ECOHYDROLOGY IN MEDITERRANEAN AREAS: A NUMERICAL MODEL TO DESCRIBE GROWING SEASONS OUT OF PHASE WITH PRECIPITATIONS

The probabilistic description of soil moisture dynamics is a relatively new topic in hydrology. The most common ecohydrological models start from a stochastic differential equation describing the soil water balance, where the unknown quantity, the soil moisture, depends both on spaces and time. Most of the solutions existing in literature are obtained in a probabilistic framework and under steady-state condition; even if this last condition allows the analytical handling of the problem, it has considerably simplified the same problem by subtracting generalities from it. The steady-state hypothesis, appears perfectly applicable in arid and semiarid climatic areas like those of African's or middle American's savannas, but it seems to be no more valid in areas with Mediterranean climate, where, notoriously, the wet season foregoes the growing season, recharging water into the soil. This moisture stored at the beginning of the growing season (known as soil moisture initial condition) has a great importance, especially for deep-rooted vegetation, by enabling survival in absence of rainfalls during the growing season and, however, keeping the water stress low during the first period of the same season. The aim of this paper is to analyze the soil moisture dynamics using a simple non-steady numerical ecohydrological model. The numerical model here proposed is able to reproduce soil moisture probability density function, obtained analytically in previous studies for different climates and soils in steady-state conditions; consequently it can be used to compute both the soil moisture time-profile and the vegetation static water stress time-profile in non-steady conditions. Here the differences between the steady-analytical and the non-steady numerical probability density functions are analyzed, showing how the proposed numerical model is able to capture the effects of winter recharge on the soil moisture. The dynamic water stress is also numerically evaluated, implicitly taking into account the soil moisture condition at the beginning of the growing season. It is also shown the role of different annual climatic parameterizations on the soil moisture probability density function and on the vegetation water stress evaluation

Daily rainfall statistics in Sicily (1920-2000)

Rainfall characteristics are crucial for vegetation patterns formation and evolution in Mediterranean ecosystems. Changes in rainfall frequency and intensity could cause vegetation water stress for some plant species and benefit, at the same time, other species, driving coexistence and competition dynamics. The changes in the precipitation characteristics are sometimes more important than the changes in the total amount of precipitation in determining the partitioning between green and blue water with several implications for both the vegetation communities health and water resource management. Decreasing rainfall is a clear signature of climate change in Mediterranean countries. Annual and winter totals have been demonstrated to decrease in the past century and GCMs forecast a progressive worsening of the current situation even if it is still not clear if and how rainfall could be modified in its temporal and seasonal patterns. This study aims to analyze daily rainfall properties in Sicily in the last century. Namely the daily depths and interarrival times between events are investigated in about 50 stations, also characterizing seasonal rainfall features. The presence of significant trend has been detected using the non parametric Mann Kendall test

Ecohydrology in Mediterranean areas: a numerical model to describe growing seasons out of phase with precipitations

International audienceThe probabilistic description of soil moisture dynamics is a relatively new topic in hydrology. The most common ecohydrological models start from a stochastic differential equation describing the soil water balance, where the unknown quantity, the soil moisture, depends both on spaces and time. Most of the solutions existing in literature are obtained in a probabilistic framework and under steady-state condition; even if this last condition allows the analytical handling of the problem, it has considerably simplified the same problem by subtracting generalities from it. The steady-state hypothesis, appears perfectly applicable in arid and semiarid climatic areas like those of African's or middle American's savannas, but it seems to be no more valid in areas with Mediterranean climate, where, notoriously, the wet season foregoes the growing season, recharging water into the soil. This moisture stored at the beginning of the growing season (known as soil moisture initial condition) has a great importance, especially for deep-rooted vegetation, by enabling survival in absence of rainfalls during the growing season and, however, keeping the water stress low during the first period of the same season. The aim of this paper is to analyze the soil moisture dynamics using a simple non-steady numerical ecohydrological model. The numerical model here proposed is able to reproduce soil moisture probability density function, obtained analytically in previous studies for different climates and soils in steady-state conditions; consequently it can be used to compute both the soil moisture time-profile and the vegetation static water stress time-profile in non-steady conditions. Here the differences between the steady-analytical and the non-steady numerical probability density functions are analyzed, showing how the proposed numerical model is able to capture the effects of winter recharge on the soil moisture. The dynamic water stress is also numerically evaluated, implicitly taking into account the soil moisture condition at the beginning of the growing season. It is also shown the role of different annual climatic parameterizations on the soil moisture probability density function and on the vegetation water stress evaluation. The proposed model is applied to a case study characteristic of Mediterranean climate: the watershed of Eleuterio in Sicily (Italy)

Spatial analysis techniques for mapping the annual surface runoff in Sicily under the Budyko\u2019s framework

This work shows a new approach, based on the Budyko framework, for mapping the mean annual surface runoff and deriving the probability distribution of the annual runoff in arid and semi-arid watersheds. We analytically provide the annual runoff distribution as the derived distribution of annual rainfall and potential evapotranspiration. The simulated long-term annual runoff and its distribution have been compared with historical records at several gauged stations, obtaining satisfactory matching

Generation of natural runoff monthly series at ungauged sites using a regional regressive model

Many hydrologic applications require reliable estimates of runoff in river basins to face the widespread lack of data, both in time and in space. A regional method for the reconstruction of monthly runoff series is here developed and applied to Sicily (Italy). A simple modeling structure is adopted, consisting of a regression-based rainfall-runoff model with four model parameters, calibrated through a two-step procedure. Monthly runoff estimates are based on precipitation, temperature, and exploiting the autocorrelation with runoff at the previous month. Model parameters are assessed by specific regional equations as a function of easily measurable physical and climate basin descriptors. The first calibration step is aimed at the identification of a set of parameters optimizing model performances at the level of single basin. Such "optimal" sets are used at the second step, part of a regional regression analysis, to establish the regional equations for model parameters assessment as a function of basin attributes. All the gauged watersheds across the region have been analyzed, selecting 53 basins for model calibration and using the other six basins exclusively for validation. Performances, quantitatively evaluated by different statistical indexes, demonstrate relevant model ability in reproducing the observed hydrological time-series at both the monthly and coarser time resolutions. The methodology, which is easily transferable to other arid and semi-arid areas, provides a reliable tool for filling/reconstructing runoff time series at any gauged or ungauged basin of a region

EHSMu: a new conceptual model for hourly discharge simulation under ecohydrological framework in urban area

A parsimonious conceptual lumped model is presented here with the aim of simulating hourly discharge in urban areas. The EHSMu (EcoHydrological Streamflow Model for urban areas) is able to reproduce the discharge at the outlet of an urban drainage system and, at the same time, soil moisture dynamics and evapotranspirative fluxes over vegetated areas within an urban catchment. In urban areas, rain falling over impervious surfaces is directly transferred towards the drainage system in a time depending on the catchment characteristics, and drainage network geometry. If the rain falls over pervious and vegetated areas the runoff generation is driven by soil moisture content, which in turn is linked to evapotranspiration and leakage. While on one side soil water content determines if rainfall produces saturation excess or a leakage loss, on the other side it constrains the evapotranspirative fluxes, so that, when it approaches to saturation, the actual evapotranspiration tends to the potential one. The hydrological scheme of the urban catchment follows these premises and consists of three interconnected elements: a soil bucket and two linear reservoirs. The soil bucket epitomizes in two distinct classes different conditions within a catchment: the first interprets impervious areas while the second describes pervious and vegetated soils. The soil bucket is linked to the two linear reservoirs: one is responsible for the runoff within the drainage system, while the other is used to delay the entry of subsurface runoff component into the drainage system. The surface reservoir is fed by the rain falling on imperviuos areas, by the saturation excess generated over pervious areas and by the delayed contribution arising from the subsurface reservoir, which is solely supplied by leakage pulses. Soil moisture dynamics in the pervious part of the basin, are simulated by a simple bucket model feed by rainfall and depleted by evapotranspiration. The latter component is calculated as a linear function of soil moisture. The model has been calibrated using Montecarlo simulations on an urban catchment in the United States. This method allows to adapt the conceptual model framework to the catchment characteristics and at the same time to obtain the set of parameters with the higher efficiency in reproducing historical discharge at the outlet. The proposed model gives reliable estimate of runoff, soil moisture traces and evapotranspiration fluxes. Model outputs could be very useful for urban ecohydrology, because they allow for the simulation of vegetation water stress and consequently the design of sustainable urban green spaces. At the same time the model structure allows to simulate the effects of stormwater management best practices for achieving the hydraulic invariance

Effetto combinato di cambiamenti climatici ed urbanizzazione sugli estremi di portata

Il termine “cambiamento idrologico” (hydrological change) è spesso utilizzato per sintetizzare quell’insieme di alterazioni della risposta idrologica dei bacini indotte da fattori naturali o antropici. ll ruolo fondamentale di tali alterazioni nel determinare fenomeni di dissesto ha stimolato l’International Association of Hydrological Scienses (IAHS) a dedicare la decade scientifica 2013-2022 (denominata “Phanta Rhei”) ai cambiamenti idrologici e all’analisi dei diversi fattori perturbanti. I cambiamenti climatici e l’urbanizzazione sono fra i fattori antropici perturbanti più influenti e, allo stesso tempo, più diffusi a livello globale. Il cambiamento climatico è stato abbondantemente studiato in passato, con chiare evidenze di trend sugli estremi (es. Burn et al., 2011; Arnone et al., 2013) e con numerosi esempi attestanti i possibili cambiamenti idrologici indotti (es. Wang and Alimohammadi, 2012; Francipane et al., 2015; Chiarelli et al., 2016; Pumo et al. 2016). Molto più recente è l’analisi degli effetti dell’urbanizzazione sulla risposta idrologica dei bacini (es. Salvadore et al., 2015). Il processo di urbanizzazione è associato a una perdita di “superfici permeabili” (suoli naturali), con conseguente impoverimento dei processi d’infiltrazione, alterazione ai sistemi di drenaggio naturale e ai processi di trasferimento (alterazione dei percorsi idrici e delle velocità di deflusso). La valutazione dell’impatto di tali perturbazioni sulle portate di picco durante eventi estremi, può risultare particolarmente utile nel definire e orientare efficaci politiche di pianificazione urbana e gestione di eventi di inondazione, nonché in attività di verifica delle infrastrutture idrauliche esistenti e di progettazione di quelle future. L’obiettivo di questo lavoro è quello di investigare gli effetti dell'interazione delle suddette perturbazioni sugli eventi estremi di deflusso. A tale scopo, è stato ideato un esperimento numerico, applicato ad un piccolo bacino fluviale, che ha permesso di generare e confrontare serie temporali di deflusso orario sotto diversi ipotetici scenari di cambiamento. Gli scenari, generati attraverso l’uso combinato di un modello di cambiamento di uso del suolo opportunamente implementato e di un modello di generazione di serie climatiche già esistente (Fatichi et al., 2011), descrivono situazioni estreme sia in termini di espansione delle aree urbane che in termini di variazioni (aumento o diminuzione) della precipitazione media annua (MAP). Nella creazione degli scenari climatici si è anche tenuto conto di un aumento della temperatura media, e, a parità di MAP, sono state create diverse configurazioni, caratterizzate da diversa frequenza e/o l’intensità media degli eventi di pioggia. La risposta idrologica del bacino ai vari scenari è stata riprodotta mediante il tRIBS (Ivanov et al., 2004), un modello idrologico, fisicamente basato e distribuito, in grado di simulare, con alta risoluzione temporale, anche le diverse componenti di deflusso. I risultati mostrano un’alta sensibilità degli indicatori della risposta idrologica utilizzati alle variazioni delle caratteristiche di pioggia. In termini di deflusso totale, gli effetti dei cambiamenti climatici sembrano essere prevalenti rispetto a quelli indotti dall’espansione urbana, anche se, a una maggiore frazione di suoli impermeabili, corrisponde un chiaro aumento della componente di scorrimento veloce, i cui effetti sul deflusso totale vengono parzialmente smorzati da una simultanea riduzione della componente di deflusso lento e profondo

Aggressiveness of eight Venturia inaequalis isolates virulent or avirulent to the major resistance gene Rvi6 on a non-Rvi6 apple cultivar

For sustainable management of scab-resistant apple cultivars, it is necessary to understand the role of aggressiveness in the adaptation of Venturia inaequalis populations and particularly the costs to the organism of acquiring additional virulence. The aims of the present study were (i) to identify the quantitative variables that are most important in determining the differences in aggressiveness among groups of V. inaequalis isolates, and (ii) to ascertain whether virulent and avirulent isolates of V. inaequalis differ significantly in aggressiveness. The aggressiveness of eight isolates that differed in their virulence to the major resistance gene Rvi6 was compared on the non-Rvi6 apple cv. Gala. Three components of aggressiveness, namely lesion density, the number of spores per square centimetre of leaf area, and the number of spores per lesion, were evaluated 21 days after inoculation, and the kinetics of lesion density over time were analysed in terms of maximum lesion density, length of latent period and rate of lesion appearance. On the second youngest but fully developed leaf at the time of inoculation, maximum lesion density in the virulent group was 20% lower and the latent period 7% longer, than in the avirulent group. However, the alternative hypothesis, namely that isolates had adapted to quantitative resistance present in cv. Gala depending on their cultivar of origin, could not be rejected. The analysis of the kinetics of lesion density by a non-linear mixed-effect model proved useful in the assessment of aggressiveness

SN 2013ab : A normal type IIP supernova in NGC 5669

We present densely-sampled ultraviolet/optical photometric and low-resolution optical spectroscopic observations of the type IIP supernova 2013ab in the nearby ($\sim$24 Mpc) galaxy NGC 5669, from 2 to 190d after explosion. Continuous photometric observations, with the cadence of typically a day to one week, were acquired with the 1-2m class telescopes in the LCOGT network, ARIES telescopes in India and various other telescopes around the globe. The light curve and spectra suggest that the SN is a normal type IIP event with a plateau duration of $\sim80$ days with mid plateau absolute visual magnitude of -16.7, although with a steeper decline during the plateau (0.92 mag 100 d$^{-1}$ in $V$ band) relative to other archetypal SNe of similar brightness. The velocity profile of SN 2013ab shows striking resemblance with those of SNe 1999em and 2012aw. Following the Rabinak & Waxman (2011) prescription, the initial temperature evolution of the SN emission allows us to estimate the progenitor radius to be $\sim$ 800 R$_{\odot}$, indicating that the SN originated from a red supergiant star. The distance to the SN host galaxy is estimated to be 24.3 Mpc from expanding photosphere method (EPM). From our observations, we estimate that 0.064 M$_{\odot}$ of $^{56}$Ni was synthesized in the explosion. General relativistic, radiation hydrodynamical modeling of the SN infers an explosion energy of $0.35\times10^{51}$ erg, a progenitor mass (at the time of explosion) of $\sim9$ M$_{\odot}$ and an initial radius of $\sim600$ R$_{\odot}$.Comment: 22 pages, 18 figures, 5 tables. Accepted for publication in MNRA

Optical and Ultraviolet Observations of the Very Young Type IIP SN 2014cx in NGC 337

Extensive photometric and spectroscopic observations are presented for SN 2014cx, a type IIP supernova (SN) exploding in the nearby galaxy NGC 337. The observations are performed in optical and ultraviolet bands, covering from -20 to +400 days from the peak light. The stringent detection limit from prediscovery images suggests that this supernova was actually detected within about 1 day after explosion. Evolution of the very early-time light curve of SN 2014cx is similar to that predicted from a shock breakout and post-shock cooling decline before reaching the optical peak. Our photometric observations show that SN 2014cx has a plateau duration of ~ 100 days, an absolute V-band magnitude of ~ -16.5 mag at t~50 days, and a nickel mass of 0.056+-0.008 Msun. The spectral evolution of SN 2014cx resembles that of normal SNe IIP like SN 1999em and SN 2004et, except that it has a slightly higher expansion velocity (~ 4200 km/s at 50 days). From the cooling curve of photospheric temperature, we derive that the progenitor has a pre-explosion radius of ~ 640 Rsun, consistent with those obtained from SNEC modeling (~ 620 Rsun) and hydrodynamical modeling of the observables (~ 570 Rsun). Moreover, the hydrodynamical simulations yield a total explosion energy of ~ 0.4*10e51 erg, and an ejected mass of ~ 8 Msun. These results indicate that the immediate progenitor of SN 2014cx is likely a red supergiant star with a mass of ~ 10 Msun.Comment: 47 pages, 12 figures and 7 tables. Accepted by Ap