Water balance estimation of the Campo de Cartagena watershed using hydrological modeling and remote sensing

This work uses hydrological modeling and remote sensing techniques to estimate the spatial and temporal patterns of the water balance of an intensively irrigated agricultural watershed in south-eastern Spain. Remote sensing-based vegetation indexes were used to estimate crop evapotranspiration rates and as an input in the model. Model outcomes give insight in the overall water account of the watershed. They highlight the critical role of the groundwater system in the water balance, and the differences between abstractions and recharge, depending on the hydrological conditions

Reference evapotranspiration of screenhouse‐grown crops

The reference evapotranspiration Eref was measured under three screenhouses and compared to outside Eref. The reduction with respect to outside Eref was quantified by means of two factors, rad and adv. rad was found to depend linearly on transmittance (), and adv on wind ratio (). A model was proposed for screenhouse Eref based on outside weather data, an

Leaf-to-branch scaling of C-gain in field-grown almond trees under different soil moisture regimes

Branch/tree-level measurements of carbon (C)-acquisition provide an integration of the physical and biological processes driving the C gain of all individual leaves. Most research dealing with the interacting effects of high-irradiance environments and soil-induced water stress on the C-gain of fruit tree species has focused on leaf-level measurements. The C-gain of both sun-exposed leaves and branches of adult almond trees growing in a semi-arid climate was investigated to determine the respective costs of structural and biochemical/physiological protective mechanisms involved in the behaviour at branch scale. Measurements were performed on well-watered (fully irrigated, FI) and drought-stressed (deficit irrigated, DI) trees. Leaf-to-branch scaling for net CO2 assimilation was quantified by a global scaling factor (fg), defined as the product of two specific scaling factors: (i) a structural scaling factor (fs), determined under well-watered conditions, mainly involving leaf mutual shading; and (ii) a water stress scaling factor (fws,b) involving the limitations in C-acquisition due to soil water deficit. The contribution of structural mechanisms to limiting branch net C-gain was high (mean fs ∼0.33) and close to the projected-to-total leaf area ratio of almond branches (ε = 0.31), while the contribution of water stress mechanisms was moderate (mean fws,b ∼0.85), thus supplying an fg ranging between 0.25 and 0.33 with slightly higher values for FI trees with respect to DI trees. These results suggest that the almond tree (a drought-tolerant species) has acquired mechanisms of defensive strategy (survival) mainly based on a specific branch architectural design. This strategy allows the potential for C-gain to be preserved at branch scale under a large range of soil water deficits. In other words, almond tree branches exhibit an architecture that is suboptimal for C-acquisition under well-watered conditions, but remarkably efficient to counteract the impact of DI and drought events

Energy balance and evaporation loss of an agricultural reservoir in a semiarid climate (South-Eastern Spain)

A typical agricultural water reservoir (AWR) of 2400 m2 area and 5 m depth, located in a semi-arid area (southern Spain), was surveyed on a daily basis for 1 year. The annual evaporation flux was 102·7 W m−2, equivalent to an evaporated water depth of 1310 mm year−1. The heat storage rate G exhibited a clear annual cycle with a peak gain in April (G ∼ 45 W m−2) and a peak loss in November (G ∼ 40 W m−2), leading to a marked annual hysteretic trend when evaporation (λE) was related to net radiation (Rn). λE was strongly correlated with the available energy A, representing 91% of the annual AWR energy loss. The sensible heat flux H accounted for the remaining 9%, leading to an annual Bowen ratio in the order of 0·10. The equilibrium and advective evaporation terms of the Penman formula represented 76 and 24%, respectively, of the total evaporation, corresponding to a annual value of the Priestley–Taylor (P–T) coefficient (α) of 1·32. The P–T coefficient presented a clear seasonal pattern, with a minimum of 1·23 (July) and a maximum of 1·65 (December), indicating that, during periods of limited available energy, AWR evaporation increased above the potential evaporation as a result of the advection process. Overall, the results stressed that accurate prediction of monthly evaporation by means of the P–T formula requires accounting for both the annual cycle of storage and the advective component. Some alternative approaches to estimating Rn, G and α are proposed and discussed.The authors acknowledge the Fundación Séneca (Murcia, Spain) for the financial support of this study through the grant 02978/PI/05

Crop coefficients parameterization using remote sensing in basin-scale hydrological modelling

[SPA] Se utiliza un modelo hidrológico distribuido para evaluar cómo diferentes métodos influyen en la estimación de la evapotranspiración (ETc) y el balance de agua a escala de cuenca. La zona de estudio se ubica en la cuenca alta del Segura (~ 2.500 km2) en el Sureste español, zona caracterizada por una elevada heterogeneidad de condiciones del terreno y usos del suelo. El modelo hidrológico SPHY fue desarrollado y calibrado para un período de simulación de 15 años. Se emplearon cinco métodos para parametrizar el coeficiente de cultivo y se compararon los patrones espaciales y las dinámicas temporales simuladas para la evapotranspiración, la humedad del suelo y los caudales. Tres de los cinco métodos utilizan información de satélite, otro los valores del coeficiente de cultivo establecidos por FAO, y el último asume un valor constante para toda la cuenca y periodo de simulación. El análisis muestra que la generación de caudales apenas se ve afectada por la selección del método de parametrización, aunque sí es importante a la hora de calcular la evapotranspiración real, especialmente durante épocas húmedas y para los valores tabulados de FAO. [ENG] A distributed hydrologic model is used to evaluate how different methods to estimate evapotranspiration (ETc) influence the water balance and hydrologic response of basins. The study site, the upper Segura basin (~2500 km2) in Spain, is characterized by a wide range of terrain, soil, and ecosystem conditions. Input and calibration data for the hydrological model SPHY are obtained from best available data sources. The model was setup for a period of 15 year. Five crop coefficient parameterization methods are compared to explore the impact of spatial and temporal variations in these input datasets on actual evapotranspiration, streamflow and soil moisture. Methods include three that are based on remote sensing information; one based on FAO literature, and another that takes the crop coefficient equal to unity for the entire basin. The analysis shows that basin-level streamflow is hardly influenced by the choice in parameterization, but actual evapotranspiration and soil moisture are quite different, especially in the wet season and for the FAO-based method

Effect of shading and insect proof nets on screenhouse light environment

Screenhouses covered by shading or insect proof screens are becoming popular among growers in arid and semiarid regions like the Mediterranean area, due to the environmental, economic and agronomic benefits they offer. The positive impact of a net-covering on plant behaviour can be mostly explained by the more favourable microclimate under a screen-house than outdoors. However, manipulation of light environment by shading using screens requires the knowledge of the characteristics and parameters of the modified light regime, on both the quantitative and qualitative aspects of light environment under the screens. Thus, the effects of cover optical properties on screenhouse radiative environment were investigat-ed, under Mediterranean conditions during summer in Central Greece, under three net-screen materials (i) a pearl insect-proof screen (IP-78), (ii) a white insect proof screen (IP-59) and (iii) a green shade-screen (GS-62) with values of the transmittance to photosynthetically active radiation (τPAR) of 78%, 59% and 62%, respectively. All screens induced impover-ishment in the blue wavelength band (B, 400-500 nm) and enrichment in near-infrared broadband (NIR, 700-1100 nm) with respect to PAR (400-700 nm), and modified photomor-phogenetic parameters such as the ratios B:FR (Blue vs Far-Red), R:FR (Red vs Far-Red) and the phytochrome ratio, ζ

Satellite‐based Algorithms for Estimating Actual Evapotranspiration. Application to Irrigation Management and Water Accounting in the Segura Basin

Se ha considerado a la Cuenca del Río Segura, localizada en el Sureste de España, como área de estudio. En esta cuenca semiárida las necesidades hídricas del sector agrícola representan el 80 % del uso total del agua. El aumento de fiabilidad en la estimación de la evapotranspiración real (ETreal), se traduce en mayor conocimiento de la necesidad hídrica real del cultivo. Se propone estimar ETreal aplicando algoritmos que permitan el cambio de escala (upscaling): (i) a escala de parcela donde se dispone de imágenes de alta resolución espacial Landsat (e incluso Sentinel cuando esté disponible), y de datos al suelo medidos en parcelas experimentales para realizar validaciones de resultados,(ii) a escala de cuenca y en base a imágenes de moderada resolución espacial (sensor MODIS) y alta resolución temporal, aplicando los algoritmos previamente validados, y su integración para el cierre de los balances hídricos a escala mensual. Esta información se integrará con datos del Plan Hidrológico de la Cuenca del Río Segura y otras fuentes de información. El objetivo es obtener, evaluar y estandarizar información detallada, incluyendo trasvases y recursos desde otras fuentes no convencionales con el fin de analizar y demostrar el potencial de la gestión, y las medidas para reducir la escasez hídrica en esta región propensa a la sequía. El Sistema de Contabilidad Hídrica (SCH) para la cuenca, complementará los balances de recursos hídricos a nivel europeo con datos locales mediante una solución innovadora en base a Sistemas Información Geográfica (SIG).Se agradece el soporte recibido desde el proyecto del Plan Nacional CGL2012‐39895‐ C02‐01, "Evaluación de la variabilidad hidroclimática desde combinaciones multimodelo climáticas regionales (HYDROCLIM)", financiado por la Secretaría de Estado de Investigación del Ministerio de Economía y Competitividad (MINECO), y fondos FEDER

Evaluation of evaporation estimation methods for a covered reservoir in a semi-arid climate (south-eastern Spain)

The main purpose of this study was to evaluate different methods of evaporation estimation for covered water reservoirs. A reservoir equipped with a suspended cover was fully monitored to register the evaporation rate and microclimate below the cover. The datasets were used to evaluate the performance of commonly used evaporation methods, namely energy budget, mass-transfer, combination (Penman and FAO-56 Penman-Monteith) and floating class-A pan. The mass-transfer formula based on the Sherwood number proposed for free convection conditions, which were observed to prevail below the cover, supplied reasonably good estimates of covered reservoir evaporation and it is a good option from a practical point of view, with low input data requirements. Detailed input data and modifications in the calculation of energy fluxes are required to get good evaporation estimations of covered surfaces with the energy budget and FAO-56 Penman-Monteith methods. Besides, some of the standard meteorological input data (such as wind speed at 2 m height) cannot be registered below the cover. Penman equation presented a poor performance related to the overestimation of the advective component for free convection conditions. The pan evaporation was found to be substantially higher than the reservoir evaporation, due to the particular characteristics of the tank, that increased surface temperature and hence evaporation rate. A simplified empirical mass-transfer formula was also proposed to estimate evaporation of covered water bodies from the only knowledge of the surface-to-air mixing ratio gradient.The authors acknowledge the Ministerio de Ciencia e Innovación (Spain) and FEDER (Fondo Europeo de Desarrollo Regional) for the financial support of this study through the grant AGL2010-15001

Comparative analysis of two polyethylene foil materials for dew harvesting in a semi-arid climate

This paper analyses the dew collection performance of two polyethylene (PE) foils in a semi-arid region (Southern Spain). The dew collecting devices consisted of two commercial passive radiative dew condensers (RDCs) of 1 m2 tilted to 30°. They were fitted with two different high-emissivity PE foils: a white hydrophilic foil (WSF) recommended as standard for dew recovery comparisons by the International Organization for Dew Utilization (OPUR), and a low-cost black PE foil (BF) widely used for mulching in horticulture. Dew yield, foil surface temperature and meteorological variables (air temperature, relative humidity, downward long wave radiation and wind speed) were recorded hourly during a 1-year period from May-2009 to May-2010. The spectral emissivity of the foils was determined in laboratory in the range 2.5–25 μm and the radiance-weighed values were calculated over different intervals, indicating that BF emitted more than WSF, especially in the range 2.5–7 μm. Dew yield was well correlated with the air relative humidity and foil net radiation in both foils and was hardly detected when the relative humidity was lower than 75% or the wind speed higher than 1.5 m s−1. WSF was more sensitive to dew formation due to its hydrophilic properties, registering more dewy nights (175) than BF (163) while the annual cumulative dew yield for BF was higher (20.76 mm) than for WSF (17.36 mm) due to the higher emissivity and emitted radiance of BF. These results suggested that increasing the surface emissivity over the whole IR spectrum could be more effective for improving RDC yield performances than increasing the surface hydrophilic properties. On a practical point of view, BF could be considered as a suitable material for large scale RDCs, as in our study it presented several advantages over the reference material, such as higher dew collection performance, longer lifespan and much lower cost.The authors acknowledge the Foundation Seneca (Murcia, Spain) and the Ministry of Science and Innovation for the financial support of this study through the grants 02978/PI/05 and AGL2010-15001 respectively