1,721,031 research outputs found
Downscaling of American National Aeronautics and Space Administration (NASA) daily air temperature in Sicily, Italy, and effects on crop reference evapotranspiration
No full textAir temperature (Ta) is one of the key factors in agro-hydrological studies including estimation of crop reference evapotranspiration (ET0), which is crucial for irrigation water management and sustainability of agro-ecosystem productivity. Because direct measurements of ET0are difficult, expensive and time consuming, the use of physically based or empirical approaches linked to meteorological information is often preferred. The Prediction of Worldwide Energy Resource project developed by the American National Aeronautics and Space Administration (POWER-NASA) provides daily meteorological information on a 1° latitude by 1° longitude grid. Despite the poor spatial resolution characterizing this archive, the data is global and continuous in time, so that it can be used in particular regions of the globe where weather measurements are not well spatially distributed and/or there are some missing weather data to fill. Procedures for downscaling and spatial disaggregation of daily air temperatures retrieved from the POWER-NASA archive were proposed and validated for the climate of Sicily, Italy. In particular, a cosine function with three empirical parameters derived from ground elevation was suggested to estimate the spatial and temporal variability of a lapse rate adjustment factor used to downscale and to disaggregate POWER-NASA air temperature. Model calibration was carried out over three years (2006–2008), whilst validation regarded the measurements acquired over the following six years (2009–2014). Downscaled daily air temperature results were consistent and comparable with local ground measurements. The spatial disaggregation technique, aimed to map the distributions of Ta, was then tested by the joint use of the Digital Elevation Model (DEM) and the proposed model. Finally, in order to assess the suitability of downscaled air temperatures, two simplified empirical equations to estimate daily reference evapotranspiration (ET0) from air temperature and solar radiation (Turc, 1961; Hargreaves, 1975) were applied. To this aim, daily ET0estimated by introducing native and downscaled POWER-NASA air temperature values into Turc and Hargreaves equations were compared to the corresponding estimations obtained with FAO 56 Penman Monteith (FAO 56 PM) equation and climate data measured on ground
Combining the FAO56 agrohydrological model and remote sensing data to assess water demand in a Sicilian irrigation district
Full text linkAgricultural water use in irrigated areas plays a key role in the Mediterranean regions characterized by semi-arid climate and water shortage. In the face of optimizing irrigation water
use, farmers must revise their irrigation practices to increase the drought resilience of agricultural systems and to avoid severe damages in agro-ecosystems. In this direction, during the last
decades, the research has been focused on mathematical models to simulate the process of driving mass transport and energy exchanges in the Soil-Plant-Atmosphere system.
The objective of the paper was to test the suitability of the combination of FAO56 agrohydrological model with remote sensing data retrieved from the Moderate Resolution Imaging
Spectroradiometer (MODIS) platform, to assess the spatiotemporal distributions of crop water requirement and to schedule irrigation in an irrigation district of the south-west of Sicily, Italy.
The proposed approach allowed obtaining the spatiotemporal distributions of soil and crop parameters used in the FAO56 model implemented in a GIS environment to simulate the water
balance, as well as to assess the actual irrigation strategy. The GIS database was organized to include soil and crop parameters, as well as the irrigation volumes actually delivered to each
farmer; the latter data can be used not only as input for water balance to evaluate the efficiency of the actual irrigation strategies but also to identify different irrigation scheduling scenario obtained
by the FAO56 procedure. The first application was carried out for the period 2014-2017, to identify a combination of irrigation scheduling parameters to be implemented in the model aimed at reproducing the ordinary strategy adopted by the farmers, based on the spatiotemporal variability of soil and climate forcings. When the model outputs were aggregated for single crop types, a fairly good agreement was found between simulated and actual seasonal irrigation volumes delivered either at the level of district and secondary units. Alternative scenarios of irrigation water distribution
were then identified and analyzed, to provide irrigation technicians and policymakers a decision support tool to improve the efficiency of irrigation systems and to optimize the distribution based
on the availability of water resources
Metodo per il monitoraggio di superfici vegetali
No full textSi descrive un metodo da impiegare per la caratterizzazione delle coperture vegetali.A method to be used for the monitoring of vegetation surfaces is described, which includes the use of a device for measuring the spectral reflectance of vegetation using images acquired with a lightening system based on visible and infrared monoband LEDs and including devignetting, image cropping, radiometric calibration procedures and calculation of reflectance values and vegetation indices
Method for monitoring vegetation ground covers
No full textA method to be used for the monitoring of vegetation surfaces is described, which includes the use of a device for measuring the spectral reflectance of vegetation using images acquired with a lightining system based on visible and infrared monoband LEDs and including devignetting, image cropping, radiometric calibration procedures and calculation of reflectance values and vegetation indices
Aridity index, soil erosion and climate drive no-till ecosystem services trade-off in Mediterranean arable land
No full textDespite the relevant literature on the advantages of no-till (NT) management, the world area under NT is only 10% of the arable land, probably due to several limiting factors as climate, soil types, farming systems and yield.
Soil conservation practices and particularly NT soil management are able to provide many ecosystem services (ESs). This paper suggests a framework to determine the area distribution of soil erosion control and food security
ESs trade-offs furnished by NT, starting from the potential soil erosion and aridity index maps. The interaction between the potential soil erosion and the aridity index showed that different trade-offs and synergies of multiple
ESs may occur and need to be interpreted. The yield success probability of NT with respect to CT (P(NT)) and soil erosion tolerance (SET) were considered to determine four classes of the NT adaptability index, which represent the NT ability to support multiple ESs, under the environmental condition. For 2020 as a baseline, and 2050 as a future scenario, in between latitudes 35◦ and 47◦, an analysis was carried out, focusing on the arable lands of five European Mediterranean countries (France, Greece, Italy, Portugal and Spain), which are potentially cropped
with durum wheat. Results showed that, for the considered arable land area, under NT soil management and from a food security point of view, the potential durum wheat area, under climate change pressure, slightly increases, if residues are retained. On the contrary, if residues are removed, the potential durum wheat area is very limited for both the baseline and the 2050 scenario. The area distribution corresponding to the NT adaptability index classes could be suitable for stakeholders to modulate payments for agri-environmental measures, based on the actual provided ESs
Using scintillometry to assess reference evapotranspiration methods and their impact on the water balance of olive groves
Full text linkReference evapotranspiration (ET0) is widely used for irrigation scheduling, to promote an efficient use of water resources for a sustainable agro-ecosystem productivity, as well as to manage water quality and to face other environmental concerns. As suggested by ASCE-EWRI and FAO, standard Penman-Monteith methods are generally applied for an accurate estimation of ET0 from hourly to daily scale. In absence of detailed meteorological information several simplified equations, using a limited number of variables, have been proposed as alternative. In this paper, the performance of different reference evapotranspiration methods, at hourly (Penman-Monteith, Pristley-Taylor, Makkink and Turc) and daily scale (Penman-Monteith, Blaney and Criddle, Hargreaves, Pristley-Taylor, Makkink and Turc), was evaluated against scintillometer measurements collected during six month in 2005 in an experimental plot maintained under "reference" conditions (alfalfa crop). The daily values of ET0 obtained with the examined methodologies were then used as input in the FAO-56 agro-hydrological model, in order to evaluate, for an olive grove in a Mediterranean environment, the impact on simulated actual evapotranspiration. The experiment was carried out in South-West Sicily, in an area where olive groves are the major crop. The comparison between estimated and measured fluxes confirmed that FAO-56 Penman-Monteith (PM) standardized equation is characterized by the lowest mean bias error (-0.15 mm d-1 and 0.06 mm d-1 using daily or hourly data, respectively). Additionally, the analysis also highlighted that the Pristley-Taylor equation can be considered a valid alternative for an accurate estimation of ET0 (mean bias error of 0.35 mm d-1 and 0.43 mm d-1 using daily or hourly data, respectively). The application of the FAO-56 water balance model on the investigated olive grove evidenced that the best estimations of actual evapotranspiration are obtained when the Pristley-Taylor ET0 data are used as input, confirming that this approach can be considered a valid alternative to the standard Penman-Monteith
Estimating crop coefficients and actual evapotranspiration in citrus orchards with sporadic cover weeds based on ground and remote sensing data
Full text linkAccurate estimations of actual crop evapotranspiration are of utmost importance to evaluate crop water requirements and to optimize water use efficiency. At this aim, coupling simple agro-hydrological models, such as the well-known FAO-56 model, with remote observations of the land surface could represent an easy-to-use tool to identify biophysical parameters of vegetation, such as the crop coefficient Kc under the actual field conditions and to estimate actual crop evapotranspiration. This paper intends, therefore, to propose an operational procedure to evaluate the spatio-temporal variability of Kc in a citrus orchard characterized by the sporadic presence of ground weeds, based on micro-meteorological measurements collected on-ground and vegetation indices (VIs) retrieved by the Sentinel-2 sensors. A non-linear Kc(VIs) relationship was identified after assuming that the sum of two VIs, such as the normalized difference vegetation index, NDVI, and the normalized differ-ence water index, NDWI, is suitable to represent the spatio-temporal dynamics of the investigated environment, characterized by sparse vegetation and the sporadic presence of spontaneous but transpiring soil weeds, typical of winter seasons and/or periods following events wetting the soil surface. The Kc values obtained in each cell of the Sentinel-2 grid (10 m) were then used as input of the spatially distributed FAO-56 model to estimate the variability of actual evapotranspiration (ETa) and the other terms of water balance. The performance of the proposed procedure was finally evaluated by comparing the estimated average soil water content and actual crop evapotranspiration with the corresponding ones measured on-ground. The application of the FAO-56 model indicated that the estimated ETa were characterized by root-mean-square-error, RMSE, and mean bias-error, MBE, of 0.48 and -0.13 mm d−1 respectively, while the estimated soil water contents, SWC, were characterized by RMSE equal to 0.01 cm3 cm−3 and the absence of bias, then confirming that the suggested procedure can produce highly accurate results in terms of dynamics of soil water content and actual crop evapotranspiration under the investigated field conditions
Assessing the performance of different model-based techniques to estimate water content in the upper soil layer
Full text linkThe knowledge of soil water content (SWC) of the upper soil layer is important for most hydrological processes
occurring over vegetated areas and under dry climate. Because direct field measurements of SWC are difficult, the
use of different type of sensors and model-based approaches have been proposed and extensively used during the
last decade.
The main objective of this work is to assess the performance of two models estimating SWC of the upper soil
layer: the transient line heat source method and the physically based Hydrus-1D model. The models’ performance
is assessed using field measurements acquired through a Time Domain Reflectometer (TDR).
The experiment was carried out on an olive orchard located near the town of Castelvetrano (South-West of Sicily
- latitude 37.6429◦
, longitude 12.8471◦
). The temporal dynamic of topsoil water content was investigated in two
samplers, under wet and dry conditions. The samplers were opened at the upper boundary and inserted into the
soil to ensure the continuity of the soil surface.
A K2D Pro sensor allowed to measure the soil thermal properties allowing to estimate soil thermal inertia and
then SWC. The physically based Hydrus-1D model was also used to estimate SWC of both samples. Hourly
records of soil water contents, acquired by a TDR100 probe, were used to validate both the considered models.
The comparison between SWCs simulated by Hydrus-1D and the corresponding values measured by the TDR
method evidenced a good agreement. Similarly, even SWCs derived from the thermal diffusion model resulted
fairly close to those measured with the TDR
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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