Publications
As active participants in the academic research community, eLEAF and its employees are frequently engaged in publications (most of them peer-reviewed) that include applications of our models and data. Also, both eLEAF employees and researchers outside eLEAF have published validation analyses of our data. This page contains an overview of these publications.
eLEAF data validation
Overview of publications that include validation analyses of eLEAF data (including publications by authors outside eLEAF):
Brombacher, J. et al., (Agricultural Water Management, 2022), A novel evapotranspiration based irrigation quantification method using the hydrological similar pixels algorithm.
Brombacher, Joost & Silva, Isadora & Degen, Jelle & Pelgrum, Henk. (2022). A novel evapotranspiration based irrigation quantification method using the hydrological similar pixels algorithm. Agricultural Water Management. 267. DOI: 10.1016/j.agwat.2022.107602.
Abstract
Globally, the agricultural sector is the largest consumer of fresh water, despite the increased efficiency in irrigation. Remote sensing is a valuable tool to monitor agricultural water use. In this study, we demonstrate a novel algorithm that computes high-resolution (10 m) remote sensing-based evapotranspiration (ET) data linked exclusively to irrigation, i.e. the incremental evapotranspiration (ETincr). The methodology compares the ET of irrigated agricultural pixels to the weighted average ET of a subset of natural Hydrological Similar Pixels (HSP). The hydrological similarity is based upon a set of features derived from DEM, soil texture, reference evapotranspiration, and precipitation datasets. The difference in ET between the subset of hydrological similar natural pixels and the corresponding irrigated agricultural pixel is explanatory for the amount of ET related to irrigation (ETincr). These results are then converted to the water use (m3) per agricultural field. The method is validated for three study areas in South Africa, Spain, and Australia. Comparing the monthly and seasonal water use estimates to water meter observations in the Hex Valley (South Africa), yielded an R2 of 0.751 and 0.780, respectively. For the Ebro (Spain) and Namoi (Australia) study areas, the accuracy of the monthly estimates decreased. In Australia, this was a result of the water meters being linked to local reservoirs, instead of the direct use of the irrigation systems. In total, 8 out of the 27 validation fields with monthly data showed a Kling-Gupta Efficiency (KGE) larger than 0.5, which highlights that the temporal variability can be captured well by the model. Generally, seasonal estimates showed to be most accurate, which makes the product suitable for comparison with seasonal water allocations and could help to monitor overconsumption in water-scarce environments.
Geshnigani, F.S. et al., (Theoretical and Applied Climatology, 2021), Evaluation of FAO’s WaPOR product in estimating the reference evapotranspiration for stream flow modeling.
Geshnigani, F.S. & Mirabbasi, R. & Golabi, M.R. (2021). Evaluation of FAO’s WaPOR product in estimating the reference evapotranspiration for stream flow modeling. Theoretical and Applied Climatology. 144, 191–201
Abstract
The evapotranspiration is a key factor in the modeling of water supply, rainfall-runoff process, crop water demand, and drought. In the present study, the reference evapotranspiration (RET) data obtained from the FAO’s WaPOR product (FWP) are compared with the corresponding values estimated by the Modified Hargreaves-Samani (MHS) and Penman-Monteith (PM) methods. Then, the effect of using each of these RET estimations as the input of HBV hydrological model for simulating the runoff was evaluated based on the root mean square error (RMSE), correlation coefficient (R), Nash-Sutcliffe efficiency coefficient (NSE), and one-way variance (ANOVA). The results showed that the validation of the remote sensing (RS) product in estimating the RET was acceptable. Also, the performance assessment of the HBV model showed that the model was well in simulating the runoff, as the NSE coefficient obtained 0.713, 0.763, and 0.760 during the validation period for the PM and MHS methods and FWP, respectively. Also, there was no significant difference between runoff simulation results using different methods of estimating RET. These results suggested that the FAO’s WaPOR product can be used as a good alternative to the PM and MHS methods where there is a shortage or lack of meteorological data.
Weerasinghe, I. et al., (Hydrology and Earth System Sciences, 2020), Can we trust remote sensing evapotranspiration products over Africa?
Weerasinghe, I. & Bastiaanssen, W. & Mul, M. & Jia, L. & Griensven van, A. 2019. Can we trust remote sensing evapotranspiration products over Africa? Hydrology and Earth System Sciences. 24, 3, 1565-1586, doi: 10.5194/hess-24-1565-2020
Abstract
Evapotranspiration (ET) is one of the most important components in the water cycle. However, there are relatively few direct measurements of ET available (e.g. using flux towers). Nevertheless, various disciplines, ranging from hydrology to agricultural and climate sciences, require information on the spatial and temporal distribution of ET at regional and global scales. Due to the limited data availability, attention has turned toward satellite-based products to fill observational gaps. Various data products, including remote sensing (RS) products, have been developed and provide a large range of ET estimations. Across Africa, only a limited number of flux towers are available; hence, they are insufficient for the systematic evaluation of the available ET products. Thus, in this study, we conduct a methodological evaluation of nine existing RS-derived ET products as well as other available ET products in order to evaluate their reliability at the basin scale. A general water balance (WB) approach is used, where ET is equal to precipitation minus discharge for long-term averages. Firstly, ET products are compared with WB-inferred ET (ETWB) for basins that do not show long-term trends. The ET products and the calculated ETWB are then evaluated against the Budyko equation, which is used as a reference condition. The spatial characteristics of the ET products are finally assessed via the analysis of selected land cover elements across Africa: forests, irrigated areas and water bodies. Additionally, a cluster analysis is conducted to identify similarities between individual ET products. The results show that CMRSET, SSEBop and WaPOR rank highest in terms of the estimation of the long-term average mean ET across basins, with low biases and good spatial variability across Africa. GLEAM consistently ranks lowest in most evaluation criteria, although it has the longest available time period. Each product shows specific advantages and disadvantages. Depending on the study in question, at least one product should be suitable for a particular requirement. The reader should bear in mind that many products suffer from a large bias. Based on the evaluation criteria in this study, the three highest ranked products, CMRSET, SSEBop and WaPOR, would suit many users’ needs due to the low biases and good spatial variability across Africa.
Blatchford, M.L. et al., (Hydrological Processes, 2019), Evaluation of WaPOR V2 evapotranspiration products across Africa.
Megan L. Blatchford & Chris M. Mannaerts & Sammy M. Njuki & Hamideh Nouri & Yijian Zeng & Henk Pelgrum & Steven Wonink & Poolad Karimi. 2019. Evaluation of WaPOR V2 evapotranspiration products across Africa. Hydrological processes, 34 (15), DOI: 10.1002/hyp.13791
Abstract
The Food and Agricultural Organization of the United Nations (FAO) portal to monitor water productivity through open-access of remotely sensed derived data (WaPOR) offers continuous actual evapotranspiration and interception (ETIa-WPR) data at a 10-day basis across Africa and the Middle East from 2009 onwards at three spatial resolutions. The continental level (250 m) covers Africa and the Middle East (L1). The national level(100 m) covers 21 countries and 4 river basins (L2). The third level (30 m) covers eight irrigation areas (L3). To quantify the uncertainty of WaPOR version 2 (V2.0) ETIa-WPRin Africa, we used a number of validation methods. We checked the physical consistency against water availability and the long-term water balance and then verify the continental spatial and temporal trends for the major climates in Africa. We directly validated ETIa-WPR against in situ data of 14 eddy covariance stations (EC). Finally, we checked the level of consistency between the different spatial resolutions. Our findings indicate that ETIa-WPR is performing well, but with some noticeable overestimation. The ETIa-WPRis shows expected spatial and temporal consistency with respect to climate classes. ETIa-WPR shows mixed results at point scale as compared to EC flux towers with an overall correlation of 0.71, and a root mean square error of 1.2 mm/day. The level of consistency is very high between L1 and L2. However, the consistency between L1 and L3 varies significantly between irrigation areas. In rained areas, the theETIa-WPR is over-estimating at low ETIa-WPR and underestimating when ETIa is high. In irrigated areas, ETIa-WPR values appear to be consistently overestimating ETa. The relative soil moisture content (SMC), the input of quality layers and local advection effects were some of the identified causes. The quality assessment of ETIa-WPR product is enhanced by combining multiple evaluation methods. Based on the results, the ETIa-WPR dataset is of enough quality to contribute to the understanding and monitoring of local and continental water processes and water management.
Javadian, M. et al., (Water, 2019), METRIC and WaPOR Estimates of Evapotranspiration over the Lake Urmia Basin: Comparative Analysis and Composite Assessment.
Javadian, M. & Behrangi, A. & Gholizadeh, M. & Tajrishy, M., 2019. METRIC and WaPOR Estimates of Evapotranspiration over the Lake Urmia Basin: Comparative Analysis and Composite Assessment. Water, 11, 1647
Abstract
Evapotranspiration is one of the main components of water and energy balance. In this study, we compare two ET products, suitable for regional analysis at high spatial resolution: The recent WaPOR product developed by FAO and METRIC algorithm. WaPOR is based on ETLook, which is a two-source model and relies on microwave images. WaPOR is unique as it has no limitation under cloudy days, but METRIC is limited by clouds. METRIC and WaPOR are more sensitive to land surface temperature and soil moisture, respectively. Using two years (2010 and 2014) of data over Lake Urmia basin, we show that in most areas, ET from METRIC is higher than WaPOR and the difference has an ascending trend with the elevation. The ET of lysimeter station is fairly consistent with METRIC based on a single observation. Our analysis using NDVI and land use maps suggests that the histogram of ET from WaPOR might be more realistic than METRIC, but not its amount. The fraction of ET to precipitation in rainfed agriculture areas shows that WaPOR is more accurate than METRIC, mainly because in the absence of other water resources such as groundwater annual ET cannot exceed annual precipitation. In contrast, METRIC produces a more realistic estimate than WaPOR over irrigated farms. The results suggest that the two products can complement each other.
Keywords: evapotranspiration; WaPOR; METRIC; ETLook; Lake Urmia; remote sensing; MODIS; lysimeter; water consumption; irrigation
Rahimpour, M et al., (Iran Water Resources Research, 2018), Validation and Calibration of FAO’s WaPOR Product (Actual Evapotranspiration) in Iran Using In-Situ Measurements.
Rahimpour, M, & Karimi, N. & Rouzbahani, R. & Eftekhari, M. 2018. Validation and Calibration of FAO’s WaPOR Product (Actual Evapotranspiration) in Iran Using In-Situ Measurements. Iran Water Resources Research, 14, 2, 254-263
Abstract
Estimation of actual evapotranspiration (ETa) at the scales of basin and field is one of the essential information for water resources allocation. Although estimating actual evapotranspiration encounters spatial, temporal and cost restrictions, but data from satellite images can usually overcome these limitations in various extents. In this regard, the objectives of the present study were; a) evaluation and validation of WaPOR ETa product using Scintillometer instrument and, b) estimation of ETa over several land use regions in Zayanderoud basin. Based on the obtained results, MAE, RMSE, MAPE and R were equal to 2.14 mm for 10 days, 2.55 mm for 10 days, 5.50 and 0.97, respectively, which represented the appropriateness of WaPOR ETa data compared to Scintillometer. Also, the analysis of WaPOR product in different land-use showed that the maximum amount of actual ETa in 2016 has occurred in dual crops (513 mm), orchards (387 mm), spring crops (272 mm), autumnal crops (271 mm), dry farming (112 mm) and rangelands (83 mm). Also the results in rice fields showed that 992 mm of fresh water was lost in the form of ETa which is considered a dramatic value due to the climate and water resources of the selected basin and its relevance challenges.
Keywords: Actual Evapotranspiration, FAO’s WaPOR Product, Scintillometer, Zayandehrood Basin.
All publications
Overview of all publications co-authored by eLEAF employees relevant to our daily practice (i.e. employed at eLEAF at the time of publication):
Brombacher, J. et al., (Agricultural Water Management, 2022), A novel evapotranspiration based irrigation quantification method using the hydrological similar pixels algorithm.
Brombacher, Joost & Silva, Isadora & Degen, Jelle & Pelgrum, Henk. (2022). A novel evapotranspiration based irrigation quantification method using the hydrological similar pixels algorithm. Agricultural Water Management. 267. 10.1016/j.agwat.2022.107602.
Abstract
Globally, the agricultural sector is the largest consumer of fresh water, despite the increased efficiency in irrigation. Remote sensing is a valuable tool to monitor agricultural water use. In this study, we demonstrate a novel algorithm that computes high-resolution (10 m) remote sensing-based evapotranspiration (ET) data linked exclusively to irrigation, i.e. the incremental evapotranspiration (ETincr). The methodology compares the ET of irrigated agricultural pixels to the weighted average ET of a subset of natural Hydrological Similar Pixels (HSP). The hydrological similarity is based upon a set of features derived from DEM, soil texture, reference evapotranspiration, and precipitation datasets. The difference in ET between the subset of hydrological similar natural pixels and the corresponding irrigated agricultural pixel is explanatory for the amount of ET related to irrigation (ETincr). These results are then converted to the water use (m3 ) per agricultural field. The method is validated for three study areas in South Africa, Spain, and Australia. Comparing the monthly and seasonal water use estimates to water meter observations in the Hex Valley (South Africa), yielded an R2 of 0.751 and 0.780, respectively. For the Ebro (Spain) and Namoi (Australia) study areas, the accuracy of the monthly estimates decreased. In Australia, this was a result of the water meters being linked to local reservoirs, instead of the direct use of the irrigation systems. In total, 8 out of the 27 validation fields with monthly data showed a Kling-Gupta Efficiency (KGE) larger than 0.5, which highlights that the temporal variability can be captured well by the model. Generally, seasonal estimates showed to be most accurate, which makes the product suitable for comparison with seasonal water allocations and could help to monitor overconsumption in water-scarce environments.
Vervoort, R.W. et al., (Sustainability, 2022), Progress in Developing Scale-Able Approaches to Field-Scale Water Accounting Based on Remote Sensing.
Vervoort, Rutger Willem & Fuentes, Ignacio & Brombacher, Joost & Degen, Jelle & Chambel-Leitão, Pedro & Santos, Flávio. (2022). Progress in Developing Scale-Able Approaches to Field-Scale Water Accounting Based on Remote Sensing. Sustainability. 14. 2732. 10.3390/su14052732.
Abstract
To increase water productivity and assess water footprints in irrigated systems, there is a need to develop cheap and readily available estimates of components of water balance at fine spatial scales. Recent developments in satellite remote sensing platforms and modelling capacities have opened opportunities to address this need, such as those being developed in the WaterSENSE project. This paper showed how evapotranspiration, soil moisture, and farm-dam water volumes can be quantified based on the Copernicus data from the Sentinel satellite constellation. This highlights distinct differences between energy balance and crop factor approaches and estimates that can be derived from the point scale to the landscape scale. Differences in the results are related to assumptions in deriving evapotranspiration from remote sensing data. Advances in different parts of the water cycle and opportunities for crop detection and yield forecasting mean that crop water productivity can be quantified at field to landscape scales, but uncertainties are highly dependent on input data availability and reference validation data.
Keywords: water use efficiency; Copernicus satellite data; irrigated agriculture
Massari, C. et al., (Remote Sensing, 2021), A Review of Irrigation Information Retrievals from Space and Their Utility for Users.
Massari, Christian & Modanesi, Sara & Dari, Jacopo & Gruber, Alexander & De Lannoy, Gabriëlle & Girotto, Manuela & Quintana Seguí, Pere & Le Page, Michel & Jarlan, Lionel & Zribi, Mehrez & Ouaadi, Nadia & Vreugdenhil, Mariette & Zappa, Luca & Dorigo, Wouter & Wagner, Wolfgang & Brombacher, Joost & Pelgrum, Henk & Jaquot, Pauline & Freeman, Vahid & Brocca, Luca. (2021). A Review of Irrigation Information Retrievals from Space and Their Utility for Users. Remote Sensing. 13. 4112. 10.3390/rs13204112.
Abstract
Irrigation represents one of the most impactful human interventions in the terrestrial water cycle. Knowing the distribution and extent of irrigated areas as well as the amount of water used for irrigation plays a central role in modeling irrigation water requirements and quantifying the impact of irrigation on regional climate, river discharge, and groundwater depletion. Obtaining high-quality global information about irrigation is challenging, especially in terms of quantification of the water actually used for irrigation. Here, we review existing Earth observation datasets, models, and algorithms used for irrigation mapping and quantification from the field to the global scale. The current observation capacities are confronted with the results of a survey on user requirements on satellite-observed irrigation for agricultural water resources’ management. Based on this information, we identify current shortcomings of irrigation monitoring capabilities from space and phrase guidelines for potential future satellite missions and observation strategies. Keywords: irrigation; satellite; soil moisture; evapotranspiration; water cycle; farmers
Blatchford, M. et al,. (Hydrological Processes, 2020), Evaluation of WaPOR V2 evapotranspiration products across Africa. Hydrological Processes.
Blatchford, Megan & Mannaerts, C.M. & Muchiri Njuki, Sammy & Nouri, Hamideh & Zeng, Yijian & Pelgrum, Henk & Wonink, Steven & Karimi, Poolad. (2020). Evaluation of WaPOR V2 evapotranspiration products across Africa. Hydrological Processes. 34. 10.1002/hyp.13791.
Abstract
The Food and Agricultural Organization of the United Nations (FAO) portal to monitor water productivity through open-access of remotely sensed derived data (WaPOR) offers continuous actual evapotranspiration and interception (ETIa-WPR) data at a 10-day basis across Africa and the Middle East from 2009 onwards at three spatial resolutions. The continental level (250 m) covers Africa and the Middle East (L1). The national level (100 m) covers 21 countries and 4 river basins (L2). The third level (30 m) covers eight irrigation areas (L3). To quantify the uncertainty of WaPOR version 2 (V2.0) ETIa-WPR in Africa, we used a number of validation methods. We checked the physical consistency against water availability and the long-term water balance and then verify the continental spatial and temporal trends for the major climates in Africa. We directly validated ETIaWPR against in situ data of 14 eddy covariance stations (EC). Finally, we checked the level consistency between the different spatial resolutions. Our findings indicate that ETIa-WPR is performing well, but with some noticeable overestimation. The ETIa-WPR is showing expected spatial and temporal consistency with respect to climate classes. ETIa-WPR shows mixed results at point scale as compared to EC flux towers with an overall correlation of 0.71, and a root mean square error of 1.2 mm/day. The level consistency is very high between L1 and L2. However, the consistency between L1 and L3 varies significantly between irrigation areas. In rainfed areas, the ETIa-WPR is overestimating at low ETIa-WPR and underestimating when ETIa is high. In irrigated areas, ETIa-WPR values appear to be consistently overestimating ETa. The relative soil moisture content (SMC), the input of quality layers and local advection effects were some of the identified causes. The quality assessment of ETIa-WPR product is enhanced by combining multiple evaluation methods. Based on the results, the ETIa-WPR dataset is of enough quality to contribute to the understanding and monitoring of local and continental water processes and water management.
KEYWORDS accuracy assessment, actual evapotranspiration, consistency, continental Africa, direct validation, penman–Montieth, remote sensing, water resources management
Singels, A. et al., (Water SA, 2018), Monitoring water use efficiency of irrigated sugarcane production in Mpumalanga, South Africa, using SEBAL.
Singels, A. & Jarmain, Caren & Bastidas-Obando, E & Olivier, Francois & Paraskevopoulos, A.L.. (2018). Monitoring water use efficiency of irrigated sugarcane production in Mpumalanga, South Africa, using SEBAL. Water SA. 44. 636. 10.4314/wsa.v44i4.12.
Abstract
The objective of this study was to assess the accuracy, spatial variation and potential value of remote sensing (RS) estimates of evapotranspiration (ET) and biomass production for irrigated sugarcane in Mpumalanga, South Africa. Weekly ET and biomass production were estimated from RS data from 2011 to 2013 using the Surface Energy Balance Algorithm for Land (SEBAL). Ground estimates of canopy interception of photosynthetically active radiation (FPAR) and aerial biomass were compared to RS estimates. ET was estimated with a surface renewal (SR) system in one field. Evaporation coefficient (Kc) values were calculated from ET and reference grass evaporation. Remote sensing FPAR and biomass estimates compared well with field measurements (R2 = 0.89 and 0.78). SEBAL ET estimates exceeded SR estimates by 5 mm/week, while full canopy Kc values for SEBAL compared better with literature values than with SR Kc values. SEBAL estimates of ET and biomass were regarded as reliable. Considerable spatial variation was observed in seasonal RS ET (1 034 ± 223 mm), biomass (45 ± 17 t/ha) and biomass water use efficiency (WUEBIO, defined as dry biomass produced per unit of ET) (4.1 ± 1.0 kg/m3 ). About 32% of sugarcane fields had values below economic thresholds, indicating an opportunity to increase productivity. Actual yields correlated well with WUEBIO values, suggesting that this may be used for monitoring crop performance and identifying areas that require remedial treatment.
Keywords: remote sensing, sugarcane, irrigation, evapotranspiration, biomass, water use efficiency, SEBAL
Bastiaanssen, W.G.M. et al., (Water Resources Research, 2012), Surface energy balance and actual evapotranspiration of the transboundary Indus Basin estimated from satellite measurements and the ETLOOK model.
Bastiaanssen, W.G.M. & Cheema, Muhammad Jehanzeb & Immerzeel, W.W. & Miltenburg, I. & Pelgrum, Henk. (2012). Surface energy balance and actual evapotranspiration of the transboundary Indus Basin estimated from satellite measurements and the ETLOOK model. Water Resources Research. 48. W11512. 10.1029/2011WR010482.
Abstract
The surface energy fluxes and related evapotranspiration processes across the Indus Basin were estimated for the hydrological year 2007 using satellite measurements. The new ETLook remote sensing model (version 1) infers information on actual Evaporation (E) and actual Transpiration (T) from combined optical and passive microwave sensors, which can observe the land-surface even under persistent overcast conditions. A two-layer Penman–Monteith equation was applied for quantifying soil and canopy evaporation. The novelty of the paper is the computation of E and T across a vast area (116.2 million ha) by using public domain microwave data that can be applied under all weather conditions, and for which no advanced input data are required. The average net radiation for the basin was estimated as being 112 Wm2 . The basin average sensible, latent and soil heat fluxes were estimated to be 80, 32, and 0 Wm2 , respectively. The average evapotranspiration (ET) and evaporative fraction were 1.2 mm d1 and 0.28, respectively. The basin wide ET was 496 6 16.8 km3 yr1 . Monte Carlo analysis have indicated 3.4% error at 95% confidence interval for a dominant land use class. Results compared well with previously conducted soil moisture, lysimeter and Bowen ratio measurements at field scale (R2 ¼ 0.70; RMSE ¼ 0.45 mm d1 ; RE ¼ –11.5% for annual ET). ET results were also compared against earlier remote sensing and modeling studies for various regions and provinces in Pakistan (R2 ¼ 0.76; RMSE ¼ 0.29 mmd1 ; RE ¼ 6.5% for annual ET). The water balance for all irrigated areas together as one total system in Pakistan and India (26.02 million ha) show a total ET value that is congruent with the ET value from the ETLook surface energy balance computations. An unpublished validation of the same ETLook model for 23 jurisdictional areas covering the entire Australian continent showed satisfactory results given the quality of the watershed data and the diverging physiographic and climatic conditions (R2 ¼ 0.70; RMSE ¼ 0.31 mmd1 ; RE ¼ –2.8% for annual ET). Eight day values of latent heat fluxes in Heibei (China) showed a good resemblance (R2 ¼ 0.92; RMSE ¼ 0.04 mm d1 ; RE ¼ 9.5% for annual ET). It is concluded that ETLook is a novel model that can be operationalized further—especially after improving the preprocessing of spaceborne soil moisture data. This preprocessing includes (1) downscaling of topsoil moisture from 25 to 1 km pixels, and (2) translation of topsoil moisture into subsoil moisture values.
Bastiaanssen, W.G.M. et al., (Journal of Irrigation and Drainage Engineering, 2005), SEBAL Model with Remotely Sensed Data to Improve Water-Resources Management under Actual Field Conditions.
Bastiaanssen, W.G.M. & Noordman, E.J.M. & Pelgrum, Henk & Davids, G. & Thoreson, B.P. & Allen, Richard. (2005). SEBAL Model with Remotely Sensed Data to Improve Water-Resources Management under Actual Field Conditions. Journal of Irrigation and Drainage Engineering. 131. 85-93. 10.1061/(ASCE)0733-9437(2005)131:1(85).
Abstract
Water management emphasis tends to shift from supply augmentation to limiting water consumption. Spatio-temporal information on actual evapotranspiration (ET) helps users to better understand evaporative depletion and to establish links between land use, water allocation, and water use. Satellite-based measurements, used in association with energy balance models, can provide the spatial distribution of ET for these linkages. This paper describes the major principles of the Surface Energy Balance Algorithm for Land (SEBAL) and summarizes its accuracy under several climatic conditions at both field and catchment scales. For a range of soil wetness and plant community conditions, the typical accuracy at field scale is 85% for 1 day and it increases to 95% on a seasonal basis. The accuracy of annual ET of large watersheds was found to be 96% on average. SEBAL has been applied in more than 30 countries worldwide, and the 26 research studies that were conducted over the past 10 years are now gradually being replaced by application studies (17 studies finished). A short case study in the Yakima River basin (Washington State) is presented as new material to demonstrate how ET from remote sensing can be used for evaluating water conservation projects.
Bastiaanssen, W.G.M. et al., (Formulation Journal of Hydrology, 1998), A remote sensing surface energy balance algorithm for land (SEBAL).
W.G.M. Bastiaanssen, M. Menenti, R.A. Feddes, A.A.M. Holtslag (1998). A remote sensing surface energy balance algorithm for land (SEBAL). 1. Formulation, Journal of Hydrology, 212-213 (p198-212)
Abstract
The major bottlenecks of existing algorithms to estimate the spatially distributed surface energy balance in composite terrain by means of remote sensing data are briefly summarised. The relationship between visible and thermal infrared spectral radiances of areas with a sufficiently large hydrological contrast (dry and wet land surface types, vegetative cover is not essential) constitute the basis for the formulation of the new Surface Energy Balance Algorithm for Land (SEBAL). The new algorithm (i) estimates the spatial variation of most essential hydro-meteorological parameters empirically, (ii) requires only field information on short wave atmospheric transmittance, surface temperature and vegetation height, (iii) does not involve numerical simulation models, (iv) calculates the fluxes independently from land cover and (v) can handle thermal infrared images at resolutions between a few meters to a few kilometers. The empirical relationships are adjusted to different geographical regions and time of image acquisition. Actual satellite data is inserted in the derivation of the regression coefficients. Part 2 deals with the validation of SEBAL. q 1998 Elsevier Science BV. All rights reserved.
Keywords: Surface energy balance; Evaporation; Remote sensing
Bastiaanssen, W.G.M. et al., (Validation Journal of Hydrology, 1998), A remote sensing surface energy balance algorithm for land (SEBAL).
Bastiaanssen, W. G. M., Pelgrum, H., Wang, J., Ma, Y., Moreno, J. F., Roerink, G. J., & van der Wal, T. (1998). A remote sensing surface energy balance algorithm for land (SEBAL); 2. Validation. Journal of Hydrology. 212-213, (p213-229).
Abstract
The surface fluxes obtained with the Surface Energy balance Algorithm for Land (SEBAL), using remote sensing information and limited input data form the field were validated with data available from the large-scale field experiments EFEDA (Spain), HAPEX-Sahel (Niger) and HEIFE (China). In 85% of the cases where field scale surface flux ratios were comparedwith SEBAL-based surface flux ratios, the differences were within the range of instrumental inaccuracies. Without any calibration procedure, the root mean square error of the evaporative fraction \Delta (latent heat flux/net available radiation) for footprints of a few hundred metres varied from LRMSE 0.10 to 0.20. Aggregation of several footprints to a length scale of a few kilometres reduced the overall error to five percent. Fluxes measured by aircraft during EFEDA were used to study the correctness of remote sensed watershed fluxes (1,000,000 ha):The overall difference in evaporative fraction was negligible. For the Sahelian landscape in Niger, observed differences were larger (15%), which could be attributed to the rapid moisture depletion of the coarse textured soils between the moment of image acquisition (18 September 1992) and the moment of in situ flux analysis (17 September 1992). For HEIFE, the average difference in SEBAL estimated and ground verified surface fluxes was 23 W m22 , which, considering that surface fluxes were not used for calibration, is encouraging. SEBAl estimates of evaporation from the subsealevel Qattara Depression in Egypt (2,000,000 ha) were consistent with the numerically predicted discharge from the groundwater system. In Egypt’s Nile Delta, the evaporation from a distributed field scale water balance model at a 700,000 ha irrigated agricultural region led to a difference of 5% with daily evaporative fluxes obtained from SEBAL. It is concluded that, for all study areas in arid zones, the errors average out if a larger number of pixels is considered. Part 1 of this chapter deals with the formulation of SEBAL. q 1998 Elsevier Science B.V. All rights reserved.
Keywords: Surface fluxes, validation, remote sensing
Brombacher, Joost & Silva, Isadora & Degen, Jelle & Pelgrum, Henk. (2022). A novel evapotranspiration based irrigation quantification method using the hydrological similar pixels algorithm. Agricultural Water Management. 267. 10.1016/j.agwat.2022.107602.
Vervoort, Rutger Willem & Fuentes, Ignacio & Brombacher, Joost & Degen, Jelle & Chambel-Leitão, Pedro & Santos, Flávio. (2022). Progress in Developing Scale-Able Approaches to Field-Scale Water Accounting Based on Remote Sensing. Sustainability. 14. 2732. 10.3390/su14052732.
Massari, Christian & Modanesi, Sara & Dari, Jacopo & Gruber, Alexander & De Lannoy, Gabriëlle & Girotto, Manuela & Quintana Seguí, Pere & Le Page, Michel & Jarlan, Lionel & Zribi, Mehrez & Ouaadi, Nadia & Vreugdenhil, Mariette & Zappa, Luca & Dorigo, Wouter & Wagner, Wolfgang & Brombacher, Joost & Pelgrum, Henk & Jaquot, Pauline & Freeman, Vahid & Brocca, Luca. (2021). A Review of Irrigation Information Retrievals from Space and Their Utility for Users. Remote Sensing. 13. 4112. 10.3390/rs13204112.
Blatchford, Megan & Mannaerts, C.M. & Muchiri Njuki, Sammy & Nouri, Hamideh & Zeng, Yijian & Pelgrum, Henk & Wonink, Steven & Karimi, Poolad. (2020). Evaluation of WaPOR V2 evapotranspiration products across Africa. Hydrological Processes. 34. 10.1002/hyp.13791.
Singels, A. & Jarmain, Caren & Bastidas-Obando, E & Olivier, Francois & Paraskevopoulos, A.L.. (2018). Monitoring water use efficiency of irrigated sugarcane production in Mpumalanga, South Africa, using SEBAL. Water SA. 44. 636. 10.4314/wsa.v44i4.12.
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