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The CloudRoots field experiment was designed to obtain a comprehensive observational dataset that includes soil, plant, and atmospheric variables to investigate the interaction between a heterogeneous land surface and its overlying atmospheric boundary layer at the sub-hourly and sub-kilometre scale. Our findings demonstrate the need to include measurements at leaf level to better understand the relations between stomatal aperture and evapotranspiration (ET) during the growing season at the diurnal scale. Based on these observations, we obtain accurate parameters for the mechanistic representation of photosynthesis and stomatal aperture. Once the new parameters are implemented, the model reproduces the stomatal leaf conductance and the leaf-level photosynthesis satisfactorily. At the canopy scale, we find a consistent diurnal pattern on the contributions of plant transpiration and soil evaporation using different measurement techniques. From highly resolved vertical profile measurements of carbon dioxide (

Dürren gehören zu den klimatischen Extremereignissen mit den größten Auswirkungen auf die Landwirtschaft und die gesamte Gesellschaft. Ihre Klassifizierung, Beobachtung und Berechnung in Computermodellen ist jedoch höchst komplex. Wir beleuchten, worin die Unsicherheiten bestehen, wie vergangene Dürreereignisse in Deutschland und anderen Teilen der Welt zu bewerten sind und welche Entwicklungen in Zukunft durch den Klimawandel zu erwarten sind. Dabei gehen wir vor allem auf landwirtschaftliche Dürren ein, d.h. Perioden mit geringer Bodenfeuchte. Wir legen dar, dass hierbei nicht nur die Entwicklung der Niederschläge, sondern auch der potentiellen Verdunstung entscheidend ist, deren Zunahme in vielen Teilen der Welt, inklusive Deutschland, zu einem zunehmenden Dürrerisiko führt. Development of droughts in Germany, Europe and world-wide: Droughts are among the climatic extreme events with the largest impacts on agriculture and the whole society. However, their classification, observation and computation in computer models is a complex endavour. We illustrate the associated uncertainties, how recent drought events in Germany and other parts of the world can be assessed, and what future developments can be expected due to climate change. With an emphasis on agricultural drought (periods with low soil moisture), we show that it is not only the change in precipitation, but also in potential evaporation, which affects the drought risk - and that this risk is expected to increase with global warming in many parts of the world, including Germany. Desarrollo de las sequías en Alemania, Europa y el mundo: Las sequías son uno de los eventos climáticos extremos con mayor impacto en la agricultura y la sociedad en su conjunto. Sin embargo, su clasificación, observación y cálculo en modelos informáticos es sumamente compleja. Arrojamos luz sobre las incertidumbres, cómo se evaluarán los eventos de sequía pasados en Alemania y otras partes del mundo y qué desarrollos se pueden esperar en el futuro como resultado del cambio climático. Nos centramos principalmente en las sequías agrícolas, es decir, períodos con baja humedad del suelo. Explicamos que no solo el desarrollo de las precipitaciones, sino también la evaporación potencial es decisivo, cuyo aumento en muchas partes del mundo, incluida Alemania, conduce a un riesgo creciente de sequía.

In various of today’s resource management and climate change adaptation challenges, versatile and reliable numerical model simulations are the basis for informed decision making. The integration of multiple compartmental models into simulation platforms allows us to reproduce interacting geosystem processes and thereby solve a wide range of problems in a variety of applications. The Terrestrial System Modelling Platform (TSMP, https://www.terrsysmp.org) is an integrated regional Earth system model that simulates processes from the groundwater across the land surface to the top of the atmosphere on multiple spatio-temporal scales. TSMP consists of the COSMO (Consortium for Small-scale Modeling) atmospheric model, the CLM (Community Land Model), and the hydrologic model ParFlow, coupled through OASIS3-MCT. TSMP is used in various studies from climate change simulations to near-real time forecasting and monitoring. Here we present the results of the evaluation of the TSMP in a monitoring setup, providing daily forecasts with a lead time of 10 days of the atmospheric, land, and subsurface states and fluxes for a heterogeneous mid mountain-ranges area in Western Germany. The model domain covers an area of 150 km x 150 km at 1 km (atmosphere) and 0.5 km (land surface and subsurface) resolution. The simulated data is compared, e.g., with observations from the TERENO (Terrestrial Environmental Observatories, https://www.tereno.net) Eifel/Lower Rhine Valley network. This TERENO observatory comprises a total area of 2354 km² and provides data from a very dense measurement network of 12 climate stations, 6 eddy covariance stations, 6 lysimeter stations, and 13 cosmic-ray neutron sensor stations. To assess the quality and suitability of the TSMP as a monitoring system of the geosystem’s state and evolution with agricultural applications in mind, forecasts from July 2019 to July 2021 are analyzed with reference to the observations. Results show that the TSMP can well represent the main subsurface hydrological and relevant meteorological features.

In the Mediterranean area, the agricultural sector often relies on irrigation. Additional pressure on these environments will come from the increasing occurrence of dry years and of heat waves that are connected to climate change. Thus, more efficient water management strategies and, when possible, precision irrigation practices should be implemented. So far, a wide range of soil moisture sensor-based systems have been successfully used to monitor soil water content (SWC) dynamics in agricultural contexts. The relatively new, and non-invasive, technique cosmic-ray neutron sensing (CRNS) relies on the negative correlation between fast neutrons originating from cosmic radiation and soil moisture content. It has the advantage of a large footprint, covering the field-scale. Despite this, only few studies explored the use of CRNS for irrigation management. In this study, we examine how CRNS can provide insights in the monitoring of irrigation and the associated fluctuations in SWC dynamics and water potential. In September 2020, two apple orchards of 1.2 and 1.3 ha in size and located in the Pinios Hydrological Observatory (Greece) were provided with an extensive instrumentation in the context of the Agricultural Interoperability and Analysis Systems (ATLAS) project. At each field, 12 SoilNet nodes measure volumetric soil moisture at three depths (5, 20, and 50 cm) and water potential at one depth (20 cm). Additionally, one Atmos41 compact climate station and a CRNS probe were placed in each of the two orchards. All these instruments are equipped with NB-IoT connections and transmit data in near-real time. The irrigation of both fields is monitored using water meter pumps equipped with a LoRaWan connection. Instrument installation was preceded by geophysical surveys and by extensive soil sampling and analysis. Moreover, soil samples from 18 locations were collected per CRNS probe on the day of installation to provide instrument calibration information. However, additional calibration was required due to temporary sensor failure and was performed using the surrounding SoilNet nodes. During the subsequent months, the CRNS probes generally showed good agreement with the SWC measured by the SoilNet stations as well as a strong response to precipitation events. Once the irrigation of the apple orchards started in April 2021, it was found that small and localized irrigation events were not featured in the CRNS signal. However, when prominent irrigation events started in May 2021, the CRNS probes showed good agreement with the changes in SWC and in water potential measured with the SoilNet nodes. Such agreement depended largely on the timing of the irrigation event as well as on the CRNP calibration strategy. These findings indicate the possibility for using the CRNS technique as a tool for precision irrigation.

For an assessment of the roles of soil and vegetation in the climate system, a further understanding of the flux components of H 2 O and CO 2 (e.g., transpiration, soil respiration) and their interaction with physical conditions and physiological functioning of plants and ecosystems is necessary. To obtain magnitudes of these flux components, we applied source partitioning approaches after Scanlon and Kustas (2010; SK10) and after Thomas et al. (2008; TH08) to high-frequency eddy covariance measurements of 12 study sites covering different ecosystems (croplands, grasslands, and forests) in different climatic regions. Both partitioning methods are based on higher-order statistics of the H 2 O and CO 2 fluctuations, but proceed differently to estimate transpiration, evaporation, net primary production, and soil respiration. We compared and evaluated the partitioning results obtained with SK10 and TH08, including slight modifications of both approaches. Further, we analyzed the interrelations among the performance of the partitioning methods, turbulence characteristics, and site characteristics (such as plant cover type, canopy height, canopy density, and measurement height). We were able to identify characteristics of a data set that are prerequisites for adequate performance of the partitioning methods. SK10 had the tendency to overestimate and TH08 to underestimate soil flux components. For both methods, the partitioning of CO 2 fluxes was less robust than for H 2 O fluxes. Results derived with SK10 showed relatively large dependencies on estimated water use efficiency (WUE) at the leaf level, which is a required input. Measurements of outgoing longwave radiation used for the estimation of foliage temperature (used in WUE) could slightly increase the quality of the partitioning results. A modification of the TH08 approach, by applying a cluster analysis for the conditional sampling of respiration-evaporation events, performed satisfactorily, but did not result in significant advantages compared to the original method versions developed by Thomas et al. (2008). The performance of each partitioning approach was dependent on meteorological conditions, plant development, canopy height, canopy density, and measurement height. Foremost, the performance of SK10 correlated page1112 negatively with the ratio between measurement height and canopy height. The performance of TH08 was more dependent on canopy height and leaf area index. In general, all site characteristics that increase dissimilarities between scalars appeared to enhance partitioning performance for SK10 and TH08.

A key question in times of climate change is, how the biosphere responds to global change and the local land use management in regard to its carbon cycle. At the present time, the land surface acts as a sink for an thropogenic carbon dioxide (CO$_{2}$) emissions. However, additional CO$_{2}$ recarried out in winter wheat, winter barley, and in an intercrop mixture during different plant development stage and at diffrent times of day. A gas analyzer continuously records the concentrations at a frequency of 20 s$^{−1}$ over a 2 m profile height. We present a post-processing technique of the measurements (e.g. the correction of timelags) and show the resulting vertical profiles as 30-minute averages over height steps of 0.025m. The profiles clearly show the effects of soil respiration and photosynthetic carbon uptake within the plant stand, which vary both during the time of day and during the vegetation period. Using the Monin-Obukhov similarity theory, measurements over bare soil and a short plant canopy were analyzed to check the validity of the elevator measurements and the raw data processing. It was found that the derived fluxes of CO$_{2}$, latent and sensible heat, and momentum correlated well with eddy-covariance (EC) measurements [...]

For an assessment of the roles of soil and vegetation in the climate system, a further understanding of the flux components of H2O and CO2 (e.g., transpiration, soil respiration) and their interaction with physical conditions and physiological functioning of plants and ecosystems is necessary. To obtain magnitudes of these flux components, we applied source partitioning approaches after Scanlon and Kustas (2010; SK10) and after Thomas et al. (2008; TH08) to high-frequency eddy covariance measurements of 12 study sites covering different ecosystems (croplands, grasslands, and forests) in different climatic regions. Both partitioning methods are based on higher-order statistics of the H2O and CO2 fluctuations, but proceed differently to estimate transpiration, evaporation, net primary production, and soil respiration. We compared and evaluated the partitioning results obtained with SK10 and TH08, including slight modifications of both approaches. Further, we analyzed the interrelations among the performance of the partitioning methods, turbulence characteristics, and site characteristics (such as plant cover type, canopy height, canopy density, and measurement height). We were able to identify characteristics of a data set that are prerequisites for adequate performance of the partitioning methods. SK10 had the tendency to overestimate and TH08 to underestimate soil flux components. For both methods, the partitioning of CO2 fluxes was less robust than for H2O fluxes. Results derived with SK10 showed relatively large dependencies on estimated water use efficiency (WUE) at the leaf level, which is a required input. Measurements of outgoing longwave radiation used for the estimation of foliage temperature (used in WUE) could slightly increase the quality of the partitioning results. A modification of the TH08 approach, by applying a cluster analysis for the conditional sampling of respiration–evaporation events, performed satisfactorily, but did not result in significant advantages compared to the original method versions developed by Thomas et al. (2008). The performance of each partitioning approach was dependent on meteorological conditions, plant development, canopy height, canopy density, and measurement height. Foremost, the performance of SK10 correlated negatively with the ratio between measurement height and canopy height. The performance of TH08 was more dependent on canopy height and leaf area index. In general, all site characteristics that increase dissimilarities between scalars appeared to enhance partitioning performance for SK10 and TH08.

Droughts and heat waves deeply interact with the exchange of energy and matter between land surface and atmosphere. The conditions associated with a combined heat wave and drought can have positive or negative effects on the sensible heat flux (H), latent heat flux (LE), and net flux of CO2 (NEE). In return, while each of these fluxes can exert different local feedbacks on temperature, atmospheric humidity and soil moisture, all of them result in bulk heating of the troposphere (H and LE through direct local and indirect non-local heat transfer, and NEE through radiative forcing). H is positively affected by increased solar irradiation, but can be supressed by advection of warm air diminishing the gradient between surface and air temperature. Potential LE is positively affected by irradiation, temperature and water vapour pressure deficit, but actual LE can be suppressed by stomatal closure of plants and by reduced soil moisture from low rainfall and high past LE. NEE is the result of plant photosynthesis (GPP) and plant and soil respiration (R), both of which can be enhanced by high temperatures or irradiation, and suppressed by drought. Focusing on direct measurements mostly by a network of Eddy-Covariance (EC) stations of the ICOS (www.icosri.eu), TERENO (www.tereno.net) and other networks, we hypothesize that the net effect of the 2018 event at a site, and thus its feedback on global warming, depends on the balance between co-existing positive and negative effects of the combined heat wave and drought on the respective fluxes. Variables such as albedo, growing degreedays (GDD), soil moisture and ecosystem-level water use efficiency help to separate these co-existing positive and negative effects from each other. Preliminary results indicate different degrees of heterogeneity between sites fordifferent variables. As expected, reduced precipitation and soil moisture, as well as increased GDD, could be found at almost all sites in the affected region. NEE was mostly less negative, indicating a weaker sink or even a source forCO2, as expected from past studies on earlier events. The network density and number of site-years available now confirms that this was true for all major ecosystem types - forest, grassland and (rainfed) cropland, and resultedin increased atmospheric CO2 concentrations. However, notable exceptions occurred at elevated low mountain range sites and during early stages of the event, supporting the hypothesis of a balance between positive andnegative effects, where the former may prevail at strongly energy-limited sites with a usually large water surplus. H was mostly above-average, indicating that local heat production contributed to the event and was typically notsuppressed by warm air advection. LE as well as inferred GPP and R reacted most heterogeneously across sites, demonstrating the large discrepancy between potentially high fluxes due to high irradiation and temperature on theone hand, and suppression by water shortage on the other hand. Despite the variability in LE, its relation to NEE was such that ecosystem-level water use was less efficient than usual at the majority of sites through reduced CO2uptake.

Forest ecosystems in the mid latitudes are a sink for atmospheric carbon dioxide (CO$_2$) and thus play an important role in the global carbon cycle [1]. Deforestation has a major impact on the CO$_2$ exchange between the forested ecosystem and the atmosphere. After deforestation, the former forest sink becomes a source for CO$_2$. We present seven years of CO$_2$ flux measurements sampled above a 70 year old spruce monoculture, of which 9 ha was partially deforested three years after the measurement started, in order to promote the natural succession towards deciduous forest.The measurements were carried out in the Wüstebach research site, a small headwater catchment (38.5 ha) within the TERENO (TERrestrial ENvironmental Observatories) network in the Eifel National Park Germany (50°30'N, 06°19'E, 595-629 m a.s.l.). An EC system, mounted on the top of a 37.8 m high tower, continuously samples fluxes of momentum, sensible heat, latent heat and CO$_2$. After the partial deforestation, a second EC station was installed in the middle of the clearcut and operated simultaneously to the forest station. Full time series and annual carbon budgets of the net ecosystem exchange of CO$_2$ (NEE) and its components gross primary production (GPP) and total ecosystem respiration were calculated by using gap filling and flux partitioning methods. Besides the NEE and its components, we also considered the measured soil respiration and compare the climate effect of changed CO$_2$ sequestration with the biophysical effect of changed albedo.In contrast to the deforested area, annual sums of NEE measured above the forest showed a strong carbon sink with small inter-annual variability. In the first year after partial deforestation, regrowth on the deforested area consisted mainly of grasses and shrub vegetation while since the second year also growth of new trees (predominantly mountain ash) increased. The recovering vegetation is reflected in the annual sums of NEE, which decreased from a carbon source of + 500 g C m-2 y-1 towards neutral over the past four years, due to an increase in the photosynthetically activities.References:[1] IPCC. Climate Change 2013: The Physical Science Basis. (eds Stocker, T. F. et al.) Cambridge Univ. Press, (2014).

Due to their high-quality routine measurement programme, ICOS sites lend themselves as anchors for additional experiments. As an example, we describe the CloudRoots campaign near the agricultural site Selhausen (DE-RuS) in spring 2018.Little is known about the two-way feedback between stomatal control (controlling the partitioning of energy into sensible and latent heat) and cloud development (affecting potential evapotranspiration). Coupled models of the soil-vegetation-boundary layer continuum have the potential to explain this, but their calculations are only as robust as the data used to parameterize or validate the model. For observations and modelling, the challenge is in interconnecting processes at leaf level to the physics of turbulence and clouds.We temporarily amend the existing radiation, flux and soil dynamics/respiration measurements of the ICOS site by scintillometry, sap-flow and leaf-level flux measurements, vertical profiles and isotope measurements. Scintillometers provide minute-scale turbulent fluxes enabling to connect stomatal responses to the energy, moisture and CO2 fluxes at this timescale [1]. Sap-flow [2], leaf-level chamber, canopy-resolving profile [3] and isotope measurements have the potential to distinguish stomatal CO2 and H2O fluxes from the eddy-covariance based net fluxes. Relating the leaf and canopy level measurements to cloud development and potential cross-scale feedbacks are integrated and explored with the CLASS model ([4], https://classmodel.github.io).The campaign is partnering with two complementary test campaigns for the FLEX mission (https://earth.esa.int/web/guest/missions/esa-future-missions/flex) and the MOSES project (https://moses.eskp.de/home/), taking place, among others, in the same region in spring and summer 2018. The poster will show first results and method intercomparisons from the CloudRoots field campaign.[1] van Kesteren et al. 2013, Agric. For. Meteorol. 178-179:75-105[2] Langensiepen et al. 2014, Agric. For. Meteorol. 186:34[3] Ney and Graf 2018, Bound.-Layer Meteorol. 166:449[4] Vilà-Guerau de Arellano et al. 2015, Atmospheric Boundary Layer: Integrating air chemistry and land interactions. Cambridge University Press.

Source partitioning of eddy covariance (EC) measurements of CO$_2$ into respiration and photosynthesis is routinely used for a better understanding of the exchange of greenhouse gases, especially between terrestrial ecosystems and the atmosphere. The most frequently used methods are usually based either on relations of fluxes to environmental drivers or on chamber measurements. However, they often depend strongly on assumptions or invasive measurements and do usually not offer partitioning estimates for latent heat fluxes into evaporation and transpiration. SCANLON and SAHU (2008) and SCANLON and KUSTAS (2010) proposed an promising method to estimate the contributions of transpiration and evaporation using measured high frequency time series of CO$_2$ and H$_2$O fluxes - no extra instrumentation necessary. This method (SK10 in the following) is based on the spatial separation and relative strength of sources and sinks of CO$_2$ and water vapor among the sub-canopy and canopy. Assuming that air from those sources and sinks is not yet perfectly mixed before reaching EC sensors, partitioning is estimated based on the separate application of the flux-variance similarity theory to the stomatal and non-stomatal components of the regarded fluxes, as well as on additional assumptions on stomatal water use efficiency (WUE).The CO$_2$ partitioning method after THOMAS et al. (2008) (TH08 in the following) also follows the argument that the dissimilarities of sources and sinks in and below a canopy affect the relation between H$_2$O and CO$_2$ fluctuations. Instead of involving assumptions on WUE, TH08 directly screens their scattergram for signals of joint respiration and evaporation events and applies a conditional sampling methodology. In spite of their different main targets (H$_2$O vs. CO$_2$), both methods can yield partitioning estimates on both fluxes. We therefore compare various sub-methods of SK10 and TH08 including own modifications (e.g., cluster analysis) to each other, to established source partitioning methods, and to chamber measurements at various agroecosystems. Further, profile measurements and a canopy-resolving Large Eddy Simulation model are used to test the assumptions involved in SK10. Scanlon, T.M., Kustas, W.P., 2010. Partitioning carbon dioxide and water vapor fluxes using correlation analysis. Agricultural and Forest Meteorology 150 (1), 89-99. Scanlon, T.M., Sahu, P., 2008. On the correlation structure of water vapor and carbon dioxide in the atmospheric surface layer: A basis for flux partitioning. Water Resources Research 44 (10), W10418, 15 pp. Thomas, C., Martin, J.G., Goeckede, M., Siqueira, M.B., Foken, T., Law, B.E., Loescher H.W., Katul, G., 2008. Estimating daytime subcanopy respiration from conditional sampling methods applied to multi-scalar high frequency turbulence time series. Agricultural and Forest Meteorology 148 (8-9), 1210-1229.

We present a portable elevator-based setup for measuring CO$_2$, water vapor, temperature and wind profiles from the soil surface to the surface layer above crop canopies. The end of a tube connected to a closed-path gas analyzer is continuously moved up and down over the profile height (currently 2 m), while concentrations are logged at a frequency of 20 Hz. Temperature and wind speed are measured at the same frequency by a ventilated finewire thermocouple and a hotwire, respectively, and all measurements are duplicated as a continuous fixed-height measurement at the top of the profile. Test measurements were carried out at the TERENO research site of Selhausen (50°52'09’’N, 06°27'01’’E, 104.5 m MSL, Germany, ICOS site DE-RuS) in winter wheat, winter barley and a catch crop mixture during different stages of crop development and different times of the day (spring 2015 to autumn 2016). We demonstrate a simple approach to correct for time lags, and the resulting half-hourly mean profiles of CO$_2$ and H$_2$O over height increments of 2.5 cm. These results clearly show the effects of soil respiration and photosynthetic carbon assimilation, varying both during the daily cycle and during the growing season.Post-harvest measurements over bare soil and short intercrop canopy (

Die terrestrische Biosphäre ist eine wichtige CO2-Senke [1]. Landwirtschaftliche Flächen als Teil der Biosphäre stehen unter besonders unmittelbarem Einfluss des Menschen. Nach derzeitiger Einschätzung sind sie im Mittel entweder CO2-neutral, so z.B. in [2] bei getrennter Betrachtung von nicht-CO2-Emissionen und Behandlung von Treibstoffeinsatz und Düngemittelproduktion in anderen Sektoren; oder durch Humusabbau Quellen [3, 4]. Zugleich wird bei angepasster Bewirtschaftung ein hohes Senkenpotential landwirtschaftlicher Flächen gesehen [2, 5].Der zunehmende Anbau von Zwischenfrüchten, unter anderem durch Förderung im Rahmen der EU-Agrarreform („Greening“), bietet eine Möglichkeit, diese Einschätzung zu überprüfen und zu spezifizieren. Anknüpfend an erste Ergebnisse aus dem Vorjahr stellen wir CO2-Messungen auf Ackerflächen mit und ohne Zwischenfruchtnutzung mit unterschiedlichen Methoden (Profile, Hauben, Eddy-Kovarianz) vor. Anhand mehrerer Messstandorte wird die Bilanz von Jahren bzw. Feldern mit Zwischenfruchtnutzung mit derjenigen von Jahren bzw. Feldern ohne Zwischenfruchtnutzung verglichen und die Mehraufnahme aufgrund des Zwischenfruchtanbaus quantifiziert. Die verschiedenen Messungen wurden unter anderem vom BMBF über die DLR im Rahmen der Projekte „ICOS“ und „IDAS-GHG“ gefördert.Literatur[1] IPCC 2013: 5th assessment report, WG I, chapter 6[2] IPCC 2014: 5th assessment report, WG III, chapter 11[3] Agriculture, Ecosystems and Environment 139, 2010: Special Issue „The carbon balance of European croplands“[4] Wiesmeier et al. (2016), Nature scientific reports 6:32525[5] 4p1000: http://4p1000.org/understand

Wie reagiert die Biosphäre auf den Globalen Wandel und die lokale Landbewirtschaftung, und wie wirkt sie sich wiederum auf den Klimawandel aus? Die Landoberfläche kann zum jetzigen Zeitpunkt ca. 33 % (±17 %) des Kohlenstoffdioxids (CO2) aus der Verbrennung fossiler Brennstoffe aufnehmen. Dem gegenüber steht allerdings eine zusätzliche CO2-Abgabe von 14 % (±10 %) aus Landnutzungsänderungen (IPCC 2013). Photosynthetische CO2-Aufnahme und respiratorische CO2-Abgabe werden unterschiedlich von Umweltfaktoren wie Temperatur, CO2-Konzentration, und Wasserverfügbarkeit beeinflusst. Diese Faktoren sind wiederum dem globalen Wandel unterworfen. Um diese Wechselwirkungen analysieren zu können, müssen Nettoflüsse von Treibhausgasen, wie sie beispielsweise mit der Eddy-Kovarianz-Methode gemessen werden können, in ihre Einzelbeiträge zerlegt werden. Derartige Versuche, den CO2-Fluss in Photosynthese und Respiration oder den latenten Wärmefluss in Evaporation und Transpiration aufzuschlüsseln, werden unter dem Begriff “Source Partitioning” zusammengefasst.Das BMBF-geförderte Forschungsprojekt IDAS-GHG (Instrumental and Data-driven Approaches to Source-Partitioning of Greenhouse Gas Fluxes: Comparison, Combination, Advancement) hat die Zielsetzung, existierende Ansätze zum Source-Partitioning von Treibhausgasflüssen systematisch miteinander zu vergleichen und zu verbessern. Diese lassen sich in zwei Gruppen gliedern: Datenbasierte Ansätze nutzen bestehende (Roh)daten aus der Eddy-Kovarianz-Messung. Instrumentelle Ansätze hingegen beinhalten die Durchführung zusätzlicher Messungen, wie z. B. Kammer- und Profilmessungen, oder die Verwendung von Tracern (z. B. stabile Isotope), die Auskunft über die Herkunft der Gasmoleküle geben können.In unserer Präsentation werden einige dieser Methoden am Beispiel des Messstandorts Selhausen beschrieben. Der Standort befindet sich im TERENO-Observatorium Eifel/Niederrheinische Bucht in der intensiv landwirtschaftlich genutzten niederrheinischen Bördelandschaft. Der Untersuchungszeitraum erstreckt sich über die Vegetationsperiode eines Winterweizenfeldes von der Aussaat im Oktober 2014 über die Ernte hinaus bis Ende September 2015. Im Messfeld installiert ist eine dauerhafte Eddy-Kovarianz-Station und ein automatisches Bodenrespirations-Kammersystem mit bis zu vier Langzeitkammern. Zusätzlich wurden stichprobenartig Profilmessungen der CO2- und H2O-Konzentrationen mit einem eigens gebauten Liftsystem durchgeführt.Mithilfe der gemessenen Eddy-Kovarianz-Daten zeigen wir einen Vergleich bestehender Ansätze zum Source-Partitioning des Netto-Ökosystem-Austauschs in Bruttoprimärproduktion (Photosynthese) und Ökosystematmung (Respiration). Unter Verwendung von Kammermessungen wird dieser um die Terme Nettoprimärproduktion und Bodenrespiration erweitert.Das Profilsystem misst Änderungen der Konzentration von CO2 und H2O mit einer hohen vertikalen und zeitlichen Auflösung zwischen Bodenoberfläche, Pflanzenbestand und Atmosphäre. Die Profile im Halbstundenmittel bilden den Effekt der photosynthetischen Kohlenstoff-Assimilation und Bodenatmung deutlich ab und geben somit qualitative Informationen über Quell- und Senkbereiche. Im nächsten Schritt wird versucht, diese zu quantifizieren und mit den bereits beschriebenen Ansätzen zu vergleichen.

We present an elevator-based facility for measuring CO₂ and water vapour concentration profiles between the soil surface and the roughness sublayer above crops and similar plant canopies. The end of a tube connected to a closed-path gas analyser is continuously moving up and down over the profile height (in our case, 2 m) while concentrations are logged at a frequency of 20 sˉ¹, collecting approximately 50 profiles during 30 minutes. Using campaign measurements in winter wheat during different stages of crop development and different times of the day, we demonstrate a simple approach to correct for time lags, and the resulting profiles of half-hourly mean concentrations and turbulent variances over height increments of 2.5 cm. During conditions favouring photosynthesis, a clear local minimum of CO₂ concentration in the canopy can be found. With more moderate effort and success, we also added measurements of temperature (based on a finewire thermocouple) and wind speed (based on hotwire anemometry). Post-harvest measurements over bare soil were analysed in the framework of Monin-Obukhov similarity theory to check the validity of the measurement and raw data processing approach, to derive CO₂ and latent heat fluxes, and to compare them to eddy-covariance and chamber measurements. We also tentatively apply an approach to derive source partitioning information for net fluxes of CO₂ (soil respiration vs. aboveground net primary production) and H₂O (evaporation vs. transpiration) from profiles measured across the green crop canopy, discuss its limitations and needed improvements.

Auf dem Poster werden Ziele und erste Ergebnisse des kürzlich gestarteten BMBF-Projekts „IDAS-GHG“ vorgestellt, dessen Gegenstand in-situ-Messungen des Austauschs klimarelevanter Spurengase (CO2, H2O, N2O) über unterschiedlich (z.B. landwirtschaftlich) genutzten Vegetationsflächen sind.Insbesondere während der ersten Projektjahre stehen methodische Fragen zum sogenannten „Source Partitioning“ (Quellenzuordnung oder Komponentenentmischung) im Vordergrund. Damit werden verschiedene bestehende und in Entwicklung befindliche Methoden bezeichnet, Messungen des Netto-Austauschs zwischen Biosphäre und Atmosphäre (z.B. mit der Eddy-Kovarianz-Methode) hinsichtlich der beteiligten Quellen- und Senken aufzuschlüsseln, etwa Respiration und Photosynthese bzw. Evaporation und Transpiration.Sollen Messungen zur Parametrisierung des Verhaltens von Pflanzenbeständen und Böden in gekoppelten Klimamodellen genutzt werden, so kann eine erfolgreiche Quellenzuordnung in den Messdaten die Unsicherheit bei der Ermittlung der Modellparameter verringern. Auch direkt aus Messungen gewonnen Aussagen zum Mitigationspotential von Landnutzungsstrategien können besser erklärt, auf Plausibilität überprüft und auf ähnliche Fälle übertragen werden, wenn beispielsweise bekannt ist, aus welcher der möglichen Kombinationen von (Boden-)Respiration und (Netto-)Primärproduktion ein bestimmter gemessener Netto-CO2-Fluss resultiert. Derartige Bewertungsmöglichkeiten sollen im weiteren Verlauf des Projekts an Beispielen wie Gründüngung in der Landwirtschaft, Waldumbau und Dachbegrünung getestet werden.Unter den untersuchten, zu vergleichenden und weiterzuentwickelnden Methoden der Quellenzuordnung befinden sich sowohl solche, die auf bereits vorhandene Messdaten bestehender Eddy-Kovarianz-Standorte angewendet werden können, als auch Zusatzmessungen. Als Beispiel für letztere wird auf erste Ergebnisse vertikal hochauflösender Profilmessungen in niedrigen Pflanzenbeständen wie Grünland oder Weizen eingegangen.

How does the biosphere react on global change and local land use management? The land surface currently acts as a sink for anthropogenic emissions from fossil fuels, but an additional CO2 release is caused by land use change. The sensitivities of photosynthetic CO2 uptake and respiratory CO2 release to environmental parameters remain uncertain. One possible way to disentangle the flux of greenhouse gases is source partitioning, e.g. into photosynthesis and respiration (CO2) or into evaporation and transpiration (H2O).The BMBF-funded project IDAS-GHG (Instrumental and Data-driven Approaches to Source-Partitioning of Greenhouse Gas Fluxes: Comparison, Combination, Advancement) aims at comparing and improving existing methods for partitioning of CO2 and H2O fluxes into their respective raw components. Data-driven approaches use existing (raw or processed) data of typical eddy-covariance stations. Instrumental approaches of source partitioning require additional measurements at different parts of ecosystems and different methods, e.g. soil-flux chamber measurements, profile measurements or tracer measurements (isotopes).We present preliminary results of a profile measurement system involving a small elevator continuously moving up and down. It measures changes in the concentration of CO2 and H2O at a high vertical and temporal resolution between the soil surface, the plant canopy and the atmosphere. Tests were carried out at the TERENO research site of Selhausen (Lower Rhine Embayment in the river Rur catchment (50°52'09’’N, 06°27'01’’E, 104.5 m MSL, Germany) on a winter wheat field for a growing season from seeding to harvest (April - August 2015).The half hourly mean profiles of CO2 and H2O show the effects of soil respiration and photosynthetic carbon assimilation very clearly, varying both during the daily cycle and during the growing season.An additional way to partition CO2 and H2O fluxes is through measurements of concentration profiles of their stable isotopologues (13CO2, 12C18O16O, 1H2H16O, and 1H218O). Following controlled-conditions experiments in the laboratory on soil columns in autumn and winter 2015, a quantum-cascade dual isotope laser will be deployed at the Selhausen test site in a low-flow (i.e., soil atmosphere and chamber measurements) and high flow (i.e., Eddy-Covariance measurements) configurations for comparison with the above-mentioned profile measurement system.

Data processing methods; Energy balance closure; Intra-annual temporal dynamics of ET; Tables S1-S2; Figures S1-S2

Data processing methods; Energy balance closure; Intra-annual temporal dynamics of ET; Tables S1-S2; Figures S1-S2

Philosophical Transactions of the Royal Society B: Biological Sciences, 375 (1810), ISSN:0962-8436, ISSN:1471-2970, ISSN:0080-4622

Climate change increases the occurrence and severity of droughts due to increasing temperatures, altered circulation patterns, and reduced snow occurrence. While Europe has suffered from drought events in the last decade unlike ever seen since the beginning of weather recordings, harmonized long-term datasets across the continent are needed to monitor change and support predictions. Here we present soil moisture data from 66 cosmic-ray neutron sensors (CRNSs) in Europe (COSMOS-Europe for short) covering recent drought events. The CRNS sites are distributed across Europe and cover all major land use types and climate zones in Europe. The raw neutron count data from the CRNS stations were provided by 24 research institutions and processed using state-of-the-art methods. The harmonized processing included correction of the raw neutron counts and a harmonized methodology for the conversion into soil moisture based on available in situ information. In addition, the uncertainty estimate is provided with the dataset, information that is particularly useful for remote sensing and modeling applications. This paper presents the current spatiotemporal coverage of CRNS stations in Europe and describes the protocols for data processing from raw measurements to consistent soil moisture products. The data of the presented COSMOS-Europe network open up a manifold of potential applications for environmental research, such as remote sensing data validation, trend analysis, or model assimilation The dataset could be of particular importance for the analysis of extreme climatic events at the continental scale. Due its timely relevance in the scope of climate change in the recent years, we demonstrate this potential application with a brief analysis on the spatiotemporal soil moisture variability. The dataset, entitled "Dataset of COSMOS-Europe: A European network of Cosmic-Ray Neutron Soil Moisture Sensors", is shared via Forschungszentrum Julich: https://doi.org/10.34731/x9s3-kr48 (Bogena and Ney, 2021)., Earth System Science Data, 14 (3), ISSN:1866-3516, ISSN:1866-3508