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Understanding the interrelation between topography and vegetation across different environments is important to assess how hydrological and climatic conditions affect tree physiological activity. This becomes especially important given the expected reduction in water availability and the increase in water demand driven by climate change. These extremes could enhance the thermal and hydrologic gradients along slopes. Here, we aimed to test if and how different climatic and hydrological conditions affect the physiological response of beech trees (Fagus sylvatica L.) to environmental variables along two different topographic sequences. For this purpose, we set up a comparative study on a gentle hillslope in the Weierbach catchment in Luxembourg (oceanic climate) and on a steep hillslope in the Lecciona catchment in Italy (Mediterranean climate). We combined sap velocity measurements with isotopic measurements of soil, precipitation, stream water, groundwater, and xylem over 2019 and 2020 for the Luxembourgish site and over 2021 for the Italian site. We found that, in the Weierbach catchment, trees' responses to environmental variables (i.e. vapour pressure deficit and relative extractable water in the soil) were similar among hillslope positions and between the two monitored years, resulting from homogeneous growing conditions along the topographic sequence. We also did not find any statistical difference in the isotopic composition of xylem water between positions, suggesting that beech trees relied on similar water sources across the landscape. In the Lecciona catchment, we observed lower sap velocities and shorter growing season in trees growing in the upper portions of the hillslope, likely related to water redistribution and different soil moisture along the hillslope catena. Xylem isotopic composition was significantly lighter at the footslope location throughout the growing season than in the upslope locations, suggesting location-specific water use. These results emphasize how differing hydrometeorological processes occurring at the hillslope scale can lead to contrasting tree responses. [ABSTRACT FROM AUTHOR]

Background: To determine whether artificial intelligence (AI) processed PET/CT images of reduced by one-third of 18-F-FDG activity compared to the standard injected dose, were non-inferior to native scans and if so to assess the potential impact of commercialization. Materials and methods: SubtlePET™ AI was introduced in a PET/CT center in Italy. Eligible patients referred for 18F-FDG PET/CT were prospectively enrolled. Administered 18F-FDG was reduced to two-thirds of standard dose. Patients underwent one low-dose CT and two sequential PET scans; "PET-processed" with reduced dose and standard acquisition time, and "PET-native" with an elapsed time to simulate standard acquisition time and dose. PET-processed images were reconstructed using SubtlePET™. PET-native images were defined as the standard of reference. The datasets were anonymized and independently evaluated in random order by four blinded readers. The evaluation included subjective image quality (IQ) assessment, lesion detectability, and assessment of business benefits. Results: From February to April 2020, 61 patients were prospectively enrolled. Subjective IQ was not significantly different between datasets (4.62±0.23, p=0.237) for all scanner models, with "almost perfect" inter-reader agreement. There was no significant difference between datasets in lesions' detectability, target lesion mean SUVmax value, and liver mean SUVmean value (182.75/181.75 [SD:0.71], 9.8/11.4 [SD:1.13], 2.1/1.9 [SD:0.14] respectively). No false-positive lesions were reported in PET-processed examinations. Agreed SubtlePET™ price per examination was 15-20% of FDG savings. Conclusion: This is the first real-world study to demonstrate the non-inferiority of AI processed 18F-FDG PET/CT examinations obtained with 66% standard dose and a methodology to define the AI solution price. [ABSTRACT FROM AUTHOR]

Summary: In this study we analyse space–time variability of soil moisture data collected at 0–6, 0–12 and 0–20cm depth over three hillslopes with contrasting steep relief and shallow soil depth in the Dolomites (central-eastern Italian Alps). The data have been collected during two summer seasons (2005 and 2006) with different precipitation distribution. Analysis of soil moisture data shows that different physical processes control the space–time distribution of soil moisture at the three soil depths, with a marked effect of dew on the 0–6cm soil depth layer. The range of skewness values decreases markedly from the surface to deeper layers. More symmetric distributions, characterised by relatively low skewness, are found for mid-range soil moisture contents, while highly skewed distributions (generally with more log–normal shape) are found at dry and wet conditions. Scatter plots drawn for the whole data set and the analysis of the correlation coefficients suggest a good persistence of soil moisture with depth: the highest degree of correlation was observed between data collected at 0–12 and 0–20cm. Examination of correlation between soil moisture fields and topographical attributes shows that, notwithstanding the steep relief and the humid conditions, terrain indices are relatively poor predictors of soil moisture spatial variability. The slope and the topographic wetness index, which are found here the best univariate spatial predictors of soil moisture, explains up to 42% of the time-averaged moisture spatial variation. A negative relationship between the soil moisture spatial mean and the corresponding spatial standard deviation is found for mean water contents exceeding 25–30%, while a transition to a positive relationship is observed with drier conditions. Overall, soil moisture variability shows the highest values at moderate moisture conditions (23–29%) and reduced values for wetter and drier conditions for all depths. A negative linear relationship between mean soil moisture content and the coefficient of variation was observed. A soil moisture dynamics model proved to successfully capture the soil moisture variability at the hillslope scale. The simulated time series of hillslope-averaged soil moisture are in good agreement with the observed ones. Moreover, the model reproduces consistently the observed relationships between soil moisture spatial mean and corresponding variability. [Copyright &y& Elsevier]

The stable isotopes of hydrogen and oxygen are commonly used as tracers in catchment hydrology research. Most studies collect isotope samples from precipitation, streamflow, groundwater, and soil water at different times during the study period, but at only a few locations, and assume that these samples are representative for the catchment. To test whether this assumption is correct, we reviewed 149 peer-reviewed papers published in international journals between 1970 and 2017 that used at least one of the stable isotopes of hydrogen and oxygen to investigate hydrological processes at the small catchment scale (up to 10 km2). The objective was i) to determine the typical observed spatial variability in the isotopic composition of different hydrological compartments in small catchments around the world, and ii) to assess how this spatial variability might affect isotope-based hydrograph separation results. The majority of published studies were conducted in temperate and cold regions of the world. Only a few studies sampled a hydrological compartment at five or more locations throughout the catchment. Most studies that sampled a compartment at more than five locations reported a large spatial variability in the isotopic composition for that compartment. The reported spatial variability in the isotopic composition was largest for snowmelt and soil water (median range in δ18O up to 6‰ and maximum range up to 44‰), followed by throughfall and shallow groundwater. To test whether the observed spatial variability was significant, we adjusted the isotopic composition of throughfall, soil water and groundwater in a small catchment in Italy by the average observed spatial variability. We then re-ran the three component hydrograph separation for two rainfall-runoff events (using electrical conductivity as the second tracer). The calculated maximum contributions of the three components to streamflow differed by up to 26% from the reference scenario. This suggests that if the variability in the isotopic composition of throughfall, soil water and groundwater in this catchment was similar to the average observed variability, we could have obtained significantly different results if we had sampled throughfall, soil water and groundwater at different locations. These results thus suggest that we need to interpret isotope hydrograph separation results with care if they are based on only one or a few sampling sites, and that even in small catchments it is important to take samples at multiple locations.Keywords: stable isotopes in water; small catchments; spatial variability; hydrological compartments. [ABSTRACT FROM AUTHOR]

The climate in the Mediterranean region is expected to become warmer and drier but future projections of precipitation are uncertain, especially in the Northern part. Additionally, the difficulty in determining the plant physiological responses caused by CO 2 rising complicates the estimation of future evaporative demand, increasing the uncertainty of future aridity assessments. Vegetation responses to rising CO 2 are expected to increase radiation use efficiency and reduce stomatal conductance, hence increasing plant's water use efficiency. These effects are often neglected when estimating future drought and aridity. Hence, the main objective of this study is to estimate the effect of climate change and vegetation stomatal conductance reduction on projected water balance components and the resulting impact on aridity in a medium-sized catchment of Central Italy. We validate and couple a hydrological model with climate projections from five regional climate models and perform simulations considering the vegetation responses or not. Results show that their inclusion significantly affects potential evapotranspiration. The other water balance components, namely actual evapotranspiration, water yield, percolation, and irrigation, are also influenced but with less significant changes. Considering or not the CO 2 suppression effect on stomatal conductance, coupled with the uncertainty related to precipitation, highly affects the estimation of future aridity as the future climate classification ranges from "humid" to "semi-arid" depending on the simulation and climate model, even if model outputs need to be evaluated cautiously with CO 2 concentration higher than 660 ppm. [Display omitted] • SWAT+ performed well in simulating monthly streamflow of the Ombrone catchment. • The multi-site calibration improved the performance of the model. • SWAT+ outputs with CO 2 concentration higher than 660 ppm seem unreliable. • Future aridity conditions in the study area are highly uncertain. • Vegetation responses to CO 2 affect future water balance components. [ABSTRACT FROM AUTHOR]

Mediterranean watersheds are expected to face increased and more severe drought events due to climate change. Urgent action is needed to shift from a reactive approach to a proactive one, for which drought risk assessment is fundamental. Nevertheless, the current methodology to calculate composite risk indicators is still debated, undermining the overall robustness and validity of drought risk assessments. Furthermore, the diversity of socio-ecological contexts, spatiotemporal scales, and data availability hamper the homogenization of assessment methods. We present a complete drought risk assessment methodology, applied to the agricultural systems of five Italian coastal watersheds, introducing a simple robustness evaluation method to validate the assessment tool and archetype analysis to link the outputs with adaptation strategies. Forty-two (42) indicators were included to represent hazard, exposure, and vulnerability. Past and future drought hazards were estimated considering multiple types of droughts with data from public observatories.The results show highest hazard for the southern part of the study region, highest exposure in the coastal and high-value wine producers' municipalities, while vulnerability patterns are less clear. Major adaptation efforts should target specific watersheds of the Grosseto province, which has the highest projected drought risk. Archetype analysis was then used to suggest possible context-specific adaptation strategies. The proposed methodology, with the integration of a robustness evaluation and the archetype analysis, represents an advancement toward shared and homogeneous guidelines in state-of-the-art drought risk assessments. [Display omitted] • A methodology to perform drought risk assessment is presented for Mediterranean watersheds. • The assessment is validated through a rapid and complete robustness evaluation. • Southernmost municipalities of Tuscany have the highest drought risk. • Tailored adaptation strategies are proposed for different clusters of municipalities. [ABSTRACT FROM AUTHOR]

The hydrological response of forested catchments is strongly influenced by evapotranspiration.Numerous studies have reported the effect of evapotranspiration on the annual water balanceat different spatial scales, but detailed eco-hydrological monitoring at the small catchmentscale is still needed to improve the estimation of evapotranspiration fluxes and runoffresponse by hydrological models. In this study, we used hydrometeorological data from two small forested catchments inItaly to i) investigate the hydrological response of the two catchments at seasonal andrainfall-runoff event time scale, and ii) analyze the daily fluctuations in streamflow and theshallow water table. The two catchments are covered by dense mixed broad-leaf forest. The Ressi catchment(0.02 km2) is located in the Italian pre-Alps and its climate is oceanic, while the Re dellaPietra catchment (2.0 km2) lies in the Northern Apennines and the climate is humidsub-tropical. Streamflow, rainfall, air temperature and solar radiation were measured continuously inboth catchments. In the Ressi catchment, shallow water table was measured in twopiezometers installed at a depth of 2.0 and 1.8 m in the riparian zone, while sap flow wasmonitored in two beech trees located in the riparian zone, and one beech tree and onechestnut tree on the hillslope. Preliminary results show that during the growing season, rainfall-runoff events had largerainfall intensities, short duration and small stormflow volumes. In the Ressi catchment,runoff coefficients varied between 0.1 and 96% (mean: 17%, n=155, period: August2012-November 2016), with event runoff coefficients in summer much smaller (mean: 7%,n=66) than during the rest of the year. In the Re della Pietra catchment, event runoffcoefficients in the period July-September were also small and varied between 1.2 and 5.1%(n=8). During dry periods, streamflow tended to decrease in both catchments, but with differentdynamics. Strong daily streamflow fluctuations were observed in summer in the Re dellaPietra catchment, with minimum streamflow lagging peak solar radiation by 1-3 hours.Conversely, no daily streamflow fluctuations were observed at the end of the growing season,probably due to the reduced impact of evapotranspiration on the catchment storage. In theRessi catchment, we did not observe clear daily streamflow fluctuations, likely due to thefrequent summer storms interrupting the baseflow. However, the shallow watertable experienced daily fluctuations. We observed that the minimum water tablelevel lagged peak sap flow by 1-6 hours, implying a role of evapotranspiration onwater table variations. Based on these results, further analyses will be carried out toestimate daily and seasonal groundwater recharge and evapotranspiration in bothcatchments. Acknowledgements: This study is part of the research project "SILVA - Water fluxesbetween soil, vegetation and atmosphere: a comparative analysis in two Italian forestedcatchments", funded by Premio Florisa Melone 2018 assigned by the Italian HydrologicalSociety. Keywords: daily streamflow fluctuations; shallow water table; evapotranspiration; runoffcoefficients; forested catchments. [ABSTRACT FROM AUTHOR]