2016
Autores
Duarte, L; Teodoro, AC; Goncalves, JA; Soares, D; Cunha, M;
Publicação
ENVIRONMENTAL MONITORING AND ASSESSMENT
Abstract
Soil erosion is a serious environmental problem. An estimation of the expected soil loss by water-caused erosion can be calculated considering the Revised Universal Soil Loss Equation (RUSLE). Geographical Information Systems (GIS) provide different tools to create categorical maps of soil erosion risk which help to study the risk assessment of soil loss. The objective of this study was to develop a GIS open source application (in QGIS), using the RUSLE methodology for estimating erosion rate at the watershed scale (desktop application) and provide the same application via web access (web application). The applications developed allow one to generate all the maps necessary to evaluate the soil erosion risk. Several libraries and algorithms from SEXTANTE were used to develop these applications. These applications were tested in Montalegre municipality (Portugal). The maps involved in RUSLE method-soil erosivity factor, soil erodibility factor, topographic factor, cover management factor, and support practices-were created. The estimated mean value of the soil loss obtained was 220 ton km(-2) year(-1) ranged from 0.27 to 1283 ton km(-2) year(-1). The results indicated that most of the study area (80 %) is characterized by very low soil erosion level (<321 ton km(-2) year(-1)) and in 4 % of the studied area the soil erosion was higher than 962 ton km(-2) year(-1). It was also concluded that areas with high slope values and bare soil are related with high level of erosion and the higher the P and C values, the higher the soil erosion percentage. The RUSLE web and the desktop application are freely available.
2014
Autores
Pocas, I; Paco, TA; Cunha, M; Andrade, JA; Silvestre, J; Sousa, A; Santos, FL; Pereira, LS; Allen, RG;
Publicação
BIOSYSTEMS ENGINEERING
Abstract
METRIC (TM) is a satellite-based surface energy balance model aimed at estimating and mapping crop evapotranspiration (ET). It has been applied to a large range of vegetation types, mostly annual crops. When applied to anisotropic woody canopies, such as olive orchards, extensions are required to algorithms for estimating the leaf area index (LAI), surface temperature, and momentum roughness length (Z(om)). The computation of the radiometric surface temperature needs to consider a three-source condition, thus differentiating the temperature of the canopy (T-c), of the shaded ground surface (T-shadow), and of the sunlit ground surface (T-sunlit). The estimation of the Z(om) for tall and incomplete cover is based upon the LAI and crop height using the Perrier equation. The LAI, Zorn, and temperature derived from METRIC after these adjustments were tested against field collected data with good results. The application of METRIC to a two year set of Landsat images to estimate ET of a super-intensive olive orchard in Southern Portugal produced good ET estimates that compared well with ground-based ET. The analysis of METRIC performance showed a quantitative improvement of ET estimates when applying the three-source condition for temperature estimation, as well as the Z(om) computation with the Perrier equation. Results show that METRIC can be used operationally to estimate and mapping ET of super-intensive olive orchards aiming at improving irrigation water use and management.
2014
Autores
Paco, TA; Pocas, I; Cunha, M; Silvestre, JC; Santos, FL; Paredes, P; Pereira, LS;
Publicação
JOURNAL OF HYDROLOGY
Abstract
The estimation of crop evapotranspiration (ETc) from the reference evapotranspiration (ETo) and a standard crop coefficient (K-c) in olive orchards requires that the latter be adjusted to planting density and height. The use of the dual K-c approach may be the best solution because the basal crop coefficient K-cb represents plant transpiration and the evaporation coefficient reproduces the soil coverage conditions and the frequency of wettings. To support related computations for a super intensive olive orchard, the model SIMDualKc was adopted because it uses the dual K-c approach. Alternatively, to consider the physical characteristics of the vegetation, the satellite-based surface energy balance model METRIC (TM) - Mapping EvapoTranspiration at high Resolution using Internalized Calibration - was used to estimate ETc and to derive crop coefficients. Both approaches were compared in this study. SIMDualKc model was calibrated and validated using sap-flow measurements of the transpiration for 2011 and 2012. In addition, eddy covariance estimation of ETc was also used. In the current study, METRIC (TM), was applied to Landsat images from 2011 to 2012. Adaptations for incomplete cover woody crops were required to parameterize METRIC. It was observed that ETc obtained from both approaches was similar and that crop coefficients derived from both models showed similar patterns throughout the year. Although the two models use distinct approaches, their results are comparable and they are complementary in spatial and temporal scales.
2015
Autores
Pocas, I; Paco, TA; Paredes, P; Cunha, M; Pereira, LS;
Publicação
REMOTE SENSING
Abstract
A new procedure is proposed for estimating actual basal crop coefficients from vegetation indices (K-cb VI) considering a density coefficient (K-d) and a crop coefficient for bare soil. K-d is computed using the fraction of ground cover by vegetation (f(c VI)), which is also estimated from vegetation indices derived from remote sensing. A combined approach for estimating actual crop coefficients from vegetation indices (K-c VI) is also proposed by integrating the K-cb VI with the soil evaporation coefficient (K-e) derived from the soil water balance model SIMDualKc. Results for maize, barley and an olive orchard have shown that the approaches for estimating both f(c VI) and K-cb VI compared well with results obtained using the SIMDualKc model after calibration with ground observation data. For the crops studied, the correlation coefficients relative to comparing the actual K-cb VI and K-c VI with actual K-cb and K-c obtained with SIMDualKc were larger than 0.73 and 0.71, respectively. The corresponding regression coefficients were close to 1.0. The methodology herein presented and discussed allowed for obtaining information for the whole crop season, including periods when vegetation cover is incomplete, as the initial and development stages. Results show that the proposed methods are adequate for supporting irrigation management.
2015
Autores
Oliveira, M; Cunha, M;
Publicação
JOURNAL INTERNATIONAL DES SCIENCES DE LA VIGNE ET DU VIN
Abstract
Aims: The main goal of this work was to describe the genetic diversity and population structure of Portuguese isolates from Erysiphe necator using a new approach for the sampling of DNA from this pathogen. Methods and results: The present study was conducted in the main demarcated wine regions of Portugal, where leaf and berry samples were collected for further genetic analysis. After DNA extraction, the Internal Transcribed Spacer from the 18S ribosomal RNA (ITS), the Intergenic Spacer (IGS), and the beta-tubulin gene were successfully amplified and sequenced. The populations of E. necator are structured into two genetically distinct groups (A and B), with the majority of the analyzed samples belonging to group B. Conclusion: Regardless of its geographical origin and the Vitis vinifera cultivar, the population of E. necator presents low genetic diversity. Significance and impact of the study: The present work will certainly help to increase the vineyard productivity through a better definition of preventive measures and a potential decrease in the direct and indirect costs associated with the use of fungicides.
2015
Autores
Cunha, M; Ribeiro, H; Costa, P; Abreu, I;
Publicação
AEROBIOLOGIA
Abstract
Airborne pollen emission model was used to determine pollen metrics and to examine their relationship with vineyard phenology in two wine regions of Northern Portugal: Vinhos Verdes (1993-2007) and Douro (1992-2011). A number of airborne pollen metrics were obtained through the rate of changes of logistic model adjusted to the time series of airborne pollen. In both regions, the mean absolute differences between observed phenology and model-predicted values for start, peak and final of flowering phenophases were always lower than 5 days and the slope of the regression through the origin is close to one. These metrics can be used to accurately and precisely predict the dynamic of Vitis flowering observed at field level. The model's simplicity and flexibility are of great advantage for its practical use in aerobiology.
The access to the final selection minute is only available to applicants.
Please check the confirmation e-mail of your application to obtain the access code.