Assessing agro-hydrological models to schedule irrigation for crops of Mediterranean Environment

Scaling properties of topologically random channel networks

Abstract The analysis deals with the scaling properties of infinite topologically random channel networks (ITRNs) fast introduced by Shreve (1967, J. Geol. , 75: 179–186) to model the branching structure of rivers as a random process. The expected configuration of ITRNs displays scaling behaviour only asymptotically, when the ruler (or ‘yardstick’) length is reduced to a very small extent. The random model can also reproduce scaling behaviour at larger ruler lengths if network magnitude and diameter are functionally related according to a reported deterministic rule. This indicates that subsets of rrRNs can be scaling and, although rrRNs are asymptotically plane-filling due to the law of la…

Actual evapotranspiration assessment by means of a coupled energy/hydrologic balance model: Validation over an olive grove by means of scintillometry and measurements of soil water contents

Summary A coupled energy/hydrologic model was applied to simulate the exchange of energy and water in the soil–plant-atmosphere system (SPA). The model, which uses a “two-source” approach to estimate the energy fluxes, and the “force-restore” approach to represent the water balance, was validated by means of evapotranspiration measurements collected via scintillometry and soil moisture measurements collected via time domain reflectometry (TDR) in a Sicilian olive grove. The comparison between measured and estimated fluxes values at an hourly scale showed good agreement. Additional comparisons on a daily timescale confirmed the model’s applicability for quantifying crop water requirements. A…

Multiple Non-linear Reservoirs to Model Water Balance Components in Sandy Soils

In the hydrologic literature, to model water flow in unsaturated soils, the Richards equation is usually applied, allowing the main components of the hydrologic cycle, as rainfall partitioning into surface runoff and infiltration, to be determined. The Richards equation is highly nonlinear, making very challenging to derive analytical solutions. Recently, for constant rainfall intensity, under the simplified hypothesis of gravity-driven infiltration, and by assuming a capacitance framework, a simplified solution of the Richards equation that considers the Brooks and Corey hydraulic conductivity function was suggested. By maintaining the assumption that the infiltration process is dominated …

Comparing Physical Quality of Forest and Pasture Soils in a Sicilian Watershed

Forest and pasture soils should have differing properties due, for example, to differing root characteristics or livestock trampling rates, but contradictory results are reported in the literature. The surface soil physical and hydraulic properties of five forest and pasture sites were determined in a Sicilian watershed. In general, forest soils had a significantly lower bulk density, b (by 17 to 35%), and a higher field saturated hydraulic conductivity, Kfs (by a factor of 3.4-11.5) than pasture soils. Differences between water retention characteristics of forest and pasture soils were low when high levels of organic matter, OM, content (> 7.1%) were detected for both land uses. The mean …

Effetti della copertura forestale sulle caratteristiche idrologiche del suolo

About time of occurrence of rainy days for Mediterranean and (sub)-Alpine areas

A simple model of hillslope response for overland flow generation

This paper deals with the derivation of the hydrological response of a hillslope on the assumption of quick runoff by surface runoff generation. By using the simple non-linear storage based model, first proposed by Horton, an analytical solution of the overland flow equations over a plane hillslope was derived. This solution establishes a generalization for different flow regimes of Horton's original solution, which is valid for the transitional flow regime only. The solution proposed was compared successfully with that of Horton and, for the turbulent flow regime, to the one derived from kinematic wave theory. This solution can be applied easily to both stationary and non-stationary rainfa…

Quick and Slow Components of the Hydrologic Response at the Hillslope Scale

It is widely recognized that the Hortonian mechanism of runoff generation occurs in arid and semi-arid regions, generally characterized by high rainfall intensity on soils exhibiting low infiltrabilities. Differently, in steeply sloping forested watersheds in humid climates, by infiltrating through a highly permeable upper soil horizon, water moves beneath the soil surface determining a slow response. However, in most real cases, for example when in arid regions mountain forested areas take place, both (quick and slow) runoff generation processes coexist and together contribute to the hydrologic hillslope response. In this paper, based on analytical solutions of the hydrologic response, ins…

Determinazione delle proprietà idrauliche del suolo in una pendice naturale

Modeling olive orchard response to water stress and definition of critical thresholds of soil water status.

Sulla risposta idrologica di un versante a prevalente deflusso hortoniano

Overland flow generation on hillslopes of complex topography: analytical Solutions

The analytical solution of the overland flow equations developed by Agnese et al. (2001; Hydrological Processes15: 3225–3238) for rectangular straight hillslopes was extended to convergent and divergent surfaces and to concave and convex profiles. Towards this aim, the conical convergent and divergent surfaces are approximated by a trapezoidal shape, and the overland flow is assumed to be always one-dimensional. A simple ‘shape factor’ accounting for both planform geometry and profile shape was introduced: for each planform geometry, a brachistochrone profile was obtained by minimizing a functional containing a slope function of the profile. Minima shape factors are associated with brachist…

Sulla distribuzione dei tempi di inter-arrivo delle piogge

La caratterizzazione probabilistica delle precipitazioni rappresenta un tema centrale in diverse aree di ricerca, come l'idrologia, la meteorologia, la climatologia, ed altre ancora, per le sue implicazioni sia teoriche sia pratiche. Un particolare interesse riguarda l’analisi della struttura probabilistica dei tempi di inter-arrivo delle piogge, alla scala giornaliera, che permette di inferire sulla probabilità della durata dei periodi di pioggia e dei periodi di siccità, dando conto sia della tendenza degli eventi di pioggia ad aggregarsi in cluster, che di quella alla persistenza dei periodi secchi. Nel presente lavoro, una siffatta analisi è stata condotta su alcune serie temporali di t…

Monitoraggio e modellazione agro-idrologica in ambiente mediterraneo:Applicazione ed indagini sperimentali.

Uso di modelli agro-idrologici per la gestione dell'irrigazione di colture arboree mediterranee

Delay times for saturation overland flow in forest soils

Modelling rainfall interarrival times and rainfall depths at daily scale

Analysis of daily rainfall data, and subsequent modelling of some derived variables concerning rainfall, is fundamental in different areas such as agricultural, ecological, and engineering disciplines. A way of studying the alternance of consecutive rainy days (wet spells) and no-rainy days (dry spells) is through the interarrival time (IT), which is the time elapsed between two consecutives rainy days. If we suppose that IT observations are independent and identically distributed (i.i.d.), ITs are usually modelled through a renewal processes. The simplest renewal process is the Bernoulli process with ITs geometrically distributed. The need to suppose a non-constant probability of rain brin…

Analisi regionale delle variazioni a lungo termine di grandezze climatiche in Sicilia

Modelling the Frequency of Interarrival Times and Rainfall Depths with the Poisson Hurwitz-Lerch Zeta Distribution

The Poisson-stopped sum of the Hurwitz–Lerch zeta distribution is proposed as a model for interarrival times and rainfall depths. Theoretical properties and characterizations are investigated in comparison with other two models implemented to perform the same task: the Hurwitz–Lerch zeta distribution and the one inflated Hurwitz–Lerch zeta distribution. Within this framework, the capability of these three distributions to fit the main statistical features of rainfall time series was tested on a dataset never previously considered in the literature and chosen in order to represent very different climates from the rainfall characteristics point of view. The results address t…

Estimation of Daily Solar Radiation from Measured Air Temperature Extremes in the Mid-Mediterranean Area

AbstractDaily solar radiation Rs at ground level is a necessary input variable required for the evaluation of evapotranspiration and crop growth, development, and yield-simulation models. Nevertheless, it is measured in few weather stations and at many locations it is not observed; also, available Rs temporal series are generally no longer than a few years. A valid surrogate of Rs measurement is the diurnal air-temperature range (ΔT); indeed, ΔT is inversely proportional to cloudiness and therefore could be a good indicator of atmospheric transmittance. As opposed to Rs, daily maximum and minimum air temperatures are measured at many locations and their observations in developed countries b…

Stima delle componenti del flusso evapotraspirativo di un oliveto con l’uso congiunto delle tecniche Sap-Flow ed Eddy Covariance.

Spatial variability of dry spells duration statistical distributions

Dry spells duration and its extent in space, is a key factor in water resources problems. In order to modelling the empirical distribution of dry spells (DS) frequencies observed in Sicily (i.e. in a typical Mediterranean climate), Agnese et al. (2014) successfully applied the two-parameter polylogarithm-series distribution. Because of the strong seasonality characterising Sicily’s rainfall regime, statistical analysis was separately applied to two data sets, referred to as “dry” and “wet” seasons, respectively. In this work, a similar analysis was carried out for a set of 26 DS time-series recorded in a large area (about 30000 km2), including Piedmont and the Aosta Valley. Area altitude ra…

CONFRONTO TRA DATI DI TEMPERATURA RILEVATI IN AREE URBANE E IN AREE AGRICOLE LIMITROFE

Il fenomeno noto come “isola di calore urbana” (Urban Heat Island, UHI), che riguarda prevalentemente i paesi più industrializzati, consiste nell’aumento della temperatura dell’aria nei centri abitati per effetto dell’urbanizzazione. La verifica di tale fenomeno è stata eseguita in Sicilia instaurando un confronto tra le temperature massime, minime e le escursioni termiche di coppie di stazioni di misura, poste rispettivamente all’interno e all’esterno di alcuni centri urbani minori nel periodo 2002-2005. L’analisi è stata sviluppata a scala annuale e semestrale (separando la stagione tipicamente secca, da Aprile a Settembre, da quella umida), in modo da rilevare in quali periodi dell’anno …

A “Case Study” for the Estimation of Daily Solar Radiation from Measured Air Temperature Extremes in the Mid-Mediterranean Area

Agro-hydrological models to schedule irrigation of Mediterranean tree crops

In this paper a comparison between two agro-hydrological models, used to schedule irrigation of typical Mediterranean tree crops, is assessed. In particular the comparison between the model proposed by FAO, using a black box processes schematization, and the SWAP model based on the numerical analysis of Richards’ equation is initially presented for two irrigation seasons, 2005 and 2006, and two Mediterranean tree crops, i.e. grapevine (Vitis vinifera, L.) and olive oil (Olea europea, L.). The comparison mainly focuses on hydrological balance components and on soil water contents. After investigating and setting the scheduling parameters ordinarily practiced by the framers in the area (i.e o…

Stima della radiazione solare giornaliera in sicilia mediante i dati di temperatura massima e minima

By using thermometric data series from 36 sicilian stations , the authors use different relationship for indirect determination of daily solar radiation. The best performance was given by Hargreaves-Samani formula which is then parameterized by the authors for the investigated region.

Un modello di generazione e trasporto del deflusso: Applicazione a un piccolo bacino

Tecnica scintillometrica per la misura dell’evapotraspirazione effettiva: principi teorici ed esempi applicativi

Estimation of actual evapotranspiration of Mediterranean perennial crops by means of remote-sensing based surface energy balance models

Abstract. Actual evapotranspiration from typical Mediterranean crops has been assessed in a Sicilian study area by using surface energy balance (SEB) and soil-water balance models. Both modelling approaches use remotely sensed data to estimate evapotranspiration fluxes in a spatially distributed way. The first approach exploits visible (VIS), near-infrared (NIR) and thermal (TIR) observations to solve the surface energy balance equation whereas the soil-water balance model uses only VIS-NIR data to detect the spatial variability of crop parameters. Considering that the study area is characterized by typical spatially sparse Mediterranean vegetation, i.e. olive, citrus and vineyards, alterna…

Assessing the agro hydrological SWAP model to simulate soil water balance in typical Mediterranean crops

Estimation of Mediterranean crops evapotranspiration by means of remote-sensing based models

Abstract. Actual evapotranspiration from typical Mediterranean crops has been assessed in a Sicilian study area by using Surface Energy Balance and Agro-Hydrological models. Both modelling approaches require remotely sensed data to estimate evapotranspiration fluxes in a spatially distributed way. The first approach exploits visible (VIS), near-infrared (NIR) and thermal (TIR) observations to solve the surface energy balance equation. To this end two different schemes have been tested: the two-sources TSEB model, where soil and vegetation components of the surface energy balance are treated separately, and the widely used one-source SEBAL model, where soil and vegetation are considered as a…

Influence of the rainfall measurement interval on the erosivity determinations in the Mediterranean area

Summary The single-storm erosion index, EI, of the USLE and RUSLE models may vary appreciably with the rainfall measurement interval, Δ t . However, the effect of Δ t on EI has not been investigated in the Mediterranean area. Approximately 700 erosive events and 1.5 years of rainfall energies measured by a rainfall impact measurement device were used to evaluate the effect of the rainfall measurement interval (5 min ⩽ Δ t  ⩽ 60 min) on the erosivity determinations in the Mediterranean semi-arid area of Sicily. According to both literature and practical considerations, a reference time interval equal to 15 min was used in this investigation. Hourly rainfall data led to an appreciable underes…

Distribuzione di probabilità della portata di piena a scala di versante generata da deflusso hortoniano

Comparison of SWAP and FAO Agro-Hydrological Models to Schedule Irrigation of Wine Grapes

This paper compares two agro-hydrological models that are used to schedule irrigation of a typical Mediterranean crop. In particular, a comparison between the Food and Agriculture Organization (FAO) model, which uses a black box approach, and the soil-water-atmosphere-plant (SWAP) model, which is based on the numerical analysis of Richards' equation, are shown for wine grape. The comparison was carried out for the 2005 and 2006 irrigation seasons and focused on hydrological balance components and on soil water contents. Next, the ordinary scheduling parameters were identified so that the performance of the two models, which aimed to evaluate the seasonal water requirements and the irrigatio…

Gestione dell’irrigazione del vigneto attraverso l’uso di modelli di simulazione e misure di campo.

In the paper the applicability of a numerical model, i.e. SWAP (Soil Water Atmosphere Plant), and a functional model, i.e. FAO 56, for irrigation scheduling is assessed. Model validation was initially carried out through the comparison between simulated and measured water content of a soil profile. The two models were then used in order to verify the possibility to simulate the typical irrigation management of the study area. In particular, the attitude of the two models to simulate the number and the distribution of watering, as well as the seasonal water consumption found in the ordinary management irrigation was assessed. Different scenarios of irrigation management allowed the analysis …

Trend of inter-arrival times of rainfall events for Italian Sub-Alpine and Mediterranean areas

Probability distribution of peak discharge at hillslope scale derived by an eco-hydrological approach

INDAGINE ECOIDROLOGICA SU UN VERSANTE CALANCHIVO IN SICILIA

Determinazione del contenuto energetico delle precipitazioni tipiche dell'ambiente mediterraneo

Derivation of slope factor S of the USLE at basin scale by geomorphological approach

Modelling the frequency distribution of inter-arrival times from daily precipitation time-series in North-West Italy

Abstract The discrete three-parameter Lerch distribution is used to analyse the frequency distribution of inter-arrival times derived from 26 daily precipitation time-series, collected by stations located throughout a 28,000 km2 area in North-West Italy (altitudes ranging from 113 m to 2,170 m a.s.l.). The precipitation regime of these Alpine regions is very different (latitude 44.5 to 46.5 N) from the typical Mediterranean precipitation regime of the island of Sicily (latitude 37 to 38 N), where the Lerch distribution has already been tested and whose results are compared. In order to verify the homogeneity of the precipitation time series, the Pettitt test was preliminarily performed. In …

Sul tempo di risposta di un versante a prevalente deflusso hortoniano

La distinzione del bacino idrografico in versanti e reticolo attiene ai differenti processi che in essi specificamente hanno luogo. In particolare i versanti sono sede dei fenomeni diffusi di formazione del deflusso superficiale e di erosione idrica, mentre la rete è sede dei fenomeni concentrati di trasporto del deflusso liquido e solido sino alla sezione di chiusura del bacino. Nell’ipotesi che la formazione prevalente del deflusso superficiale avvenga secondo lo schema hortoniano, tipico dei versanti privi di vegetazione, nel presente lavoro è suggerita una metodologia, applicabile anche ad altre modalità di formazione, per la valutazione del tempo caratteristico di risposta del versante…

A model of dunnian flow at hillslope scale

The development of a thin stream above the soil surface (overland flow) is associated to two mechanism of runoff generation on the hillslope: the infiltration excess (hortonian flow) and saturation excess (dunnian flow) mechanism. The first one is typical of arid and semi-arid regions, usually characterised by high rainfall intensities on soil exhibiting low permeability. The second one, firstly introduced by Hewlett and Hibbert, constitutes the main mechanism of runoff generation in humid regions, characterised by high groundwater table. In the last mechanism runoff is produced by contributing areas of restricted extent that expands with time, where near to the bottom of the hillslope a hi…

Applicability of a displaced-beam laser scintillometer in a sparse tall Mediterranean vegetation

Recent studies showed that the sensible heat flux (H) measured with an array of eddy-correlation system has an high spatial and temporal variability over sparse tall vegetation, such as olive trees, whereas H determined with a displaced-beam laser scintillometer (DBLS) appeared to behave more stable. In this study, the results are shown of two field experiments performed over an olive tree plantation in Sicily in 2007 and 2008, in order to investigate the applicability of a DBSL in combination with remote sensing techniques for the actual evapotranspiration assessment. In 2007 the laser beams was closer to the top of the canopy than in 2008. Various aspects of the scintillation method will …

Statistical analysis of inter-arrival times of rainfall events for Italian Sub-Alpine and Mediterranean areas

Abstract. In this work a set of time-series of inter-arrival times of rainfall events, at daily scale, was analysed, with the aim to verify the issue of increasing duration of dry periods. The set consists of 12 time-series recorded at rain gauges in 1926–2005, six of them belong to an Italian Sub-Alpine area (Piedmont) and six to a Mediterranean one (Sicily). In order to overcome the problem related to limited sample size for high values of inter-arrival times, the discrete probability polylog-series distribution was used to fit the empirical data from partial (20 yr) time-series. Moreover, a simple qualitative trend analysis was applied to some high quantiles of inter-arrival times as wel…

Probability Distribution of Peak Discharge at the Hillslope Scale Generated by Hortonian Runoff

In this work, the probability distribution of peak discharge at the hillslope bottom is determined hypothesizing a prevalent Hortonian mechanism of runoff production for a given rainfall duration. As is well known, the probability distribution of peak discharge depends on the probability of both the rainfall event as well as that of the antecedent soil moisture conditions. In particular, the probability of the rainfall event is calculated according to the familiar rainfall duration-intensity-frequency approach, whereas the ecohydrological method from the literature is used here to define the probability of the antecedent soil moisture conditions. The latter depends on a set of parameters de…

Applying a probabilistic model of rainfall and snow days occurrence to daily series recorded in NW Italy.

Daily precipitation records exist spanning several decades. A valuable amount of climatic information exists in the time-series of interarrival times (IT), defined as the succession of times (number of days) elapsed from a rainy (or snowy) day to the one immediately preceding it.In a previous work, Agnese et al. (2014) have been successfully tested some probabilistic modelling of rain occurrence on Sicily rainfall data; particularly, the better fitting of IT’s observed frequencies was obtained by 3-parameter Lerch-series distribution. In this work thisdistribution is tested on 70 years of 20 precipitation time-series taken in the North-West Italy, both in the plain and in the mountains, up …

Modelling the occurrence of rainy days under a typical Mediterranean climate

The statistical inference of the alternation of wet and dry periods in daily rainfall records can be achieved through the modelling of inter-arrival time-series, IT, defined as the succession of times elapsed from a rainy day and the one immediately preceding it. In this paper, under the hypothesis that ITs are independent and identically distributed random variables, a modelling framework based on a generalisation of the commonly adopted Bernoulli process is introduced. Within this framework, the capability of three discrete distributions, belonging to the Hurwitz–Lerch-Zeta family, to reproduce the main statistical features of IT time-series was tested. These distributions namely Lerch-se…

Coupling overland and subsurface flow model at hillslope scale

POSSIBILI MODIFICAZIONI DELLE COMPONENTI DEL BILANCIO IDROLOGICO INDOTTE DALLE VARIAZIONI CLIMATICHE

AN ANALYTICAL SOLUTION OF KINEMATIC WAVE EQUATIONS FOR OVERLAND FLOW UNDER GREEN-AMPT INFILTRATION

This paper deals with the analytical solution of kinematic wave equations for overland flow occurring in an infiltrating hillslope. The infiltration process is described by the Green-Ampt model. The solution is derived only for the case of an intermediate flow regime between laminar and turbulent ones. A transitional regime can be considered a reliable flow condition when, to the laminar overland flow, is also associated the effect of the additional resistance due to raindrop impact. With reference to the simple case of an impervious hillslope, a comparison was carried out between the present solution and the non-linear storage model. Some applications of the present solution were performed…

Combined use of eddy covariance and sap flow techniques for partition of ET fluxes and water stress assessment in an irrigated olive orchard

Correct estimation of crop actual transpiration plays a key-role in precision irrigation scheduling, since crop growth and yield are associated to the water passing through the crop. Objective of the work was to assess how the combined use of micro-meteorological techniques (eddy covariance, EC) and physiological measurements (sap flow, SF) allows a better comprehension of the processes involving in the Soil–Plant–Atmosphere continuum. To this aim, an experimental dataset of actual evapotranspiration, plant transpiration, and soil water content measurements was collected in an olive orchard during the midseason phenological period of 2009 and 2010. It was demonstrated that the joint use of …

Primo contributo all'estensione di alcune serie climatiche siciliane mediante analisi di serie dendrocronologiche

Partitioning ET measurements for sparse vegetation: application to an olive orchard.

Modeling olive ecophysiological response to soil water deficit.