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Accurate and reliable estimation of actual evapotranspiration (AET) is essential for various hydrological studies, including drought prediction, water resource management, and the analysis of atmospheric–terrestrial carbon exchanges. Gridded AET products offer potential for application in ungauged areas, but their uncertainties may be significant, making it difficult to identify the best products for specific regions. While in situ data directly estimate gridded ET products, their applicability is limited in ungauged areas that require FLUXNET data. This paper employs an Extended Triple Collocation (ETC) method to estimate the uncertainty of Global Land Evaporation Amsterdam Model (GLEAM), Famine Early Warning Systems Network (FLDAS), and Maximum Entropy Production (MEP) AET product without requiring prior information. Subsequently, a merged ET product is generated by combining ET estimates from three original products. Furthermore, the study quantifies the uncertainty of each individual product across different vegetation covers and then compares three original products and the Merged ET with data from 645 in situ sites. The results indicate that GLEAM covers the largest area, accounting for 39.1% based on the correlation coefficient criterion and 39.9% based on the error variation criterion. Meanwhile, FLDAS and MEP exhibit similar performance characteristics. The merged ET derived from the ETC method demonstrates the ability to mitigate uncertainty in ET estimates in North American (NA) and European (EU) regions, as well as tundra, forest, grassland, and shrubland areas. This merged ET could be effectively utilized to reduce uncertainty in AET estimates from multiple products for ungauged areas. [ABSTRACT FROM AUTHOR]

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The components of water balance (WBC) that involve precipitation, evapotranspiration, runoff, irrigation, and groundwater recharge are critical for understanding the hydrological cycle and water management of resources in semi-arid and arid areas. This paper assesses temporal and spatial distributions of surface runoff, actual evapotranspiration, and groundwater recharge upstream of the New Assiut Barrage (NAB) in the Nile Valley, Upper Egypt, using the WetSpass-M model for the period 2012–2020. Moreover, this study evaluates the effect of land cover/land use (LULC) alterations in the study period on the WBC of the NAB. The data provided as input for the WetSpass-M model in the structure of raster maps using the Arc-GIS tool. Monthly meteorological factors (e.g., temperature, rainfall, and wind speed), a digital elevation model (DEM), slope, land cover, irrigation cover, a soil map, and depth to groundwater are included. The long-term temporal and spatial mean monthly irrigation and precipitation (127 mm) is distributed as 49% (62 mm) actual evapotranspiration, 15% (19 mm) groundwater recharge, and 36% (46 mm) surface runoff. The replacement of cropland by built-up areas was recognized as the primary factor responsible for the major decrease in groundwater, an increase in evapotranspiration and an increase in surface runoff between LCLU in 2012 and 2020. The integration of the WetSpass model with GIS has shown its effectiveness as a powerful approach for assessing WBC. Results were more accurate and reliable when hydrological modeling and spatial analysis were combined. The results of this research can help make well-informed decisions about land use planning and sustainable management of water resources in the upstream area of the NAB. [ABSTRACT FROM AUTHOR]

Evapotranspiration is a key part of the water cycle between the atmosphere and the land surface, and it is an important parameter for studying the land–atmosphere system. Change and evolution have important implications. Therefore, the understanding and research of actual evapotranspiration (AET) can profoundly affect water use, ecological environment, temperature, and precipitation. In this paper, the single-layer monthly average reanalysis meteorological data of the Qinghai–Tibet Plateau from 1981 to 2020 was used to study and calculate the actual evapotranspiration in the Qinghai–Tibet Plateau, and the temporal and spatial variation characteristics, variation laws, and changes were analyzed by methods such as cumulative anomalies and the Mann–Kendall trend test. The results showed the following: (1) The evapotranspiration gradually decreased from southeast to northwest. The evapotranspiration in the southeastern region is strong, and the maximum value appears in the Hengduan Mountains. (2) The evapotranspiration was the largest in summer and gradually decreased from southeast to northwest; the evapotranspiration in spring and autumn was relatively uniform, with little overall difference, and the evapotranspiration was the lowest in winter. (3) There were mainly three spatial distribution modes of evapotranspiration in the Qinghai–Tibet Plateau, which were characterized by a significant and consistent change centered on the Tibet region, an east–west reverse type, and an east–west "negative-positive-negative" of the distributed three-pole space. The corresponding time coefficients characterized the interdecadal and interannual variation, and the decadal variation characteristics are more significant than the annual variation characteristics. (4) The actual evapotranspiration had step change; the step change years were 1989, 2002, 2011, and 2015, and there was an interval of about 5 years. [ABSTRACT FROM AUTHOR]

The paper presents the estimated changes in the soil water content, the total runoff, the sediment yield and the actual evapotranspiration for the small Bystra catchment in the east of Poland. The findings are based on the results of three simulations covering the years of 2041–2050. The simulations were based on a calibrated and validated SWAT model (2010–2017). The first variant covers just the climate change and the existing structure of soil cultivation for the three regional climate models supported by the EC-EARTH global climate model in the emission scenarios RCP4.5 and RCP8.5. Variants two and three are based on the first variant in terms of the changing climate. The second variant, however, involves placing a pond in each farm in the catchment, while the third variant involves designing huge reservoirs as a result of land consolidation. Variants two and three occur in five adaptation scenarios each. The first adaptation scenario (V2.1 and V3.1) involves only increasing the number of ponds on the farm or increasing the number of reservoirs for non-irrigated arable land crops, i.e., WWHT (winter cereals), BARL (spring cereals), CANP (rapeseed) and CRDY (other crops). The second adaptation scenario (V2.2 and V3.2) involves growing vegetables without irrigation (instead of cereals). The third adaptation scenario (V2.3 and V3.3) involves growing vegetables with irrigation (instead of cereals). The fourth adaptation scenario (V2.4 and V3.4) involves partial cultivation of vegetables and cereals. The fifth adaptation scenario (V2.5 and V3.5) involves partial cultivation of orchards and cereals. The adaptation scenarios of the irrigation of vegetables from deep water-bearing layers (second variant) or reservoirs (third variant) contribute to the increase in water content in the soil, especially in summer, in comparison with the adaptation scenarios for vegetable cultivation without irrigation. What is more, the actual evapotranspiration was higher in the adaptation scenarios involving irrigation than in scenarios without irrigation. It is known that the changes in water content in soil and the intensification of water erosion are gravely affected by modifications in crops and soil cultivation. A change from cereal cultivation to irrigated vegetable cultivation or orchards increased the water content in the soil in most climatic projections. However, the increase in the number of ponds in the second variant had little impact on the soil water content, actual evapotranspiration and overall runoff, while the erosion loss decreased. With the lower precipitation levels in the years 2041–2050 relative to 2010–2017, as presented in the emissive scenario RCP 4.5, the soil water content decreases by up to 14% for most variants. Total runoff for most variants will also be lower by 4–35%. The percentage change in sediment yield will fluctuate between −86% and 116%. On the other hand, the actual evapotranspiration for most variants will be higher. With higher precipitation levels in the years 2041–2050 relative to 2010–2017, as presented in the emissive scenario RCP 8.5, the soil water content changes slightly from −7% to +3%. Total runoff for most variants will also be higher by as much as 43%. Sediment yield for most scenarios may increase by 226%. The actual evapotranspiration for most variants will also be higher. Irrigation variants tend to increase soil available water while increasing evapotranspiration and total outflow in the catchment as compared to non-irrigated LULC. The largest increase in the soil water content is observed in most irrigation variants for RCP 4.5 (annual average 316–319 mm) (V2.3-V2.5, V3.2, and V3.3) and RCP 8.5 (annual average 326–327 mm) (V2.3-V2.5 and V3.3) as compared to V1 (BaU) (315 mm–RCP 4.5 and 324 mm–RCP 8.5) for the years 2041–2050. On the other hand, the lowest increase in soil water content is observed in the V3.5 variant, with an annual average of 292 mm for RCP 4.5 and an annual average of 311 mm for RCP 8.5. Thus, for future climate change scenarios, irrigation with water reservoirs (ponds and storage reservoirs) should be considered. The study proves the rationale behind building ponds in small catchments in order to increase water resources in a landscape and also to counteract adverse effects of climate changes, i.e., sediment outflow and surface water erosion. [ABSTRACT FROM AUTHOR]

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The objective of this paper is to contribute to improve ETa estimation in semiarid environments by proposing two variations to the TDMT model. These variations are based on the use of MODIS products from TERRA or AQUA satellites and on the use of NDVI instead of EVI, to estimate the fraction of vegetation cover. The proposed changes were validated with the original methodology for the 2012-2014 period with data obtained from two flux towers (ES-LJu and ES-Amo). The best results were obtained when using the alternative methodology (RMSE of 0.64-0.67mm in ES-Lju and of 0.97-1.02mm in ES-Amo). Additionally, a correction of the temporal systematic errors of the model based on RandomForest is proposed. With this correction, RMSE of 0.31-0.35mm in ES-Lju and 0.30-0.34mm in ES-Amo were obtained. The spatial distribution obtained with this corrected model is the most consistent with the characteristics of the study area. [ABSTRACT FROM AUTHOR]

Determining the actual evapotranspiration value and analyzing its temporal trend is essential for optimal water resources management in a basin. In the present paper, the actual evapotranspiration time series is simulated and its trend is analyzed according to the trend of climatic variables and land use in the Ajichi basin during the period of 2015- 1987. The comprehensive SWAT model was set up, calibrated, and validated for the Ajichi basin. Also, the average of simulated actual evapotranspiration of crops (in wet years) was compared with similar values in the National Water Document. The results of the Mann-Kendall trend test showed that the annual rainfall in most meteorological stations had a decreasing trend and the rainfall trend in the ten stations decreased significantly. While the annual maximum temperature at all stations and the annual minimum temperature in most of them have significantly increased. Investigation of land use maps illustrated that the irrigated land area of the basin has increased by a 39% during the study period. According the study's results, the potential evapotranspiration of the basin has had a significant increasing trend with a rate of 2.54 mm per year. The results indicated that despite the increasing trend of potential evapotranspiration and irrigated land area, the actual evapotranspiration of the basin had a significant decreasing trend with a rate of 2.2 mm per year due to the decrease in rainfall. [ABSTRACT FROM AUTHOR]

Caatinga biome, located in the Brazilian semi-arid region, is the most populous semi-arid region in the world, causing intensification in land degradation and loss of biodiversity over time. The main objective of this paper is to determine and analyze the changes in land cover and use, over time, on the biophysical parameters in the Caatinga biome in the semi-arid region of Brazil using remote sensing. Landsat-8 images were used, along with the Surface Energy Balance Algorithm for Land (SEBAL) in the Google Earth Engine platform, from 2013 to 2019, through spatiotemporal modeling of vegetation indices, i.e., leaf area index (LAI) and vegetation cover (VC). Moreover, land surface temperature (LST) and actual evapotranspiration (ETa) in Petrolina, the semi-arid region of Brazil, was used. The principal component analysis was used to select descriptive variables and multiple regression analysis to predict ETa. The results indicated significant effects of land use and land cover changes on energy balances over time. In 2013, 70.2% of the study area was composed of Caatinga, while the lowest percentages were identified in 2015 (67.8%) and 2017 (68.7%). Rainfall records in 2013 ranged from 270 to 480 mm, with values higher than 410 mm in 46.5% of the study area, concentrated in the northern part of the municipality. On the other hand, in 2017 the lowest annual rainfall values (from 200 to 340 mm) occurred. Low vegetation cover rate was observed by LAI and VC values, with a range of 0 to 25% vegetation cover in 52.3% of the area, which exposes the effects of the dry season on vegetation. The highest LST was mainly found in urban areas and/or exposed soil. In 2013, 40.5% of the region's area had LST between 48.0 and 52.0 °C, raising ETa rates (~4.7 mm day−1). Our model has shown good outcomes in terms of accuracy and concordance (coefficient of determination = 0.98, root mean square error = 0.498, and Lin's concordance correlation coefficient = 0.907). The significant increase in agricultural areas has resulted in the progressive reduction of the Caatinga biome. Therefore, mitigation and sustainable planning is vital to decrease the impacts of anthropic actions. [ABSTRACT FROM AUTHOR]

Wetlands located in cities are among the most diverse and productive natural based systems which provide important benefits such as water quality improvement, flood control, soil erosion protection, recreation opportunities, support for wildlife and natural products. This paper presents the water budget in Văcărești wetland in order to provide an overview of the hydrological processes that make wetlands unique. Văcărești wetland is located in south part of Bucharest city and represents the single urban Natural Park in Romania. The existing wetland has been formed on an area conceived initially as the bottom of an artificial lake where the nature and the wildlife developed on their own. Using historical data and several algorithms, this paper presents the analysis of the water budget on the considered area which would lead to a better assessment of the hydrological processes. The goal of the study was to gain knowledge on how the wetland is sustained and, as a result, to develop solutions to prevent the ecosystem deterioration conducted by external pressures like climate change with extended periods of droughts or anthropic influences. [ABSTRACT FROM AUTHOR]

The Upper Paraná River Basin (UPRB) has undergone remarkable land use and cover changes (LUCC) in recent decades. This paper analyses the hydrologic response to LUCC in the UPRB between 1985 and 2015, using the Soil and Water Assessment Tool (SWAT) model. The impacts of LUCC were examined for annual, wet, and dry season (both during calibrated and validated periods) between 1984 and 2015. The most substantial LUCC were the extensive reduction of the cerrado and the expansion of agriculture areas. The simulations demonstrated that the LUCC caused important changes in basin hydrology. For instance, an increase (decrease) of surface runoff in the wet (dry) season at most UPRB subbasins was observed. In addition, the simulation results revealed a reduction in actual evapotranspiration and an increase in soil moisture in the annual and wet season. Consequently, most of the major rivers of the basin presented an increase (decrease) in their discharge in the wet (dry) period. The major changes in the hydrologic components were observed in the central-western and southern parts of the UPRB. At the river mouth of the UPRB, the LUCC led to an increase in long-term mean discharge values of 4.2% and 1.1% in the annual and wet season and a decrease of about 2.2% in the dry period. This study provides a large-scale modeling and valuable information that could be used to improve planning and sustainable management of future water resources within the basin. [ABSTRACT FROM AUTHOR]

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Copyright of Acta Scientiarum Polonorum. Formatio Circumiectus is the property of Wydawnictwo Uniwersytetu Rolniczego im. Hugona Kollataja w Krakowie and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A limited number of publications in the literature address the measurement of actual evapotranspiration (AET) from peat soils. AET is an important parameter in the description of water pathways of an ecosystem. In peatlands, where the water table is near the surface, the measurement of AET represents a challenge. This paper discusses the development of an automated lysimeter installed between July 12 and 27, 2010, at an 11-ha bog site, Pont-Rouge (42 km west of Quebec City, Canada). This system was made of an isolated block of peat, maintained at the same water level as the surrounding water table by a system of submersible pressure transmitters and pumps. The change in water level in millimeters in the isolated block of peat was used to calculate the water lost through evapotranspiration while for accounting the precipitation. The rates of AET were calculated for each day of the study period. This relatively inexpensive and simple to install system may eventually be used to calculate AET on peaty soils in the years to come. [ABSTRACT FROM AUTHOR]

Actual evapotranspiration is one of the most important component for efficient water management and planning. Until recently, evapotranspiration computations and measurements have been performed locally. But, in recent years, actual evapotranspiration computations can be calculated regionally thanks to improvements on remote sensing discipline and satellites. Surface Energy Balance Algorithm for Land (SEBAL) is one of the most commonly preferred technics for actual evapotranspiration mapping. However, this algorithm has some difficulties such as mismatch with Landsat 8 and hot-wet pixel selection which require expert knowledge. In this paper, a novel SEBAL based approach (SEBAL-BSA), which can use Landsat 8 images as data and can automatically perform hot-wet pixel selection using Backtracking Search Algorithm (BSA) with ground control points, has been proposed. SEBAL-BSA was developed and tested using January 22-2015, April 28-2015 and July 01-2015 dated Landsat 8 images in Akarsu Irrigation Water User Association command area in the Çukurova Region of Turkey and actual evapotranspiration mapping was realized without albedo measurements. Accuracy of SEBAL-BSA has been examined by comparing values of predefined ground truth points and values obtained from proposed approach. According to results of parametric matched pairs T test and nonparametric Wilcoxon sign rank test, SEBAL-BSA is highly successful. Applications also show that the SEBAL-BSA is a user-friendly approach for institutions and organizations related to water authorization and management. [ABSTRACT FROM AUTHOR]

Agriculture water use accounts for 70% of the total water withdrawal worldwide. The evapotranspiration during crop growth is one of the important hydrological processes in the agricultural water cycle. This study proposed the concept of artificial irrigation evapotranspiration of irrigated crops to describe that the evapotranspiration caused by irrigation water use. Irrigated crops rely on two kinds of water sources: precipitation and irrigation water. With the construction of irrigation schemes, the artificial irrigation evapotranspiration plays an increasingly important role in the dualistic water cycle system of irrigated cropland. To reveal the amount of artificial irrigation evapotranspiration of 17 categories of irrigated crops in China, this study proposed a new quantitative model system which was established based on traditional evapotranspiration models and soil water balance models. Based on the new model system, we calculated the annual artificial irrigation evapotranspiration of irrigated crops for the period 2013 to 2017 in China. The results showed that the proportion of artificial irrigation evapotranspiration to the total evapotranspiration of irrigated crops was 41.3%, whose value was 228.1 km3 a−1. The artificial irrigation evapotranspiration in different agricultural water management regions were 90.0 km3 a−1 in the northeast region, 86.0 km3 a−1 in the southeast region, and relatively low 52.2 km3a−1 in the west region. The results of this study can provide methods for water management and policy–making in agricultural irrigated areas, and it can also provide a preliminary understanding of the influence of human activities on the dualistic water cycle in cropland. [ABSTRACT FROM AUTHOR]

As urbanization continues to increase, changes in the ecological characteristics of urban areas are becoming more reasonable to meet the needs of a growing population. However, the profound impact of human-induced urban pressures on land, often called the "billing impact", is strongly emphasized in research publications. In many cases, contemporary anthropogenic processes alter the dynamics of environmental functions in complex ways. Urban regions meet a particular climate regime characterized by increased air temperatures compared to peripheral areas and a significant reduction in wind speed, attributable to the interaction of natural and anthropogenic factors. An urban heat island (UHI) occurs when the air above populated areas heats up additionally, causing air to flow from the site's edges to its center and creating a heat dome. This study reveals the influence of urbanization on microclimatic changes, encompassing increased evapotranspiration, altered vegetation cover, and temperature fluctuations. The results illustrate environmental transformations caused by abrupt and unregulated urbanization in the mountainous area of Zlatibor, Serbia, a trend that has intensified over the past decade. [ABSTRACT FROM AUTHOR]

Background and Aims Irrigation is one of the most important viticultural practices in semi-arid regions. For this reason, the Food and Agriculture Organization's Irrigation and Drainage Paper No. 56 single and dual crop coefficient approaches were evaluated to estimate actual evapotranspiration ( ETa) over a drip-irrigated Merlot vineyard. Methods and Results Vine transpiration was measured using sap flow sensors, and ETa was measured by an eddy covariance system. Soil evaporation was calculated as the difference between ETa and sap flow sensors. Reference evapotranspiration ( ETo) was calculated using the Penman- Monteith equation. This information was used to evaluate single ( Kc) and dual crop coefficients [ Kcb and Ke] approaches during the 2007/08 and 2008/09 grapevine growing seasons. Conclusions Results indicated that vine transpiration is the most important component of ETa for a drip-irrigated Merlot vineyard trained on a vertical shoot-positioned system. In midseason, the observed values of single crop coefficients and Kcb were lower by 11 and 19% than those recommended by the Food and Agriculture Organization's Irrigation and Drainage Paper No. 56 for grapevines, respectively. The application of site-specific Kcb values reduced the error in the estimation of ETa by about 10%. Significance of the Study The study indicates that the use of sap flow sensors could be an alternative method for obtaining site-specific Kcb values for vineyards under field conditions. [ABSTRACT FROM AUTHOR]

Soil draught is defined as the lack of water in soil, which plants can use for their growth. If plants have no access to the water, they wither. Accessibility of soil water for plants is determined by soil moisture potential (hw). Soil moisture potential increases with the decrease of water content. In order to determine water accessibility characteristic values were defined on the retention curve, or pF = log hw. These are wilting point (WP), threshold point (TP) and field water capacity (FWC). This paper presents the quantification of the course of actual and potential evapotranspiration with regard to the soil water storage. Soil water storage is evaluated according to the FWC, TP and WP. The impact of evaporation deficit on the soil water deficit in the course of and after the state of soil draught was also monitored. The results presented herein come from the investigation realized in the area of Eastern-Slovakian Lowland, Slovakia. [ABSTRACT FROM AUTHOR]

【Objective】 Evapotranspiration in terrestrial ecosystems is not only a component of hydrological cycle but also controls plant productivity. Understanding its spatiotemporal variation in a region is hence important for improving its water and agronomic management. This paper is to present a method for accurately and rapidly evaluating evapotranspiration at high spatial resolution in irrigation areas using remote sensing technology and energy balance model. 【Method】 The model is based on the surface energy balance algorithm (SEBAL) model by using Landsat-8 remote sensing imageries and meteorological data. Using this model, we calculate the evapotranspiration in the Luhun Irrigation area and analyzed its variation. 【Result】 The simulated SEBAL values are strongly correlated with both evapotranspiration products (v 1.5) and ground-true data, with the associated correlation coefficients exceeding 0.8 and 0.96, respectively. As plants grow, their evapotranspiration increases progressively from February to May, with the evapotranspiration in cropped regions higher than that in forested regions. Peak evapotranspiration is 106.52 mm, occurring from June to July primarily in cropped regions. The evapotranspiration decreases from August to September, with the region having higher evapotranspiration shifting toward the northeast of the region. 【Conclusion】 Using remote sensing satellite imagery and other complementary data, the SEBAL model is accurate for estimating evapotranspiration at high spatial resolution in a region. It has important implication for improving irrigation management in irrigation districts.

Evapotranspiration is the key and predominant component of the water balance in wetlands. Direct evapotranspiration measurements are challenging in wetlands due to their remoteness and high surface water level. This article describes the actual (ETa and reference evapotranspiration (ET0) from a cultivated wet meadow located in the Biebrza National Park - the largest national park in north-east Poland, Central Europe. The data were sourced from a micrometeorological station equipped with an eddy covariance system to measure heat and vapour fluxes and such meteorological elements as radiation balance components, air temperature and humidity. The values of directly measured ETa were presented daily in the context of available energy and ET0. Daily sums of ETa ranged from below 0.2 mm in winter to 6.5 mm in summer. The share of daily sums of ETa in the ET0 usually ranged from 50 to 60%, with extreme values from 10 to 170%. Aside from giving more insight into Biebrza wetlands' functioning, the actual data produced in this study may be used instead of indirect methods, which were used the most in modelling wetlands areas. [ABSTRACT FROM AUTHOR]

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• The performance of models to estimate daily evapotranspiration varies by ecosystems. • Automatic machine learning can improve the accuracy and generalization of estimated ETa. • Hybrid models are limited by uncertainty in model parameters and strict constraints of physical models. • The two models in this paper provide methods to better estimate daily ETa for wetlands. The performances of physics-based, data-driven, and hybrid models for estimating terrestrial actual evapotranspiration (ETa) is currently under debate, which requires thorough evaluations of those models particularly with recent developments in automatic machine learning (AML) techniques. In this study, six AML-based models were first constructed using the H2O-AML platform, from which an optimal (AML-OP) model was selected for estimating daily ETa at ecosystem scales. In addition, hybrid models were developed by combining the six AML models with surface conductance (Gs) inverted from the Penman-Monteith equation and an optimal (PM-OP) model was also selected. With 15 predictor variables as model inputs that were compiled from various data sources, the performances of those models for estimating daily ETa were evaluated using observed data from the FLUXNET2015 dataset. The results revealed that no models showed consistently low noise levels across different ecosystem types, making it necessary to use AML techniques for selecting ecosystem-specific models. Interestingly, the AML-OP models (root mean square error (RMSE) and symmetric mean absolute percentage error (SMAPE) were 0.16–0.31 mm d-1 and 9 %–36 % respectively) showed slightly better predictive results than the PM-OP models (RMSE and SMAPE were 0.23–0.36 mm d-1 and 15 %–68 % respectively), likely owing to model parameter uncertainties and tight constraints of physical models on application condition. Secondly, as ETa nonlinearly responds to environmental variables, model predictability under extreme weather (drought and heatwave) conditions was examined. The results showed that the prediction of the AML-OP and PM-OP models expectedly worsened (RMSE and SMAPE increased by 0.06–0.77 mm d-1 and −19 % to 79 %, respectively); however, the AML-OP model still outperformed the PM-OP model in most ecosystems, further underscoring the need to understand ETa regulation mechanisms under varying climatic conditions. Finally, the PM-OP models developed here provided better daily ETa estimates compared to other recently proposed hybrid models (RMSE reduced by 0.98–1.80 mm d-1). Both models can be better applied to wetlands that have been less frequently evaluated previously (RMSE reduction of 0.22 mm d-1 and 0.18 mm d-1 for the AML-OP and PM-OP models). [ABSTRACT FROM AUTHOR]

The mitigation of uncertainties in the identification of natural systems is a fundamental aspect in the development of hydrological models, and represents a major challenge for the improvement of modelling techniques. In particular, the calibration of hydrological models based on streamflow measurements at the outlet of a catchment is exposed to significant sources of uncertainty, such as the impact of landscape features on runoff generation. Remote sensing-based actual evapotranspiration (AET) data can be incorporated with streamflow to improve model accuracy and reduce the uncertainty in hydrological modelling, resulting in a significant enhancement of the model performance. The selection of the right AET dataset for hydrological modelling is a crucial task, in front of the availability of multi-source datasets that differ in methods, parameters, and spatiotemporal resolution. Despite the existence of a few studies proposing the usage of remote sensing-based AET data, there is a lack of systematic comparisons between different products, in terms of performance for hydrological modelling. This paper aims to compare the efficacy of different remote sensing-based AET products in improving the simulation of hydrological responses, both in single and in multi-variable scenarios. In this investigation, the Soil and Water Assessment Tool (SWAT) hydrological model was calibrated with observed streamflow data by experimenting with eight different AET datasets. The findings of our study suggest that the incorporation of remote sensing-based AET data in the calibration process of a hydrological model can significantly enhance the accuracy and reliability of model predictions. Thus, the proposed approach can contribute to improving the effectiveness of hydrological modelling as a quantitative tool for the management of water resources. Another finding of this study is that the calibration of the model based solely on AET yields reasonable simulation results of the streamflow, which is an advantageous and promising feature for ungauged basins. • Incorporating evapotranspiration improves hydrological model accuracy. • Model calibration tested with 8 evapotranspiration products combined with streamflow. • Multi-variable calibration reduces uncertainties and improves peak simulation. • Calibrating the model with only evapotranspiration can yield reasonable performance. • A novel analysis approach for ungauged basins can rely on evapotranspiration datasets. [ABSTRACT FROM AUTHOR]

As the main expenditure item in water balance, evapotranspiration has an important impact on the surface ecosystem. Assessing the impact of changes in meteorological elements on evapotranspiration is essential to identify the spatiotemporal heterogeneity of hydrographic responses to climate changes. Based on the actual evapotranspiration (ETa) product (GPR-ET) generated by Gaussian process regression (GPR), as well as temperature and precipitation datasets, our study employed various statistical analysis methods, including geographic detector, the center of gravity migration model, spatial variation coefficients, and partial differential models, to investigate the spatiotemporal variation in ETa in China from 2000 to 2018. The analysis covered future trends in ETa changes and the contribution of meteorological factors. Our results showed that the ETa in northwest China had stronger spatial heterogeneity and the mean value was generally lower than that in the southeast. But the center of gravity of ETa was shifting towards the northwest. In most areas, the future trend was expected to be inconsistent with the current stage. ETa in the regions of north and west was mainly driven by precipitation, while its increase in southeast China was largely attributed to temperature. In addition to spatial variations, the joint enhancement effect of temperature and precipitation on ETa exists. According to the contribution analysis, precipitation contributed more to the change in ETa than temperature. These findings have enhanced our comprehension of the contribution of climate variability to ETa changes, providing scientific proof for the optimization apportion of future water resources. [ABSTRACT FROM AUTHOR]

Key message: We established silver birch phenology in the Pyrenees. We highlight actual evapotranspiration as the main driver and the altitudinal effect within a north–south phenological pattern. Research into the phenology of trees is one of the most important issues in making reliable predictions of possible range shifts due to current climate change. Under the current climate change, warming and water stress can threaten tree performance by altering phenological events, specially at the edge of the southern especies distribution. We aimed at establishing bud burst, leaf and stem growth phenology of the Betula pendula in the Spanish Pyrenees, to determine the environmental cues triggering phenological events and to assess the effect of climate and soil water balance on annual growth cycle. The most important cues for bud burst are heat accumulation and long days that reduced the thermal time to bud burst. Leaf unfolding, the period of stem cambial activity, and the variation of the stem radial growth rates throughout the year are mainly regulated by the actual evapotranspiration. Leaf yellowing and abscission are advanced when hydric stress is pronounced shortening leaf longevity. The increase in spring temperatures brings forward the date of bud burst and the start of stem growth. However, the increase in the duration of hotter droughts causes an advance in the date of cessation of birch growth. From the southern Pyrenees to the boreal birch populations, there is a marked latitudinal gradient of phenological events, which are not linear except for the maximum stem growth rate. In the Pyrenees, the growing season is longer than in the boreal forests, but ring thickness is similar. [ABSTRACT FROM AUTHOR]

This paper analyzes potential impacts of climate change on biomass carbon (C) density and water-use (actual evapotranspiration, AET) of savannah woodlands in Sudan. Climate change scenarios were developed from five General Circulation Models (GCMs; CGCM2, CSIRO2, ECHam4, HadCM3 and PCM) under two IPCC (Intergovernmental Panel on Climate Change) emission scenarios (A1FI and B1). Baseline (1961-90) climate and climate change scenarios for 2080s for eight map sheet grids (1° latitude x 1.5° longitude) were constructed. Compared to baseline values, mean annual precipitation (MAP) showed both increases (+112 to +221 mm) and decreases (−13 to −188 mm) but mean annual temperature (MAT) only showed increases (+1.2 to +8.3 °C). Baseline biomass C densities showed an exponential relationship with MAP ( y = 6.798 e , R = 0.70). Depending on climate change MAP, biomass C densities increased (+14 to +241 g C m) or decreased (−1 to −148 g C m). However, because of uncertainty in biomass C density estimates, the changes were only significant (P <0.05) for some of the climate change scenarios and for grids with MAP >260 mm. Under A1FI emission scenarios, only HadCM3 did not have a significant effect while under B1 emission scenarios, only CGCM2 and ECHam4 had a significant effect on biomass C density. AET also showed both increases (+100 to +145 mm for vertisols and +82 to +197 mm for arenosols) and decreases (−12 to −178 mm for vertisols and −12 to −132 mm for arenosols). The largest relative changes in AET (up to 31 %) were associated with grids receiving the lowest rainfall. Thus, even if MAP increases across the study region, the increase will have little impact on biomass levels in the driest areas of the region, emphasizing the need for improved management and use of savannah woodlands. [ABSTRACT FROM AUTHOR]

Accurate and reliable estimation of actual evapotranspiration (AET) is essential for various hydrological studies, including drought prediction, water resource management, and the analysis of atmospheric–terrestrial carbon exchanges. Gridded AET products offer potential for application in ungauged areas, but their uncertainties may be significant, making it difficult to identify the best products for specific regions. While in situ data directly estimate gridded ET products, their applicability is limited in ungauged areas that require FLUXNET data. This paper employs an Extended Triple Collocation (ETC) method to estimate the uncertainty of Global Land Evaporation Amsterdam Model (GLEAM), Famine Early Warning Systems Network (FLDAS), and Maximum Entropy Production (MEP) AET product without requiring prior information. Subsequently, a merged ET product is generated by combining ET estimates from three original products. Furthermore, the study quantifies the uncertainty of each individual product across different vegetation covers and then compares three original products and the Merged ET with data from 645 in situ sites. The results indicate that GLEAM covers the largest area, accounting for 39.1% based on the correlation coefficient criterion and 39.9% based on the error variation criterion. Meanwhile, FLDAS and MEP exhibit similar performance characteristics. The merged ET derived from the ETC method demonstrates the ability to mitigate uncertainty in ET estimates in North American (NA) and European (EU) regions, as well as tundra, forest, grassland, and shrubland areas. This merged ET could be effectively utilized to reduce uncertainty in AET estimates from multiple products for ungauged areas.

Highlights • The performance of different evapotranspiration models was compared with the performance of Penman-Montieth evapotranspiration model. • Response of crop coefficient (Kc) for wheat was measured with reference to Indian context. • The Makkink evapotranspiration model shows R2 (0.88) with respect to Penman-Montieth evapotranspiration model. Abstract Accurate and reliable estimation of reference crop evapotranspiration (ET o) is important due to its critical role in determining crop water requirement in irrigated agriculture. The aim of the paper was to estimate the evapotranspiration (ET c) using spatially distributed crop coefficient (K c) and open access earth observing datasets in a semi-arid environment. We have estimated the actual evapotranspiration (ET c) based on spatially distributed crop coefficient (K c) using following models namely Surface Energy Balance Algorithm for Land (SEBAL), Makkink model, Hargreaves and Samani model, Camargo method and Jensen-Haise model. Further, these models estimates were compared with Penman-Monteith estimate. Comparative evaluation of models was performed through statistical tests, and it was found that the Makkink model performed satisfactory compared with standard Penman-Monteith model estimate (R2 = 0.88). Leaf area index (LAI) and the K c was in strong (second order polynomial) relationship (R2 = 0.98). The analysis also shows distributed actual evapotranspiration based on Makkink model has good agreement with actual evapotranspiration from Penman-Monteith with R2 of 0.84, respectively, for the study area. The finding suggests that the Makkink model estimates ET o are very close to the universally accepted Penman-Monteith model based ET o. [ABSTRACT FROM AUTHOR]

Water evaporation is one of the most important elements of hydrologic cycle. The paper analyses the impact of groundwater on intensity and course of actual evapotranspiration. Analysis is based on numerical experiment using the mathematical model GLOBAL. Prior to the experiment, the model was verified by comparing calculated and measured soil water storage in the examined localities at the depth of 0,8 m. The experiment quantifies the groundwater level (GWL) impact on actual evapotranspiration. Three phases of groundwater influence were identified. Threshold values of GWL were identified in the examined profiles. They are borders between non-linear and residual phase of the impact. At the residual phase, GWL impact on potential evapotranspiration intensity is negligible. [ABSTRACT FROM AUTHOR]

Abstract: There is a growing interest in quantifying regional scale actual evapotranspiration (ET) for water accounting and for water productivity assessments at river basin scale. Methods that provide point values fail to describe the situations at larger scales. Remote sensing measurements can be used at different spatial scales. This paper applies the theory of the Surface Energy Balance Algorithm for Land (SEBAL). SEBAL was originally derived for Egypt, Spain and Niger [Bastiaanssen, W.G.M., 1995. Regionalization of surface flux densities and moisture indicators in composite terrain: a remote sensing approach under clear skies in Mediterranean climates. Ph.D. dissertation, CIP Data Koninklijke Bibliotheek, Den Haag, The Netherlands. 273 pp.] and was calibrated and validated using ground measurements from four flux sites and from seven agro-meteorological stations in the semi-arid region of the Low-Middle São Francisco River basin, Brazil. Measured parameters included surface albedo, surface temperature, atmospheric and surface emissivity, soil heat flux, surface roughness, net radiation, air temperature gradients, sensible heat flux, latent heat flux, evaporative fraction, and photosynthetically active radiation. The daily ET was estimated (RMSE of 0.38mmd−1) for mixed agricultural and natural ecosystems. The improved coefficients for the local conditions can now be used to study the impact of expanding irrigated agriculture on the regional water balance and to quantify the water productivity of irrigated horticulture that is the largest water consumer in the Brazilian semi-arid region. Both applications are described in an accompanying paper (Part B). [Copyright &y& Elsevier]

• We demonstrate flaws in the CMRSET implementation in Bretreger et al. (2020). • Actual evapotranspiration biases were because they used an incorrect Landsat band. • The calculation of GVMI should have used Landsat SWIR1 band instead of SWIR2. • CMRSET's suitability for irrigation monitoring is demonstrated via new experiments. • CMRSET evapotranspiration using the correct SWIR1 band did not show large biases. In a recent paper published in this journal, Bretreger et al. (2020) estimate irrigation water use from satellite remotely sensed estimates of actual evapotranspiration in five irrigated districts of the Murray-Darling Basin (southeast Australia). They used three models that scale crop reference evapotranspiration with vegetation indices acquired by recent Landsat satellites: (i) IrriSAT, (ii) Kamble and (iii) CMRSET. In their paper, irrigation water use computed with CMRSET generally overestimated observed irrigation water use, sometimes fivefold. Based on these results, Bretreger et al. (2020) discouraged the use of CMRSET for irrigation monitoring. In this comment, we reproduce the experiments in Bretreger et al. (2020), and demonstrate that their overestimation was because they used an incorrect Landsat band in their implementation of CMRSET. CMRSET was originally calibrated using both MODIS-derived Enhanced Vegetation Index (EVI) and Global Vegetation Moisture Index (GVMI). To calculate GVMI, a shortwave infrared (SWIR) band with a wavelength of ∼1.6 μm was used, which for MODIS is named SWIR2, and for Landsat is named SWIR1 (i.e., different sensors have different bands and a different number of bands and SWIR1 in MODIS has a wavelength of ∼1.2 μm). In their Landsat CMRSET implementation, Bretreger et al. (2020) computed GVMI using the Landsat SWIR2 band, which has a wavelength of ∼2.1 μm (see their Table 3). We show that CMRSET implemented with the Landsat SWIR1 band (i.e., with a wavelength of ∼1.6 μm, so being the correct Landsat band to calculate GVMI) yields similar results (both for temporal patterns and magnitude) when compared to the other two remote sensing actual evapotranspiration models in Bretreger et al. (2020). For the irrigation districts, these similar results meant that the mean water year (i.e., July to next June from 2010 to 2017) actual evapotranspiration mean absolute relative difference was 15.3% (with a 5.4%–26.5% range) and the water year irrigation water use mean absolute relative difference was 4.1% (with a 9.8%–18.9% range). Conversely, we show that a Landsat CMRSET implementation using the incorrect Landsat band for the calculation of GVMI (i.e., with a wavelength of ∼2.1 μm) led to a large overestimation agreeing with the CMRSET results reported by Bretreger et al. (2020), both for water year actual evapotranspiration (mean absolute relative difference of 64.6%, with a 51.1%–83.6% range) and irrigation water use (mean absolute relative difference of 44.1%, with a 31.4%–65.1% range). The use of the incorrect Landsat band means that the Bretreger et al. (2020) recommendation specific to their Landsat CMRSET implementation is invalid. A demonstration of Bretreger et al.'s (2020) incorrect Landsat CMRSET implementation and the correct one can be accessed at: https://jorgepena.users.earthengine.app/view/comment-on-bretreger-2020-joh-paper. Despite Bretreger et al.'s (2020) shortcomings in their implementation of the Landsat CMRSET actual evapotranspiration model, timely monitoring of irrigation water use via satellite remote sensing is required at Landsat resolutions (i.e., 30 m) or higher due to the heterogeneous nature of irrigation in most agricultural landscapes, and we applaud them for pursuing this line of research. [ABSTRACT FROM AUTHOR]

Summary: For predicting annual percolation rate at regional scales, we need robust methods that require only easily-available site information. This paper presents hydro-pedotransfer functions (HPTFs) that can be used to calculate annual percolation rates using such data for two land use categories: (i) plant-covered sites and (ii) urban sites with various degrees of surface sealing (i.e., % impervious surface). This paper explains the principle concepts and gives instructions for users. A two-step procedure was used to derive HPTFs for plant-covered sites: (1) Step #1 involved scenario calculations of evapotranspiration and percolation rates for various soil, climate, groundwater, and crop conditions using a calibrated “Soil-Water-Vegetation Model” (aka “SVAT”). (2) Step #2 used nonlinear multiple regression analysis of >50,000 annual SVAT simulations to develop easy-to-use HPTFs for cropland, grassland, coniferous forests, and deciduous forests. The new HPTFs require only these input data: (1) annual values of the FAO grass reference evapotranspiration and water supply during the vegetation growth period (these data summarize soil available water); (2) summer precipitation; and (3) capillary rise from the groundwater. Two HPTFs were developed for each land use type – one for site conditions with, and one without, water supply limitations. To handle urban areas, we also developed HPTFs for partly sealed areas, using data from lysimeter studies and inner-city percolation experiments. The HPTFs successfully calculated the mean annual percolation rate from soil within the “Hydrological Atlas of Germany.” HPTF results were validated by comparisons with gauge measured values taken in 106 catchments areas in Germany. [Copyright &y& Elsevier]

The irrigated Indus Basin in Pakistan has insufficient water resources to supply all its stakeholders. Information on evaporative depletion across the Basin is an important requirement if the water resources are to be managed efficiently. This paper presents the Surface Energy Balance Algorithm for Land (SEBAL) method used to compute actual evapotranspiration for large areas based on public domain National Oceanic and Atmospheric Administration (NOAA) satellite data. Computational procedures for retrieving actual evapotranspiration from satellites have been developed over the last 20 years. The current work is among the first applications used to estimate actual evapotranspiration on an annual scale across a vast river basin system with a minimum of ground data. Only sunshine duration and wind speed are required as input data for the remote sensing flux algorithm. The results were validated in the Indus Basin by comparing results from a field-scale transient moisture flow model, in situ Bowen ratio measurements, and residual water balance analyses for an area of 3 million ha. The accuracy of assessing time-integrated actual annual evapotranspiration varied from 0% to 10% on a field scale to 5% at the regional level. Spatiotemporal information on actual evapotranspiration helps to evaluate water distribution and water use between large irrigation project areas. Wide variations in evaporative depletion between project areas and crop types were found. Satellite-based measurements can provide such information and avoid the need to rely on field databases. [ABSTRACT FROM AUTHOR]

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Central Asia is a drought-prone region that is sensitive to global climate change. The increased actual evapotranspiration intensifies the drought impacts in this area. However, little is known about the similarities and differences between various types of drought in Central Asia, as well as the relative importance of water income and consumption processes during drought events. Therefore, this study evaluates the trends and characteristics of meteorological, agricultural, and hydrological droughts in Central Asia using precipitation, soil moisture, and terrestrial water storage as indicators; explores the temporal correlation of and spatial similarity between various types of drought; and quantitatively assesses the contribution of water balance variables to drought intensity. The results indicate that drought has intensified in Central Asia, and the trends of precipitation, soil moisture, and terrestrial water storage in this region were −0.75 mm·yr−1 (p = 0.36), −0.0003 m3·m−3 yr−1 (p < 0.01), and −0.3742 cm·yr−1 (p < 0.001), respectively. Severe droughts are typically short in duration and high in intensity. Three various types of drought have low temporal correlation and spatial similarity. Furthermore, agricultural and hydrological droughts were primarily driven by actual evapotranspiration, accounting for relative contributions of 64.38% and 51.04% to these drought types, respectively. Moreover, the extent of increased actual evapotranspiration expanded to cover 49.88% of the region, exacerbating agricultural and hydrological droughts in 23.88% and 35.14% of the total study area, respectively. The study findings demonstrate that actual evapotranspiration plays a critical role in causing droughts. This study establishes a theoretical foundation to carry out drought assessment, the construction of multivariate drought indices, and water resource management in Central Asia. [ABSTRACT FROM AUTHOR]

We enhanced the agro-hydrologic VegET model to include snow accumulation and melt processes and the separation of runoff into surface runoff and deep drainage. Driven by global weather datasets and parameterized by land surface phenology (LSP), the enhanced VegET model was implemented in the cloud to simulate daily soil moisture (SM), actual evapotranspiration (ETa), and runoff (R) for the conterminous United States (CONUS) and the Greater Horn of Africa (GHA). Evaluation of the VegET model with independent data showed satisfactory performance, capturing the temporal variability of SM (Pearson correlation r: 0.22–0.97), snowpack (r: 0.86–0.88), ETa (r: 0.41–0.97), and spatial variability of R (r: 0.81–0.90). Absolute magnitudes showed some biases, indicating the need of calibrating the model for water budget analysis. The seasonal Landscape Water Requirement Satisfaction Index (L-WRSI) for CONUS and GHA showed realistic depictions of drought hazard extent and severity, indicating the usefulness of the L-WRSI for the convergence of an evidence toolkit used by the Famine Early Warning System Network to monitor potential food insecurity conditions in different parts of the world. Using projected weather datasets and landcover-based LSP, the VegET model can be used not only for global monitoring of drought conditions, but also for evaluating scenarios on the effect of a changing climate and land cover on agriculture and water resources. [ABSTRACT FROM AUTHOR]

This paper is aimed to assess the impact of climate change on water regime of wetland in the area of Poiplie Ramsar site. To simulate the climate change the CGCM3.1 global model (SRES A2 pessimistic scenario and SRES B1 optimistic scenario) and KNMI and MPI regional models were selected as the most appropriate. For the 20-year reference period the years 1977–1996 was chosen, which is within the evaluation compared with the 20-year time horizons 2020, 2050 and 2080. Simulation of soil water regime was carried out using the GLOBAL model. Within the soil water regime evaluation actual evapotranspiration was evaluated in this paper. Actual evapotranspiration has in the future in the studied area also increasing course over the reference period, while the SRES A2 pessimistic scenario expected the increase of 24%, KNMI regional model the increase of 21% and SRES B1 optimistic scenario and MPI regional model the increase of 19%. The development of actual evapotranspiration is derived from the predicted increase in air temperature and pre- cipitation. On the base of these results the ongoing climate change does not cause dramatic changes in Poiplie Ramsar site, thereby this unique wetland ecosystem should be preserved in the future.

The components of water balance (WBC) that involve precipitation, evapotranspiration, runoff, irrigation, and groundwater recharge are critical for understanding the hydrological cycle and water management of resources in semi-arid and arid areas. This paper assesses temporal and spatial distributions of surface runoff, actual evapotranspiration, and groundwater recharge upstream of the New Assiut Barrage (NAB) in the Nile Valley, Upper Egypt, using the WetSpass-M model for the period 2012–2020. Moreover, this study evaluates the effect of land cover/land use (LULC) alterations in the study period on the WBC of the NAB. The data provided as input for the WetSpass-M model in the structure of raster maps using the Arc-GIS tool. Monthly meteorological factors (e.g., temperature, rainfall, and wind speed), a digital elevation model (DEM), slope, land cover, irrigation cover, a soil map, and depth to groundwater are included. The long-term temporal and spatial mean monthly irrigation and precipitation (127 mm) is distributed as 49% (62 mm) actual evapotranspiration, 15% (19 mm) groundwater recharge, and 36% (46 mm) surface runoff. The replacement of cropland by built-up areas was recognized as the primary factor responsible for the major decrease in groundwater, an increase in evapotranspiration and an increase in surface runoff between LCLU in 2012 and 2020. The integration of the WetSpass model with GIS has shown its effectiveness as a powerful approach for assessing WBC. Results were more accurate and reliable when hydrological modeling and spatial analysis were combined. The results of this research can help make well-informed decisions about land use planning and sustainable management of water resources in the upstream area of the NAB.