186,779 research outputs found
Assessing the impact of seasonal rainfall anomalies on catchment-scale water balance components.
No full textAlthough water balance components at the catchment scale are strongly related to annual rainfall, the availability of water resources in Mediterranean catchments also depends on rainfall seasonality. Observed seasonal anomalies in historical records are fairly episodic, but an increase in their frequency might exacerbate water deficit or water excess if the rainy season shortens or extends its duration, e.g., due to climate change. This study evaluates the sensitivity of water yield, evapotranspiration, and groundwater recharge to changes in rainfall seasonality by using the Soil Water Assessment Tool (SWAT) model applied to the upper Alento River catchment (UARC) in southern Italy, where a long time series of daily rainfall is available from 1920 to 2018. We compare two distinct approaches: (i) a “static” approach, where three seasonal features (namely rainy, dry, and transition fixed-duration 4-month seasons) are identified through the standardized precipitation index (SPI) and (ii) a “dynamic” approach based on a stochastic framework, where the duration of two seasons (rainy and dry seasons) varies from year to year according to a probability distribution. Seasonal anomalies occur when the transition season is replaced by the rainy or dry season in the first approach and when season duration occurs in the tails of its normal distribution in the second approach. Results are presented within a probabilistic framework. We also show that the Budyko curve is sensitive to the rainfall seasonality regime in UARC by questioning the implicit assumption of a temporal steady state between annual average dryness and the evaporative index. Although the duration of the rainy season does not exert a major control on water balance, we were able to identify season-dependent regression equations linking water yield to the dryness index in the rainy season
Analysis of Groundwater Recharge in Mongolian Drylands Using Composite Vadose Zone Modeling
No full textKnowledge of groundwater recharge (GR) is important for the effective management of water resources under semi-arid continental climates. Unfortunately, studies and data in Mongolia are limited due to the constraints in funding and lack of research infrastructures. Currently, the wide accessibility of freely available global-scale digital datasets of physical and chemical soil properties, weather data, vegetation characteristics, and depths to the water table offers new tools and basic information that can support low-cost physically based and process-oriented models. Estimates of GR over 41 study sites in Mongolia were obtained using HYDRUS-1D in a 2-m-thick soil profile with root depths of either 0.30 or 0.97 m by exploiting the daily precipitation and biome-specific potential evapotranspiration values. The GR simulated by HYDRUS-1D arrives at the water table and becomes the actual GR with a lag time that has been calculated using a simplified form of the Richards equation and a traveling wave model. The mean annual precipitation ranges from 57 to 316 mm year−1, and on average about 95% of it is lost by mean annual actual evapotranspiration. In the steppe region, the vegetation cover induces higher-than-normal actual transpiration losses and consequently lower GR. The mean annual GR rates span between 0.3 and 12.0 mm year−1, while travel times range between 4 and 558 years. Model prediction uncertainty was quantified by comparing actual evapotranspiration and GR with available maps and by a sensitivity assessment of lag time to the soil moisture in the deep vadose zone. The partial least squares regression (PLSR) was used to evaluate the impact of available environmental properties in explaining the 47.1 and 59.1% variability of the spatially averaged mean annual GR and travel time, respectively. The most relevant contributors are clay content, aridity index, and leaf area index for GR, and depth to the water table and silt content for the lag time. In data-poor, arid, and semi-arid regions such as Mongolia, where the mean annual GR rates are low and poorly correlated to precipitation, the ever-increasing availability of world databases and remote sensing products offers promise in estimating GR
How effective is bimodal soil hydraulic characterization? Functional evaluations for predictions of soil water balance.
No full textTo overcome some drawbacks of the unimodal relations commonly used to describe soil hydraulic properties (SHPs), previously we developed bimodal lognormal relations that have the following main features: (i) they are closed-form expressions, (ii) they have a sound theoretical basis and provide a more general conceptualization of soil and (iii) they improve the description of both the water retention (WRF) and hydraulic conductivity (HCF) functions. Nevertheless, the reliability of soil hydraulic analytical relations is often tested only at the curve fitting level. Comparisons between unimodal and bimodal soil hydraulic relations are more effective and informative when performed within a functional evaluation approach. We use the HYDRUS-1D package to quantify and compare soil moisture dynamics and storage regimes for hydrological processes at both the event and annual time-scales when the soil domain is characterized by either unimodal or bimodal hydraulic properties. Seven soil samples taken from a previous study were used in numerical simulations of drainage or infiltration processes; there were large relative discrepancies in terms of simulated soil water storage. A subsequent test that involved simulations of soil water budget for the period 2000–2012 was implemented for a peach-orchard field by a conventional scaling method. This test also enables soil spatial variation to be taken into consideration. Two different scenarios enable the epistemic uncertainty to be evaluated when different hydraulic models are considered for soil with weak or strong bimodality. With Willmott's refined index of agreement, discrepancies in soil water storage were about 15% (weak bimodality) or more than 30% (strong bimodality).
Highlights:
Main aim of this study is the assessment of epistemic uncertainty in modelling soil water dynamics.
We make functional evaluations for both event-based and long-term hydrological processes.
Disregard of bimodal soil hydraulic behaviour can lead to large epistemic errors.
Better predictions of soil hydraulic properties should be sought in future research
Perceptions of disease and therapy are factors influencing adherence to antiretroviral therapy
No full textRevisiting the definition of field capacity as a functional parameter in a layered agronomic soil profile beneath irrigated maize
No full textThe soil water content at the condition of field capacity (θFC) is a key parameter in irrigation scheduling and has been suggested to be determined by running a synthetic drainage experiment until the flux rate (q) at the bottom of the soil profile achieves a predefined negligible value (qFC). We question the impact of qFC on the assessment of field capacity. Moreover, calculating θFC as the integral mean of the water content profile when q is equal to qFC is strictly valid only for uniform soil profiles. By contrast, this practice is ambiguous and biased for stratified soil profiles due to the soil water content discontinuity at the layer interfaces. In this study, the concept of field capacity was revisited and adapted to practical agronomic heuristics. By resorting to the assessment of root-zone water storage capacity (W), we envision field capacity as a functional hydraulic parameter derived from synthetic irrigation scheduling scenarios to minimize drought stress, drainage, and nitrate leachate below the root zone.
A functional analysis was carried out on a 135-cm-thick layered soil profile beneath maize in eastern Nebraska. On-farm irrigation scheduling applications and agricultural practices were recorded for 20 years (2001–2020) at a daily time step. Hydrus-1D was calibrated and validated with direct measurements of the soil water retention curve and soil water content data, respectively, in each soil layer. A set of functional field capacity values was derived from 24 irrigation scheduling scenarios, and the optimal water storage capacity at field capacity (WFC) was approximately 50 cm (corresponding to about 80% saturation in the soil profile). An average irrigation amount of 217.5 mm distributed over 21 events was obtained by using optimal irrigation scheduling, which was initiated when the matric pressure head took on a value of -700 cm and the irrigation rate was set at 1.0 cm d-1. This irrigation practice ensured water storage at approximately the same level (ideally at WFC) by sustaining only evapotranspiration fluxes in the uppermost portion of the root zone and by limiting excessive drainage. This protocol can be transferred to other agricultural fields
Reasons for complementary therapies and characteristics of users among HIV-infected people
No full textThe aim of this study was to analyse in a large sample of HIV-infected subjects the expectations toward complementary therapies (CT) and the characteristics of users. Self-administered anonymous questionnaires were distributed in seven European countries among HIV-infected subjects consecutively attending the offices of AIDS organizations. Among 632 ever CT users, nutritional supplements (124 subjects) and psycho-physiological approaches (116 subjects) were the most frequent CT used: 61.4% used CT to improve energy. Half the CT users wanted to prevent or alleviate the highly active antiretroviral therapy (HAART) side effects. General malaise and neuropathy were the most common HAART side effects, where CT users found improvement (62.0% and 54.7%, respectively). Acupuncture improved neuropathy in a high proportion of subjects (87.5%); whereas for others CT. were considered less effective (range 20.0-36.4%). The most common expectations from CT were to improve energy and to prevent or alleviate the HAART side effects. This suggests that HIV-infected people expect not so much specific help as general support from CT
Use of complementary and alternative medicine in HIV-infected subjects
No full textObjectives: To compare the characteristics of HIV-infected subjects who had ever used with those who had never used Complementary and Alternative Medicine (CAM). Design: The European Level Epidemiology of Complementary Therapies in HIV project (ELECTHIV 2), a case-control study, was conducted in seven European countries. All HIV-infected subjects who consecutively attended the offices of the collaborating organizations were eligible for this study. Information was obtained from self-administered, anonymous questionnaires. Setting: A total of 1066 subjects entered the study: 632 were CAM users and 434 had never used CAM. Results: CAM use was more common among females than males (odds ratio (OR) 1.6; 95% confidence interval (CI) 1.2-2.2) and in more educated subjects. CAM use was less common among subjects taking highly active antiretroviral therapy (HAART) (OR 0.5; 95% CI 0.3-0.8), but was more common in outpatients who reported HAART-related side effects (specifically neuropathy). Conclusion: This study indicates that CAM use in HIV-infected subjects is related to female gender, higher levels of education and longer duration of HIV infection
Prediction of biome-specific potential evapotranspiration in mongolia under a scarcity of weather data
No full textWe propose practical guidelines to predict biome-specific potential evapotranspiration (ETp) from the knowledge of grass-reference evapotranspiration (ET0) and a crop coefficient (Kc) in Mongolia. A paucity of land-based weather data hampers use of the Penman–Monteith equation (FAO-56 PM) based on the Food and Agriculture Organization (FAO) guidelines to predict daily ET0. We found that the application of the Hargreaves equation provides ET0 estimates very similar to those from the FAO-56 PM approach. The Kc value is tabulated only for crops in the FAO-56 guidelines but is unavailable for steppe grasslands. Therefore, we proposed a new crop coefficient, Kc adj defined by (a) net solar radiation in the Gobi Desert (Kc adjD) or (b) leaf area index in the steppe region (Kc adjS) in Mongolia. The mean annual ETp obtained using our approach was compared to that obtained by FAO-56 guidelines for forages (not steppe) based on tabulated Kc values in 41 lo-cations in Mongolia. We found the differences are acceptable (RMSE of 0.40 mm d−1) in northern Mongolia under high vegetation cover but rather high (RMSE of 1.69 and 2.65 mm d−1) in central and southern Mongolia. The FAO aridity index (AI) is empirically related to the ETp/ET0 ratio. Ap-proximately 80% and 54% reduction of ET0 was reported in the Gobi Desert and in the steppe loca-tions, respectively. Our proposed Kc adj can be further improved by considering local weather data and plant phenological characteristics
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