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Setting Irrigation Thresholds for Building a Platform Aimed at the Improved Management of Citrus Orchards in Coastal Syria.
Publication . Darouich, Hanaa; Karfoul, Razan; Ramos, Tiago B.; Pereira, Luís S.
Citrus is one of the most valuable crops in Syria, with the largest production areas being in
the coastal provinces of Tartus and Latakia, where this study was performed. A companion paper
reported on the basal crop coefficients derived from the field water balance and on the performance
assessment of various irrigation methods used in a citrus orchard located in the same region. That
study evidenced the need for the improved management of irrigation water, mainly reducing water
applications and increasing productivity, thus leading to the current research. The main objectives
consisted of (i) providing a set of reliable basal (Kcb) and average (Kc) crop coefficients to be used
in practice in the citrus orchards of the Syrian coastal area, while accounting for the diversity of
characteristics observed; (ii) to estimate the seasonal consumptive use of typical orchards under
different climate-demand and deficit-irrigation scenarios; and (iii) to assess possible water savings
and related yield reductions. The previously calibrated water balance model SIMDualKc was used
for these purposes. The computed Kcb values for the mid-season and average demand for water
ranged from 0.52, when the plant density was low, to 0.84, when plant density was very high. The
corresponding Kc values, which further reflected the impact of drip irrigation on controlling soil
evaporation, were 0.72 and 0.97, respectively. Overall, the consumptive use of water was estimated to
range from 867 to 1573 mm. The assessed water-saving scenarios consisted of adopting increased
management-allowed depletion (MAD) thresholds relative to the p depletion fraction for no stress:
MAD = 1.05, 1.10, 1.20, and 1.30 p. For trees under a very high climatic demand, water savings ranged
from 12 to 34%, but the yield losses induced by the water deficits ranged from 8 to 48%. Although
the selection of optimal strategies should be based upon economic terms, these may only be used
when the Syrian economy recovers from civil war and the current crisis. The present results show the
feasibility of adopting such MAD thresholds for building an irrigation management platform. The
data provided by the current study are valuable because they can be efficiently used to support of the
irrigation management of Syrian citrus production systems.
Water use and soil water balance of Mediterranean tree crops assessed with the SIMDualKc model in orchards of southern Portugal
Publication . Ramos, Tiago B.; Darouich, Hanaa; Oliveira, Ana R.; Farzamian, Mohammad; Monteiro, Tomás; Castanheira, Nádia; Paz, Ana; Gonçalves, Maria C.; Pereira, Luís S.
Orchards consist of complex agricultural systems, with a variety of characteristics (planting density, tree height,
training system, canopy cover, irrigation method, interrow management) influencing crop evapotranspiration
(ETc). Thus, irrigation water management requires finding crop coefficients (Kc) that represent the characteristics
of local orchards, evidencing the need for site specific data. The main objective of this study was to derive the Kc
of almond, olive, citrus, and pomegranate orchards in Alentejo, southern Portugal, wherein they became
dominant over the last decade. Monitoring was carried out in nine orchards, which management decisions were
performed by the farmers. The ETc was estimated from the soil water balance computed for each orchard using
the FAO56 dual-Kc approach with the SIMDualKc model. The model successfully simulated the soil water contents measured in the various fields along two growing seasons, with root mean square error values lower than
0.005 m3 m− 3 and modeling efficiencies from 0.363 to 0.782. The estimated basal crop coefficients (Kcb) for the
initial, mid- and end-seasons were respectively 0.22, 0.58, and 0.50 for almond; 0.32–0.33, 0.35–0.36, and
0.33–0.34 for olive; 0.40, 0.40–41, and 0.40–0.41 for citrus; and 0.24, 0.60, and 0.52 for pomegranate. Small
variations in olive and citrus Kcb values were found to be related to differences in the fraction of the ground
covered by trees’ canopies and tree height. The single Kc values, which included the component relative to soil
evaporation, were also estimated. Furthermore, evaluation of the soil water balance in the nine case studies
showed salinity effects in one almond orchard, mild irrigation water deficits in olive systems, and large nonconsumptive water use in citrus and pomegranate orchards. These results evidence the need for better management of orchards irrigation water in the region, and the current study provides for reliable information on the
Kc of tree crops to support improving the management of local orchard systems and the preservation of soil and
water resources. Aimed at these resources and the sustainability of their use, simulated alternative irrigation
schedules were performed, which identified possible water savings of 20 mm in case of olives, up to 855 mm for
citrus.
Assessing spatial variability and trends of droughts in Eastern Algeria using SPI, RDI, PDSI, and MedPDSI—A novel drought index using the FAO56 evapotranspiration method
Publication . Merabti, Abdelaaziz; Darouich, Hanaa; Paredes, Paula; Meddi, Mohamed; Pereira, L.S.
Drought is one of the most severe natural disasters worldwide, but with a particular
emphasis in sub-humid and semi-arid climates. Several indices have been created to appropriately
identify drought’s characteristics and variability. The main objectives of this study consisted of
analyzing the behavior of different indices applied in northeast Algeria and comparing them across a
long-term data set (1961–2014). The SPI and RDI at 9-month time scales were compared to the PDSI
and MedPDSI based on 123 rainfall stations and gridded PET data interpolated to all the locations.
A principal component analysis (PCA) in S-mode with varimax rotation (RPC) was applied to the
monthly values of all indices to analyze the spatiotemporal patterns of droughts. Two principal
components were retained, which identified two sub-regions with coherent differences related to their
distance from the Mediterranean Sea and the UNEP aridity index. Trends in the RPC scores were
assessed using the modified Mann–Kendall (MMK) test and Sen’s slope estimator, which showed
a fundamental difference between the two sub-regions. The RPC of all drought indices showed
trends of decreases in the frequency and severity of droughts in the northern sub-region, and trends
of increases in the frequency and severity of droughts in the southern region, where the climate is
mostly semi-arid and arid. Only a few cases were statistically significant, mostly when using the PDSI
and MedPDSI for the southern sub-region. The spatial patterns of moderate, severe, and extreme
drought occurrences were similar for the SPI and RDI pair of indices based on the probability of
rainfall anomalies, and for the Sc-PDSI and MedPDSI pair based on water balance anomalies. The
interpretation of the spatial variability of droughts, mainly of the extreme ones, was supported by an
analysis of semi-variograms. The novel index MedPDSI compared well with the other indices and
showed advantages of performing the soil water balance following the FAO56 dual Kc method with
the actual olive evapotranspiration instead of PET, and of better explaining the spatial variability
of extreme droughts; in addition, the trends detected were significant for both the northern and
southern sub-regions.
Searching for Sustainable-Irrigation Issues of Clementine Orchards in the Syrian Akkar Plain: Effects of Irrigation Method and Canopy Size on Crop Coefficients, Transpiration, and Water Use with SIMDualKc Model
Publication . Darouich, Hanaa; Karfoul, Razan; Ramos, Tiago B.; Moustafa, Ali; Pereira, Luís Santos
Citrus is one of the most valuable crops in Syria, with the largest production areas in the
Tartus and Latakia provinces. Water-saving policies have been adopted to modernize the irrigation
systems and increase water productivity. Following dedicated research, this study aimed to evaluate
the water balance in clementine trees irrigated with diverse methods and schedules using the
SIMDualKc software model. Two experiments are reported: one with 10–14 years old trees irrigated
with different methods (20072011) and the other with the same trees but now 1820 years old,
irrigated with different schedules (20152019). The SIMDualKc model successfully simulated the
soil water contents measured in the various field plots, with root mean square error values lower
than 0.004 m3 m3 and modeling efficiencies up to 0.83. The model-calibrated standard basal crop
coefficients (Kcb) were approximately constant throughout all growing stages, assuming values of
0.540.55 for the mature trees having smaller height (h) and fraction of ground cover (fc), and 0.64 for
older trees with larger canopies, i.e., larger h and fc. With drip irrigation, single Kc had a higher value
(1.14) at the end, non-growing, and initial stages, and a lower value (0.75–0.76) during mid-season
(Kc mid), because precipitation was lesser then, contributing less to soil evaporation. On the other
hand, Kc values were nearly constant with micro-sprinkler and surface irrigation techniques because
the ground was fully wetted. The Kcb values derived from the fraction of ground cover and height
(A&P approach) were similar to those obtained from the model, thus showing that the A&P approach
represents a practical alternative to estimate Kcb in the practice of irrigation management. The soil
water balance further revealed a large weight of the terms corresponding to the non-beneficial water
consumption and non-consumptive water use when the fraction wetted was large and the application
efficiencies were low. These terms were reduced, namely, evaporation losses when drip irrigation
was used. This study, thus, provides a valuable tool for improving the irrigation management, water
saving, and water productivity of Syrian citrus production systems
Water use and soil water balance of Mediterranean vineyards under rainfed and drip irrigation management: evapotranspiration partition and soil management modelling for resource conservation
Publication . Darouich, Hanaa; Ramos, Tiago B.; Pereira, Luís Santos; Rabino, Danilo; Bagagiolo, Giorgia; Capello, Giorgio; Simionesei, Lucian; Cavallo, Eugenio; Biddoccu, Marcella
Vineyards represent complex Mediterranean agrosystems that deliver significant ecosystem services to society. Yet, many vine-growers still need to assimilate the importance of crop and
soil management to the conservation of soil and water resources. The main objective of this study
was to evaluate water use and the water balance terms in rainfed and irrigated vineyards in Italy
and Portugal, respectively, in both cases aiming at the sustainability of natural resources use. The
SIMDualKc model is used for both sites after calibration and validation by fitting soil water content
measurements. The Italian case study focused on the impacts of inter-row conservation management
in hillslope vineyards while the Portuguese case study analyzed irrigation water management under
scarcity in flat vineyards. For the Italian vineyards, the model results focused on the evapotranspiration fluxes and their partition, control of surface runoff, and soil water recharge provided by the
inter-row soil management using cover crops. Model results of the Portuguese case study showed
the need for improving irrigation water use and the terms of water balance, namely referring to
percolation and soil water evaporation. Both case studies further demonstrated the advantages of
using computational tools to better cope with climate variability in the Mediterranean region and
made evident the benefits of improved crop and soil management practices in counteracting land
degradation and valuing the use and conservation of natural resources.
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Fundação para a Ciência e a Tecnologia
Programa de financiamento
CEEC IND 2017
Número da atribuição
CEECIND/01153/2017/CP1430/CT0002