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Wageningen, Netherlands

de Teixeira A.H.C.,Embrapa Semiarido | Bastiaanssen W.G.M.,WaterWatch | Bastiaanssen W.G.M.,Technical University of Delft
Irrigation Science | Year: 2012

Energy balance measurements were carried out in a mango orchard during two growing seasons in the semi-arid region of Brazil. The actual evapotranspiration (ET) was acquired by eddy correlation (EC) and Bowen ratio energy balance (BR) techniques. The daily energy balance closure in the EC measurements showed an average gap of 12%, with a root mean square error (RMSE) of 1.7 MJ m-2 d-1. Three different correction procedures were tested for closing the energy balance from the EC system: (1) the surface energy balance residual method (RES), (2) the Bowen ratio determined from the EC fluxes, the combination approach (EC_BR), and (3) a new regression energy balance closure technique (REG). All closing energy balance methods presented good correlation with the direct EC measurements, but the trends were not similar. The latent heat fluxes estimated by the BR method-λEBR-were higher than those from the direct EC measurements-λEEC. When using the RES method, the half-hour λEEC measurements represented around 88% of the λERES values, as the uncertainties of net radiation-Rn-and soil heat fluxes-G-are propagated into the RES method. The latent heat flux derived from the combination approach-λEEC_BR-also brings these uncertainties, being the agreements comparable with those for RES method. It was therefore concluded that a single correction method for EC measurements considering only the latent and sensible heat fluxes does not exist. A new way to solve the lack of energy balance closure from EC techniques was tested by means of a curve fitting, the REG method. Considering the REG corrections applied to the energy balance components involving all periods of the day and the average conditions of the two growing seasons, half-hour values of λEEC were overmeasured by 18%, HEC was undermeasured by 17%, and G values required a correction of 466%. The REG method appeared promising because it considers different weights for all energy balance components in the optimization process. Taking the REG results for the drier second growing season as a reference, it was concluded that seasonal ET values by the other methods in mango orchard ranged from 7 to 28% higher, showing that turbulent flux measurements lack accuracy for executing on-farm water-saving programmes and calibrating transient soil water flow models. © 2010 Springer-Verlag.

Hellegers P.J.G.J.,LEI Part of Wageningen UR | Jansen H.C.,Wageningen University | Bastiaanssen W.G.M.,WaterWatch | Bastiaanssen W.G.M.,Technical University of Delft
Irrigation and Drainage | Year: 2012

This paper presents an interactive web-based rapid assessment tool that generates key water related indicators to support decision making by stakeholders in land use planning. The tool is built on a consistent science based method that combines remote sensing with hydrological and socioeconomic analyses. It generates transparent, impartial, and verifiable information regarding the impact of land use changes on water productivity, water consumption, water availability, and employment. The usefulness of the tool was demonstrated in the Inkomati River Basin in Southern Africa, where the tool was used to assess the impact of converting land use on the water resources to prioritize areas for conversion and to track required changes in land use to comply with tripartite water allocation agreements. This contributed to confidence building and to strengthening the process of conscientious land use planning, which is an extension of conventional work in this field. © 2011 John Wiley & Sons, Ltd.

Allen R.G.,University of Idaho | Hendrickx J.,New Mexico Institute of Mining and Technology | Bastiaanssen W.,WaterWatch | Kjaersgaard J.,University of Idaho | And 2 more authors.
ASABE - 5th National Decennial Irrigation Conference 2010, Held in Conjunction with Irrigation Show 2010 | Year: 2010

Satellite-based models for determining evapotranspiration (ET) are now routinely applied as part of water and water resources management operations of state and federal agencies. Strengths and weaknesses of more common models are briefly described. The more dependable and universal satellite-based models employ a surface energy balance (EB) where ET is computed as a residual of surface energy. This determination requires a thermal imager onboard the satellite, which is not common. The 'CIMEC approach ("calibration using inverse modeling of extreme conditions") used by two moderate resolution, operational models is described where CIMEC calibrates around uncertainties and biases in satellite based energy balance components. Creating 'maps' of ET that are useful in management and in quantifying and managing water resources requires the computation of ET over monthly and longer periods such as growing seasons or annual periods. Interpolation between images from 'snapshot' models involves treatment of clouded areas of images, accounting for evaporation from wetting events occurring prior to or following overpass dates. A technique currently used in the METRIC model for accounting for evaporation from precipitation between images is described. How the interpolation is done substantially impacts the quality and accuracy of the final ET product.

Wu B.,CAS Institute of Remote Sensing Applications | Yan N.,CAS Institute of Remote Sensing Applications | Xiong J.,CAS Institute of Remote Sensing Applications | Bastiaanssen W.G.M.,WaterWatch | And 3 more authors.
Journal of Hydrology | Year: 2012

The latent heat of evapotranspiration (ET) plays an important role for water resource management in water scarcity areas. Compared to the water balance method or to in situ measurements, an operational integrated monitoring method of regional surface ET from remote sensing data is a potentially useful approach to achieve water saving. This study presents new algorithms for the aerodynamic roughness length for complex landscape, for gap filling for cloud days, and for data fusion at different resolutions, based on the Penman-Monteith equation. It also presents an improved algorithm for ET calculation with remotely sensed data for clear days. Algorithms were integrated into the ETWatch. The research objective was to present the enhanced features of the ETWatch algorithm and its validation in the 320,000km 2 Hai Basin in Northern China. This area faces serious over-exploitation of groundwater. ET was modeled and extensive field campaigns were done to collect data on soil moisture depletion, lysimeter measurements, eddy covariance measurements, and water balance calculations at diverse landscapes. The overall deviation for individual fields on a seasonal basis was 12% and decreased to 6% for an annual cycle. For larger areas, the deviation was 3% for an annual cycle. These levels of deviation are within the error bands for in situ measurements. The study concludes that data sets from ETWatch are able to aid consumptive water use reduction management in the study area. © 2012 Elsevier B.V.

Zwart S.J.,WaterWatch | Zwart S.J.,Technical University of Delft | Leclert L.M.C.,WaterWatch
Irrigation Science | Year: 2010

The irrigation performance of the Office du Niger in Mali, a large-scale rice-based irrigation scheme, was analysed with the use of remote sensing technology. The major advantage of remote sensing derived data over field measured data is that it provides system-wide, spatially distributed and objective information. Four irrigation performance indicators, entirely based on remote sensing, were applied at different organisational levels of the system. The surface energy balance algorithm for land model was applied to high-resolution Landsat images to calculate rice production and water consumption spatially. These maps were used to analyse the productivity of water, the uniformity of water consumption and head-/tail-enders issues at the level of the system, the five administrative zones and smaller management units (casiers). The sustainability of the system was assessed using a long-term time series of the normalised difference vegetation index. The results were discussed and interpreted with the irrigation managers of the Office du Niger. The analysis provided new insights in the performance of the system such as existing head-tail patterns in water consumption and rice yields. © 2009 The Author(s).

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