Author Correction: The FLUXNET2015 dataset and the ONEFlux processing pipeline for eddy covariance data

The following authors were omitted from the original version of this Data Descriptor: Markus Reichstein and Nicolas Vuichard. Both contributed to the code development and N. Vuichard contributed to the processing of the ERA-Interim data downscaling. Furthermore, the contribution of the co-author Frank Tiedemann was re-evaluated relative to the colleague Corinna Rebmann, both working at the same sites, and based on this re-evaluation a substitution in the co-author list is implemented (with Rebmann replacing Tiedemann). Finally, two affiliations were listed incorrectly and are corrected here (entries 190 and 193). The author list and affiliations have been amended to address these omissions in both the HTML and PDF versions

The FLUXNET2015 dataset and the ONEFlux processing pipeline for eddy covariance data.

The FLUXNET2015 dataset provides ecosystem-scale data on CO2, water, and energy exchange between the biosphere and the atmosphere, and other meteorological and biological measurements, from 212 sites around the globe (over 1500 site-years, up to and including year 2014). These sites, independently managed and operated, voluntarily contributed their data to create global datasets. Data were quality controlled and processed using uniform methods, to improve consistency and intercomparability across sites. The dataset is already being used in a number of applications, including ecophysiology studies, remote sensing studies, and development of ecosystem and Earth system models. FLUXNET2015 includes derived-data products, such as gap-filled time series, ecosystem respiration and photosynthetic uptake estimates, estimation of uncertainties, and metadata about the measurements, presented for the first time in this paper. In addition, 206 of these sites are for the first time distributed under a Creative Commons (CC-BY 4.0) license. This paper details this enhanced dataset and the processing methods, now made available as open-source codes, making the dataset more accessible, transparent, and reproducible

Effects of measurement uncertainties of meteorological data on estimates of site water balance components

Numerical water balance models are widely used in ecological and hydro sciences. However, their application is related to specific problems and uncertainties. The reliability of model prediction depends on (i) model concept, (ii) parameters, (iii) uncertainty of input data, and (iv) uncertainty of reference data. How model concept (i) and parameters (ii) effect the model’s performance is an often treated problem. However, the effects of (iii) and (iv) are typically ignored or only barely treated in context of regionalisation and generalisation. In this study, the actual measurement uncertainties of input and reference data are the main focus. Furthermore, the evaluation of model results is analysed with regard to uncertainties of reference data. A special feature is the use of evapotranspiration (measured via the eddy covariance) instead of runoff for evaluation of simulation results. It is shown that seemingly small uncertainties of measurements can create significant uncertainties in simulation results depending on the temporal scale of investigation. As an example, the uncertainty of measurements of daily global radiation sum up to an uncertainty of 250 MJ (equivalent to 100 mm) on an annual scale, which causes an uncertainty of 40 mm in simulated grass-reverence evapotranspiration. Summarised and generalised, the measurement uncertainties of all input data create an uncertainty on average of around 5% in the simulated annual evapotranspiration and of around 10% in the simulated annual seepage. However, the effects can be significantly higher in years with extreme events and can reach up to 15%. It is demonstrated that uncertainties of individual variables are not simply superposed but interact in a complex way. Thereby, it has become apparent that the effects of measurement uncertainties on model results are similar for complex and for simple models

Estimating the components of the sensible heat budget of a tall forest canopy in complex terrain

Ultrasonic wind measurements, sonic temperature and air temperaturedata at two heights in the advection experiment MORE II were used to establisha complete budget of sensible heat including vertical advection, horizontal advec-tion and horizontal turbulent flux divergence. MORE II took place at the long-termCarbo-Europe IP site in Tharandt, Germany. During the growing period of 2003 threeadditional towers were established to measure all relevant parameters for an estima-tion of advective fluxes, primarily of CO2. Additionally, in relation to other advectionexperiments, a calculation of the horizontal turbulent flux divergence is proposed andthe relation of this flux to atmospheric stability and friction velocity is discussed. Inorder to obtain a complete budget, different scaling heights for horizontal advectionand horizontal turbulent flux divergence are tested. It is shown that neglecting advec-tive fluxes may lead to incorrect results. If advective fluxes are taken into account, thesensible heat budget based upon vertical turbulent flux and storage change only, isreduced by approximately 30%. Additional consideration of horizontal turbulent fluxdivergence would in turn add 5–10% to this sum (i.e., the sum of vertical turbulentflux plus storage change plus horizontal and vertical advection). In comparison withavailable energy horizontal advection is important at night whilst horizontal turbulentflux divergence is rather insignificant. Obviously, advective fluxes typically improvepoor nighttime energy budget closure and might change ecosystem respiration fluxesconsiderably

A new mass conservation approach to the study of CO2 advection in an alpine forest

A new method is proposed for the computation of CO 2 Net Ecosystem Exchange(NEE) and its components in a forest ecosystem. Advective flux is estimated by takinginto account the air mass conservation principle. For this purpose, wind and dry airdensity values on the surface of the control volume are first corrected and then theadvective flux is estimated on the surface of the control volume. Turbulent flux is alsocomputed along the surface of the control volume while storage flux is computed insidethe volume. Additional characteristics of this method are that incompressibility of themean flow is not assumed a priori, and that vertical and horizontal advective fluxes are nottreated separately, but their sum is estimated directly. The methodology is applied toexperimental data collected with a three-dimensional scheme at the alpine site of Renonduring the Advex project (July 2005). The advection flux was found to be prevailingpositive at night and negative during the day, as was found in previous studies onadvection for the same site, but showed a lower scatter in half-hour calculated values. Wetested the effect of its summation on turbulent and storage fluxes to produce half-hourlyvalues of NEE. Nighttime NEE values were used in functional relations with soiltemperature, daytime values with PPFD. The effect of addition of the advectioncomponent was an increase in the values of parameters indicating ecosystem respiration,quantum yield, and photosynthetic capacity. The coefficient of correlation between NEEand environmental drivers increased

Available energy and energy balance closure at four coniferous forest sites across Europe

The available energy (AE), driving the turbulent fluxes of sensible heat and latent heat at the earth surface, was estimated at four partly complex coniferous forest sites across Europe (Tharandt, Germany; Ritten/Renon, Italy; Wetzstein, Germany; Norunda, Sweden). Existing data of net radiation were used as well as storage change rates calculated from temperature and humidity measurements to finally calculate the AE of all forest sites with uncertainty bounds. Data of the advection experiments MORE II (Tharandt) and ADVEX (Renon, Wetzstein, Norunda) served as the main basis. On-site data for referencing and cross-checking of the available energy were limited. Applied cross checks for net radiation (modelling, referencing to nearby stations and ratio of net radiation to global radiation) did not reveal relevant uncertainties. Heat storage of sensible heat J (H), latent heat J (E), heat storage of biomass J (veg) and heat storage due to photosynthesis J (C) were of minor importance during day but of some importance during night, where J (veg) turned out to be the most important one. Comparisons of calculated storage terms (J (E), J (H)) at different towers of one site showed good agreement indicating that storage change calculated at a single point is representative for the whole canopy at sites with moderate heterogeneity. The uncertainty in AE was assessed on the basis of literature values and the results of the applied cross checks for net radiation. The absolute mean uncertainty of AE was estimated to be between 41 and 52 W m(-2) (10-11 W m(-2) for the sum of the storage terms J and soil heat flux G) during mid-day (approximately 12% of AE). At night, the absolute mean uncertainty of AE varied from 20 to about 30 W m(-2) (approximately 6 W m(-2) for J plus G) resulting in large relative uncertainties as AE itself is small. An inspection of the energy balance showed an improvement of closure when storage terms were included and that the imbalance cannot be attributed to the uncertainties in AE alone

Contrasting response of European forest and grassland energy exchange to heatwaves

Recent European heatwaves have raised interest in the impact of land cover conditions on temperature extremes. At present, it is believed that such extremes are enhanced by stronger surface heating of the atmosphere, when soil moisture content is below average. However, the impact of land cover on the exchange of water and energy and the interaction of this exchange with the soil water balance during heatwaves is largely unknown. Here we analyse observations from an extensive network of flux towers in Europe that reveal a difference between the temporal responses of forest and grassland ecosystems during heatwaves. We find that initially, surface heating is twice as high over forest than over grassland. Over grass, heating is suppressed by increased evaporation in response to increased solar radiation and temperature. Ultimately, however, this process accelerates soil moisture depletion and induces a critical shift in the regional climate system that leads to increased heating. We propose that this mechanism may explain the extreme temperatures in August 2003. We conclude that the conservative water use of forest contributes to increased temperatures in the short term, but mitigates the impact of the most extreme heat and/or long-lasting events