By continuously monitoring greenhouse gas emissions from densely populated urban areas, we can independently assess and monitor emission reduction efforts at a policy-relevant scale. The EU-funded project PAUL (Pilot Application in Urban Landscapes - Towards integrated city observatories for greenhouse gases) develops, evaluates, and refines innovative greenhouse gas monitoring technologies including observational strategies for urban areas that enhance the capabilities of the Integrated Carbon Observation System at urban scales (ICOS Cities). In 2022, three pilot observatories have been set up to test, refine and optimize approaches for monitoring emissions from a metropolitan area (Paris, France), a large isolated city (Munich, Germany) and a mid-size city (Zurich, Switzerland). The three observatories have been developed in a co-design approach and integrated different observational technologies in support of inverse and inventory modelling. The pilot observatories focus on carbon dioxide (CO₂) emitted from fossil-fuel sources.

The three observatories operate for a pilot phase of two years and collect comparative data across cities with a multitude of instrument networks that serve three main goals: (1) to assess the input for inverse models of CO₂ at city-scale and attribute inferred CO₂ emissions to sub-city scale and emission sectors; (2) to refine spatial, temporal, and sectoral attribution of emissions in emission inventories and parametrize process models that separate urban fossil-fuel and biogenic fluxes; and (3) as independent validation datasets to evaluate estimated emission products.

In all three cities, CO₂ concentrations and selected co-emitted species are continuously sampled on tall towers, on top of high buildings and/or at street level. In the Paris metropolitan area, 10 tall tower sites and 30 roof-top sites continuously measure high-precision CO₂ and co-emitted species in the boundary layer upwind, over and downwind of the city. The Munich and Zurich observatories feature a combination of roof-top and street-level sensor networks placed closer to sources and sinks, with a stronger signal strength that is more forgiving in terms of the sensitivity, hence allowing the deployment of mid- and low-cost sensors. In Paris and Munich, additionally, total column observations of CO₂ are performed upwind, over and downwind of the main urban emission sources using concurrent ground-based FTIR spectrometers. Three new tall-tower eddy-covariance (EC) systems have been established in central Paris, Munich and Zurich. The EC-towers provide total CO₂ fluxes for defined sub-areas of each city and their characteristic diurnal, weekly and seasonal cycles. Further, the three EC-towers provide sector-specific emission ratios and fossil-fuel CO₂ fluxes based on differences of measured CO₂-fluxes, six co-emitted species and radiocarbon fluxes. Finally, all cities have observational systems in place that monitor biogenic fluxes, vegetation dynamics and meteorological conditions, including lidars for wind and mixed layer determination for an improved quantitative description of atmospheric transport and vertical mixing.

We highlight design considerations for the three observatories and exemplarily show how multi-scale systems can efficiently complement and constrain fossil-fuel emissions in urban areas. Knowledge and experience from these observations will feed into the establishment of guidelines for operational greenhouse gas monitoring systems in European cities on their way to climate neutrality.

How to cite: Christen, A., Emmenegger, L., Hammer, S., Kutsch, W., D’Onofrio, C., Chen, J., Eritt, M., Haeffelin, M., Järvi, L., Kljun, N., Lauvaux, T., Loubet, B., Mauder, M., Mensah, A. A., Papale, D., Rivier, L., Stagakis, S., and Vermeulen, A. and the ICOS Cities Team: ICOS pilot observatories to monitor greenhouse gas emissions from three different-size European cities, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9884, https://doi.org/10.5194/egusphere-egu23-9884, 2023.

As cities are taking actions to reduce and offset part of their anthropogenic carbon dioxide (CO₂) emissions, urban vegetation has become vitally important in pursuing carbon neutrality and climate mitigation. Its effectiveness in carbon sequestration, however, has large uncertainties due to the complex urban environment comprising both natural and artificial elements. By considering seven interacting land surface covers (buildings, pavement, evergreen trees, deciduous trees, grass, soil and water) within each model grid, the Surface Urban Energy and Water balance Scheme (SUEWS) is an urban land surface model that can simulate energy, water and CO₂ exchanges in cities. For SUEWS to simulate the CO₂ fluxes in urban green spaces, it requires information of maximum photosynthesis and surface conductance of specific urban vegetation as well as the response of surface conductance to environmental conditions. To derive these parameters, it is necessary to utilize on-site measurements conducted over urban green spaces for an accurate description of the surface processes and variables.

To our knowledge, only the mixed vegetation type and street trees in Helsinki have been parameterized in SUEWS so far. In order to extend the flexibility and usability of SUEWS modelling across different cities and for specific urban vegetation, this research aims to (1) derive surface conductance and photosynthesis parameters from eddy covariance and chamber measurements conducted over several urban sites corresponding to different urban vegetation types, such as non-irrigated lawn, turf grass, park trees, urban fields, green roof and urban forests (evergreen and mixed-leaf); and (2) evaluate the impact of selected surface conductance and photosynthesis parameters on SUEWS model performance in two mid-latitude cities: Swindon, UK and Minneapolis-Saint Paul, USA.

The surface conductance and photosynthesis parameters for specific urban vegetation are derived by fitting measurements to an empirical canopy-level photosynthesis model where the effect of the local conditions (i.e. meteorology and ecology) is considered. Using the bootstrapping method to randomly select seven-eighths of the available measurements for 100 times, the fitted maximum photosynthesis rates range from 5.27 μmol m-2 s-1 over an non-irrigated lawn to 10.72 μmol m-2 s-1 over an evergreen forest with the dependencies on the local environmental response functions such as air temperature, incoming shortwave radiation, specific humidity deficit and soil moisture deficit. As a following step, the choice of model parameters in SUEWS simulations will be examined in the two cities along with on-site measurements. 

This research improves SUEWS simulations over urban areas by deriving new surface conductance and photosynthesis parameters specific to different urban vegetation types and provides a more accurate quantification of their biogenic CO₂ flux in a complex urban environment. The results also provide a better understanding on the carbon sequestration potential of urban vegetation, which will be useful in planning urban green spaces to maximize natural carbon sinks and in setting climate mitigation strategies.

How to cite: Lee, H. S., Havu, M., Karvonen, A., Ahongshangbam, J., Soininen, J., Ward, H. C., McFadden, J. P., Lohila, A., Weber, S., and Järvi, L.: Parameterizing surface conductance of different urban vegetation types for the urban land surface model SUEWS with evaluation in two mid-latitude cities, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10032, https://doi.org/10.5194/egusphere-egu23-10032, 2023.

Understanding how cities impact the atmospheric boundary layer is crucial for many processes such as air-pollution dispersion and concentrations, and is therefore important as part of weather and climate modelling. To improve modelling of those dynamic processes observation are critical as they inform development and evaluation of models, and enhance delivery of services to citizens and the management of urban infrastructure, which is vulnerable to different strengths of heat and pollutant exposure.

During a year-long field campaign from Autumn 2021 to Autumn 2022 a comprehensive set of ground-based remote sensing observations were gathered in Berlin, Germany. These allow us to explore the impact of a large city on the regional atmospheric boundary layer. The campaign, undertaken within the European Research Council funded urbisphere project, involved a grid-like network of instruments in the densely built-up city centre, with ground-based remote sensing (e.g. automatic lidars and ceilometers ALC, Doppler-wind lidars) for mixed/mixing layer height (MLH) detection. Additional instruments were located along two perpendicular rural-urban-rural transects, with existing instruments in the city and surrounding region complementing the network. During Intensive Observation Periods (IOP) in spring and summer 2022 radiosonde releases within and outside the city during selected days allow air temperature, humidity and wind-distribution profiles in the atmospheric boundary layer to be investigated.

This contribution showcases how an urban environment modifies the dynamics and convective cloud properties under varying regional-scale weather conditions. We focus on case studies for different synoptic conditions to show the extent of impact of a large city on the MLH within and beyond the urban area, including urban-rural contrasts, upwind-downwind effects, and intra-urban variability of MLH.

How to cite: Fenner, D., Christen, A., Chrysoulakis, N., Grimmond, S., Van Hove, M., Kotthaus, S., Meier, F., Morrison, W., and Zeeman, M.: Impact of a large isolated city on the mixed layer height during different weather conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11585, https://doi.org/10.5194/egusphere-egu23-11585, 2023.

In this study, geostationary satellite observations are used to develop and validate two high-resolution cloud-masking approaches for the region of Paris to show and improve applicability for analyses of urban effects on clouds. 

Firstly, the Local Empirical Cloud Detection Approach (LECDA) uses an optimised threshold to separate the distribution of visible reflectances into cloudy and clear sky for each individual pixel accounting for its locally specific brightness. Secondly, the Regional Empirical Cloud Detection Approach (RECDA) uses visible reflectance thresholds that are independent of surface reflection at the observed location.

Results show that

• A decrease of cloud cover during typical fog or low-stratus conditions over the urban area of Paris for the month of November is likely a result of urban effects on cloud dissipation.
• The regional approach, RECDA, is a more appropriate choice for the high-resolution satellite-based analysis of cloud cover modifications over different surface types than LECDA with regional biases of ±5 %.

This approach can provide comprehensive insights into spatiotemporal patterns of land-surface-driven modification of cloud occurrence and locally induced cloud processes, such as the diurnal variation of the occurrence of fog holes and cloud enhancements attributed to the impact of the urban heat island. Further, it is potentially transferable to other regions and temporal scales for analysing long-term natural and anthropogenic impacts of land cover changes on clouds.

How to cite: Fuchs, J., Andersen, H., Cermak, J., Pauli, E., and Roebeling, R.: High-resolution satellite-based cloud detection for the analysis of land surface effects on boundary layer clouds, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6854, https://doi.org/10.5194/egusphere-egu23-6854, 2023.

The near-surface humidity is a crucial variable in many atmospheric processes, mostly in those related to development of clouds and rain. The humidity at the height of a few tens of meters above surface is highly influenced by the surface characteristics. In many cases the land-cover (LC) is responsible for the spatial variation of the surface humidity field, therefore, it is a major factor in determining the conditions for rainfall. Cities are one of the primary LCs which have a substantial impact on the humidity field. Large urban areas are expanding, causing a significant change in the near-surface humidity field. Measuring the near-surface humidity in high resolution, where most of the humidity’s sinks and sources are, is challenging with the common tools available today. Current measurement tools do not satisfactorily assess the cities’ effects on the humidity field. A new approach for measuring the humidity, based on the cellular network, provides high resolution information on the near-surface humidity. Therefore, we can examine the land-cover effect on the humidity in the low atmosphere in fine scale. In this study, the humidity field around Tel Aviv was retrieved from the cellular network during the summer of 2017. The results show a well-noticed impact of the city and other LC types on the humidity field over the Tel Aviv metropolitan area. The method presented here can offer an improved description of the humidity field at the city-canopy level and therefore provide a better assessment of the urban/LC effects on the environment, atmospheric modeling, and particularly on clouds/rain development.

How to cite: Rubin, Y., Sohn, S., and Alpert, P.: Urban moisture based on commercial microwave links (CML) data and relation to land-cover – case of Tel- Aviv metropolitan area, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4355, https://doi.org/10.5194/egusphere-egu23-4355, 2023.

Kolkata, one of the oldest and largest urban centres in Asia echoes all the major characteristics of cities from developing countries experiencing rapid urbanization and unplanned development. This study focuses on understanding the impact of intra-urban variations within a morphologically complex metropolis and its capability to modify the enveloping atmospheric conditions at the meso to micro-scale. The Weather Research and Forecasting (WRF) model was configured using a 3-tier nested domain to conduct high-resolution simulations incorporating improved land surface and urban parameterization and appropriate physical parameterization. Local Climate Zone (LCZ) map representing the land use land cover (LULC) was prepared for the innermost domain covering the city and surroundings using Planet-Scope datasets for 2019, adopting Artificial Neural Network (ANN) approach and validated using ground information. This was then integrated into the model with redefined values of specific urban parameters for a better representation of the city’s morphology. It was observed that LCZ-2 (Compact Mid-rise) and LCZ-3 (Compact Low-rise) cover almost the entire core city and around 70 % of the total built-up extent of the study area, which also consists of LCZ-5 (Open Mid-Rise) and LCZ-6 (Open Low-Rise) regions. Thus, the model was calibrated according to the surface and atmospheric conditions of the region and its performance was evaluated in comparison with ground observations. Simulations were conducted at hourly intervals for a 10-day period (August 2019) during the peak summers coinciding with the south-west monsoon period receiving heavy rain spells, to analyse the impact of heterogenous urban form on the micro-climatic variations within the city as well as its surroundings. The modelled results obtained for 2m air temperature (T_air), surface temperature (T_skin), 10m Wind Speed (WS) and Rainfall (RF) indicated a significant influence of the different LCZ classes and their spatial variations over the city. The average daytime T_air and T_skin values in the LCZ-2 is about 1℃ and 1.5℃ higher than LCZ-3, which is again 0.7℃ and 1.5℃ higher compared to the other urban LULC classes where the internal variation is relatively less. Further, the average temperature differences between the compact and open built-up structures increase significantly during night (2℃ – 3.5℃), further increasing when compared to the peri-urban (around 5℃). The inter-urban heterogeneity however, has a reverse effect on the average WS even during the typical monsoon period, with lowest speed observed in the compact core (2ms^-1 – 5ms^-1) due to highest surface drag (d), increasing (3ms^-1 – 7ms^-1) along LCZ-5 and LCZ-6 with reduction in d; which further increases substantially in the peri-urban areas (10ms^-1 – 15ms^-1) with lowest value of d. The variations in total RF received from the complex towards peripheral urban also depicts a similar pattern, as average RF intensity is the lowest within LCZ-2 and LCZ-3 (7mm/hr – 15 mm/hr), moderate in LCZ-5 and LCZ-6 (10mm/hr – 20mm/hr) and highest along the peri-urban areas (15mm/hr – 35 mm/hr). Thus, urban structural and morphological complexity can have a substantial effect on the local-scale climatic variations even along small horizontal distances within a city.

How to cite: Bhattacharjee, S. and Bharti, R.: Intra-urban morphological heterogeneity and its impact on the micro-climatic variations in the Kolkata Metropolitan region of India, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16058, https://doi.org/10.5194/egusphere-egu23-16058, 2023.

Understanding the role of surface heterogeneity of surface fluxes in the development of convection is a critical topic in land-atmosphere interactions. This is especially relevant in the context of Earth System Models (ESMs), where simulated sub-grid surface heterogeneity over the land surface is mostly ignored by the overlying modeled atmosphere. Indeed, previous studies using Large Eddy Simulation (LES) have shown that heterogeneities in the surface field below ESM spatial resolution (~100 km) can cause appreciable secondary circulations and, at times, a significant increase in convective cloud development. These large scale changes initiated by small scale heterogeneity have yet to be adequately parameterized in ESMs. To address this particular weakness, this presentation presents a parameterization scheme for a near surface density driven circulation between two lower atmosphere columns with variable surface heating for use within ESMs.

The secondary circulation parameterization is fit to data from 184 LES runs over 92 days, one run each day with a homogeneous surface and one run each day with a heterogeneous surface derived from land surface model output, over a 100 km square domain centered around the ARM site in the US Southern Great Plains (SGP) in Oklahoma. It is then tested over those 92 simulation days at the SGP site, as well as shallow convective days over four heterogeneous sites where differential heating is common: Wisconsin (lake-land), Florida (ocean-land), Missouri (urban-rural) and Appalachia (elevation). 

To test the circulation scheme, we use standalone columns of Cloud Layers Unified by Binormals (CLUBB) a boundary layer, cloud and shallow convection scheme used in multiple modern ESMs. CLUBB is run for three cases on each simulation day at each site: 1) as a single homogeneous column model over the domain, 2) as two separate columns over high and low sensible heat portions of the domain, and 3) following 2) with the addition of the circulation parameterization scheme. The homogeneous CLUBB simulations and those with secondary circulations are compared to evaluate the impact of the secondary circulation on cloud development, turbulent kinetic energy, and profiles of the means and variances of heat and moisture. Results over the SGP site show that the parameterized circulation yields similar changes in cloud development and profiles of heat and moisture to LES.

How to cite: Waterman, T., Bragg, A., Hay-Chapman, F., Dirmeyer, P., Fowler, M., and Chaney, N.: Parameterizing the Large Scale Impact of Land Surface Heterogeneity Induced Circulations on Convective Cloud Development, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10938, https://doi.org/10.5194/egusphere-egu23-10938, 2023.

Land-atmosphere energy and moisture exchange can strongly influence local and regional climate changes. However, high uncertainties exist in the representation of land-atmosphere interactions in numerical models and the coupling strength between land and atmosphere is largely overestimated, in which the determination of surface exchange coefficient is one of the main problems. Here, we show the improvements from a dynamic vegetation-type-dependent exchange scheme in the offline Noah land surface model with multi-parameterization options and the Weather Research and Forecasting model when applied to China. Compared to the default schemes, the dynamic exchange scheme significantly reduces land-atmosphere coupling strength overestimations, and comparisons to flux tower observations reveal its capability to better match observed surface energy and water variations. In particular, the above remarkable improvements produced by the dynamic exchange scheme primarily occur in areas covered with short vegetation. The improved version benefits from the treatment of the roughness length for heat. Further, land-surface processes play significant roles in cloud formation and precipitation generation by affecting local planetary boundary layer profiles. The dynamical exchange scheme could narrow the positive discrepancies in the simulated precipitation. Using 3-km-resolution convection-permitting models for three heavy precipitation cases, the dynamic coupling simulations could achieve the closest agreement with the field observations, especially the intensity and location of the heaviest rainfall during the precipitation process. Overall, our findings highlight the applicability of the dynamic scheme as a better physical alternative to the current treatment of surface exchange processes in atmosphere coupling models and could help achieve more accurate simulations.

How to cite: Zhang, X., Chen, L., and Ma, Z.: Improvement of surface exchange coefficient parameterization and its application to regional numerical simulation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3423, https://doi.org/10.5194/egusphere-egu23-3423, 2023.

Irrigation is still widely neglected in land surface models which are used for numerical weather prediction. However, with the general improvement of coupled surface-atmosphere models and the evolution towards kilometer or hectometer grids, this omission is beginning to be reconsidered. Better understanding the links between the strong surface heterogeneity and local meteorology is one of the objectives of the LIAISE (Land surface Interactions with the Atmosphere In Semi-Arid Environment) project. The work presented here focuses on two clear and warm days of the special observation period of the LIAISE campaign that took place during the summer of 2021 in northeastern Spain. The coupled surface-atmosphere model Surfex-MesoNH is used to model two days of interest with and without an irrigation parameterization. The model outputs are then compared to multiple surface-based and airborne observational data. A clear improvement is provided by the irrigation representation. In particular, the modeled sensible and latent heat fluxes are reconciled with the observations, the temperature biases at 2m are corrected up to 5°C, and the specific humidity is increased by about 50% around noon near the surface. It is also shown that irrigation leads to changes in the structure and height of the atmospheric boundary layer. A breeze-like, non-classical mesoscale circulation induced by the surface contrasts between the irrigated area and the surrounding semi-arid area is highlighted.

How to cite: Lunel, T., Boone, A., and Le Moigne, P.: Influence of irrigation on land-surface interactions and the atmospheric boundary layer in a semi-arid region – Results from the LIAISE campaign, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2253, https://doi.org/10.5194/egusphere-egu23-2253, 2023.

Turbulence is essential for land atmosphere interactions; however, it is difficult to quantify because of its statistical nature. Typically, turbulence is determined using time series data, on which Taylor’s hypothesis is applied to obtain turbulent data over a length scale. Taylor’s frozen turbulence hypothesis is an assumption in the core of turbulence research, however currently turbulence measurements are limited to either time series (e.g., sonic anemometers) or integrated spatial measurements (e.g., scintillometers). Therefore, the spatiotemporal nature of turbulence cannot be independently assessed. In this study we use fiber-optic distributed sensing (FODS) to measure turbulence over both time and space.

The turbulence parameter used is the structure parameter of temperature, C_T², which quantifies the intensity of temperature fluctuations over a certain scale. The structure parameter can be determined using temperature series directly, using its definition. Alternatively, the inertial range of the turbulent temperature spectrum can be used to obtain structure parameter through the Kolmogorov -5/3 power law.

A FODS experiment was conducted in the LIAISE (Land surface Interactions with the Atmosphere over the Iberian Semi-arid Environment) field campaign during 15-30 July 2021 in the north-east of Spain. A set-up was installed with a horizontal extent of 70 m, measuring at four heights between 0.40 m and 2.05 m. A thin 0.5 mm cable was used in an effort to obtain the fastest possible time response. Measurements were made at 1 Hz and 12.7 cm resolution, however the actual sampling frequency appeared to be 0.15 Hz in the temperature spectrum, likely because of the long response time of the cable.               

Despite the limited 0.15 Hz sampling rate it was possible to obtain turbulence information through the use of the structure parameter of temperature. This parameter indicates the intensity of temperature fluctuations and was calculated over time, as is conventional. In a novel approach, it was also calculated over space. The spatial structure parameter obtained through the definition method was found to have the best correlation with a sonic anemometer reference, with a correlation coefficient of 0.88.

The temporal structure parameter lacks the structure that is shown in the spatial method, which is likely due to the use of 30-min averaged data for horizontal wind speed from the sonic anemometer or to Taylor's frozen turbulence hypothesis not being a suitable assumption within the dimensions of this research. Determining structure parameters through the turbulent spectrum was successful for limited data points for the time seriess and is currently inconclusive for the spatial series. This work provides a first step towards using FODS in capturing turbulent information along spatial temperature series.

How to cite: Vis, G., Hartogensis, O., ten Veldhuis, M.-C., and Coenders, M.: Can fiber-optic distributed sensing be used to resolve temperature turbulence values over time and space?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15992, https://doi.org/10.5194/egusphere-egu23-15992, 2023.

Representing the diurnal variability of state meteorological variables, including carbon dioxide, is still an open challenge as shown by the large discrepancies with observations and weather and climate models. These discrepancies translate into different diurnal exchanges of heat, water and carbon dioxide between the canopy and atmosphere. These sub-diurnal differences can propagate to larger temporal and spatial scales.

With a systematic approach, we investigate the diurnal gas exchange of both water and carbon dioxide for an irrigated crop. Our investigation is based on a comprehensive observational dataset that ranges from scales covering from the leaf level to the canopy level  to the atmospheric boundary layer gathered at the LIAISE campaign. This campaign took place over two weeks in summer of 2021 in a region of the Ebro basin located in Catalonia, Spain. We focus specially on one of the “supersites” of the campaign: La Cendrosa, which is an irrigated alfalfa field surrounded by a very dry region.

Our observational approach is bottom-up in which we first analyze the leaf, second the canopy and third the interactions with the atmosphere at a local field scale. Among the observations, we analyzed leaf gas exchange measurements, turbulent surface fluxes and vertical profiles of driving environmental variables such as radiation, wind, temperature, and specific humidity. To support the observational analysis, we use a land-atmospheric interactive model (CLASS model). This model allows the representation at each of the three levels mentioned: (1) leaf, (2) canopy and (3) field.

Our observations show an asymmetry in the diurnal variability of the stomatal conductance, which indicates a larger opening of the stomata during the morning than during the afternoon. To attribute processes to the causality in the stomatal opening, we derive new expressions of the tendency of the stomatal aperture as a function of the mean meteorological drivers including radiation, temperature, atmospheric CO₂ concentration, and water vapor deficit. The asymmetry is only simulated by models once specific characteristics of the crop are considered. It is also observed that dynamics at the leaf level such as a closure of the stomata during the midday can cause a dip in the evapotranspiration and enhance the sensible heat flux. Our results open the debate on the circumstances under which it is important to constrain the leaf gas exchange.

How to cite: González Armas, R., Vilà-Guerau de Arellano, J., de Boer, H., Hartogensis, O., Mangan, M. R., and Gibert, F.: On the impact of leaf-level processes on the water and carbon canopy-turbulent fluxes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10397, https://doi.org/10.5194/egusphere-egu23-10397, 2023.

Isoprene and monoterpene emissions from the terrestrial biosphere play a significant role in major atmospheric processes. Such emissions account for 90% of the total volatile organic compound (VOC) emissions and exert a significant influence on the atmosphere's oxidation capacity, aerosol formation and in turn, clouds and climate. Emissions depend on the vegetation response to atmospheric conditions (primarily temperature and light), as well as other stresses e.g. from droughts and herbivory. The El Niño-Southern Oscillation (ENSO) is a natural cycle, arising from sea surface temperature (SST) anomalies in the tropical Pacific, which perturbs the natural seasonality of weather systems on both global and regional scales. Several studies evaluated the sensitivity of BVOC fluxes during ENSO events using transient simulations. While these studies employ realistic scenarios, it is difficult to assess the individual impact of ENSO given multiple forcing on the climate system (e.g. from CO₂, aerosol, etc.). In this work, simulations from a global atmospheric chemistry-climate model with enabled interactive vegetation are used to assess changes in vegetation (net primary production (NPP) and leaf area index (LAI)), meteorology (surface temperature, surface radiation, and precipitation), and consequently, isoprene and monoterpene emission changes attributed to ENSO. Global isoprene emissions could increase by 4% during strong El Niño events with substantial regional changes e.g. + 20% over Amazonia. Changes in isoprene and monoterpene emissions are evaluated in response to meteorological and vegetational variability.

How to cite: Vella, R., Pozzer, A., Lelieveld, J., Forrest, M., and Tost, H.: Isoprene and monoterpene emission response to the El Niño-Southern Oscillation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1565, https://doi.org/10.5194/egusphere-egu23-1565, 2023.

Biogenic volatile organic compounds (BVOCs) are emitted into the atmosphere by plants and other living organisms and play a significant role in various plant functions, such as growth, reproduction, and defense. BVOCs are also an essential part of many chemical reactions in the atmosphere and contribute to the formation of ozone and secondary organic aerosols and affect the radiation balance.

Investigating the atmospheric vertical profile concentrations of BVOCs has become an important focus for understanding these processes. There are various methods that can be used to study the atmospheric vertical profile, including towers, balloons, aircraft, and unmanned aerial vehicles (UAVs). Among these methods, UAVs offer greater flexibility for local air sampling by hovering over a target area and can reach altitudes of up to 1000m, making them ideal for permanent BVOCs monitoring that requires repeated measurements in a specific spatial and temporal domain. However, the source contribution area of the obtained BVOCs concentrations is often not identified, potentially leading to inaccurate conclusions about the exchange between the surface, vegetation, and atmosphere above the target area.

In this study, the vertical profile of BVOCs concentrations was obtained at SMEAR Estonia (Station for Measuring Ecosystem Atmosphere Relations) to analyze the composition and distribution of these compounds in the near-surface layer. The vertical samples were collected in 2020-2021 using a commercially available pump equipped with cartridges filled with adsorbents and mounted on a UAV. The UAV was used to collect samples from heights between 0 m and 90 m.

To address the issue of space-time representativeness related to the source signal, a footprint analysis was conducted. Micrometeorological data for four target areas were obtained from three SMEAR Estonia flux towers. The Flux Footprint Prediction model (Kljun et al., 2015) was used for the footprint calculation. We determined temporal and spatial changes in roughness length (z0) and zero-displacement height (zd) for each day when BVOCs measurements were carried out using meteorological and geospatial data on land cover types and corresponding canopy heights. Due to the presence of surface heterogeneity, z0 and zd varied significantly for each wind sector. Therefore, we ran the spin-up of the FFP model with updated input parameters at each step. For the measurement results interpretation, we also evaluated the representativeness of the obtained footprints over the target areas in the space-time domain and analysed the land cover composition and vegetation characteristics.

In this work, we show how the source contribution area of BVOCs concentrations can vary in size and shape depending on atmospheric conditions, and spatial and temporal variation and thus have an effect on the obtained species composition of BVOCs.  Based on the presented findings we discuss the potential implementation of this approach for similar research and its future development.

How to cite: Krasnov, D., Zolotarjova, V., Krasnova, A., Kask, K., Niinemets, Ü., and Noe, S.: An implementation of the advanced footprint analysis for UAV-based BVOC measurements, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11370, https://doi.org/10.5194/egusphere-egu23-11370, 2023.

Methane (CH₄) is a strong greenhouse gas that is produced in anoxic soil conditions. Wetlands are the largest natural source of CH₄ globally because their anoxic soils provide suitable habitats for CH₄-producing Archaea. Both global and regional wetland CH₄ budgets remain unconstrained due to large uncertainties in wetland extent and high spatio-temporal variability in CH₄ dynamics that are in part driven by wetland spatial heterogeneity. High wetland spatial heterogeneity often results from the variability in microtopography, soil hydrological and chemical properties, and vegetation and microbial composition. Intertwined together, the different abiotic and biotic variables further contribute to the ratio between CH₄ production, consumption and transport processes in wetland soil, resulting in either net CH₄ emission or uptake. However, the contribution of different abiotic and biotic factors to CH₄ flux variability in wetlands remains unclear, increasing uncertainties in up-scaling CH₄ emissions from plot to ecosystem and regional scales. Therefore, including well-defined spatial heterogeneity into wetland CH₄ bottom-up estimates can help improve the regional and global CH₄ budget calculations.

This study investigates the effect of spatial heterogeneity on observed CH₄ emissions in ten different wetland sites with varying climatic conditions. Our approach will include up-scaling chamber measurements from different land cover classes to the level of the eddy covariance (EC) footprint. The compiled chamber datasets include both manual (n=5) and automatic (n=5) measurements that have been combined with EC measurements (FLUXNET-CH4 database) based on matching timestamps. First, the chamber observations will be compared to the corresponding EC measurements without accounting for spatial heterogeneity. Then, various remotely sensed environmental variables, such as leaf area index (LAI) and topographic wetness index (TWI), in high spatial resolution will be used to create land cover classes and combined with a modeled footprint to include spatial heterogeneity in the up-scaling of point-level measurements in all sites. 

Preliminary results suggest that the chamber and EC observations differ significantly in magnitude between seasons and sites. In general, chamber observations had a larger range than EC, which we expected, given that chambers capture finer spatial heterogeneity than EC. However, no consistent trends emerged in the difference in magnitude between chamber and EC. We expect that the inclusion of spatial heterogeneity into the footprint model will decrease the differences  between up-scaled chamber and EC observations for all sites. Notably, we expect that the inclusion of proxies for soil moisture, plant functional type (PFT) and aerenchyma  will improve footprint-level comparisons to chamber-level data. We will present updated comparisons of EC and chamber data with and without inclusion of spatial heterogeneity. Altogether, this study will establish a workflow for combining wetland CH₄ data from different measurement types (EC and chamber) and will allow global syntheses to use more of the available data to constrain CH₄ budgets. 

How to cite: Määttä, T. and Malhotra, A. and the FLUXNET-CH4 EC-chamber working group: Effects of spatial heterogeneity within the eddy covariance (EC) footprint on up-scaled methane fluxes across multiple wetland sites, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3338, https://doi.org/10.5194/egusphere-egu23-3338, 2023.

Non-rainfall water can play a critical role in many ecosystems, but is understudied in most regions due to a lack of continuous, specialized measurements. One of the most commonly used techniques to quantify in situ ecosystem water fluxes is Eddy Covariance (EC). However, its use for the quantification of the two most famous non-rainfall water sources, dew and (radiation) fog, is limited because they often occur under humid conditions and nighttime stable stratification, making EC measurements particularly uncertain or non-valid.

Here we describe how a non-rainfall water input observed under dry conditions, namely water vapor adsorption by soil particles (VWA), can be monitored using existing eddy covariance datasets, giving insight into this little-studied soil water source. Unlike dew and radiation fog, atmospheric stability is not a prerequisite for WVA. Instead, WVA is driven by a highly negative soil matric potential inducing water vapor to condensate already at relative humidity < 100 %. Therefore, EC measurements may be more suitable to detect and quantify this flux than for dew and fog.

In this study, we test EC measurements for inferring WVA by comparing them to observations from large-weighing lysimeters, where the latter can be considered as a reference system for the measurement of WVA. Our aim is to explore the potential and limitations of the EC technique to detect and quantify WVA. We assess the quantitative and qualitative agreement between WVA estimated with the lysimeters and negative (downward) LE fluxes from EC. Our analysis uses four years of observations from a semi-arid tree-grass ecosystem and one year of a temperate agricultural ecosystem during the 2018 drought.

Our results show that during dry conditions the water vapor gradient between the relatively humid atmosphere and the dry soil pores leads to WVA in both ecosystems. We find a decent agreement between the timing of fluxes detected as WVA with lysimeters and with EC instruments, but the magnitudes (i.e. the amount of flux) differ. Furthermore, we aim to characterize the conditions under which negative LE fluxes from EC measurements can and should be interpreted as WVA. This way, our study expands the possibilities to investigate the relevance of WVA as a non-rainfall water source and, more generally, sheds light on a mostly overlooked aspect of land-atmosphere interaction during dry conditions in different ecosystems.

How to cite: Paulus, S. J., El-Madany, T. S., Orth, R., Hildebrandt, A., Reichstein, M., Nelson, J. A., Carrara, A., Moreno, G., Mauder, M., Groh, J., Lee, S.-C., and Migliavacca, M.: Interpretability of negative latent heat fluxes from Eddy Covariance measurements during dry conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7666, https://doi.org/10.5194/egusphere-egu23-7666, 2023.

Most of the water input to the ecosystem comes from rainfall. However, depending on the local climatic conditions a considerable amount of water can also be produced by different fractions of non-rainfall water inputs (NRWIs), namely dew, hoarfrost, rime, fog, and the adsorption of water vapour in the soil. Such NRWIs are often neglected because they are typically small compared to rainfall on the daily scale. Nevertheless, these NRWIs provide our ecosystems with additional water, which is important for the survival of the fauna and flora in the ecosystem, especially during dry periods. 

In the past different devices were used to determine some of these fractions, based on artificial surfaces (e.g., dew or fog collector). We will present a conceptual measurement set-up that allows us to determine each non-rainfall water (NRW) component for natural surfaces of agricultural ecosystems. The method is based on precise weighable lysimeter measurement to determine the incoming water fluxes of NRW. The partitioning between the NRW components will be done based on parallel observations on the surface and air temperature, humidity, rain gauge, and dust collector. Based on this conceptual system, we will compare the temporal development and occurrence of different NRW components for eight different agroecosystems under similar climatic conditions.

How to cite: Groh, J., Pütz, T., Beysens, D., Vereecken, H., and Amelung, W.: A conceptual system for identifying and distinguishing different non-rainfall water fractions in agroecosystems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5833, https://doi.org/10.5194/egusphere-egu23-5833, 2023.

Accurate quantification of evapotranspiration (ET) is crucial for understanding variability in the global water cycle, yet state-of-the-art estimates of ET derived from models and remote sensing products contain large uncertainties. Taking the advantage of extensive eddy covariance measurements and machine learning algorithms, ET can be upscaled from globally distributed in-situ observations by combining them with global meteorological and satellite data (e.g., FLUXCOM ensembles, Jung et al., 2019). However, eddy covariance measurements suffer from well-known energy balance non-closure problems, and those uncertainties are further propagated to the global ET estimates. Here, we first estimate the energy balance non-closure within dynamic sliding windows for flux tower site, then we compute correction factors for ET measurements following different hypothesis (that assign errors to latent and/or sensible heat fluxes) according to insights from large eddy simulation studies. Then energy balance closure corrected ET data are used in FLUXCOM to estimate global ET. The upscaled ET then is evaluated by comparison with water-balance-drived ET at the catchment level. This comparison helps to determine the most consistent correction of ET for different regions and conditions. By providing improved global ET estimates, water-related studies can be further facilitated, and model parameterizations can be further optimized to address the challenges posed by climate change on ecosystems and water resources.

How to cite: Zhang, W., Nelson, J. A., Miralles, D. G., Poyatos, R., Reichstein, M., and Jung, M.: Towards reducing uncertainties of global evapotranspiration due to the energy balance closure gap in flux tower data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11031, https://doi.org/10.5194/egusphere-egu23-11031, 2023.

The eddy covariance (EC) method, nowadays the standard method for determining forest ecosystem-atmosphere turbulent exchange, faces a major threat in its application: the air masses below the canopy are regularly decoupled from the air masses above the canopy. Consequently, the EC measurements above the canopy like e.g. H₂O and particularly CO₂ fluxes can be biased due to missing signals from below-canopy processes. This decoupling is strongly site dependent and influenced by meteorological conditions, canopy properties and tower-surrounding topography. It can be verified and addressed by subsequent EC measurements below and above the canopy. Specifically, the correlation of σ_w below and above the canopy gives information about the coupling state as this correlation is linear during periods of full coupling.

The current study aims to address the decoupling issue on a global scale. For this purpose, approximately 30 forest sites from around the world will be analyzed in a standard way with regards to decoupling. The study sites cover manifold vegetation types and climate zones, all sites are equipped with concurrent below and above canopy EC measurements. Preliminary results highlight the dependence of decoupling on meteorological conditions, canopy properties and tower surrounding topography. Nevertheless, the final goal of this action is to derive global relations between these influence factors and decoupling which will be applicable in a general way on each forest site worldwide. Highest quality turbulent fluxes will be the outcome and the accuracy of EC derived forest water and carbon budgets will improve.

How to cite: Jocher, G.: Addressing forest canopy decoupling on a global scale, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4877, https://doi.org/10.5194/egusphere-egu23-4877, 2023.

Evapotranspiration (ET) from the land surface to the atmosphere consists of transpiration (T) from plants and evaporation (E) from soil and vegetated surfaces. These biological and physical component fluxes respond differently to changes in temperature, water availability and atmospheric composition. ET can be measured directly at the ecosystem scale with the eddy covariance (EC) method but similar measurements are not currently available for the component fluxes E and T. Concurrent EC measurements above and below forest canopies provide a promising approach to partition ET into T and E. However, our understanding of the performance of such measurements is still very limited. To address these challenges, we measured and partitioned ET with three concurrent EC towers (1 above & 2 below canopy) in a montane forest at Sagehen Creek in the Sierra Nevada, California from late June 2017 to September 2020. We observed a total forest ET of 606 mm yr^-1 with 275 mm yr^-1 measured in the understory and a tree transpiration of 331 mm yr^-1. Below-canopy measurements replicated at two locations within the above-canopy footprint indicated only small spatial variability for understory ET near the creek at Sagehen. Interannual variability in ET above and below canopy was small during the water years 2018 to 2020, despite large variability in precipitation totals. Accordingly, vegetation water use was relatively stable across years and the P–ET water balance was mainly driven by variations in water supply. Partitioning the components of total forest ET at Sagehen with concurrent EC measurements showed that on average 67–74% originated from T (47% from trees and 20–27% from understory grasses), while 26–33% were from E (mostly from the understory). Our results demonstrate the strength of concurrent above- and below-canopy EC measurements for the partitioning of ET.

How to cite: Wolf, S., Paul-Limoges, E., Sayler, D., and Kirchner, J. W.: Evapotranspiration dynamics and partitioning from concurrent above and below canopy flux measurements in a Montane Sierra Nevada Forest, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12068, https://doi.org/10.5194/egusphere-egu23-12068, 2023.

Water vapor flux plays a crucial role in surface-atmosphere exchange processes as evapotranspiration regulates the energy balance of the surface. Moreover, it transfers water vapor into the atmosphere and, as a result, shapes the hydrological cycle. The eddy-covariance (EC) technique is the most commonly applied method to directly measure water vapor flux over a wide variety of surfaces. An EC arrangement consists of a 3D sonic anemometer and a gas analyzer. To derive surface fluxes, wind components and the gas concentration (e.g. water vapor) have to be recorded with high-frequency (at least at 10 Hz). In the case of open-path (sampling-free) EC systems, infrared (IR) gas analyzers are used dominantly, which are still quite large so that e.g. they cannot be easily mounted on drones. In contrast, small and light sonic anemometers are available for flux measurements.

In this study, we present the application of a sampling-free photoacoustic (PA) sensor for water vapor flux measurement employing the EC technique. The fast response PA sensor records the water vapor concentration through an open cylindrical chamber having an overall size of less than 1 dm³. On the one hand, a previous first test showed that the vertical covariance functions obtained by the PA cell follow closely to those resulting from an accepted IR sensor. On the other hand, the PA system showed some underestimation at higher frequencies based on the analysis of co-spectra.  

To comprehensively test and evaluate the PA cell for flux measurements, a seven-week-long field measurement was performed over a plain grassland when a calibrated EC150 IR sensor (Campbell Sci.) was used as a reference gas analyzer. We analyze the accuracy of the PA system: (i) depending on the orientation of the cell or i.e. the wind direction, and (ii) for a broad range of meteorological conditions, such as different wind speeds and atmospheric stability. Furthermore, to overcome the high-frequency attenuation, we establish and apply empirical spectral transfer functions following the literature and standard EC postprocessing procedures. The characteristic response time of the PA sensor is also assessed.

How to cite: Torma, P., Weidinger, T., Juhász, V., Molnár, B., Horváth, L., Huszár, H., and Bozóki, Z.: Application of open photoacoustic cell in an eddy covariance system for water vapor flux measurement, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12898, https://doi.org/10.5194/egusphere-egu23-12898, 2023.

Monitoring of trace gas fluxes and greenhouse gas fluxes is key to understand the interaction between atmosphere, plants, and soil and therefore to improving our understanding of the climate system in general.

The complex flux systems require measurement of many different inert and reactive trace gases and greenhouse gases simultaneously to obtain a complete budget. This is especially the case in urban environments where both biogenic and anthropogenic sources and sinks play a role.

The eddy covariance (eddy flux) technique is often used to determine fluxes of the gases in question. Until recently, however, the monitoring was usually limited to only a few gases per measurement device making the technique complex and expensive but providing only a limited picture. MIRO Analytical has developed a novel multicompound gas analyzer that can monitor up to 10 air pollutants (CO, NO, NO₂, O₃, SO₂ and NH₃) and greenhouse gases (CO₂, N₂O, H₂O and CH₄) simultaneously with the high time resolution necessary for eddy-covariance flux measurements. The compact system combines several mid-infrared lasers (QCLs) providing outstanding precision, selectivity and accuracy for the gas measurements.

In our contribution we will introduce the measurement technique and will demonstrate application examples of this all-in-one atmospheric flux monitor. The system will be compared to alternative devices in parallel measurements and results of long-term observations and shorter campaigns will be presented.

How to cite: Hundt, M., Brunner, M., and Aseev, O.: Simultaneous eddy flux monitoring of 10 greenhouse gases and air pollutants with a single instrument, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7803, https://doi.org/10.5194/egusphere-egu23-7803, 2023.

Two micrometeorological methods that utilize high frequency sampling of air temperature were tested against eddy covariance (EC) sensible heat flux (H) measurements at three sites representing agricultural, agro-forestry and forestry systems. The two methods encompass conventional and newly proposed forms of the flux-variance (FV) and surface renewal (SR) schemes.  In terms of measurement setup, the sites represent surface, roughness and roughness to surface transitional layers, respectively. After the selection of the most reliable approaches, regression analyses against EC showed that both methods can estimate H with slopes within ±10 % from unity, and coefficient of determination R² >0.9 across all three sites. The best performance, of both FV and SR, was at the agricultural field, where the measurements were within the surface layer.  The worst performance occurred in the tall, relatively heterogeneous forest, where the measurements were taken in the roughness sublayer, the depth of which (with its inherent uncertainty) needs to be taken into account in the calculations. In addition to the evaluation of the FV and SR forms, an alternative perspective relating ramp-like structures to the vertical temperature gradients in the surface boundary layer is introduced here. Ramp-like structures carry much of the heat flux and temperature variance, representing opportunities to constrain the coefficients of the two methods. As a corollary, we introduce a novel approach emerging from bridging FV and SR methods that combines information about the coherent structures with the overall variance to obtain heat fluxes in a turbulent atmosphere. The proposed approach yields reliable H estimates without the need for site-specific calibration and instrumentation other than a single fast thermocouple.

Acknowledgement: This study was conducted with support of SustES - Adaptation strategies for sustainable ecosystem services and food security under adverse environmental conditions (CZ.02.1.01/0.0/0.0/16_019/0000797) and USDA NIFA-AFRI Sustainable Bioenergy Program, 2011-67009-20089, Loblolly pine-switch grass intercropping for sustainable timber and biofuels production in the Southeastern United States.  Funding for AmeriFlux core site US-NC4 (natural forested wetland) was provided by the USDA NIFA (Multi-agency A.5 Carbon Cycle Science Program) award 2014-67003-22068. Additional funding was provided by the DOE NICCR award 08-SC-NICCR-1072, the USDA Forest Service award 13-JV-11330110-081, and the DOE LBNL award DE-AC02-05CH11231. 

How to cite: Fischer, M., Katul, G., Noormets, A., Pozníková, G., Domec, J.-C., Orság, M., Trnka, M., and King, J. S.: Evaluating and bridging the flux-variance and surface renewal methods, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9744, https://doi.org/10.5194/egusphere-egu23-9744, 2023.

Tall tower eddy covariance (TTEC) flux measurements are employed to estimate turbulent matter and energy fluxes at landscape scales (e.g. within 1 to 5 km radius around a tower). Virtually all landscapes feature horizontal surface heterogeneity. One main complication for the interpretation of TTEC is the sampling bias by the varying local meteorological conditions. While the wind direction bias can only be considered by the choice of the location of the TTEC, we examine here how the effects of atmospheric stability can be alleviated by sampling from different measurement heights (z_m). The objective is to define an optimal set of measurement heights to minimize sampling bias from variation in atmospheric stratification for TTEC long-term flux observation. To our knowledge, this problem has not yet been addressed in the scientific literature.

We used a two years’ dataset from the 122 m tall tower at Risø (Denmark, 55°41'39.15" N, 12°5'17.93" E) and two flux footprint models to develop an objective statistical approach for the definition of a set of measurement heights for optimal sampling of the landscape heterogeneity. The tower is equipped with 3D ultrasonic anemometers in five different heights. The evaluations concern the Eastern sector, which is comprised of a mosaic of land uses, small settlements and comparably sparse road infrastructures.

We define the criteria for optimal landscape flux sampling from the distributions of the source weights (contribution to the measured flux per unit area) sampled in a number of stability classes relative to a frequent unstable stability class as reference. The upper sampling height is set a priory to match measurements and the targeted area; here z_m equal to 120 m for the 70% cumulated footprint to stay within a 5 km radius around the tower.

Theoretical analysis with the footprint model shows the limitation of the attempt to compensate for lateral footprint extension at different stabilities, while the longitudinal sampling of the landscape heterogeneity can be maintained more homogeneously by the systematic choice of the measurement height according to atmospheric stability and wind speed.

The results rely on the accuracy of the footprint estimation, which is generally an essential criterion for the interpretation of TTEC measurements in heterogeneous landscapes.

How to cite: Kissas, K., Scheutz, C., and Ibrom, A.: Reducing the effects of weather on the sampling bias in tall tower eddy covariance flux measurements, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15533, https://doi.org/10.5194/egusphere-egu23-15533, 2023.

The boreal biome exchanges large amounts of carbon (C) with the atmosphere and thus significantly affects the global climate. A managed boreal landscape typically consists of various sinks and sources of carbon dioxide (CO₂), methane (CH₄), and dissolved organic and inorganic carbon (DOC and DIC) across forests with different stand ages, mires, lakes, and streams. Due to the spatial heterogeneity, a full understanding of the landscape-scale C balance requires capturing all C fluxes. Here, we investigate the five-year interannual variability in the net landscape carbon balance (NLCB) by compiling terrestrial and aquatic fluxes of CO₂, CH₄, DOC, DIC, and harvested C obtained from 2016 to 2020. For that purpose, we applied tall-tower eddy covariance measurements, stream monitoring, and remote sensing of biomass stocks (i.e. harvested C via clearcutting) to estimate the landscape-scale C fluxes across the land-water-atmosphere continuum for an entire boreal catchment (~68 km²) in Sweden. Our results show that this managed boreal forest landscape was a net C sink during 2016-2020 (123 ± 63 g C m^-2 yr^-1) with the lowest and highest sink-strength occurring during a wet year 2017 (16 g C m^-2 yr^-1) and a drought year 2019 (182 g C m^-2 yr^-1), respectively. The net landscape-atmosphere CO₂exchange was the dominant component of NLCB, followed by the C export via harvest and streams. We further found that global radiation and vapor pressure deficit regulated the inter-annual variations of NLCB, whereas forest biomass and source area contribution of mires determined its spatial variability. Overall, our multi-year NLCB investigations provide a holistic understanding of the inter-annual variations in NLCB of managed boreal forest landscapes to better evaluate their potential for mitigating climate change.

How to cite: Chi, J., Klosterhalfen, A., Nilsson, M., Laudon, H., Lindroth, A., Kljun, N., Wallerman, J., Fransson, J., Lundmark, T., and Peichl, M.: Five-year inter-annual variation in the net landscape carbon balance of a managed boreal forest landscape in Sweden, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16012, https://doi.org/10.5194/egusphere-egu23-16012, 2023.