Evaluation of Turbulent Fluxes on a mountain slope

Studies about turbulent exchanges, momentum and mass transfer and energy balance on mountain slopes allow a better comprehension of the interactions between soil and atmosphere in complex orography. In addition, if long periods of observations are considered, the evolution of energy and mass fluxes can be derived. This is useful for model delicate ecosystems such as in the highlands. Furthermore, the study on carbon dioxide fluxes can be related to the increase of greenhouse gas. The eddy-covariance technique has some critical points: one of the most important is related to the relative uncertainty in the fluxes estimation when there are bad weather or low-wind and nocturnal conditions. Our aim is divided into two parts: in the first one, the meandering was explored. In the second part, we compared two approaches, the planar fit and the double rotation techniques for the computation of turbulent fluxes. Because of the high number of low-wind speed conditions (LWS), we investigated the “meandering”: in LWS conditions, wind speed components and scalars such as temperature can show oscillations visible in the auto-correlation function of the signals. In these cases, turbulent fluxes estimation may be difficult. We analysed 11 months of data collected at 10 Hz, considering a 1-hour time scale, with the identification of surface-layer parameters. Meandering phenomenon was explored following the works of Mortarini et al. (2013, 2015). We evaluated also the impact of clear-sky conditions on our data. We observed the validity of the formula for spectral analysis proposed in the aforementioned papers in most part of the analysed hours. Meandering conditions occur in 305 hours over more than 8000, especially during winter and night, although there are diurnal episodes. Meteorological conditions seem to play some role on the local phenomena because, although no certain relationship between stability and meandering parameters was found, the sky was cloudy in most part of meandering hours. In the second part, 30-minutes turbulent fluxes (sensible heat flux, latent heat flux and mass fluxes of water vapour and carbon dioxide) were determined using planar fit and double rotation techniques and the eddy-covariance technique use was tested for our site having a slope of about 26. Then, computation of the energy balance was done. We made comparisons between estimated and measured data and considerations on sensible and latent heat fluxes, then energy and mass fluxes and net radiation were computed also at the daily scale. We found that anemometer rotations improve robustness of computation and the difference between planar fit and double rotation is not so high in fluxes computations. Planar fit seems to give more reliable values. Considering the ground heat flux, G, we obtained a better approximation of energy balance. In particular, the computation of the energy balance ratio (EBR) showed that in general the balance is better during the daytime, while the seasons in which the energy balance is nearer to closure are summer and autumn

Quality control on eddy covariance diurnal fluxes of energy and carbon dioxide on a mountain slope

Eddy covariance data were collected at a station located on a slope characterised by a very common and increasing land cover in the Alpine region, that is, the abandoned pasture. Three diurnal growing season (2014, 2016 and 2017) were considered. The site is located at 1730 m asl in Cogne (Valle d’Aosta, Italy). The sensible and latent heat fluxes, as well as the carbon dioxide flux, were estimated. The in-situ fluxes and their quality were examined to assess whether an acceptable amount of good quality data was collected, and then proposing a simple step by step quality control procedure. Finally, the assessment on the typical daily cycle was computed. The results suggest that there is a relatively high amount of reliable data (82.3%, 82.5% and 72.2% for the three explored fluxes, namely the sensible and latent heat and the carbon dioxide fluxes, after all the quality control). The eddy covariance technique gives a rather acceptable performance in the evaluation of daytime fluxes and especially in evaluating the cumulative fluxes for energy and CO2. In fact, the data are of better quality when the fluxes are higher, while the lower quality is found usually when the fluxes are weak. Finally, another information on the reliability of the evaluated fluxes is given by the energy balance closure computation, which yields, using the energy balance ratio method, an overall value of 0.69

Long-Range Low-Power Electronic System for Drip Irrigation in Precision Agriculture

Nowadays, food security is threatened by population growth, wars, climate change, and desertification due to human activities. Precision agriculture is a novel concept to minimize the usage of natural resources in the agriculture field, mitigating the anthropological effects. This is possible by adopting electronic systems to measure plants' requirements and to make optimal decisions on the crop, avoiding wastefulness. One critical aspect of agriculture is the handling of potable water: an essential resource for all living entities. This paper proposes a long-range, low-power electronic system for drip irrigation in orchards, especially Actinidia and apple trees, to control the distributed water to the cultivars. In this way, the irrigation cycle depends on the plants' needs, saving water and energy resources. The node communicates using LoRa radiofrequency protocol, and it can be used in rural areas where no internet connection is present

Evapotranspiration of an Abandoned Grassland in the Italian Alps: Modeling the impact of shrub encroachment

Shrub encroachment of grasslands in the Alps is still a poorly studied phenomenon. Therefore, this study analyses the possible effect of shrub encroachment on actual evapotranspiration (ETa) at an abandoned grassland in the Northwestern Italian Alps, colonised by Elaeagnus Rhamnoides shrubs. This is done by means of micrometeorological and eddy covariance data collected during four growing seasons. Additionally, the Hydrus 1D hydrological model modified to account for a soil column with two vegetation types is used. This modified model is run with a variable percentage of shrubs on evapotranspiration, ranging from 0 to 80% and it is validated by using the measured eddy covariance-derived ETa. The Hydrus 1D model is also applied in its usual set-up, having only one vegetation type, to estimate the ETa from both grassland and shrubs separately. The performance of the modified model with two vegetation types is acceptable, although it is very variable between different growing seasons and in dry condition it could be further improved (R between 0.50 in 2016 and 0.73 in 2014 considering the probable actual percentage of ETa affected by shrubs. The percentage varies between 20% in 2016 and 60% in 2014). Besides, the model captures the inter-annual variability of ETa. The agreement of cumulative simulated and observed ETa is good, since the deviation between observed and modelled cumulative ETa is always lower, in the four analysed growing seasons, than 50 mm. The simulated ETa approximates the eddy covariance-derived ETa, however the modelled soil water content is very sensitive to precipitation events, more than the measured soil water content. Both models, with the modified and the usual setup, tend to overestimate the vegetation stress during dry periods. Nevertheless, the single vegetation model results allow us to conclude that the shrubs likely are responsible for an enhancement of ETa and an alteration of the hydrological cycle accordingly. Finally, we explore how some micro-meteorological drivers of ETa (vapour pressure deficit – VPD, net radiation, wind speed, air temperature and ground heat flux - G0) affect the difference between modelled and simulated ETa, and between simulated ETa from shrubs and from grass. Frequently, higher deviations from zero are found especially with high VPD and G0