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Forests are currently experiencing an unprecedented period of progressively drier growing conditions around the globe, which is threatening many forest ecosystem functions. Trees as long-living organisms are able to withstand drought periods. Our understanding on critical drought severity resulting in substantial decline in net primary productivity and/or eventually tree mortality is underdeveloped. A wide range of remote sensing products and ground observations, including information on productivity, tree vitality, climate, and soil moisture with high temporal and spatial resolution are now available. Linking these data sources could improve our understanding of the complex relationship between forest growth and drought. We introduce here a conceptual framework using satellite remotely sensed net primary productivity (MOD17A3 and MODIS EURO), ground observations of tree mortality (ICP level I survey data), soil moisture anomaly (Copernicus European Drought Observatory), and spatially-downscaled daily climate data for entire Europe. This unique analysis will enable us to test the influence of biotic and abiotic covariates such as tree age, stand history, and drought legacy using historic droughts for model development. This conceptual framework, as evident from the preliminary results shown here, can help anticipating the effects of future droughts and optimize global climate models considering drought effects.

Studies have shown that the footprint of a single eddy covariance (EC) system may not yield representative measurements of the turbulent fluxes at the field scale for sparse vegetated surfaces, whereas scintillometry, due to its larger footprint, may be more suitable for this purpose. However, the latter approach strongly relies on the Monin-Obukov similarity theory (MOST) that strictly applies in the inertial sub-layer only. This work aims at experimentally confirm the reliability of displaced-beam laser scintillometers (DBLS) measurements over an olive orchard against two EC systems during summer and autumn months of 2007 through 2009. It was found that the DBLS underestimated both the momentum and sensible heat fluxes by 15 to 20% when established retrieval procedures were applied. A new method to determine the sensible heat flux from the DBLS based on the addition of a single-height wind speed measurement was tested, yielding estimates that compare well with the EC observations, with discrepancies in sensible heat fluxes of about 30 to 40 W m-2.

The concept of reference potranspiration is widely used to support water resource management in agriculture and for irrigation scheduling, especially under arid and semi-arid conditions. The Penman-Monteith standardized formulations, as suggested by ASCE and FAO-56 papers, are generally applied for accurate estimations of ETo, at hourly and daily scale. When detailed meteorological information are not available, several alternative and simplified equations, using a limited number of variables, have been proposed (Blaney-Criddle, HargreavesSamani, Turc, Makkinen and Pristley-Taylor). In this paper, scintillometer measurements collected for six month in 2005, on an experimental plot under “reference” conditions, were used to validate different ETo equations at hourly and daily scale. Experimental plot is located in a typical agricultural Mediterranean environment (Sicily, Italy), where olive groves is the dominant crop. As proved by other researches, the comparison confirmed the best agreement between estimated and measured fluxes corresponds to FAO-56 Penman-Monteith standardized equation, that was characterized by both the lowest average error and the minimum bias. However, the analysis also evidenced a quite good performance of Pristley-Taylor equation, that can be considered as a valid alternative to the more sophisticated PenmanMonteith method. The different ETo series, obtained by the considered simplified equations, were then used as input in the FAO-56 water balance model, in order to evaluate, for olive groves, the errors on estimated actual evapotranspiration ET. To this aim soil and crop model input parameters were settled by considering previous experimental researches already used to calibrate and validate the FAO-56 water balance model on olive groves, for the same study area. Also in this case, assuming as the true values of ET those obtained using the water balance coupled with Penman- Monteith ETo input values, the Priestley-Taylor equation, requiring a limited number of input meteorological data, was characterized by the best performance if compared to the other equations used to evaluate ETo. Under environments conditions similar to those considered therefore, according to the good performance associated to the Priestley-Tailor approach, FAO-56 model can allow realistic estimation of ET, even in absence of a full meteorological dataset.

L’uso razionale della risorsa idrica in agricoltura richiede, unitamente all’adozione di tecniche irrigue avanzate che assicurino la migliore efficienza degli interventi irrigui, l’individuazione dei tempi e dell’entità dei singoli interventi. Perché questi ultimi obiettivi siano raggiunti è necessario stimare con precisione i consumi di evapotraspirazione delle colture che, nell’ambiente mediterraneo, caratterizzato da un periodo vegetativo tipicamente non in fase con quello piovoso, si manifestano sotto condizioni di stress idrico. Nel presente lavoro è descritta un’applicazione a una piantagione di oliveto della tecnica scintillometrica, che permette una stima indiretta del flusso di calore latente attraverso l’equazione del bilancio energetico. Più in particolare, lo scintillometro è uno strumento ottico, che misura il flusso di calore sensibile dal sistema suolo-pianta sulla base degli effetti che tale flusso induce sull’indice di rifrazione della luce coerente emessa da un trasmettitore; misurando contemporaneamente la radiazione netta e il flusso di calore nel suolo, è possibile dedurre il flusso di evapotraspirazione come termine residuo dell’equazione che esprime il bilancio energetico di superficie. Sono in particolare presentati i risultati di un’indagine sperimentale effettuata nel corso della stagione irrigua 2007 nell’area di Castelvetrano, tipicamente vocata alla coltura dell’olivo. I dati di evapotraspirazione giornaliera ottenuti mediante la tecnica scintillometrica sono stati quindi confrontati con i corrispondenti valori stimati utilizzando il modello Agroidrologico SWAP, la cui applicazione ha richiesto una approfondita caratterizzazione biofisica dell’area di studio. I dati di evapotraspirazione giornaliera ottenuti mediante la tecnica scintillometrica sono stati confrontati con i corrispondenti valori stimati utilizzando sia il modello agroidrologico SWAP che la procedura semplificata proposta di recente dalla FAO che prevede l’adozione di un coefficiente colturale Kc,r che tiene conto delle eventuali condizioni di stress idrico.