Future climate warming is expected to enhance plant growth in temperate ecosystems and to increase carbon sequestration. But although severe regional heatwaves may become more frequent in a changing climate their impact on terrestrial carbon cycling is unclear. Here we report measurements of ecosystem carbon dioxide fluxes, remotely sensed radiation absorbed by plants, and country-level crop yields taken during the European heatwave in 2003.We use a terrestrial biosphere simulation model to assess continental-scale changes in primary productivity during 2003, and their consequences for the net carbon balance. We estimate a 30 per cent reduction in gross primary productivity over Europe, which resulted in a strong anomalous net source of carbon dioxide (0.5 Pg Cyr21) to the atmosphere and reversed the effect of four years of net ecosystem carbon sequestration. Our results suggest that productivity reduction in eastern and western Europe can be explained by rainfall deficit and extreme summer heat, respectively. We also find that ecosystem respiration decreased together with gross primary productivity, rather than accelerating with the temperature rise. Model results, corroborated by historical records of crop yields, suggest that such a reduction in Europe's primary productivity is unprecedented during the last century. An increase in future drought events could turn temperate ecosystems into carbon sources, contributing to positive carbon-climate feedbacks already anticipated in the tropics and at high latitudes.

Europe-wide reduction in primary productivity caused by the heat and drought in 2003

Investigating soil moisture-climate interactions in a changing climate: A review

FLUXNET is a global network of micrometeorological flux measurement sites that measure the exchanges of carbon dioxide, water vapor, and energy between the biosphere and atmosphere. At present over 140 sites are operating on a long-term and continuous basis. Vegetation under study includes temperate conifer and broadleaved (deciduous and evergreen) forests, tropical and boreal forests, crops, grasslands, chaparral, wetlands, and tundra. Sites exist on five continents and their latitudinal distribution ranges from 70°N to 30°S. FLUXNET has several primary functions. First, it provides infrastructure for compiling, archiving, and distributing carbon, water, and energy flux measurement, and meteorological, plant, and soil data to the science community. (Data and site information are available online at the FLUXNET Web site, http://www-eosdis.ornl.gov/FLUXNET/.) Second, the project supports calibration and flux intercomparison activities. This activity ensures that data from the regional networks are intercomparable. And third, FLUXNET supports the synthesis, discussion, and communication of ideas and data by supporting project scientists, workshops, and visiting scientists. The overarching goal is to provide information for validating computations of net primary productivity, evaporation, and energy absorption that are being generated by sensors mounted on the NASA Terra satellite. Data being compiled by FLUXNET are being used to quantify and compare magnitudes and dynamics of annual ecosystem carbon and water balances, to quantify the response of stand-scale carbon dioxide and water vapor flux densities to controlling biotic and abiotic factors, and to validate a hierarchy of soil–plant–atmosphere trace gas exchange models. Findings so far include 1) net CO 2 exchange of temperate broadleaved forests increases by about 5.7 g C m −2 day −1 for each additional day that the growing season is extended; 2) the sensitivity of net ecosystem CO 2 exchange to sunlight doubles if the sky is cloudy rather than clear; 3) the spectrum of CO 2 flux density exhibits peaks at timescales of days, weeks, and years, and a spectral gap exists at the month timescale; 4) the optimal temperature of net CO 2 exchange varies with mean summer temperature; and 5) stand age affects carbon dioxide and water vapor flux densities.

/pdf/fluxnet-a-new-tool-to-study-the-temporal-and-spatial-2izxj9ikwz.pdf

FLUXNET: A New Tool to Study the Temporal and Spatial Variability of Ecosystem-Scale Carbon Dioxide, Water Vapor, and Energy Flux Densities

This paper discusses the advantages and disadvantages of the different methods that separate net ecosystem exchange (NEE) into its major components, gross ecosystem carbon uptake (GEP) and ecosystem respiration (Reco). In particular, we analyse the effect of the extrapolation of night-time values of ecosystem respiration into the daytime; this is usually done with a temperature response function that is derived from long-term data sets. For this analysis, we used 16 one-year-long data sets of carbon dioxide exchange measurements from European and US-American eddy covariance networks. These sites span from the boreal to Mediterranean climates, and include deciduous and evergreen forest, scrubland and crop ecosystems. We show that the temperature sensitivity of Reco, derived from long-term (annual) data sets, does not reflect the short-term temperature sensitivity that is effective when extrapolating from night- to daytime. Specifically, in summer active ecosystems the long

https://www.bgc-jena.mpg.de/bgi/uploads/Publ/Publications/Reichstein_etal_2005.pdf

On the Separation of Net Ecosystem Exchange into Assimilation and Ecosystem Respiration: Review and Improved Algorithm

The chapter gives an overview of the research at the Waldstein site related to “fluxes of energy and matter of a forest ecosystem” from the founding of BITOK (Bayreuth Institute of Terrestrial Ecosystem Research) in 1992 up to the present. This includes tables of all relevant projects and experiments together with the scientific focus of these initiatives and the link to the relevant chapters of the book. The research periods can be separated into two parts: the BITOK funding up to 2004, with additional funding for carbon fluxes by the European Community, and the single projects, funded mainly by the German Science Foundation, under the umbrella of BayCEER (Bayreuth Center of Ecology and Environmental Research) since 2005. Due to a stable program of climate and air pollution monitoring, it was easy to piggyback comprehensive experimental activities. The FLUXNET station DE-Bay has a nearly 20-year measuring file covering a change from a more homogeneous to a heterogeneous forest.

History of the Waldstein Measuring Sites

I believe that the authors are right to see the problem as an unrealistic correlation between the sonic temperature and the vertical wind velocity. From my own experience, I do not believe that the problem lies with either a deformation of the instrument, or the firmware of the CSAT3 sonic anemometer. It is of importance that whereas in Eq. (2) the part (1/t1+1/t2) represents the sonic temperature, the relevant equation for the wind velocities has the part (1/t1-1/t2). If one of the times (t1 or/and t2) has an error, a self-correlation is generated between the sonic temperature and the wind velocity, C88

Interactive comment on "Using sonic anemometer temperature to measure sensible heat flux in strong winds" by S. P. Burns et al.

The paper reviews the investigations of the Working Group Oceanology of the Univer- sity of Leipzig with respect to internal boundary layers in the coastal zone. After an introduction covering the definition of and approaches to determine the height of the internal boundary layers, it is clear from the experimental results that the height of the internal boundary layer can be determined with a simple parametrization based on the fetch and nearly independent of the roughness change (smooth to rough or rough to smooth). The strong practical relevance of the investigation is highlighted. 1. Einleitung An einer Kuste andern sich die aerodynamischen und thermischen Eigenschaften der Unterlage der Atmosphare gravierender als an jedem anderen Ort der Erde, sofern man in den Betrachtungen Veranderung der Hohenlage ausschliest. Das Stromungsfeld muss sich bei seiner Bewegung uber die Kustenline, physikalisch gesehen uber eine plotzli- che Veranderung der aerodynamischen und thermischen Eigenschaften hinweg, an die neue Unterlage anpassen. Das erfolgt nicht plotzlich, sondern allmahlich mit zuneh- mender Entfernung von Unterlagenveranderung. Der Teilbereich der atmospharischen Grenzschicht in dem sich die Stromung bis in immer grosere Hohen an die neue Unter- lage anpasst wird als interne Grenzschicht bezeichnet. Der Teil der Herausbildung einer internen Grenzschicht, der innerhalb der Bodenschicht der Atmosphare erfolgt ist dabei einer experimentellen Untersuchung und theoretischen Beschreibung relativ leicht zu- ganglich. In der Literatur finden sich seit gut 50 Jahren (ELLIOTT, 1958) experimentelle (BRADLEY, 1968, TAYLOR, 1969), analytische und numerische Darstellungen (z.B. CLAUsEN, 1991) dieses Transformationsprozesses (Zusammenfassungen in GARRATT, 1990; RAABE, 1991a). Dazu sind auch die Arbeiten zu zahlen, die unter Leitung von P. HUPFER uber mehrere Jahre hinweg durch Mitarbeiter seiner Arbeitsgruppe Ozeanolo- gie der Universitat Leipzig vorgelegt wurden (HUPFER ET AL., 1976, HUPFER und RAABE, 1994). Die experimentelle Untersuchungen erfolgten dabei an verschiedenen Kusten. Besonders die experimentelle Untersuchung der internen Grenzschicht, die sich bei ablandiger Windrichtung uber der beweglichen Seeoberflache herausbildet, hebt sich nach wie vor aus der Masse der Daten heraus, die es von anderen Autoren beson- ders auch fur die auflandige Windrichtung gibt. Die aus diesen Daten resultierenden Ergebnisse werden im folgenden kurz dargestellt. Dabei steht die Herausbildung eines neuen Gleichgewichtswindprofils uber einer neuen Unterlage im Mittelpunkt (DELLWIK und JENSEN, 2000), so dass die Transformation der thermischen Struktur der Atmosphare in Hohen auch oberhalb der Bodenschicht der Atmosphare hier nicht dis- kutiert wird (VENKATRAM, 1977, GRYNING und BATCHVAROVA, 1990).

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Die Höhe der internen Grenzschicht im Windfeld nach einer sprunghaften Änderung der aerodynamischen Rauhigkeit der Unterlage - Beispiel Küste

. The WPL (Webb,
Pearman, and Leuning) correction is fully accepted to
correct trace gas fluxes like CO 2 for density fluctuations due to water
vapour and temperature fluctuations for open-path gas analysers. It is known
that this additive correction can be on the order of magnitude of the actual
flux. However, this is hardly ever included in the analysis of data quality.
An example from the Arctic shows the problems, because the size of the
correction is a multiple of the actual flux. As a general result, we
examined and tabulated the magnitude of the WPL correction for carbon
dioxide flux as a function of sensible and latent heat flux. Furthermore, we
propose a parameter to better estimate possible deficits in data quality and
recommend integrating the quality flag derived with this parameter into the
general study of small carbon dioxide fluxes.

Importance of the Webb, Pearman, and Leuning (WPL) correction for the measurement of small CO2 fluxes

/pdf/towards-a-consistent-eddy-covariance-processing-a-comparison-1u0ohwbuns.pdf

Thomas Foken

Papers

History of the Waldstein Measuring Sites

Interactive comment on "Using sonic anemometer temperature to measure sensible heat flux in strong winds" by S. P. Burns et al.

Die Höhe der internen Grenzschicht im Windfeld nach einer sprunghaften Änderung der aerodynamischen Rauhigkeit der Unterlage - Beispiel Küste

Importance of the Webb, Pearman, and Leuning (WPL) correction for the measurement of small CO2 fluxes

Towards a consistent eddy-covariance processing: a comparison between EddyPro and TK3