Wageningen, Netherlands
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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).


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.


Wipfler E.L.,Wageningen University | Metselaar K.,Wageningen University | Van Dam J.C.,Wageningen University | Feddes R.A.,Wageningen University | And 8 more authors.
Hydrology and Earth System Sciences | Year: 2011

The skill of the land surface model HTESSEL is assessed to reproduce evaporation in response to land surface characteristics and atmospheric forcing, both being spatially variable. Evaporation estimates for the 2005 growing season are inferred from satellite observations of the Western part of Hungary and compared to model outcomes. Atmospheric forcings are obtained from a hindcast run with the Regional Climate Model RACMO2. Although HTESSEL slightly underpredicts the seasonal evaporative fraction as compared to satellite estimates, the mean, 10th and 90th percentile of this variable are of the same magnitude as the satellite observations. The initial water as stored in the soil and snow layer does not have a significant effect on the statistical properties of the evaporative fraction. However, the spatial distribution of the initial soil and snow water significantly affects the spatial distribution of the calculated evaporative fraction and the models ability to reproduce evaporation correctly in low precipitation areas in the considered region. HTESSEL performs weaker in dryer areas. In Western Hungary these areas are situated in the Danube valley, which is partly covered by irrigated cropland and which also may be affected by shallow groundwater. Incorporating (lateral) groundwater flow and irrigation, processes that are not included now, may improve HTESSELs ability to predict evaporation correctly. Evaluation of the model skills using other test areas and larger evaluation periods is needed to confirm the results. Based on earlier sensitivity analysis, the effect of a number of modifications to HTESSEL has been assessed. A more physically based reduction function for dry soils has been introduced, the soil depth is made variable and the effect of swallow groundwater included. However, the combined modification does not lead to a significantly improved performance of HTESSEL. © 2011 Author(s).


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.


Samain B.,Ghent University | Simons G.W.H.,WaterWatch | Voogt M.P.,WaterWatch | Defloor W.,Flemish Environmental Agency | And 2 more authors.
Hydrology and Earth System Sciences | Year: 2012

The catchment averaged actual evapotranspiration rate is a hydrologic model variable that is difficult to quantify. Evapotranspiration rates - up till present - cannot be continuously observed at the catchment scale.

The objective of this paper is to estimate the evapotranspiration rates (or its energy equivalent, the latent heat fluxes LE) for a heterogeneous catchment of 102.3 km2 in Belgium using three fundamentally different algorithms. © Author(s) 2012. CC Attribution 3.0 License.


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.


Hellegers P.J.G.J.,LEI Wageningen UR | Soppe R.,WaterWatch | Perry C.J.,Technical University of Delft | Bastiaanssen W.G.M.,WaterWatch
Water Resources Management | Year: 2010

This paper demonstrates that combining spatial land surface data with socio-economic analysis provides a number of indicators to strengthen decision making in integrated water and environmental management. It provides a basis to: track current water consumption in the Inkomati Basin in South-Africa; adjust irrigation water management; select crop types; facilitate planning; estimate crop yields before harvesting, and consequently to forecast market price development. Remote sensing data and economic analysis can also be used to study the spatial distribution of water consumption as an indicator of equity in access to water resources. It even enables identification of farms that consume more irrigation water than formally allocated. Finally, it provides a basis to assess the cost-effectiveness of various ways to reduce agricultural water consumption. So, this approach is potentially useful for determining water consumption, refining water allocation policies, and determining the potential for water transfers through mechanisms such as water trading. © 2009 The Author(s).


Zwart S.J.,WaterWatch | Zwart S.J.,Technical University of Delft | Zwart S.J.,Africa Rice Center | Bastiaanssen W.G.M.,WaterWatch | And 3 more authors.
Agricultural Water Management | Year: 2010

Water productivity in agriculture needs to be improved significantly in the coming decades to secure food supply to a growing world population. To assess on a global scale where water productivity can be improved and what the causes are for not reaching its potential, the current levels must be understood. This paper describes the development and validation of a WATer PROductivity (WATPRO) model for wheat that is based on remote sensing-derived input data sets, and that can be applied at local to global scales. The model is a combination of Monteith's theoretical framework for dry matter production in plants and an energy balance model to assess actual evapotranspiration. It is shown that by combining both approaches, the evaporative fraction and the atmospheric transmissivity, two parameters which are usually difficult to estimate spatially, can be omitted. Water productivity can then be assessed from four spatial variables: broadband surface albedo, the vegetation index NDVI, the extraterrestrial radiation and air temperature. A sensitivity analysis revealed that WATPRO is most sensitive to changes in NDVI and least sensitive to changes in air temperature. The WATPRO model was applied at 39 locations where water productivity was measured under experimental conditions. The correlation between measured and modelled water productivity was low, and this can be mainly attributed to differences in scales and in the experimental and modelling periods. A comparison with measurements from farmer's fields in areas surrounded by other wheat fields located in Sirsa District, NW India, showed an improved correlation. Although not a validation, a comparison with SEBAL-derived water productivity in the same region in India proved that WATPRO can spatially predict water productivity with the same spatial variation. © 2010 Elsevier B.V.


Zwart S.J.,WaterWatch | Zwart S.J.,Technical University of Delft | Zwart S.J.,Africa Rice Center | Bastiaanssen W.G.M.,WaterWatch | And 3 more authors.
Agricultural Water Management | Year: 2010

The growing pressure on fresh water resources demands that agriculture becomes more productive with its current water use. Increasing water productivity is an often cited solution, though the current levels of water productivity are not systematically mapped. A global map of water productivity helps to identify where water resources are productively used, and identifies places where improvements are possible. The WATPRO water productivity model for wheat, using remote sensing data products as input, was applied at a global scale with global data sets of the NDVI and surface albedo to benchmark water productivity of wheat for the beginning of this millennium. Time profiles of the NDVI were used to determine the time frame from crop establishment to harvest on a pixel basis, which was considered the modelling period. It was found that water productivity varies from approximately 0.2 to 1.8kg of harvestable wheat per cubic metre of water consumed. From the 10 largest producers of wheat, France and Germany score the highest country average water productivity of 1.42 and 1.35kgm-3, respectively. The results were compared with modelling information by Liu et al. (2007) who applied the GEPIC model at a global scale to map water productivity, and by Chapagain and Hoekstra (2004) who used FAO statistics to determine water productivity per country. A comparison with Liu et al. showed a good correlation for most countries, but the correlation with the results by Chapagain and Hoekstra was less obvious. The global patterns of the water productivity map were compared with global data sets of precipitation and reference evapotranspiration to determine the impact of climate and of water availability reflected by precipitation. It appears that the highest levels of water productivity are to be expected in temperate climates with high precipitation. Due to its non-linear relationship with precipitation, it is expected that large gains in water productivity can be made with in situ rain water harvesting or supplemental irrigation in dry areas with low seasonal precipitation. A full understanding of the spatial patterns by country or river basin will support decisions on where to invest and what measures to take to make agriculture more water productive. © 2010 Elsevier B.V.

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