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

Chapter 4: Corrections and data quality control

The Bowen ratio energy balance (BREB) method is the most widely used for estimating the fluxes of sensible heat and latent heat near the surface largely because of its conceptual simplicity and the robustness of instrumentation required. We have adopted the same technique here to study partitioning of measured available energy (difference of net radiation and soil heat flux) over bare soil at a humid tropical location in Ile-Ife, Nigeria (7° 33' N, 4° 34' E) between 7 and 10 March, 1999. Results obtained of the diurnal variations of the both fluxes in relation to the changing surface conditions (case studies) are quite satisfactory. For dry days, the sensible heat flux is comparatively of the same magnitude as the latent heat flux but it is less, about 10-60% for the wet surface conditions. It is clear from the present study that for the tropical forest zone, evaporation is the next important factor after radiation in the energy balance due to the humid conditions that usually prevail. Except for the few instances when very weak gradients exist, particularly of moisture, during transition periods (at sunrise or sunset), the technique has worked satisfactorily for day as well as night time periods regardless of prevailing weather conditions.

https://mausamjournal.imd.gov.in/index.php/MAUSAM/article/download/1739/1552

Bowen ratio determination of sensible and latent heat fluxes in a humid tropical environment at Ile- Ife, Nigeria

Possibilities of an optimal encoding of SODAR information

GaFiR: a gap-filling package for ecosystem-atmosphere carbon dioxide flux and evapotranspiration data

After an historical introduction into the research activities of Prof. Hinzpeter and the author, because of their roots in the Meteorological Observatory Potsdam the investigation of the molecular temperature sublayer over the ocean was selected as one field of a common interest. The experimental investigations made in Kiel and Leipzig are presented. It is shown that the thickness of the molecular sublayer depends on the friction velocity and the conditions of the wavy surface. Based on this data, parametrizations of the viscous sublayer on the basis of these investigations and of hydrodynamical measurements are discussed. Possibilities to use this parametrizations in air-sea interaction models are considered. Zusammenfassung Nach einer historischen Einleitung zu den wissenschaftlichen Wurzeln von Prof. Hinzpeter und dem Autor im Meteorologischen Observatorium Potsdam wird die Untersuchung der molekularen Grenzschicht iiber dem Ozean als ein gemeinsames wissenschaftliches Interessengebiet nliher betrachtet. Dabei werden die in Kiel und Leipzig durchgefiihrten Untersuchungsergebnisse dargestellt. Es wird gezeigt, dass die Dicke der molekularen Temperaturgrenzschicht von der Schubspannungsgeschwindigkeit und von der Entwicklung der Oberfllichenwellen abhlingt. Auf Grund dieser experimentellen Befunde werden Parametrisierungen fiir die viskose Unterschicht auf der Basis dieser Daten und hydrodynamischer Untersuchungen sowie Moglichkeiten zu deren Einbeziehung in Wechselwirkungsmodelle Mcer-Atmosphlire diskutiert.

Thomas Foken

Papers

Chapter 4: Corrections and data quality control

Bowen ratio determination of sensible and latent heat fluxes in a humid tropical environment at Ile- Ife, Nigeria

Possibilities of an optimal encoding of SODAR information

GaFiR: a gap-filling package for ecosystem-atmosphere carbon dioxide flux and evapotranspiration data

Some aspects of the viscous sublayer