The Kentucky Mesonet is a great asset for the Commonwealth of Kentucky, from realtime storm monitoring to building a detailed climate record. A detailed climate record is essential as causality between observations and extreme weather can be identified. The climate record being developed at the 80+ Kentucky Mesonet observation stations consists of approximately 75 indices. The indices include frequency, extremes, range, duration, and trends of precipitation, droughts, and temperature. For example, calculations of Warm/Dry days (daily mean temperature > 75th percentile of daily mean temperature and daily mean rainfall < 25th percentile of daily precipitation sum where the percentiles are based on a climatology taken from reanalysis between 1961 and 1990) are done for daily, monthly, seasonal, bi-annual, and annual aggregation periods. Particular attention will given to soil moisture - precipitation feedbacks as Kentucky has a karst geology which generates soil moisture gradients. Soil Moisture-precipitation feedbacks, the beginning and ending of land-atmosphere interactions in general, are highly dependent on the wind flow regime and atmospheric stability, so these relationships will elucidated in the presentation.  Tools will be developed based on interactions with policymakers and stakeholders as they will be making decisions today that impact the region’s main economic sectors (e.g. water, energy, transportation, etc.) as infrastructure erected today will likely be in place when the climate is different than at present. Examples will be provided that sample the different climate zones of the state, relative elevations of site locations, as well as different land cover and land uses.

How to cite: Rappin, E.: Land-Atmosphere Interactions as Observed by a Statewide in-situ Surface Observation Network, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22465, https://doi.org/10.5194/egusphere-egu24-22465, 2024.

The optimal solution for solving many uncertainties associated with weather and climate data is accurate field measurement. This enhances various climate services that can be offered to different sectoral case studies and solve societal weather-related challenges by ensuring the obstacles are overcome amicably, for instance, climate adaptation barriers in the face of climate variability. The main goal of our study was to make long-term meteorological measurements in Mount Kenya region rainforest biome at an elevation of 1998 m above sea level (Karatina University weather station) and 3055 m above sea level (Mount Kenya field station) used at various scales from 2022. We are using Temperature-Moisture-Sensor (TMS) burial (1 m) and TMS Long (45 cm) soil sensors as well as temperature/relative humidity data loggers. These devices provide us with crucial data and reshape field measurement campaigns in data-scarce regions of Kenya. The soil moisture sensors also measure soil temperature, surface, and air temperature. The soil moisture data and temperature at various scales is acquired at an interval of 10 minutes while the data logger records data at an interval of 30 minutes.  Another key goal was to acquire soil moisture data at tropical rainforest biome which is scarce as well as relative humidity and temperature. The objectives of the study are to analyze reference evapotranspiration and estimation of real evapotranspiration in humid Mount Kenya climatic region, Nyeri County; compare climate parameters in two different elevations; to understand microclimatic changes associated with varying elevations and ensure data quality control in analysis by checking uncertainties and sensitivities associated with ERA5 reanalysis, synoptic (GFS/ECMWF) and station datasets. Therefore, to narrow the gap between missing data, uncertainties, and quality control of data, meteorological field measurements cannot be misconstrued.

Keywords: data loggers, field measurement, soil moisture, quality control, Kenya,

How to cite: Musyimi, P. K., Székely, B., Kamiri, H. W., Ouna, T., and Weidinger, T.: Meteorological and Soil Moisture Measurements in Mount Kenya Region at Various Scales, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-579, https://doi.org/10.5194/egusphere-egu24-579, 2024.

Agriculture is an important economic sector of Vietnam, the most common is wet rice cultivation. Wet rice cultivation is known as the main contributor to national greenhouse gas emissions. To better understand greenhouse gas exchange in wet rice cultivations and to investigate the factors influencing carbon cycling and sequestration in these types of ecosystems, since 2019, the first eddy covariance station has been installed in a paddy field in Long An province, Mekong Delta, Vietnam. The station is equipped with state-of-the-art equipment for CO₂ and CH₄ gas exchange and meteorological ancillary measurements. Data from the station are processed following the ICOS recommendations (Integrated Carbon Observation System) for CO₂. For CH₄, data are separately processed and gap-filled using a random forest model from methane-gap fill-ml, a machine learning package, as there is no standard method for CH₄ flux gap-filling yet. Finally, the CO₂ equivalent (CO₂eq) based on CO₂ and CH₄ fluxes was estimated. The study area implemented a new water management practice called alternate wetting and drying, which helps to save water and reduce methane emissions. This practice resulted in the minor release of 0.8 kg CH₄ per hectare in 2020 and 0.67 kg CH₄ per hectare in 2021. However, CO₂eq from the rice fields was negative, indicating that the rice fields acted as a sink for CO2eq, with -5.54 kg CO₂eq per hectare in 2020 and -7.03 kg CO₂eq per hectare in 2021. On a provincial level, rice cultivation activities in Long An, with a total area of 498293 ha, resulted in a CO₂eq uptake of 2760 and 3503 tons in 2020 and 2021, respectively. This result is in contrast to the initial hypothesis that rice fields are a source of greenhouse gases. However, N₂O was not investigated in this study, which is also known as a strong greenhouse gas.

How to cite: Vu Hoang Ngoc, K., Jocher, G., Le D. A., V., Le T., S., Bui T., A., Ho Q., B., and Pham Q., H.: Measuring Greenhouse Gas Exchange from Paddy Field Using Eddy Covariance Method in Mekong Delta, Vietnam, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16949, https://doi.org/10.5194/egusphere-egu24-16949, 2024.

Although occupying only 7% of the earth's surface, wetlands store 33% of the world's terrestrial carbon. When these ecosystems are drained to be converted into agricultural, forestry or mining exploitations, they release greenhouse gases contributing to climate change. While bringing together 18 partners from 9 countries, the REWET (REstoration of WETlands to minimise emissions and maximise carbon uptake – a strategy for long term climate mitigation) project focuses on determining how the restoration and management of wetlands can be optimised to maximise their carbon uptake while in balance with type-specific natural processes and biodiversity.

The REWET project draws upon a network of seven Open Labs (OLs) located in different geographical areas of Europe and covers different types of terrestrial wetlands: freshwater wetlands, peatlands and floodplains. The heterogeneity of the Open labs allows the application of different restoration methodologies while following the same monitoring plan to provide replicable knowledge.

This paper presents the measurements and the first result of the OL in Austria within the REWET project. The site is a restored and now protected floodplain area at the Morava River. EC measurements are used to calculate the CO₂ and CH₄ fluxes and the seasonal as well as annual carbon balance of the ecosystem. Furthermore, the effect of floodplain water levels and grazing in this area is investigated. The EC instruments have been set up on a floating platform to allow measurements also during flood events, when understudied, critical transition of GHG fluxes may occur. The CO₂/H₂O analyser started collecting the first data in the middle of October 2023 whereas the CH₄ analyser was added in end of December 2023. Since the CO₂ analyser was put on site first flood events occurred end of December, which is the first data to be processed and analysed. Additional to the results the challenges in setting up an EC tower in a floodplain area will be presented.

Funded by the European Union. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or CINEA. Neither the European Union nor the granting authority can be held responsible for them.

How to cite: Lindenberger, A., von der Thannen, M., and Rauch, H. P.: Eddy Covariance (EC) measurements in a restored floodplain area at the Morava River in Austria within the EU funded REWET project, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5207, https://doi.org/10.5194/egusphere-egu24-5207, 2024.

Eddy covariance (EC) flux measurements are relevant for the study of global change biology when integrated over long-term periods (Baldocchi, 2019). This could lead to researchers being reluctant to adopt state-of-the-art correction methods, especially for sites that have collected continuous data and trends for the last 20 years. The storage change (SC) correction has often been overlooked and simplified and is generally under-investigated in the literature. The present study highlights the dynamics of the storage change term in two different landscapes and proposes a simple correction factor that can be applied backwards to historical data in a forested ecosystem.

The first studied site is a mixed deciduous forest in Denmark (DK-Sor), where a sequential vertical profile system (12 heights) has been installed in 2021 to characterize the vertical component of the storage change more accurately. We compare the often-used 1 point method with the results from the profile system for CO₂ and H₂O. We study the SC component in terms of its diurnal course, its impact on the annual carbon budget, and its relation to atmospheric stability parameters.

The second site is a Danish rural area (DK-Hove), where four different greenhouse gas fluxes are measured with EC sensors installed at 3 heights on a 200 m tall telecommunication tower. The SC profile system here consists of 5 levels and needs to adapt to the dynamic eddy covariance measurement height of the landscape-scale GHG monitoring system. We present 6 months of SC data from the tall tower for CO₂, CH₄, N₂O and CO, their diurnal courses and relation to meteorological variables.

Overall, this work aims at bringing an additional contribution to shed light on the often-neglected SC term.

Reference:

Baldocchi, Dennis D. How eddy covariance flux measurements have contributed to our understanding of Global Change Biology. United Kingdom: N. p., 2019. Web. doi:10.1111/gcb.14807.

How to cite: Gorlenko, A., Kissas, K., Scheutz, C., and Ibrom, A.: Quantification of storage change at two contrasting eddy covariance sites, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22205, https://doi.org/10.5194/egusphere-egu24-22205, 2024.

The assessment of net ecosystem CO₂ exchange often relies on eddy covariance systems. However, this method overlooks CO₂ advection, even if it is often non-negligible. This is especially the case under stable, low-turbulence nighttime conditions. Hence, there is a need to filter nighttime eddy covariance data for periods when advection can be expected to be non-negligible. This study evaluates both well-established and novel filtering methods at a mountain forest site in Tyrol, Austria (Forest-Atmosphere-Interaction-Research (FAIR) site, AT-Mmg). Established methods, including friction velocity (u_*) filtering, its counterpart using the standard deviation of vertical velocity  fluctuations (σ_w) and an after-sunset flux maxima approach (commonly referred to as van Gorsel method) are applied. Additionally we use a more recent approach with a physically-derived measure of flow decoupling for filtering. With this method also stability information is taken into account, not only a turbulence scale, as in the commonly used u_* filtering. As often seen in literature, the uncorrected CO₂ flux underestimates the nighttime respiration, as it appears for all the filtering methods. Despite being based on widely differing assumptions, the various filtering approaches yielded relatively similar carbon budget estimates over 14 months of measurements (-252 to -290 g C/m²). in contrast to the uncorrected budget of -521 g C/m^2.

Furthermore, we introduce a novel K-means clustering approach that groups flow situations into clusters based on vertical profiles of temperature, σ_w and wind speed. These clusters need then to be evaluated to determine whether they represent a flow situation in which CO₂ advection is expected to be irrelevant. Such scenarios are often Foehn periods or early-night situations with high turbulence and low stability. This approach is relatively straightforward to implement, works with an unlimited number of input variables and has the advantage that the identified periods are easy to interpret. This method results in a 14-month budget of -232 g C/m² for our study site. 

The universality of the clustering method allows not only for an unlimited number of input variables, it can be also easily extended for the entire day. There is no a priori reason not to filter eddy covariance data during the daytime when low-turbulence situations with persistent in-canopy flows may lead to non-negligible advection, especially in complex terrain. We made an attempt of daytime filtering in this study with the clustering method, but also with some adapted versions of the benchmark methods. All of these daytime filtering methods suggest that there is an underestimation of the CO₂ uptake in the morning for the uncorrected measurements. Filtering for both nighttime and daytime leads to a range of 14-month budgets of -451 to -359 g C/m².

Further analysis, incorporating different established sites, direct advection measurements or numerical simulations, could be used in future to explore the full potential of the novel clustering approach, especially with its application to daytime flux data.

How to cite: Platter, A., Scholz, K., Hammerle, A., Rotach, M. W., and Wohlfahrt, G.: Uncertainty of eddy covariance-derived net ecosystem CO2 exchange over a mountain forest reduced by multiple nighttime filtering approaches, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5340, https://doi.org/10.5194/egusphere-egu24-5340, 2024.

Nocturnal advection significantly influences the accurate estimation of net ecosystem exchange (NEE). This phenomenon is prevalent in Taiwan's subtropical montane forests, introducing a potential bias when relying solely on eddy covariance data for carbon budget calculations. From the preliminary analysis, the wind speed can be well estimated through the temperature difference between the heated and unheated fiber optical.The derived five-minute average wind speed exhibits a high coefficient of determination (R^2) of up to 0.94.

In the current study, a fiber observational setup consisting of a 40m vertical section and a 90m horizontal section has been implemented to investigate temperature dynamics and airflow in complex terrain. The wind speed profile can be well reflected from the preliminary data analysis. Insights gained through this approach contribute to a better understanding of the nocturnal canopy advection model, offering valuable corrections to NEE estimates.

How to cite: Li, Y. F., Ma, K. F., Lin, C. J., Lai, Y. J., Lin, P. H., and Nakai, T.: Exploring Nocturnal Canopy Advection in Complex Terrain Through Active Heating Fiber Optics: Unraveling Temperature Dynamics and Airflow Patterns, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10295, https://doi.org/10.5194/egusphere-egu24-10295, 2024.

The eddy covariance (EC) method has been widely used to capture the temporal and spatial patterns of nitrous oxide (N₂O) emissions from a wide variety of agricultural ecosystems. Technological advancements in the recent years have brought new tunable infrared laser-based closed-path gas analyzers suitable for EC measurements. To achieve high sensitivity and low measurement noise, these analyzers use multi-pass optical cells with long sensing path. A drawback of these cells is the relatively large internal volume requiring high-flow rate, high-power pumps to attain fast response to changes in gas concentration.  Additionally, these cells are prone to contamination and require in-line filters. In this study we evaluate the frequency response of a novel, low-power, field deployable N₂O closed-path EC system consisting of: (1) a gas analyzer with a small volume single-pass optical cell, (2) a 3 m sulfonated tetrafluoroethylene ionomer intake tube acting as water vapor permeable membrane to dry the air sample, (3) a cyclone type, non-barrier inertial particle separator (IPS) to mitigate the effects of particulates contamination of the optical sample cell, and (4) a small, low-power pump module with an automatic pressure and flow control. The performance of the new N₂O EC system is evaluated in-situ 3 m above a fertilized agricultural wheat field and compared to a co-located fast-response H₂O and CO₂ open-path gas analyzer and sonic anemometer (IRGASON). Tube delays, determined by cross-covariance of N₂O with vertical wind, were consistent over time and varied between 0.2 and 0.5 s. Spectral and co-spectral analysis of vertical wind, temperature, H₂O, CO₂ and N₂O showed good agreement. Ogive functions demonstrated that the new system has adequate frequency response to capture >90% of the N₂O fluxes for a wide range of wind speeds and atmospheric stabilities and is suitable for deployment in remote areas.

How to cite: Bogoev, I.: Frequency Response Evaluation of a Low-power Closed-path Eddy Covariance System for Measuring Nitrous Oxide Fluxes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6604, https://doi.org/10.5194/egusphere-egu24-6604, 2024.

Monitoring of trace 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.

Complex flux systems, in environments where both biogenic and anthropogenic sources and sinks play a role, require measurement of many different inert and reactive trace gases and greenhouse gases simultaneously to obtain a complete budget.

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), greenhouse gases (CO₂, N₂O, H₂O and CH₄) and other atmospheric trace gases such as (OCS, HONO, CH₂O) simultaneously at ppb level.

The eddy covariance (eddy flux) technique is often used to measure fluxes of trace gases but requires a high time resolution. Our compact instrument, combing several mid-infrared lasers (QCLs), offers 10 Hz sampling rate, outstanding precision, selectivity and accuracy and an automatic water vapor correction, which makes it ideal for eddy covariance flux 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., Bruckhuisen, J., and Aseev, O.: Simultaneous trace gas flux monitoring of 10 greenhouse gases and air pollutants with a single instrument, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7892, https://doi.org/10.5194/egusphere-egu24-7892, 2024.

Slope flows, resulting from the interplay between buoyancy and gravitational forces, are well-known to govern a plethora of local weather phenomena. In particular, orographic features and the associated surface roughness can induce turbulent mixing in the planetary boundary layer. While orographic drag models have been proposed to understand the effects of turbulence and waves due to orography, numerical simulations locally rely on closures based on the Monin-Obukhov Similarity Theory. The validity of these models and their interaction regarding turbulence production due to orography at unresolved scales is questionable. We study the turbulence generation by small-scale orography under the influence of stable stratification and weak mixing. To bypass the common complications with surface modeling, we use direct numerical simulation featuring a shallow valley to study the problem at a reduced scale. To imitate the intricate boundary conditions, an Immersed Boundary Method is used that features fully resolved three-dimensional roughness elements in the form of a local valley. However, modeling such flows also poses challenges due to the numerous parameters governing the triggering of turbulence. In this presentation, we introduce a scaling framework orographic for the problem and a viable numerical set-up along with the first results from preliminary studies at intermediate scale separation.

* This work is funded by the ERC Starting Grant ”Turbulence-Resolving Approaches of the Intermittently Turbulent Atmospheric Boundary Layer [trainABL]” of the European Research Council (funding ID 851347).

How to cite: Deshpande, S. and Ansorge, C.: Turbulence generation by unresolved orography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9790, https://doi.org/10.5194/egusphere-egu24-9790, 2024.

At the local scale, energy exchange shapes microclimates and ecosystems crucial for human health and well-being. For urban areas, the effect, such as Urban Heat Island, is directly manifested in these surface energy fluxes with contrasting responses in values between urban and rural areas. Although progress has been achieved in modeling the land surface energy balance, challenges arise from complex, variable parameterizations linked to surface and climate characteristics, introducing uncertainties. In this work, we utilized the thermodynamic theory that considers the land-atmosphere as a radiative-convective system to analytically estimate total turbulent heat flux and land surface heat storage flux for 20 Urban sites and compared them with Eddy covariance observations. The heat fluxes are determined only from four primary parameters: incoming and outgoing longwave and shortwave radiations at the terrestrial surface. Using the monthly averages derived from the total turbulent flux estimates at the eddy covariance sites, we observed root-mean-square error (RMSE) of 29.16 ± 11.3 Wm⁻², a mean bias error (MBE) of -7.09 ± 19.6 Wm⁻² and R² value of 0.82 ± 0.16. We further tested the analytical estimates with land use land cover of Urban sites. Our findings illustrate the distribution of land surface heat storage flux estimates following land use land cover characteristics. The analytical estimates of heat fluxes for urban areas offer several advantages, such as ease of implementation and inexpensive computation, facilitating the evaluation of urban land use feedback for informed urban planning.

How to cite: Gupta, M., Khandare, A., and Ghosh, S.: Urban Surface Energy Flux Estimations Utilizing a Thermodynamic Analytical Framework, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18634, https://doi.org/10.5194/egusphere-egu24-18634, 2024.

While there are several series of daily observations of temperature, precipitation and few other parameters available in many locations in the world, sometimes lasting more than a century, there are much less series of other variables related to the surfae atmospheric layer or underground soil, such as sensible and latent heat fluxes, soil heat flux, soil temperature and moisture in the root layer and below it. This work aims to propose a method to evaluate such parameters at a climatic time scale using a trusted land surface model, taking the variables from the outputs of the simulation and creating a database. In this work, the selected model is the UTOPIA (University of TOrino land surface Process Interaction model in Atmosphere). This technique can be applied in general to each site in which hourly observations of the seven parameters needed for the simulation are available (temperature, humidity, pressure, the two components of the horizontal wind velocity, precipitation and solar radiation or cloudiness). In a preliminary phase, the database will be created on the period 1992-2023, on which we have the availability of hourly measurements carried out at the Department of Physics of the Turin University. In a second phase, we plan to develop a methodology to derive hourly observtions from the existing series of data gathered in the city of Turin, using peculiar methods to interpolate or extrapolate the missing observations of required inputs and to downscale hourly observations from daily observations. This methodology could be tested using the eisting data in the recent climate period.

How to cite: Cassardo, C., Andreoli, V., Bertoni, D., Lim, S., Manfrin, M., and Park, S. K.: Climatology of surface parameters for the city of Turin using UTOPIA (Italy) land surface model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15005, https://doi.org/10.5194/egusphere-egu24-15005, 2024.

Precipitation (i.e. rain, snow, hail) is the main form of water input to our ecosystem. However, depending on local climatic conditions, a significant amount of water can also be produced by various fractions of non-rainfall water inputs (NRWIs), namely dew, hoar-frost, rime, fog, and adsorption of water vapour in the soil. Such NRWIs are often neglected because they are typically small compared to daily rainfall. However, these NRWIs provide our ecosystems with additional water, which is important for the survival of the fauna and flora in the ecosystem, especially during drier periods.

Although NRWIs are understood in principle, much remains to be learnt about their precise determination at the ecosystem level, their spatial and temporal distribution, and their ecological function for the ecosystem. We present a conceptual measurement setup that allows us to determine each non-rainfall water component for natural and extensive grasslands as well as for agricultural ecosystems. Our results for the experimental site Selhausen (Germany, TERENO-SOILCan) show that i) the main part of NRWI comes from dew formation, ii) the rate and frequency of dew formation differs significantly between vegetation types under similar atmospheric boundary conditions, and iii) the drivers of dew formation during a dry down period differ between ecosystems (grassland and arable land). A better understanding of these vegetation and soil-dependent effects will help us to better predict dew formation processes in our ecosystems in the future.

How to cite: Groh, J., Pütz, T., Beysens, D., Vereecken, H., and Amelung, W.: Role of vegetation and soil-induced effects of microclimate on non-rainfall water inputs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7308, https://doi.org/10.5194/egusphere-egu24-7308, 2024.

Water vapor adsorption (WVA), a non-rainfall water input, is a poorly documented phenomenon despite its role in regulating water and energy fluxes in soils of coastal deserts. Water vapor movement towards the soil surface and its absorption by the soil occurs whenever the atmospheric water potential is higher than that of the air-filled soil pores. The latter is influenced by soil characteristics, in particular the soil surface area and pore connectivity. Thus, it is expected that under similar atmospheric conditions,  absorption of water vapor will be determined by soil characteristics. We carried out a detailed field trial in which we compared two loamy soils with different salt content.

Water vapor absorption was measured using micro-lysimeters (MLs) instrumented with relative humidity (RH) and temperature sensors at depths 0.5cm, 2cm, 5cm, 10cm, and 45cm in both MLs during the 2022 and 2023 summers. Total absorption was determined as the increase in mass from a minimum (obtained during late afternoon) to a peak observed on the next day before sunrise. Concurrent changes in soil water potential at each depth were computed by applying the Kelvin equation.

Relative humidity in both soils was low during the entire season with the average computed water potential values being lower in the high salt content soil. The total daily water vapor absorption was lower in the low salt content soil, and the rate of absorption was different . The temperature and RH distribution patterns with depth also differed consistently throughout the measuring season for both soils. The effect of salt on water vapor absorption will be highlighted.

How to cite: Berliner, P., Boadi Manu, M. A., Kool, D., and Agam, N.: The dynamics of water vapor  absorption by soils typical of arid lands, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12298, https://doi.org/10.5194/egusphere-egu24-12298, 2024.

Drylands are 57% of the terrestrial area of the world, and are disproportionally affected by climate change. This is particularly pertinent in so-called “climate-change hotspots” such as the Mediterranean, where temperature increases at a rate of up to 0.45 ^oC/decade and precipitation is expected to decline. Given the sparsity of studies in drylands and the consequent lack of understanding of the unique processes in drylands, the degree to which these projections are accurate for drylands is questionable. The fact that drylands, by definition, are classified according to the aridity index, exposes the inherent assumption that desert hydrology is primarily governed by precipitation and potential evapotranspiration (ET₀). There is increasing evidence, however, that non-rainfall water inputs (NRWIs; fog, dew, and water vapor adsorption) are a substantial source of water in multiple desert environments. In arid and hyper-arid drylands, water vapor adsorption is not only the least studied of the three NRWIs, but also likely the most common. In the Negev desert, Israel, the projected decrease in rainfall and increase in temperature, and therefore increase in ET₀, is expected to result in drier soils. This potentially will increase the amount of water vapor adsorption. Here we present the actual rate of warming and the corresponding changes in ET₀ in the Negev desert. We then elucidate, for the first time, the contribution of water vapor adsorption to desert hydrology and how it might be affected by climate change based on changes observed in the last 20 years.

How to cite: Agam, N. and Kool, D.: Can dry get wetter even if rainfall declines?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2642, https://doi.org/10.5194/egusphere-egu24-2642, 2024.

This study comprehensively investigates the vertical geometry of low-level clouds in the Namib desert. Using ceilometer measurements and meteorological station observations, a precise determination of cloud-base height and the separation of low-level stratus and fog is performed.
The Namib Desert, known for hyper-arid conditions and frequent cloudiness, presents an intriguing environment for the study of low-level clouds and their vertical geometry. Fog (ground-touching low-level clouds), a common atmospheric phenomenon in the Namib Desert, is influenced by the interplay of coastal upwelling and spatial temperature differences. Differentiation of fog from other low-level clouds and understanding cloud dynamics are crucial, as fog impacts the water balance in this arid region. Here, ceilometer measurements of cloud base altitude are analyzed and combined with local station measurements with the aim of developing a statistical model to robustly predict cloud base altitude.
Initial results suggest a robust correlation between the cloud base height and surface relative humidity, as well as other meteorological variables. This finding proves beneficial for utilizing meteorological parameters such as the lifted condensation level as a surrogate for cloud-base height. The outcomes of this study hold significance for modeling of satellite-based fog probability product and ecological studies.

How to cite: Malik, D., Andersen, H., and Cermak, J.: Investigation of the Vertical Geometry of Low Level Clouds in the Namib Desert, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6150, https://doi.org/10.5194/egusphere-egu24-6150, 2024.

Fog forecasting and fog nowcasting events are challenging issues especially when the fog phenomenon appears in the vicinity of airports because the reduced visibility associated with fog represent a high risk for air traffic events. Bucharest Henri Coandă International Airport (OTP, 44.57°N, 26.1°E, 95 m above sea level) is the largest airport in Romania and is located about 16 km north of Bucharest, the capital and most developed city of Romania. Its surroundings are comprised partly of residential and natural protected areas, and partly have agricultural use. Due to its geographic position, the airport is an important air traffic hub on the routes between western and eastern world destinations. In terms of numbers of flights, during the observation period analyzed here, the air traffic at OTP was significantly lowered during the spring of 2020 due to COVID-19 pandemic but soon after the restrictions were lifted and due to redirection of the flights over Ukraine after 2022, the air traffic is significantly increased in present.

Data and analyses reported here cover a period of 2 decades from the beginning of 2003 to the end of 2023. Meteorological data, including fog events, relative humidity, wind speed and direction, were measured by the weather station of Romanian Air Traffic Services Administration ROMATSA R.A. Data about boundary layer and solar radiation was extracted from the public available database from the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5.

Present study reports the analysis of the evolution of the frequency of fog events and the relationships between fog events and speed and direction of the wind, and between fog events and the relative humidity. The correlations between the boundary layer height, solar radiation and the fog events were also investigated. Bivariate polar plots revealed fog appears with higher frequency (about 32%) during cold season, from October to March, and during early morning hours. Overview of the entire data set shows in some years mono-modal distributions of the fog frequency of occurrence with respect to the local time with peaks during the night and in the early morning hours and mono-modal flat distributions in other years. We observed the fog events are correlated with dominant wind directions of east-nord-east (ENE) and west-south-west (WSW). Statistical analysis of the data also showed a prevalence of the radiation fog over the advection fog.

Acknowledgement: AV was supported by the University of Bucharest, PhD research grant. AV acknowledges the partial funding from the NO Grants 2014-2021, under Project contract no. 31/2020, EEA-RO-NO-2019-0423 project. Data regarding boundary layer and solar radiation was extracted from the public available database from the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5. We thank ROMATSA R.A. for access to the database.

How to cite: Vlad, A., Iorga, G., Barbu, N., and Stefan, S.: Examining the fog occurrence over the Bucharest Henri Coandă International Airport and its adjacent area, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16368, https://doi.org/10.5194/egusphere-egu24-16368, 2024.

Based on the understanding of long-term field observations, we monitored the amount of precipitation and dew/frost with field experimental studying in mountainous catchment, using the precipitation observation network in alpine mountainous regions and independently designed observation methods for dew and frost. The purposes of field experiments were to quantitatively identify the distribution pattern of precipitation and dew/frost, characterize the vertical water inputs in catchment scale, and further analyze the formation and transformation law of water resources in inland river source regions.  This dissertation also aimed to rationally develop and utilize precipitation and dew/frost resources, and identify the relationship between precipitation and dew/frost in alpine ecosystems, which will provide the perspective and knowledge of cold region hydrology for promoting regional sustainable development. The main conclusions of the dissertation are as follows:

(1) the relationships between dew/frost and precipitation, and dew/frost and evaporation in the alpine steppe of Hulu catchment.

The interannual ranges in the alpine steppe of Hulu catchment was from 32.36 to 59.68 mm for dew/frost formation, from 404.1 to 557.9 mm for the precipitation and from 343.9 to 372.0 mm for the evaporation.  Therefore, the amount of dew/frost accounts for 5.7% to 12.7% of the precipitation and 7.2% to 17.4% of the evaporation in the same period.

(2) Dew/frost had a significant impact on eco-hydrological system in dry season and comparatively high percentage of frost.

In the dry season, averaged amount of multi-year dew/frost accounted for 54.5% and 40.9% of the multi-year mean precipitation and multi-year mean evapotranspiration, respectively.  Therefore, dew/frost mostly occurred in the dry season.  The annual mean dew amount was 5.90 mm, and the annual mean amount in the dew proportion of dew/frost was 15.26%, while the annual mean frost amount was 31.33 mm, and the frost proportion in dew/frost was 84.74%.  On the monthly scale, frost was mainly generated from March to May and from September to November, which corresponded to the stages of freezing-thawing and thawing-freezing, respectively.

(3) dew/frost events highly depending on precipitation events based on isotope results.

Stable isotope of atmospheric precipitation in the Hulu catchment changed between each season which was noticeable from May to September; not obvious from October to April of the following year.  The spatial and temporal distribution patterns of δ18O and δD isotopes were mainly influenced by the sources of water vapor and small-scale environment.  The occurrence of dew/frost often occurred a few days after a precipitation event, and its stable isotope composition and its variation law were consistent with that of precipitation.  The results showed that the formation and source of dew/frost water are highly dependent on the occurrence of precipitation.  Dew had similar characteristics of precipitation occurred earlier.  However, frost mainly happened in the freezing-thawing process of soil, and is closely related to the isotope value of soil vegetation, which needed further analysis of soil and vegetation isotope samples.

How to cite: Han, C., Chen, R., and Li, H.: Comparative observation and estimation of precipitation and dew/frost on the Northeastern Tibetan Plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3683, https://doi.org/10.5194/egusphere-egu24-3683, 2024.

Interception of fog droplets in cloud forests leads to wetting of the canopy, hampering transpiration and affecting the energy dynamics of the vegetation due to evaporation of the leaf water lamina and the reduction in the incoming solar radiation. We carried out continuous concurrent measurements of the canopy temperature (through infrared thermometers), artificial leaf wetness (LWS) and the micrometeorology of a cloud forest in the Anaga Biosphere Reserve (Tenerife, Canary Islands) during a 4-month period. Fog presence at the site, characterized by visibility measurements (Ω), was coincidental with variations in LWS and a decline in net solar radiation, R_n, i.e. 62.2 W m^-2 during foggy conditions (Ω < 1 km) versus 245.0 W m^-2 for fog-free conditions (Ω ≥ 1 km). Infrared readings during foggy conditions of one of the representative species of the cloud forest stand, the perennial tree Erica platycodon, showed that differences between canopy and ambient temperatures were primarily driven by R_n. After a fog event, E. platycodon was estimated to remain wet for at least 30 minutes up to 2.25 hours. This study provides information about the consequences of fog in the wetting/drying dynamics of cloud forests of the Canary Islands and their leaf thermoregulation.

How to cite: Regalado, C. M., Garcia-Tejera, O., and Ritter, A.: Leaf thermoregulation and fog wetting dynamics of Erica platycodon in a Macaronesian cloud forest, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16844, https://doi.org/10.5194/egusphere-egu24-16844, 2024.

Fog harvesting, an ancient water extraction technique, has gained renewed attention in recent years with the introduction of the Fog Water Collector. Comprising a mesh and supporting structure, this collector has proven effective in extracting water from atmospheric moist air. The Raschel mesh, initially designed for agricultural purposes, has become the predominant choice due to its affordability and widespread availability. Current research endeavors aim to enhance fog water yield by optimizing both collector design and mesh properties.

While Raschel mesh coatings have traditionally been explored to improve efficiency, recent findings suggest that alternative meshes may outperform the conventional Raschel mesh. However, challenges persist in understanding the resistance, lifespan, and maintenance requirements of these newer materials.

Our research takes a systematic approach to address this gap by assessing the durability of various fog harvesting meshes under laboratory conditions. A series of standardized tests are conducted to evaluate their efficiency, providing insights into the intricate relationship between cost, water collection efficiency, duration, and environmental impact. The study aims to inform decision-making processes surrounding fog harvesting mesh selection, considering factors such as initial investment, operational efficiency, and long-term sustainability.

By conducting these analyses in a controlled laboratory environment, we aim to provide valuable insights without the logistical challenges associated with field studies. This approach allows for a thorough examination of fog harvesting mesh performance, contributing to the broader understanding of NRWIs and their potential applications at different scales.

How to cite: Di Bitonto, M. G., Monticelli, C., Viscuso, S., and Zanelli, A.: Laboratory analysis on fog harvesting meshes employing durability tests, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20860, https://doi.org/10.5194/egusphere-egu24-20860, 2024.