C(3)and C-4 productivity are the main drivers of their IAV. But the year-to-year variability in the isotopic disequilibrium flux is much lower (1 sigma=1.5PgCyr(-1)) than required (12.5PgCyr(-1)) to match atmospheric observations, under the common assumption of low variability in net ocean CO2 fluxes. This contrasts with earlier published results. It is currently unclear how to increase IAV in these drivers suggesting that SiBCASA still misses processes that enhance variability in plant discrimination and relative C-3/C(4)productivity. Alternatively, C-13 budget terms other than terrestrial disequilibrium fluxes, including possibly the atmospheric growth rate, must have significantly different IAV in order to close the atmospheric C-13 budget on a year-to-year basis.
    On the potential role of marine calcifiers in glacial-interglacial dynamics
    Omta, A.W. ; Voorn, G.A.K. van; Rickaby, R.E.M. ; Follows, M.J. - \ 2013
    Global Biogeochemical Cycles 27 (2013)3. - ISSN 0886-6236 - p. 692 - 704.
    benthic foraminiferal b/ca - carbonate saturation state - deep-sea sediments - food-web dynamics - atmospheric co2 - calcium-carbonate - late-pleistocene - atlantic-ocean - southern-ocean - coral-reef
    [1] Ice core measurements have revealed a highly asymmetric cycle in Antarctic temperature and atmospheric CO2 over the last 800 kyr. Both CO2 and temperature decrease over 100 kyr going into a glacial period and then rise steeply over less than 10 kyr at the end of a glacial period. There does not yet exist wide agreement about the causes of this cycle or about the origin of its shape. Here we explore the possibility that an ecologically driven oscillator plays a role in the dynamics. A conceptual model describing the interaction between calcifying plankton and ocean alkalinity shows interesting features: (i) It generates an oscillation in atmospheric CO2 with the characteristic asymmetric shape observed in the ice core record, (ii) the system can transform a sinusoidal Milankovitch forcing into a sawtooth-shaped output, and (iii) there are spikes of enhanced calcifier productivity at the glacial-interglacial transitions, consistent with several sedimentary records. This suggests that ecological processes might play an active role in the observed glacial-interglacial cycles.
    Quantifying the uncertainties of advection and boundary layer dynamics on the diurnal carbon dioxide budget
    Pino, D. ; Kaikkonen, J.P. ; Vilà-Guerau de Arellano, J. - \ 2013
    Journal of Geophysical Research: Atmospheres 118 (2013)16. - ISSN 2169-897X - p. 9376 - 9392.
    co2 mixing ratios - atmospheric co2 - regional-scale - error characterization - transport models - cabauw tower - tall tower - exchange - flux - entrainment
    [1] We investigate the uncertainties in the carbon dioxide (CO2) mixing ratio and inferred surface flux associated with boundary layer processes and advection by using mixed-layer theory. By extending the previous analysis presented by Pino et al. (2012), new analytical expressions are derived to quantify the uncertainty of CO2 mixing ratio or surface flux associated to, among others, boundary layer depth, early morning CO2 mixing ratio at the mixed layer or at the free atmosphere; or CO2 advection. We identify and calculate two sorts of uncertainties associated to the CO2 mixing ratio and surface flux: instantaneous and past (due to advection). The numerical experiments are guided and constrained by meteorological and CO2 observations taken at the Cabauw 213 m tower. We select 2 days (25 September 2003 and 12 March 2004) with a well-defined convective boundary layer but different CO2 advection contributions. Our sensitivity analysis shows that uncertainty of the CO2 advection in the boundary layer due to instantaneous uncertainties represents at 1600 LT on 12 March 2004 a contribution of 2¿ppm and 0.072 mg m-2s-1 in the uncertainty of the CO2 mixing ratio and inferred surface flux, respectively. Taking into account that the monthly averaged minimum CO2 surface flux for March 2004 was -0.55 mg m-2s-1, the error on the surface flux is on the order of 10%. By including CO2 advection in the analytical expressions, we demonstrate that the uncertainty of the CO2 mixing ratio or surface flux also depends on the past uncertainties of the boundary layer depth.
    Climate Change and Potato Production in Contrasting South African Agro-ecosystems 1. Effects on Land and Water Use Efficiencies
    Haverkort, A.J. ; Franke, A.C. ; Engelbrecht, F.A. ; Steyn, J.M. - \ 2013
    Potato Research 56 (2013)1. - ISSN 0014-3065 - p. 31 - 50.
    elevated carbon-dioxide - solanum-tuberosum l. - co2 concentration - atmospheric co2 - crop yields - model - growth - simulation - enrichment - quality
    Explorations of the impact of climate change on potential potato yields were obtained by downscaling the projections of six different coupled climate models to high spatial resolution over southern Africa. The simulations of daily maximum and minimum temperatures, precipitation, wind speed, and solar radiation were used as input to run the crop growth model LINTUL-Potato. Pixels representative for potato growing areas were selected for four globally occurring agro-ecosystems: rainy and dry winter and summer crops. The simulated inter-annual variability is much greater for rainfall than for temperature. Reference evapotranspiration and radiation are projected to hardly decline over the 90-year period, whilst temperatures are projected to rise significantly by about 1.9 °C. From literature, it was found that radiation use efficiency of potato increased with elevated CO2 concentrations by almost 0.002 g¿MJ-1¿ppm-1. This ratio was used to calculate the CO2 effect on yields between 1960 and 2050, when CO2 concentration increases from 315 to 550 ppm. Within this range, evapotranspiration by the potato crop was reduced by about 13% according to literature. Simulated yield increase was strongest in the Mediterranean-type winter crop (+37%) and least under Mediterranean summer (+12%) and relatively warm winter conditions (+14%) closer to the equator. Water use efficiency also increased most in the cool rainy Mediterranean winter (+45%) and least so in the winter crop closer to the equator (+14%). It is concluded from the simulations that for all four agro-ecosystems possible negative effects of rising temperatures and reduced availability of water for potato are more than compensated for by the positive effect of increased CO2 levels on water use efficiency and crop productivity.
    A high-resolution and harmonized model approach for reconstructing and analysing historic land changes in Europe
    Fuchs, R. ; Herold, M. ; Verburg, P.H. ; Clevers, J.G.P.W. - \ 2013
    Biogeosciences 10 (2013). - ISSN 1726-4170 - p. 1543 - 1559.
    mediterranean landscapes - atmospheric co2 - cover changes - future - carbon - maps - classification - emissions - centuries
    Human-induced land use changes are nowadays the second largest contributor to atmospheric carbon dioxide after fossil fuel combustion. Existing historic land change reconstructions on the European scale do not sufficiently meet the requirements of greenhouse gas (GHG) and climate assessments, due to insufficient spatial and thematic detail and the consideration of various land change types. This paper investigates if the combination of different data sources, more detailed modelling techniques, and the integration of land conversion types allow us to create accurate, high-resolution historic land change data for Europe suited for the needs of GHG and climate assessments. We validated our reconstruction with historic aerial photographs from 1950 and 1990 for 73 sample sites across Europe and compared it with other land reconstructions like Klein Goldewijk et al. (2010, 2011), Ramankutty and Foley (1999), Pongratz et al. (2008) and Hurtt et al. (2006). The results indicate that almost 700 000 km2 (15.5%) of land cover in Europe has changed over the period 1950–2010, an area similar to France. In Southern Europe the relative amount was almost 3.5% higher than average (19%). Based on the results the specific types of conversion, hot-spots of change and their relation to political decisions and socio-economic transitions were studied. The analysis indicates that the main drivers of land change over the studied period were urbanization, the reforestation program resulting from the timber shortage after the Second World War, the fall of the Iron Curtain, the Common Agricultural Policy and accompanying afforestation actions of the EU. Compared to existing land cover reconstructions, the new method considers the harmonization of different datasets by achieving a high spatial resolution and regional detail with a full coverage of different land categories. These characteristics allow the data to be used to support and improve ongoing GHG inventories and climate research
    Simultaneous assimilation of satellite and eddy covariance data for improving terrestrial water and carbon simulations at a semi-arid woodland site in Botswana
    Kato, T. ; Knorr, W. ; Scholtze, M. ; Veenendaal, E.M. ; Kaminski, T. ; Kattge, J. ; Gobron, N. - \ 2013
    Biogeosciences 10 (2013). - ISSN 1726-4170 - p. 789 - 802.
    land-surface model - isba-a-gs - atmospheric co2 - soil-moisture - exchange - photosynthesis - transpiration - uncertainties - variability - biosphere
    Terrestrial productivity in semi-arid woodlands is strongly susceptible to changes in precipitation, and semi-arid woodlands constitute an important element of the global water and carbon cycles. Here, we use the Carbon Cycle Data Assimilation System (CCDAS) to investigate the key parameters controlling ecological and hydrological activities for a semi-arid savanna woodland site in Maun, Botswana. Twenty-four eco-hydrological process parameters of a terrestrial ecosystem model are optimized against two data streams separately and simultaneously: daily averaged latent heat flux (LHF) derived from eddy covariance measurements, and decadal fraction of absorbed photosynthetically active radiation (FAPAR) derived from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS). Assimilation of both data streams LHF and FAPAR for the years 2000 and 2001 leads to improved agreement between measured and simulated quantities not only for LHF and FAPAR, but also for photosynthetic CO2 uptake. The mean uncertainty reduction (relative to the prior) over all parameters is 14.9% for the simultaneous assimilation of LHF and FAPAR, 8.5% for assimilating LHF only, and 6.1% for assimilating FAPAR only. The set of parameters with the highest uncertainty reduction is similar between assimilating only FAPAR or only LHF. The highest uncertainty reduction for all three cases is found for a parameter quantifying maximum plant-available soil moisture. This indicates that not only LHF but also satellite-derived FAPAR data can be used to constrain and indirectly observe hydrological quantities.
    Leaf adaptations of evergreen and deciduous trees of semi-arid and humid savannas on three continents
    Tomlinson, K.W. ; Poorter, L. ; Sterck, F.J. ; Borghetti, M. ; Ward, D. ; Bie, S. de; Langevelde, F. van - \ 2013
    Journal of Ecology 101 (2013)2. - ISSN 0022-0477 - p. 430 - 440.
    carbon-isotope ratios - functional traits - tropical forest - water relations - life-span - growth-responses - seedling growth - atmospheric co2 - root morphology - high-rainfall
    1. Drought stress selects for a suite of plant traits at root, stem and leaf level. Two strategies are proposed for trees growing in seasonally water-stressed environments: drought tolerance and drought avoidance. These are respectively associated with evergreen phenology, where plants retain their leaves throughout the year, and deciduous phenology, where plants drop their leaves during dry seasons. Evergreen species are thought to have leaf traits supporting lower photosynthesis and transpiration rates, in order to conserve water during dry periods. 2. We evaluated 18 morphological, chemical and physiological leaf traits of 51 abundant savanna tree species that differed in leaf habit (deciduous and evergreen), selected from two climate types (semi-arid and humid) in three continents (Australia, Africa and South America) (annual rainfall range: 500–1550 mm), and grown in a common garden experiment. We hypothesised that evergreen species have more conservative water use and differ more across climate types than deciduous species because evergreen species are forced to endure extended water deficits during dry seasons. 3. Trait shifts between semi-arid and humid savannas did not differ between evergreen and deciduous species. 4. Evergreen species had similar assimilation rates but lower photosynthetic water-use efficiency (PWUE) than deciduous species, possibly to extend their leaf lifespans by protecting their photosynthetic machinery from overheating through evaporative cooling. 5. Species of humid and semi-arid environments did not differ with respect to assimilation rate or PWUE, but semi-arid species did have smaller leaf sizes and greater leaf potassium and phosphorus concentrations. These traits may enable semi-arid species to maximize growth during episodes of favourable moisture availability. 6. Species from the three continents differed in their leaf traits. These probably reflect the greater proportion of evergreen species in Australia as compared to the other continents and generally infertile soils in the South American sampling sites compared to the wider fertility range in the African sites. 7. Synthesis: Water stress in savannas does not select for more conservative water use, but may select for rapid adjustment to prevailing water conditions and for heat avoidance mechanisms.
    The European land and inland water CO2, CO, CH4 and N2O balance between 2001 and 2005
    Luyssaert, S. ; Abril, G. ; Andres, R. ; Bastviken, D. ; Bellassen, V. ; Bergamaschi, P. ; Bousquet, P. ; Chevallier, F. ; Ciais, P. ; Corazza, M. ; Dechow, R. ; Erb, K.H. ; Etiope, G. ; Fortems-Cheiney, A. ; Grassi, G. ; Hartmann, J. ; Jung, M. ; Lathiere, J. ; Lohila, A. ; Mayorga, E. ; Moosdorf, N. ; Njakou, D.S. ; Otto, J. ; Papale, D. ; Peters, W. ; Peylin, P. ; Raymond, P. ; Rodenbeck, C. ; Saarnio, S. ; Schulze, E.D. ; Szopa, S. ; Thompson, R. ; Verkerk, P.J. ; Vuichard, N. ; Wang, R. ; Wattenbach, M. ; Zaehle, S. - \ 2012
    Biogeosciences 9 (2012)8. - ISSN 1726-4170 - p. 3357 - 3380.
    north-atlantic oscillation - net ecosystem exchange - organic-carbon changes - atmospheric co2 - climate-change - nitrous-oxide - terrestrial biosphere - dioxide - fluxes - emissions
    Globally, terrestrial ecosystems have absorbed about 30% of anthropogenic greenhouse gas emissions over the period 2000-2007 and inter-hemispheric gradients indicate that a significant fraction of terrestrial carbon sequestration must be north of the Equator. We present a compilation of the CO2, CO, CH4 and N2O balances of Europe following a dual constraint approach in which (1) a land-based balance derived mainly from ecosystem carbon inventories and (2) a land-based balance derived from flux measurements are compared to (3) the atmospheric data-based balance derived from inversions constrained by measurements of atmospheric GHG (greenhouse gas) concentrations. Good agreement between the GHG balances based on fluxes (1294 +/- 545 Tg C in CO2-eq yr(-1)), inventories (1299 +/- 200 Tg C in CO2-eq yr(-1)) and inversions (1210 +/- 405 Tg C in CO2-eq yr(-1)) increases our confidence that the processes underlying the European GHG budget are well understood and reasonably sampled. However, the uncertainty remains large and largely lacks formal estimates. Given that European net land to atmosphere exchanges are determined by a few dominant fluxes, the uncertainty of these key components needs to be formally estimated before efforts could be made to reduce the overall uncertainty. The net land-to-atmosphere flux is a net source for CO2, CO, CH4 and N2O, because the anthropogenic emissions by far exceed the biogenic sink strength. The dual-constraint approach confirmed that the European biogenic sink removes as much as 205 +/- 72 Tg C yr(-1) from fossil fuel burning from the atmosphere. However, This C is being sequestered in both terrestrial and inland aquatic ecosystems. If the C-cost for ecosystem management is taken into account, the net uptake of ecosystems is estimated to decrease by 45% but still indicates substantial C-sequestration. However, when the balance is extended from CO2 towards the main GHGs, C-uptake by terrestrial and aquatic ecosystems is offset by emissions of non-CO2 GHGs. As such, the European ecosystems are unlikely to contribute to mitigating the effects of climate change.
    What eddy-covariance measurements tell us about prior land flux errors in co 2-flux inversion schemes
    Chevallier, F. ; Wang, T. ; Ciais, P. ; Maignan, F. ; Bocquet, M. ; Moors, E.J. - \ 2012
    Global Biogeochemical Cycles 26 (2012)1. - ISSN 0886-6236 - 9 p.
    carbon-dioxide exchange - interannual variability - soil respiration - atmospheric co2 - pine forests - water-vapor - oak forest - assimilation - uncertainty - grassland
    To guide the future development of CO2-atmospheric inversion modeling systems, we analyzed the errors arising from prior information about terrestrial ecosystem fluxes. We compared the surface fluxes calculated by a process-based terrestrial ecosystem model with daily averages of CO2flux measurements at 156 sites across the world in the FLUXNET network. At the daily scale, the standard deviation of the model-data fit was 2.5 gC·m-2·d-1; temporal autocorrelations were significant at the weekly scale (>0.3 for lags less than four weeks), while spatial correlations were confined to within the first few hundred kilometers (
    Inverse carbon dioxide flux estimates for the Netherlands
    Meesters, A.G.C.A. ; Tolk, L.F. ; Peters, W. ; Hutjes, R.W.A. ; Vellinga, O.S. ; Elbers, J.A. ; Vermeulen, A.T. ; Laan, S. van der; Neubert, R. ; Meijer, H.A.J. ; Dolman, A.J. - \ 2012
    Journal of Geophysical Research: Atmospheres 117 (2012). - ISSN 2169-897X - 13 p.
    transport models - atmospheric co2 - regional-scale - tower - emissions - exchange
    CO2 fluxes for the Netherlands and surroundings are estimated for the year 2008, from concentration measurements at four towers, using an inverse model. The results are compared to direct CO2 flux measurements by aircraft, for 6 flight tracks over the Netherlands, flown multiple times in each season. We applied the Regional Atmospheric Mesoscale Modeling system (RAMS) coupled to a simple carbon flux scheme (including fossil fuel), which was run at 10 km resolution, and inverted with an Ensemble Kalman Filter. The domain had 6 eco-regions, and inversions were performed for the four seasons separately. Inversion methods with pixel-dependent and -independent parameters for each eco-region were compared. The two inversion methods, in general, yield comparable flux averages for each eco-region and season, whereas the difference from the prior flux may be large. Posterior fluxes co-sampled along the aircraft flight tracks are usually much closer to the observations than the priors, with a comparable performance for both inversion methods, and with best performance for summer and autumn. The inversions showed more negative CO2 fluxes than the priors, though the latter are obtained from a biosphere model optimized using the Fluxnet database, containing observations from more than 200 locations worldwide. The two different crop ecotypes showed very different CO2 uptakes, which was unknown from the priors. The annual-average uptake is practically zero for the grassland class and for one of the cropland classes, whereas the other cropland class had a large net uptake, possibly because of the abundance of maize there.
    A conceptual framework to quantify the influence of convective boundary layer development on carbon dioxide mixing ratios
    Pino, D. ; Vilà-Guerau de Arellano, J. ; Peters, W. ; Schröter, J.S. ; Heerwaarden, C.C. van; Krol, M.C. - \ 2012
    Atmospheric Chemistry and Physics 12 (2012). - ISSN 1680-7316 - p. 2969 - 2985.
    atmospheric co2 - transport models - sensible heat - tall tower - exchange - fluxes - ecosystem - temperature - entrainment - variability
    Interpretation of observed diurnal carbon dioxide (CO2) mixing ratios near the surface requires knowledge of the local dynamics of the planetary boundary layer. In this paper, we study the relationship between the boundary layer dynamics and the CO2 budget in convective conditions through a newly derived set of analytical equations. From these equations, we are able to quantify how uncertainties in boundary layer dynamical variables or in the morning CO2 distribution in the mixed-layer or in the free atmosphere (FA) influence the bulk CO2 mixing ratio. We find that the largest uncertainty incurred on the midday CO2 mixing ratio comes from the prescribed early morning CO2 mixing ratios in the stable boundary layer, and in the free atmosphere. Errors in these values influence CO2 mixing ratios inversely proportional to the boundary layer depth (h), just like uncertainties in the assumed initial boundary layer depth and surface CO2 flux. The influence of uncertainties in the boundary layer depth itself is one order of magnitude smaller. If we “invert” the problem and calculate CO2 surface exchange from observed or simulated CO2 mixing ratios, the sensitivities to errors in boundary layer dynamics also invert: they become linearly proportional to the boundary layer depth. We demonstrate these relations for a typical well characterized situation at the Cabauw site in The Netherlands, and conclude that knowledge of the temperature and carbon dioxide profiles of the atmosphere in the early morning are of vital importance to correctly interpret observed CO2 mixing ratios during midday.
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