HS10.2 | Estimating evapotranspiration using in-situ and remote sensing methods
Estimating evapotranspiration using in-situ and remote sensing methods
Co-organized by BG3
Convener: Sibylle K. Hassler | Co-conveners: Hamideh Nouri, Neda AbbasiECSECS, Ana Andreu, Jannis GrohECSECS, Pamela Nagler, Corinna Rebmann
Orals
| Mon, 24 Apr, 08:30–12:30 (CEST)
 
Room 3.16/17
Posters on site
| Attendance Mon, 24 Apr, 14:00–15:45 (CEST)
 
Hall A
Posters virtual
| Attendance Mon, 24 Apr, 14:00–15:45 (CEST)
 
vHall HS
Orals |
Mon, 08:30
Mon, 14:00
Mon, 14:00
Evapotranspiration (ET) is the key water flux at the interface of soil, vegetation and atmosphere. ET is difficult to measure directly, therefore a range of methods have been developed within different research disciplines to estimate ET. These methods cover different scales and contain measurement-specific uncertainties.

In-situ measurements include for example lysimeters, sap flow sensors, eddy covariance stations, scintillometers and approaches like the Bowen ratio method and others to estimate ET from ground-based measurements. However, estimating and scaling in-situ ET is prone to large method-specific uncertainties which are rarely communicated across the different disciplines. This is problematic if in-situ measurements are to be compared, combined or scaled up to match the grid resolution of remote sensing products or models.

Remote sensing of actual ET needs to be estimated and precisely mapped due to the broadening scope in the demand for more accurate and longer-term ET estimation in different fields of hydrology, water management, agriculture, forestry, and urban greening. Over the last five decades, numerous spaceborne and airborne sensors have been used to model, map, monitor and forecast ET at different spatiotemporal scales in various climates and eco-geographical regions for a range of vegetative land covers. Recent advances in image processing and artificial intelligence (machine learning, deep learning, etc.), as well as the growing number of satellites and sensors, have improved the accessibility and quality of images, which open more avenues for regular updating and upscaling.

This session addresses ET estimation with both in-situ and remote sensing methods. We invite contributions that (1) assess and compare established and new in-situ and remote sensing ET estimates, (2) evaluate and enhance accuracy, and address uncertainty in the respective methods, (3) bridge spatio-temporal scales in the different ET estimates or (4) incorporate remote sensing and in-situ measurements into process-based modelling approaches.

Orals: Mon, 24 Apr | Room 3.16/17

Chairpersons: Sibylle K. Hassler, Jannis Groh, Corinna Rebmann
In-situ methods to estimate ET
08:30–09:00
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EGU23-7847
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HS10.2
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solicited
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On-site presentation
Oscar Hartogensis, Mary Rose Mangan, Francisca Aguirre Correa, Felipe Lobos Roco, Robin Stoffer, and Jordi Vilà-Guerau de Arellano

This contribution deals with the spatial and temporal scales involved in the processes that control evapotranspiration (ET) and confront these with the merits and limitations of various observation and modelling techniques. We make a strong case for integrated approaches to further develop our understanding of evapotranspiration.

The most challenging, but at the same time most relevant conditions to accurately represent ET are found in semi-arid regions, specifically complex terrains with strong thermal contrasts between dry and wet (irrigated) areas. We will present three cases with different objectives in terms of processes that control ET and the methods used to study them. First is the LIAISE campaign, where we will focus on how to describe ET depending on the spatial scale considered ranging from regional to landscape to local scale. Second is the E-DATA campaign, where ET is controlled by a thermally driven and topographically enhanced regional flow that alters the turbulent mixing and the structure of the atmospheric boundary layer. Third deals with a machine learning approach to determine ET based on standard weather station data.

LIAISE took place during the summer of 2021 in the Pla d’Urgell region of the Ebro River Valley in Catalonia, Spain. The surface was homogeneous at the field scale (e.g. fields of alfalfa). However, the surface was heterogeneous at the regional scale (~10-100km) because of the spatial distribution of irrigated crops and dry natural vegetation. We examined the impact of the boundary layer on surface fluxes at two of the LIAISE sites: one in the irrigated, crop-covered area and one in the dry, naturally-vegetated area.  We use an atmospheric mixed-layer column model that is heavily constrained by the surface and boundary layer observations from the LIAISE experiment.

The E-DATA experiment took place during November 2018 and focussed on quantifying the processes that drive ET in a shallow lake surrounded by extremely dry conditions in a salt flat (Salar del Huasco) of the Chilean Atacama desert. We use the WRF model at 100-m resolution to represent the local processes as well as the heterogeneity and regional transport to understand the evaporation and ABL dynamics over the water.

The machine learning study explores whether a physics-informed machine learning  approach can be used to improve the estimated evapotranspiration for irrigated fields located in a desert environment, without arbitrary tuning after training  and only using readily available data (standard meteorological data and satellite derived vegetation indices). We focus on an irrigated pecan orchard in Northwest Mexico. Multi-year eddy-covariance ET estimates are used to train and validate the model.

How to cite: Hartogensis, O., Mangan, M. R., Aguirre Correa, F., Lobos Roco, F., Stoffer, R., and Vilà-Guerau de Arellano, J.: Measuring and Modelling Evapotranspiration over Complex Terrain, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7847, https://doi.org/10.5194/egusphere-egu23-7847, 2023.

09:00–09:10
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EGU23-14383
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HS10.2
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ECS
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Virtual presentation
Yogi Suardiwerianto, Sofyan Kurnianto, Muhammad Fikky Hidayat, Nurcahaya Simamora, Mhd. Iman Faisal Harahap, Nurul Azkiyatul Fitriyah, Abdul Jabbar, Chandra Prasad Ghimire, and Chandra Shekhar Deshmukh

Waterlogged and anoxic conditions facilitate the preservation of carbon-rich peat layers in tropical peatlands coexisting with peat swamp forests. Peatlands in Southeast Asia, which host one-third of the tropical peatland area, have high temperatures throughout the year and high soil moisture availability, which support high evapotranspiration rates. The majority of existing land cover in Southeast Asia peatland is a canopy-covered ecosystem. Therefore, these ecosystems are considered to support high transpiration rates. However, the understanding of transpiration rates and their governing factors for existing land cover in Southeast Asia peatlands remains poorly understood due to limited measurements.

Here, we quantified transpiration rates and explored governing factors in Acacia crassicarpa plantations (fast-growing species, harvested on a 4-5 year rotation) in the coastal peatland of Eastern Sumatra, Indonesia, between 2020 and 2022. Transpiration was quantified by measuring in situ sap flow rate using the HFD8-50 and SFM1 (ICT International, Australia) during the plantation age of 2 to 4 years. We measured the sapwood cross-sectional area using an increment borer (Haglöf, Sweden). In addition, we implemented a sampling strategy that considered tree size, azimuth, height, and radial factors, to account for the variability and upscaling from tree to stand level of transpiration.

Our results showed that the greatest source of variability to determine transpiration were the radial and tree size. On a diel and daily basis, tree transpiration was affected by vapour pressure deficit and solar radiation. Further, we did not observe a relationship between seasonal rainfall variations and transpiration. We found that stand-level transpiration in deeper groundwater level sites (around -80 cm below peat surface) was higher by 20% than those in shallower sites (around -40 cm below peat surface) due to the higher stand density and total sapwood area. Overall measured transpiration rates (0.8 – 1.0 mm d-1) represent 20-24 % of evapotranspiration measured by eddy covariance. This study provides the first insights into the eco-hydrological characteristics of the Acacia crassicarpa plantation and improves the understanding of water balance from this globally important ecosystem.

How to cite: Suardiwerianto, Y., Kurnianto, S., Hidayat, M. F., Simamora, N., Harahap, Mhd. I. F., Fitriyah, N. A., Jabbar, A., Ghimire, C. P., and Deshmukh, C. S.: Transpiration of Acacia plantations in a managed tropical peatland Sumatra, Indonesia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14383, https://doi.org/10.5194/egusphere-egu23-14383, 2023.

09:10–09:20
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EGU23-12768
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HS10.2
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ECS
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On-site presentation
Adrian Dahlmann, Mathias Hoffmann, Gernot Verch, Marten Schmidt, Michael Sommer, Jürgen Augustin, and Maren Dubbert

In light of the ongoing global change in climatic conditions and a related trend to increases in extreme hydrological events, it is increasingly crucial to assess ecosystem resilience and - in agricultural systems - to ensure sustainable management and food security.  A comprehensive understanding of ecosystem water cycle budgets and spatio-temporal dynamics is indispensable. Evapotranspiration (ET) plays a pivotal role returning up to 90 % of ingoing precipitation back to the atmosphere. Here, we studied impacts of soil types and management on an agroecosystem's water budgets and agronomic water use efficiencies (WUEagro). To do so, a plot experiment with winter rye (September 17, 2020 to June 30, 2021) was conducted at an eroded cropland which is located in the hilly and dry ground moraine landscape of the Uckermark region in NE Germany. Along the experimental plot (110 m x 16 m), a gantry crane mounted mobile and automated two chamber system (FluxCrane as part of the AgroFlux platform within the CarboZALF-D research site) was used for the first time to continuously measure water fluxes and determine evapotranspiration. Three soil types representing the soil erosion gradient related to the hummocky ground moraine landscape (extremely eroded: Calcaric Regosol, strongly eroded: Nudiargic Luvisol, non-eroded: Calcic Luvisol) and additional soil manipulation (topsoil removal and subsoil admixture) were investigated (randomized block design, 3 replicates per treatment). Five different gap-filling approaches were used and compared in light of their potential for reliable water budgets over the entire crop growth period as well as reproduce short-term (day-to-day, diurnal) water flux dynamics. The best calibration performance was achieved with approaches based on machine learning, such as support vector machine (SVM) and artificial neural networks (with Bayesian regularization; ANN_BR), while especially SVM yielded in most reliable predictions of measured ET during validation.

We found significant differences in dry biomass (DM) and minor in evapotranspiration between soil types, resulting in different water use efficiencies (WUEagro). The Calcaric Regosol (extremely eroded) shows a maximum of around 37% lower evapotranspiration and a maximum of around 52% lower water use efficiency (WUEagro) compared to the non-eroded Calcic Luvisol.  The key period contributing to ~ 70% of overall ET of the entire growth period was from April until June (harvest), however differences in the overall ET budget (ETsum) between soil types and manipulation resulted predominantly from small differences between the treatments over the entire growth period.

 

How to cite: Dahlmann, A., Hoffmann, M., Verch, G., Schmidt, M., Sommer, M., Augustin, J., and Dubbert, M.: Evapotranspiration measurements on an eroded cropland using an automated and mobile chamber system: gap filling strategies and impact of soil type and topsoil modification, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12768, https://doi.org/10.5194/egusphere-egu23-12768, 2023.

09:20–09:30
09:30–09:40
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EGU23-12065
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HS10.2
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ECS
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Virtual presentation
Han Zheng and Yuchen Sun

Evapotranspiration (ET) is an important part of surface hydrological cycle and energy exchange process. Under the background of frequent drought and water resource shortage, it is of great significance to study the seasonal and interannual variations in ET and energy budget of farmland ecosystem in arid regions. This will help to reveal the process of crop ET and water consumption in farmland ecosystems and its response to drought conditions and environmental factors. Based on continuous eddy-covariance observation data, this study analyzed the seasonal and interannual variations in ET and energy budget of one maize farmland ecosystem in the semi-arid region of Chinese Loess Plateau and its response to environmental changes during 2019-2020. Results showed that ET and meteorological factors presented obvious seasonal and interannual changes during the study period. The annual total ET was 339.3 mm/yr and 386.5 mm/yr during the drought year 2019 and the normal year 2020, respectively. It was 16.4% and 30.4% lower than the annual total precipitation (P) in the same period. The ET/P ratio for two years was 0.84 and 0.70, respectively. While the latent heat flux and sensible heat flux showed obvious seasonal and interannual variation trends, it also reflected that the latent heat flux dominated the net radiation energy budget in the growing season and the sensible heat flux is the main consumption component of the net radiation energy budget in the non-growing season. During 2020, due to better moisture conditions, the Bowen ratio was smaller and sensible heat exchange was more moderate, making the air more stable. The volatility of albedo in 2020 was significantly greater than that in 2019, which was closely related to the frequent precipitation in the normal year. The results of the path analysis model showed that soil water content (SWC) had stronger impacts on the ET variation during the drought year (2019) at the scales of entire year, growing season and non-growing season. Meanwhile, leaf area index (LAI) had more significant impacts on the ET variation during the hydrologically normal year (2020) when the water supply was much more sufficient. We also found that there was a strong coupling relationship between the atmosphere and vegetation during the study period (decoupling factor Ω varied between 0 and 0.5), indicating that the ecosystem ET is mainly controlled by canopy conductance(gs) and vapor pressure deficit (VPD). Moreover, gs decreased with the increase of VPD, and VPD played a stronger role in controlling gs during 2020 which was with better water supply condition.

How to cite: Zheng, H. and Sun, Y.: Seasonal and interannual variations in evapotranspiration and energy budget over a rainfed maize field in the Chinese Loess Plateau, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12065, https://doi.org/10.5194/egusphere-egu23-12065, 2023.

09:40–09:50
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EGU23-11808
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HS10.2
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ECS
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On-site presentation
Xiao Lu, Jannis Groh, Thomas Pütz, Harry Vereecken, and Harrie-Jan Hendricks Franssen

Actual evapotranspiration (ETa) is difficult to measure and limited long-term information is available about ETa. With eddy covariance systems ETa can be measured at the field scale, but the method is associated with energy balance closure issues. For measuring ETa, weighing lysimeters are considered to be the most accurate and reliable method. However, weighing lysimeters have some disadvantages like elevated costs of installation and maintenance, and a small footprint (e.g., about 1 m2). A main question is therefore whether the precise ETa-measurements by lysimeters are representative for a larger area like a field, a meso-scale catchment, or even a larger region. Our hypothesis was that a lysimeter provides information about ETa that represents a larger area than its underlying measurement area. To this end, we examined here the daily ETa measurements from lysimeter at four study sites across Germany (separation distances 10 - 500 km) for the years 2015 to 2020. The Pearson correlations of the standardized anomalies (SA) of daily ETa between different lysimeters were calculated and compared with SA of daily ETa obtained from the corresponding eddy covariance tower. The correlations were further analyzed and related to spatial correlations of SA of environmental controls like precipitation, potential evapotranspiration (ET0), and soil moisture. We found that SA of daily ETa shows high spatial correlations (>0.5) for considerable separation distances between sites of up to 50km, with similar correlations for lysimeters and eddy covariance systems. ET0 is the dominant factor for the spatial correlation of ETa, as SA of ET0 shows stronger spatial correlations than SA of ETa.

How to cite: Lu, X., Groh, J., Pütz, T., Vereecken, H., and Hendricks Franssen, H.-J.: Analysis of Scale-dependent Spatial Correlations of Actual Evapotranspiration Measured by Lysimeters, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11808, https://doi.org/10.5194/egusphere-egu23-11808, 2023.

09:50–10:00
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EGU23-14103
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HS10.2
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ECS
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On-site presentation
Jacob A. Nelson, Sophia Walther, Basil Kraft, Weijie Zhang, Gregory Duveiller, Fabian Gans, Ulrich Weber, Zayd Mahmoud Hamdi, and Martin Jung

While eddy covariance (EC) is a standard for measuring total ecosystem evaporation (evapotranspiration, ET), upscaling from the tower to the regional and global scales is still marred with uncertainties. Here, we explore this scale translation via the FLUXCOM-X framework, which links data from EC measurements and remote sensing to machine learning techniques to produce models for generating globally gridded products. In particular, we explore potential sources of uncertainty inherent to this pipeline and how these influence the resulting gridded products: training data quality including site-selection and coverage of in-situ data, and modelling distinct water flux components (i.e., transpiration (T) and abiotic evaporation) individually compared to total evapotranspiration.

Overall, changes in the FLUXCOM-X framework compared to previous versions (Jung et al. 2019) results in tangible improvements to the spatial and temporal patterns of the global evapotranspiration products. Furthermore, the predictions of a corresponding transpiration product provide an empirical estimate of plant controlled water fluxes. The resulting global T/ET ratios are consistent with current estimates from isotopic analyses, but with the advantage of high spatio-temporal coverage. Lessons learned from this analysis provide a more targeted line of inquiry into potential avenues for further improvements in global evapotranspiration modeling.

Jung, M., Koirala, S., Weber, U. et al. The FLUXCOM ensemble of global land-atmosphere energy fluxes. Sci Data 6, 74 (2019). https://doi.org/10.1038/s41597-019-0076-8

How to cite: Nelson, J. A., Walther, S., Kraft, B., Zhang, W., Duveiller, G., Gans, F., Weber, U., Hamdi, Z. M., and Jung, M.: From site-scale land-atmsophere water fluxes to globally gridded products: Advances with the FLUXCOM-X framework, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14103, https://doi.org/10.5194/egusphere-egu23-14103, 2023.

10:00–10:15
Coffee break
Chairpersons: Ana Andreu, Neda Abbasi, Corinna Rebmann
10:45–10:55
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EGU23-8184
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HS10.2
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ECS
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Virtual presentation
Qiong Han, Thomas Pütz, Harry Vereecken, Tiejun Wang, Alexander Graf, Matthias Mauder, Sinikka Paulus, Sung-Ching Lee, Tarek El-Madany, Katrin Schneider, Jeremy Price, Daniel Martínez-Villagrasa, Joan Cuxart, and Jannis Groh

Accurate measurements of actual evapotranspiration (ETa) play an important role in understanding land surface processes and agricultural management. Two of the most commonly used and established methods for quantifying ETa are eddy covariance (EC) and weighable lysimeters measurements. Previous studies on hourly or daily basis indicated sometimes large differences between the ETa of the two methods (Δly-EC). It is still unclear which factors influence these differences. Here, we examine and compare half-hourly ETa measurements from EC (ETEC) and weighable lysimeters (ETly) at four different sites. The four sites span a climatic gradient from humid conditions at a pre-alpine (Fendt, DE) and a mid-mountain grassland (Rollesbroich, DE) to semi-arid conditions at two sites with a natural grass and shrub (Els Plans, ES) and a tree-grass ecosystem (Majadas de Tiétar, ES). We used a boosted regression tree method to identify environmental drivers of Δly-EC during day and night at the half-hourly resolution.

Our results revealed that substantial differences were found with a mean annual Δly-EC of 117 mm, and Δly-EC displayed obvious spatiotemporal variabilities across the sites. Energy balance non-closure of EC was found to be the most important factor contributing to the large annual Δly-EC, especially at Majadas de Tiétar site. With the distinct climatic gradient, Δly-EC was negatively correlated with mean annual wind speed and vapor pressure deficit when they reached a specific level. Monthly ETEC and ETly agreed well with Δly-EC peaking in summer at the sites in Germany, while Δly-EC peaked earlier due to the different climate in Spain. Differences in grass height caused by field management and EC footprint also affected Δly-EC, especially at daily timescales for the pre-alpine and the mid-mountain grassland ecosystem. The relative impacts of different environmental variables to half-hourly ETEC and ETly were almost the same with soil water content (SWC) being more important for nighttime ETly. Meanwhile, we found that the dominant controlling factors of daytime Δly-EC changed with climatic conditions, but nighttime Δly-EC were mainly regulated by SWC. These findings provide a critical evaluation for the roles of climatic and land surface conditions on turbulent flux dynamics from different measurements, which has important implications for ecosystem water and energy balance.

How to cite: Han, Q., Pütz, T., Vereecken, H., Wang, T., Graf, A., Mauder, M., Paulus, S., Lee, S.-C., El-Madany, T., Schneider, K., Price, J., Martínez-Villagrasa, D., Cuxart, J., and Groh, J.: Actual evapotranspiration differences between measurements of eddy covariance and lysimeters over grasslands, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8184, https://doi.org/10.5194/egusphere-egu23-8184, 2023.

10:55–11:05
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EGU23-14179
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HS10.2
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ECS
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On-site presentation
Stefanie Fischer, Uta Moderow, Ronald Queck, and Christian Bernhofer

Interception of a Norway spruce stand was analysed based on canopy water balance measurements Emass and for Eddy Covariance (EC) related measurements. The study site is located in the Tharandt Forest (Germany) and the analysis covers a long period from 2008 to 2018. Emass was calculated as residual between gross rainfall above and net rainfall below the canopy. EC related observations are based on the water equivalent either directly measured (uncorrected) by Eddy Covariance (ETEC) or as residual in the Energy Balance equation (ETEB). Additionally, evaporation of intercepted water was modelled with the Penman-Monteith equation, which was adapted for a gradually wetted canopy (ERutter) by the use of the Rutter model. The latter approach was used to integrate the time series of all methods over the duration of modelled interception events leading to different estimates of wet canopy evaporation.

The canopy water balance from 2008 to 2018 shows a mean annual gross precipitation of 936±173mm and a mean annual interception evaporation of 376±56mm (Emass). The majority of rainfall events (81%) is characterized by a depth less than 5mm, which leads to a high fraction of annual precipitation being captured by the canopy surface (0.41). The application of the Rutter model yielded good results with a mean modelled annual interception ERutter of 361±47mm being very close to Emass. Thus, the model served as a good standard to define interception events. The water equivalent of wet canopy evaporation as the residual of the energy balance ETEB and from gas analyser measurements ETEC are both systematically underestimating Emass, to a higher extent for the winter than summer half-year. On a mean annual basis, ETEB and ETEC underestimate Emass by 145mm and 288mm, respectively. Comparing the totals over the majority of interception events, ETEB corresponds to only 72% and ETEC to only 33% of canopy water balance based measurements.

One reason for this underestimation might be a scaling problem between the interception measurement site and the flux tower footprint, which could not be resolved by the application of a simple scaling factor. A more likely explanation is the underestimation of turbulent fluxes by the EC method. The data is most affected during raining conditions with the highest gap in winter. An annual analysis of the linear relation between the sum of turbulent fluxes and available energy shows the lowest slope (0.57±0.15) for measurements during rain, while the highest slopes occur under completely dry conditions (0.76±0.03). Wet canopy conditions without rainfall seem not to be as crucial for energy imbalance as rain, but affect the closure gap for the winter half-year.

Records of EC measurements are generally too low and the magnitude of supplied sensible heat and sustained latent heat flux rates during interception events remains unclear. We conclude that gap filling and correction of both turbulent fluxes should be done separately for rain (interception) and dry (transpiration) conditions in order to determine proper amounts of evapotranspiration with the eddy-covariance method.

How to cite: Fischer, S., Moderow, U., Queck, R., and Bernhofer, C.: Rainfall interception – a year-round crucial component of evapotranspiration and potential consequences for eddy-covariance measurements. Comparing long-term measurements of canopy water budget and eddy-covariance fluxes at a Norway spruce site, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14179, https://doi.org/10.5194/egusphere-egu23-14179, 2023.

11:05–11:15
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EGU23-10936
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HS10.2
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On-site presentation
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Christian Bernhofer, Thomas Pluntke, Thomas Grünwald, Maik Renner, Heiko Prasse, and Stefanie Fischer

We combine long-term hydro-meteorological data from the small research catchment Wernersbach (WB, 4.6 km², dominated by Norway spruce) in operation since 1967 and from two eddy-covariance (EC) flux towers, all located in the Tharandt Forest, Germany. This combination forms an observatory, addressing actual evapotranspiration ET from a water budget perspective (catchment) and from an energy perspective (EC flux towers). However, obvious differences exist in time resolution. The spruce dominated tower DE-Tha is located a few kilometres east of the catchment. After a windbreak of another spruce stand (situated inside the catchment) and planting of deciduous oaks, the tower DE-Hzd was set up in 2009. We recently reported systematically about the observatory and the long-term water budgets in Pluntke & Bernhofer et al. (https://doi.org/10.1016/j.jhydrol.2022.128873).

The catchment and both towers did not show any systematic differences in meteorological data (especially wind-loss corrected precipitation totals are almost identical), allowing us to address observed differences in ET as (i) due to different soil and hydrogeological characteristics as well as (ii) due to methodological aspects. The catchment term ET plus storage, derived from precipitation P minus runoff R, showed the expected high variability with a significant increase over the more than 50 years of operation. The older, spruce-dominated flux-tower DE-Tha showed much lower inter-annual variability in ET with an average annual total of 486 mm (1997 to 2019), but no significant trend. For the same period, average catchment ET was 734 mm/year. The younger flux-tower DE-Hzd showed ET values closer to catchment ET at the very dry end of the ten-year record (2010 to 2019).

For the 23 years of parallel measurements, annual ET from EC was about 250 mm lower than catchment ET, despite the careful correction of tower ET for energy balance closure. Catchment ET = P – R might have a small bias towards larger ET, as the subsurface catchment size of WB could be up to 0.4 km² smaller. In addition, precipitation and runoff may contribute to higher catchment ET. However, the difference is too large to be explained by measurement bias alone. Flux tower ET is compared to (i) independent measurements of ET components, and (ii) model output of BR90. There is evidence from interception and transpiration measurements at the flux tower that more than 100 mm of intercepted water could be missing in the annual ET from EC. Model results show a large additional contribution of interception due to negative sensible fluxes in fall and winter. The difference in ET between tower and catchment of 250 mm is probably due to a variety of reasons: overestimation of catchment ET (up to 50 mm), soil characteristics (50-100 mm), and underestimation of tower ET (100-150 mm).

We conclude that the EC closure correction during interception events needs to be revisited. Generally, results of ET monitoring of similar evergreen forests in a humid climate should be checked for missing contribution of interception, as EC records might be generally too low. This illustrates the necessity of redundant and complementary measurements when dealing with large system complexity.

How to cite: Bernhofer, C., Pluntke, T., Grünwald, T., Renner, M., Prasse, H., and Fischer, S.: Do eddy-covariance measurements systematically underestimate evapotranspiration of coniferous forests? Results from a paired catchment – flux tower observatory near Dresden (Germany), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10936, https://doi.org/10.5194/egusphere-egu23-10936, 2023.

11:15–11:25
Remote sensing methods to estimate ET
11:25–11:35
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EGU23-12253
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HS10.2
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ECS
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On-site presentation
Petra Hulsman, Akash Koppa, and Diego Miralles

Reliable, high-resolution evaporation data are needed for large-scale agricultural and hydrological management applications. However, field observations are too sparse to monitor large regions continuously, and satellite-based datasets are often too coarse or restricted to specific regions. An example of such satellite-based datasets is the Global Land Evaporation Amsterdam Model (GLEAM)1. GLEAM is a state-of-the-art, global evaporation product which has been widely applied over the past decade in climate studies. However, due to its coarse original resolution (0.25 degree), it has not been used in hydrological and agricultural applications until recently2. Ongoing developments have culminated in a high-resolution (HR, i.e. ~1 km) GLEAM version covering the Mediterranean region, over the 2015–2021 period. The Mediterranean region is characterised by intense human activities, different hydroclimatic conditions ranging from temperate cold to tropical, and intense seasonal rainfall at irregular spatial distributions. As a result, the region is prone to droughts, floods and landslides, making it an ideal testbed for GLEAM-HR. Here, we present current activities and future plans regarding this new dataset. Prospective plans include the extension from the Mediterranean domain to the entire European and African continents, by adopting a series of developments that have so far been confined to the coarse-scale application of the model. These include modifications in the interception module3, the incorporation of groundwater effects4, and the use of deep learning for the estimation of transpirational stress5.

 

 

1 Miralles, D. G., Holmes, T. R. H., De Jeu, R. A. M., Gash, J. H., Meesters, A. G. C. A., and Dolman, A. J.: Global land-surface evaporation estimated from satellite-based observations, Hydrol. Earth Syst. Sci., 15, 453–469, https://doi.org/10.5194/hess-15-453-2011, 2011.
2 Martens, B., De Jeu, R. A. M., Verhoest, N. E. C., Schuurmans, H., Kleijer, J., and Miralles, D. G.: Towards estimating land evaporation at field scales using GLEAM. Remote Sens., 10, 1720, https://doi.org/10.3390/rs10111720, 2018.
3 Zhong, F., Jiang, S., van Dijk, A. I. J. M., Ren, L., Schellekens, J., and Miralles, D. G.: Revisiting large-scale interception patterns constrained by a synthesis of global experimental data, Hydrol. Earth Syst. Sci., 26, 5647–5667, https://doi.org/10.5194/hess-26-5647-2022, 2022.
4 Hulsman, P., Keune, J., Koppa, A., Schellekens, J., and Miralles, D. G: Incorporating plant access to groundwater in existing global, satellite-based evaporation estimates, ESS Open Archive, https://doi.org/10.1002/essoar.10512478.1, in review, 2022.
5 Koppa, A., Rains, D., Hulsman, P., Poyatos, R., and Miralles, D. G.: A deep learning-based hybrid model of global terrestrial evaporation, Nat. Commun., 13, 1912, https://doi.org/10.1038/s41467-022-29543-7, 2022.

How to cite: Hulsman, P., Koppa, A., and Miralles, D.: GLEAM-HR: current state and future prospects, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12253, https://doi.org/10.5194/egusphere-egu23-12253, 2023.

11:35–11:45
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EGU23-15128
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HS10.2
|
ECS
|
On-site presentation
Chloé Ollivier, Luis Olivera-Guerra, Pierre Laluet, Vincent Rivalland, Vincent Simonneaux, Jérôme Demarty, Olivier Merlin, and Gilles Boulet

Remote sensing data provide valuable information on the spatial distribution of land surface conditions and properties, such as soil moisture, soil and vegetation water status. However, the frequency and resolution of remotely sensed data vary depending on the satellite and sensor. The frequency of observation of thermal infrared that allows an estimation of evapotranspiration is carried out daily by the satellites AQUA and TERRA (res. 1km), every 2 days by Sentinel-3 (res. 1km), 8 days by LANDSAT-8 and 9 (res. 60m) and will be 3 times per period of 8 days by the satellite TRISHNA (res. 60m). In addition, there is no data on days with heavy cloud cover. In order to obtain a daily evaluation of ET, we propose to correct the trajectory of a surface model based on the water balance with the assimilation of ET data from remote sensing. The question is what are the advantages of assimilation compared to open-loop or interpolation of observation. We present our work on modelling evapotranspiration and irrigation at the field scale with the SAMIR (Satellite monitoring of irrigation) model. This is a crop water balance model forced by weather data, soil and crop parameters to simulate the daily components of the water balance. A particle filter method is implemented to assimilate evapotranspiration from remote sensing. This evaluation is performed on several types of crops (wheat, barley and olive), irrigated or not, and in a semi-arid Mediterranean context (Tunisia and Morocco). Compared to open loop simulations, data assimilation allows to quickly reduce the simulation uncertainty. On the other hand, the higher the revisit frequency, the more the simulation uncertainty depends on the observation uncertainty and the model uncertainty is reduced.

How to cite: Ollivier, C., Olivera-Guerra, L., Laluet, P., Rivalland, V., Simonneaux, V., Demarty, J., Merlin, O., and Boulet, G.: The contribution of remote sensing data assimilation to simulate daily evapotranspiration of irrigated and non-irrigated crops in semi-arid context, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15128, https://doi.org/10.5194/egusphere-egu23-15128, 2023.

11:45–11:55
|
EGU23-8428
|
HS10.2
|
ECS
|
On-site presentation
Paulina Bartkowiak, Mariapina Castelli, Bartolomeo Ventura, and Alexander Jacob

Remote sensing data play an important role in understanding the spatio-temporal variations in hydro-meteorological conditions at different spatial scales. In particular, one of the key processes of hydrological cycle for monitoring water loss from space is evapotranspiration (ET). In contrast to sparsely distributed in-situ measurements, development of two surface energy balance (TSEB) models forced by satellite observations has made a significant contribution to estimate ET with global coverage. In this regard, in the framework of ESA’s 4DMED-Hydrology project, we combine Copernicus data from Sentinel-2 (S2) Multispectral Instrument (MSI) and Sentinel-3 (S3) Land Surface Temperature Radiometer (SLSTR) with ERA5 climate reanalysis dataset derived within the period 2017-2021 for daily ET retrieval at high (100 m) spatial resolution. In this work, an open-source implementation of TSEB developed in the framework of the ESA’s Sen-ET project has been applied over wide areas represented by four Mediterranean basins in Italy, Spain, France, and Tunisia (Po, Ebro, Hérault and Medjerda). Considering large volume of satellite data and high computational requirements of the Sen-ET, all processes have been optimized to be run in the automatic manner by combining multiple steps into one processing workflow utilized in cloud computing platforms offered by EODC and ESA HPC of CloudFerro. First, due to incomplete time-series of S2 Level-2A, we pre-process Sentinel-2 data for further retrieval of 100-m reflectance and biophysical parameters needed for the ET estimation afterwards. Next, we downscale S3 land surface temperature (LST) product by exploiting relationships between 1-km Sentinel-3 and time-coincident 100-m S2 reflectances using decision trees (DT) algorithm. Apart from biophysical properties (e.g., leaf area index and fractional vegetation cover) and sharpened LST data, meteorological forcings and solar radiation from ERA5 have been generated for estimating instantaneous energy fluxes and daily evapotranspiration. Based on preliminary results over Po basin, DT algorithm allowed predicting 100-m LST with the average root mean square error (RMSE) of 3.2°C when compared to ground-derived skin temperature from two eddy covariance (EC) towers. Meanwhile, turbulent fluxes driven by downscaled LST resulted in RMSE equal to 52 Wm-2 and 108 Wm-2 for sensible and latent heat fluxes, respectively. Despite some limitations mainly related to the EC locations in complex mountain areas, ET estimates forced by satellite observations have potential for providing energy fluxes at wider scale.

Keywords: evapotranspiration, Sentinel-3, land surface temperature, Mediterranean region

How to cite: Bartkowiak, P., Castelli, M., Ventura, B., and Jacob, A.: Large scale two-source energy balance modelling of evapotranspiration over Mediterranean region, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8428, https://doi.org/10.5194/egusphere-egu23-8428, 2023.

11:55–12:05
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EGU23-9385
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HS10.2
|
ECS
|
On-site presentation
Ali Mokhtari, Morteza Sadeghi, Yasamin Afrasiabian, and Kang Yu

To bypass the thermal data requirement for actual evapotranspiration (ETa) estimation in satellite remote sensing, two general approaches have been taken into practice based on previous efforts: (1) Multi-sensor data fusion for thermal sharpening and (2) the use of the process-based models such as the Penman-Monteith and Shuttleworth-Wallace equations augmented with satellite-based crop parameters. To address this issue, this study introduced an optical satellite data-based ETa estimation model, OPTRAM-ET, based on the optical trapezoid model (OPTRAM) estimates of soil moisture. The new model has been applied to Sentinel-2 and Landsat-8 images over 16 eddy covariance flux towers in the United States and Germany. The flux towers were chosen in a way to cover different ranges of landcover types, e.g., agriculture, orchard, permanent wetlands, and foothill forests. In order to assess the model in comparison to a thermal-based conventional method, the land surface temperature (LST)-vegetation index (VI) model was utilized. The results of the proposed OPTRAM-ET model showed promising performance in all the studied regions. While agricultural sites showed higher correlation due to their wider range of ETa values, error indicators were lower in foothill forests because soil moisture changes were smaller compared to irrigated and wet lands. In addition, the OPTRAM-ET model showed comparable performance to the conventional LST-VI model. The OPTRAM-ET model however does not need thermal data, and it benefits from higher spatial and temporal resolution data provided by ever-increasing drone- and satellite-based optical sensors to predict crop water status and demand. It is worth noting that the thermal sharpening step was excluded in this model which subsequently makes the model substantially less computationally demanding than a thermal-based model. Unlike the LST-VI model, which needs to be calibrated for each satellite image, a temporally-invariant region-specific calibration is possible in the OPTRAM-ET model. Importantly, the model requires further enhancement due to limitations caused by the simplified basic assumptions.

How to cite: Mokhtari, A., Sadeghi, M., Afrasiabian, Y., and Yu, K.: A novel method for actual evapotranspiration from a soil moisture optical trapezoid model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9385, https://doi.org/10.5194/egusphere-egu23-9385, 2023.

12:05–12:15
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EGU23-7291
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HS10.2
|
On-site presentation
Chiara Corbari, Nicola Paciolla, Tian Hu, Franz Kai Ronellenfitsch, Martin Schlerf, Christian Bossung, Alessandro Ceppi, Mouna Feki, Rafael Llorens, Drazen Skokovic Jovanovic, Ahmad Al Bitar, Kaniska Mallick, Josè Sobrino, and Marco Mancini

Agriculture is the largest consumer of water worldwide, accounting for about 70% of the global freshwater      withdrawals. Thus, crop water use efficiency and impacts of water stress on crop water consumption are the key concerns for agricultural water management.

Present study investigates the variability of evapotranspiration (ET) and crop water use efficiency by integrating very high spatial resolution (1 – 4 m) thermal infrared (TIR) data from airborne measurements and visible to near infrared data from Planet satellite with a numerical water-energy balance model and a diagnostic surface energy balance model.     

The analysis is done for an intensive agriculture area in central Italy near the city of Modena, where several fruit trees fields are present along with fresh vegetables. An intensive airborne campaign was organized in the summer of 2022 for three consecutive days in July. A hyperspectral TIR camera (Telops Hyper-Cam LW) has been operated at a spectral resolution of 8 cm-1, resulting in 64 wavebands, and covering a wavelength range of 850 cm-1 to 1350 cm-1 (7,39 µm – 11,8 µm).  During the 3 days of flight acquisitions, three overpasses per day are planned: 9:00, 12:30 and 16:00 h, respectively and two areas were intensively      surveyed at both 4 and 1 m spatial resolution. Planet data at 3.7 m spatial resolution were used to derive different vegetation indices, such as vegetation fraction coverage, NDVI and leaf area index. During airborne overpasses ground data of spectral reflectance, vegetation variables, LST and soil water content (SM) were collected in different fields. In addition, two different pear trees fields were monitored with an eddy covariance station and soil moisture profile measurements, respectively.

To investigate the diurnal and spatial patterns of evapotranspiration, soil moisture variability and crop water use efficiency, we used two numerical models: the surface energy balance model STIC based on Penman-Monteith and Shuttleworth-Wallace (Mallick et al., 2018) and the water-energy balance model FEST-EWB which computes continuously in time and is distributed in space soil moisture and evapotranspiration fluxes solving for a land surface temperature that closes the energy–water balance equations (Corbari et al., 2011).

Differences and similarities in ET estimates have been analysed from the two models for different soil moisture conditions and crop types, considering crop water use efficiency and water stress, and have been compared to eddy covariance measurements for accuracy evaluation considering both instantaneous and daily data. The assimilation of instantaneous estimates of ET into the water-energy balance model allowed to directly derived soil moisture maps at high spatial resolution which have been found in agreement with ground SM measurements.

How to cite: Corbari, C., Paciolla, N., Hu, T., Ronellenfitsch, F. K., Schlerf, M., Bossung, C., Ceppi, A., Feki, M., Llorens, R., Skokovic Jovanovic, D., Al Bitar, A., Mallick, K., Sobrino, J., and Mancini, M.: Evapotranspiration and crop water use efficiency from airborne thermal infrared data at 1 to 4 m spatial resolution, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7291, https://doi.org/10.5194/egusphere-egu23-7291, 2023.

12:15–12:30

Posters on site: Mon, 24 Apr, 14:00–15:45 | Hall A

Chairpersons: Sibylle K. Hassler, Ana Andreu, Jannis Groh
In-situ methods to estimate ET
A.181
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EGU23-4147
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HS10.2
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ECS
|
Huibin Gao, Qin Ju, and Zhenchun Hao

Shallow groundwater evaporation (Eg) is a major component of the hydrological cycle, especially in semiarid and arid locations. Existing Eg estimation processes mainly rely on three approaches: direct measurements, numerical models, and empirical methods. Empirical methods are more commonly used in practical applications due to good performances with more accessible inputs and simple forms. However, most of commonly used empirical methods can only weakly represent Eg variations along the soil depth and do not consider the energy driver. Therefore, a temperature coefficient was proposed and incorporated into two preferred empirical models to characterize the impacts of soil temperature and air temperature lags on Eg. The method was evaluated using in situ daily data obtained from nonweighing bare soil lysimeters. The results indicated that the models that considered the temperature gradient variable (T) conformed to the changes in the actual Eg values with depth more appropriately than the original models, accompanied by 4.3%–8.8% accuracy improvements overall. Shallow groundwater evaporation Eg was found to be influenced by the water table depth (H), T, and pan evaporation (E0) in descending order, and strong interactions were found between H and T. Moreover, bias of Eg measurement results from precipitation was investigated; measurements from dry days without precipitation revealed the actual Eg process, the relative errors in the cumulative Eg values derived at different depths demonstrated a positive relationship with infiltration recharge, and the errors related to precipitation induced 6.7%–8.3% Eg underestimations. These results contribute to a better understanding of evaporative losses from shallow groundwater and the typical Eg situation that occurs simultaneously with recharge, and they provide promising perspectives for corresponding integrated hydrologic modeling research.

How to cite: Gao, H., Ju, Q., and Hao, Z.: Empirical Estimation of Daily Evaporation from Shallow Groundwater with a Temperature Coefficient, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4147, https://doi.org/10.5194/egusphere-egu23-4147, 2023.

A.182
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EGU23-7856
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HS10.2
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ECS
Dóra Incze, Zoltán Barcza, and Nándor Fodor

Among other factors, water availability strongly influences the amount and quality of crop yield. International interest in sustainable management of limited freshwater supplies has resulted in increased demand for measurements and modeling methods of cropland water balance components. In order to ensure adequate and sustainable crop production, it is necessary to understand the full water cycle of crop production including evapotranspiration. The purpose of the presented research is to quantify the soil water balance components of arable lands based on an experimental platform that can provide reference data for understanding processes and for model validation. Measurements by large weighing lysimeters are commonly used to test different evapotranspiration estimation methods. The data used for the research is provided by a weighing lysimeter station that was installed in 2018 at Martonvásár in Hungary. The station consists of twelve scientific lysimeters with soil temperature, soil water content, soil water potential sensors installed at several depths in the 2 m deep undisturbed soil profiles, and an ancillary meteorological tower. Every year since 2018 different crop varieties have been grown in six lysimeters. The other six lysimeters are not cultivated and are maintained vegetation-free (bare soil). The measurements are made with high accuracy and fine time resolution (1 reading per minute). Despite our best efforts, several types of errors occurred due to various reasons. The quality assurance and quality control (QA/QC) procedures used in the research help to minimize these errors in processing lysimeter datasets. A web application also contributes to a better interpretation of the data. The poster presents the first results with case studies focusing on wheat evapotranspiration.

How to cite: Incze, D., Barcza, Z., and Fodor, N.: Quantification of soil water balance components based on lysimeter measurements, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7856, https://doi.org/10.5194/egusphere-egu23-7856, 2023.

A.183
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EGU23-15995
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HS10.2
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ECS
Belen Marti, Aaron Boone, Daniel Martinez-Villagrasa, Joan Cuxart, and Jeremy Price

The Land surface Interactions with the Atmosphere over the Iberian Semi-arid Environment (LIAISE) campaign took place in Catalonia near Lleida, in the northeastern part of the Iberian Peninsula. It lasted from April to October with an intensive measurement period for the last half of July, 2021, when surface conditions between a large irrigated area and the much drier surroundings was maximum. Measurements of surface energy fluxes and atmospheric and soil conditions were made over several locations which comprised several crop types in irrigated, drip irrigated and non irrigated areas. These data were used to test the quality of the approximations made when modeling in semi-arid environments.
 
Turbulent fluxes can be estimated using two measurements at different heights of the relevant atmospheric variable with statistically-based methods like Monin-Obukhov theory or simulated from LSMs (Land Surface Models). For latent heat flux, the first approach is limited by the lack of development of the necessary functions when they are used in locations with different conditions from which they were originally developed. The second requires the determination of many parameters which depend on large scale databases or a derived land cover classification to be accurate, together with an appropriate parameterization of the physical processes. Furthermore,  evapotranspiration (ET) estimates for the LIAISE sites are affected by more complex interactions such as the heterogeneity of the region, with areas irrigated by flooding (mainly corn and alfalfa) or drip irrigation (e.g. fruit trees, vineyards) verses relatively dry rain-fed surfaces (natural grass or low vegetation, bare soil), and sudden man-induced changes such as flooding or harvest.  
    
The relationship between the lower atmospheric vertical gradients and fluxes is explored and the LSM SURFEX (Surface Externalisée in French) is evaluated with field data of LIAISE to test its ability to simulate the key processes modulating the surface fluxes (notably the impact of irrigation) over several contrasting sites.

How to cite: Marti, B., Boone, A., Martinez-Villagrasa, D., Cuxart, J., and Price, J.: Land surface models and vertical gradient estimation of evapotranspiration and other turbulent fluxes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15995, https://doi.org/10.5194/egusphere-egu23-15995, 2023.

A.184
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EGU23-16565
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HS10.2
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ECS
Fangzhong Shi, Xiaoyan Li, and Deliang Chen

 Saline lakes on the Qinghai–Tibet Plateau (QTP) profoundly affect the regional climate and water cycle through loss of water (E, evaporation under ice–free (IF) and sublimation under ice–covered (IC) conditions). Due to the observation difficulty over lakes, E and its underlying driving forces are seldom studied targeting saline lakes on the QTP, particularly during the IC. In this study, E of Qinghai Lake (QHL) and its influencing factors during the IF and IC were first quantified based on six years of observations. Subsequently, two models were chosen and applied in simulating E and its response to climate variation during the IF and IC from 2003 to 2017. The annual E sum of QHL is 768.58 ± 28.73 mm, and E sum during the IC reaches 175.22 ± 45.98 mm, accounting for 23% of the annual E sum. The E is mainly controlled by the wind speed, vapor pressure difference, and air pressure during the IF, but driven by the net radiation, the difference between the air and lake surface temperatures, wind speed, and ice coverage during the IC. The mass transfer model simulates lake E well during the IF, and the model based on energy achieves a good simulation during the IC. Moreover, wind speed weakening results in an 11.14% decrease in E during the IC of 2003–2017. Our results highlight the importance of E in IC, provide new insights into saline lake E in alpine regions, and can be used as a reference to further improve hydrological models of alpine lakes. 

How to cite: Shi, F., Li, X., and Chen, D.: Evaporation measurement and modelling of an alpine saline lake influenced by freeze–thaw on the Qinghai–Tibet Plateau, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16565, https://doi.org/10.5194/egusphere-egu23-16565, 2023.

A.185
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EGU23-16933
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HS10.2
Nadav G. Lensky, Shai Abir, Guy Tau, Hamish McGowan, and Ziv Mor

Rifts, tectonic depressions, stretches along continents and typically collect a wide variety of waterbodies, including wetlands, lakes, terminal lakes and locked seas. Here we exploit the waterbodies along the Dead Sea Rift, which vary by geo-climatic settings (from humid Mediterranean to hyper-arid), water depth, water salinity, etc., by simultaneously measuring surface heat, gas and momentum fluxes using Eddy Covariance towers. These waterbodies are subjected to similar radiative forcing. We show that in the two desert waterbodies differ significantly by surface heat flux partitioning: In the Gulf of Eilat (extension of the Red Sea), the evaporation rate is three times larger than in the Dead Sea (a hypersaline terminal lake), this is due to the effect of water salinity in reducing water vapor pressure. In the two northern water (Lake Kinneret and Agmon Hula), which resides in the more humid, Mediterranean region, the evaporation rate is suppressed by humidity, in comparison to the Gulf of Eilat. These two waterbodies differ by their depth, which determines the dynamics of evaporation, surface heat fluxes and thermoregulation. We analyze the role of the timing of the Mediterranean Sea Breeze on evaporation rate. This observational setup, of concurrent measurements of air-water interactions along the gradients within the Dead Sea Rift provides a rare opportunity to quantify various aspects of water management policies, the formation of rocks within these waterbodies, the effect of local micrometeorology and synoptic scale circulation on the waterbodies and their surroundings.

How to cite: Lensky, N. G., Abir, S., Tau, G., McGowan, H., and Mor, Z.: Air-Water Interactions Along the Dead Sea Rift, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16933, https://doi.org/10.5194/egusphere-egu23-16933, 2023.

Remote sensing methods to estimate ET
A.186
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EGU23-5535
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HS10.2
Ana Andreu, Rafael Pimentel, Elisabet Carpintero, María P. González-Dugo, Hector Nieto, Timothy Dube, and María José Polo

Semiarid rangelands (grasslands with scattered trees and shrubs) are one of Africa’s most complex and variable biomes. They are a mosaic of land uses, where extensive livestock is the main economic activity, and agriculture or conservational uses are also crucial. They are highly controlled by the availability of water, e.g., pasture and rainfed crop production. Although the vegetation is adapted to variable climatic conditions and dry periods, the increase in drought intensity, duration, and frequency, the changes in agricultural practices, and other socioeconomic and environmental factors precipitate their degradation. The combined differential functioning and characteristics of the vegetation components and communities affect water dynamics, resulting in high spatiotemporal variability that creates distinct patches. Therefore, the precision, resolution, and accuracy of the information required for water management differ according to the scales of these patches: from the local to the basin. We want to assess the optimal spatiotemporal scale when monitoring semiarid mosaic vegetation cover and its water consumption.

 

To answer this question, we evaluated the water use patterns of the typical vegetation patches (tree+grass savanna, grassland, crop area, and creek shore) estimated by different modeling approaches (FAO56 and TSEB) with spatial resolutions of 30 m, 250 m, and 1 km. From a farm/agricultural management viewpoint, we demonstrated the need for sufficient spatial and temporal resolution when evaluating water consumption and the difficulties when significant temporal gaps are present. Higher spatial-temporal scales were crucial to determining the pasture drying cycle and crop water use. In humid or denser areas that provide essential ecosystem services (e.g., wildlife habitat), transpiration rates were higher throughout the year and often underestimated when using coarse data. Over savanna patches, products with coarse resolution (1 km) reflected well the water use pattern. These metrics reflected the severe drought experienced during the 2015-2016 seasons due to an intense El Niño event, other dry events (e.g., 2002, 2007), and the recovery time of each vegetation patch.

How to cite: Andreu, A., Pimentel, R., Carpintero, E., González-Dugo, M. P., Nieto, H., Dube, T., and Polo, M. J.: Influence of scale in water resources management for heterogeneous African semiarid rangelands., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5535, https://doi.org/10.5194/egusphere-egu23-5535, 2023.

A.187
|
EGU23-6897
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HS10.2
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ECS
Hassan Awada, Mirko Castellini, Simone Di Prima, Filippo Giadrossich, Costantino Sirca, Serena Marras, Donatella Spano, and Mario Pirastru

Evapotranspiration (ET) is the process by which water is lost from the Earth's surface through the combined mechanisms of evaporation from surfaces and transpiration from plants. It is an important factor in the soil-plant-atmosphere (SPA) system and plays a key role in the functioning of ecosystems. In semi-arid regions such as the Mediterranean, ET is a major contributor to water loss. An accurate understanding of the spatiotemporal dynamics of ET is crucial for effective water resource management and conservation, particularly in the face of increasing water resource pressure and potential climate change. Remote sensing (RS) can provide long-term data with relatively high spatial and temporal resolution, which can be valuable for sustainable ecosystem management. Surface energy balance (SEB) techniques based on satellite RS data have proven useful for quantifying actual evapotranspiration (ETa eb) at various temporal and spatial scales. However, limitations such as the temporal resolution of satellite data and gaps in image acquisition due to cloud cover can limit the usefulness of RS. This study proposes a model-based approach for constructing daily crop actual evapotranspiration (ETc act) between Landsat 8 acquisition days. The modeling approach aims to simulate the dynamics in the SPA system that occur between two Landsat acquisitions in order to estimate the daily time series of ETc act. The model integrates ETa eb estimates by SEBAL model on Landsat-8 acquisition days, RS-derived vegetative biomass dynamics, field measurements of potential evapotranspiration, and a hydrological modeling approach using the transient flow Richards equation to estimate soil moisture in the root zone. The results show that the proposed approach is well suited for modeling the dynamics in the soil-plant-atmosphere system that occurs between two Landsat acquisitions to estimate the daily time series of ETc act. This approach can provide valuable information for water resource management, drought monitoring, and climate change research, moreover accurate ETc act estimates can make significant contributions to near real time irrigation modeling and scheduling.

How to cite: Awada, H., Castellini, M., Di Prima, S., Giadrossich, F., Sirca, C., Marras, S., Spano, D., and Pirastru, M.: Satellite Remote Sensing and Hydrological Modeling for Estimating Daily Actual Evapotranspiration in a Semi-Arid Mediterranean Ecosystem, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6897, https://doi.org/10.5194/egusphere-egu23-6897, 2023.

A.188
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EGU23-8311
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HS10.2
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ECS
Philipp Jordan, Stenka Vulova, Alby Duarte Rocha, Dörthe Tetzlaff, and Birgit Kleischmit

As the urban population has become predominant globally, heat stress and its negative consequences on human health have grown due to increasingly dense and artificial environments. Urban green infrastructures (UGI) mitigate heat stress by providing cooling services through evapotranspiration (ET) and by blocking solar radiation through shading. Even though ET is a crucial component of urban water and energy regimes, our understanding of the role of vegetation on urban water cycling is still poor when observed through remote sensing. To better understand the seasonal and diurnal variability of ET from urban vegetation, a comprehensive sampling campaign combining an unmanned aerial aircraft system (UAS) and field-based measurements in an urban ecohydrological research observatory in Berlin (Germany) was conducted. The sampling was undertaken throughout an entire growing period (from April to October 2019) to characterize the seasonality of both climatic drivers and phenological effects on ET. Three vegetation types were sampled in the study site  (grassland, forest, and shrubs). 

Field-based measurements included sap flow and stomatal conductance (LI-6800 gas exchange), to capture monthly and diurnal dynamics of transpiration, leaf area index (LAI), grassland vegetation height as well as soil moisture. Soil moisture and sap flow were available at hourly resolution while LAI, stomatal conductance and vegetation height were measured at monthly intervals. The images were captured by UAS flights with multi-spectral (Tetracam MCA) and thermal (Flir Tau 2) cameras on a monthly basis and, on some dates, at multiple times during the day to capture diel variability. UAS data were divided into shaded and unshaded areas within the three vegetation classes. ET estimates from UAS observations were derived using the inference method based on vegetation indices (VI) as described in (Nouri et al., 2013), Eddy flux data was used to validate modeled ET and also provided hydroclimatic data . 

Results showed clear differences for ET and land surface temperature (LST) between vegetation classes throughout the year, with trees and shrubs showing lower overall temperatures and higher ET estimations than grassland during the observation period. The influence of shadow on modeled ET and observed LST also became apparent for all classes, especially when multiple UAS observations were taken during a single day. Shaded areas exhibited lower overall LST and ET than non-shaded areas, with the starkest contrast exhibited for grassland where shaded areas showed up to 50% lower LST and estimated ET was reduced by up to 25%. Both ET and LST showed correlation to the measured sap flow and stomata conductance at both diurnal and seasonal temporal scale.

Our findings provide important insights into the influence of  different urban vegetation types in both ET and LST with respect to shaded and unshaded surfaces. Our study also highlights the importance of a detailed understanding of UGI characteristics and its cooling potential for further improvements in urban green management. Moreover, it could improve models of the urban water cycle and is important for upscaling ET to a broader city scale.

How to cite: Jordan, P., Vulova, S., Duarte Rocha, A., Tetzlaff, D., and Kleischmit, B.: Using spectral and thermal UAS data to infer the influence of shaded and unshaded urban vegetation on evapotranspiration and land surface temperature, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8311, https://doi.org/10.5194/egusphere-egu23-8311, 2023.

A.189
|
EGU23-8359
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HS10.2
|
ECS
jingjing sun

Although the Operational Simplified Surface Energy Balance (SSEBOP) has been successfully applied to mesoscale evapotranspiration (ET) monitoring, its spatial resolution (1000 m) is too coarse for local and regional water resource management in agricultural applications. Based on land surface temperature and Normalized Difference Vegetation Index, a novel spatio-temporal evapotranspiration fusion method considering underlying surface factors was proposed. The proposed evapotranspiration spatio-temporal fusion method was applied to the SSEBOP evapotranspiration product to obtain temporally continuous high spatial resolution 30-m ET data corresponding to the spatial resolution of the Landsat Satellite images. The middle reaches of the Heihe River Basin in China were selected for an experimental study. The accuracy difference between the fused 30-m ET and in situ measurements will be discussed here in detail. We will also discuss the differences in spatial distribution texture between the SSEBOP and spatio-temporal fusion ET results. Finally, the influence mechanism of underlying surface factors on evapotranspiration spatio-temporal fusion will be discussed.

How to cite: sun, J.: A novel spatio-temporal fusion method of evapotranspiration for SSEBOP evapotranspiration product, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8359, https://doi.org/10.5194/egusphere-egu23-8359, 2023.

A.190
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EGU23-10312
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HS10.2
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ECS
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Ting Liang and Hanbo Yang

    Accurate estimation of high resolutions of evapotranspiration (ET) is essential to study the variation of water resources in highly heterogeneous regions, but there is a severe paucity of ET products with high spatial resolution for long time series. This research improves the PML_V2 model to estimate a 30 m resolution monthly ET, called the PML_30 model. Furthermore, it is applied to estimate the monthly ET from 2000 to 2020 in the Yarkand Oasis. The method uses a linear transformation to harmonize remote sensing data from the Landsat-5 Thematic Mapper (TM), and the Landsat-7 Enhanced Thematic Mapper (ETM+) to the Landsat-8 Operational Land Imager (OLI), resulting in multi-source Landsat data with long time series. High spatial resolution and long-time series of leaf area index, land surface emissivity, and albedo are derived from the multi-source Landsat data to produce 30 m resolution ET products. The PML_30 model and PML_V2 models were compared to the regional water balance’s multi-year average ET of 380mm. The former is estimated at 344 mm with a relative error of 0.09, whereas the latter is at 304 mm with 0.2. At the point scale, the PML_30 model’s ET was compatible with the water consumption pattern of the related plant, and the variation in groundwater. The average annual ET for the Yarkand Oasis and its lower reaches is 343 mm/yr and 168 mm/yr, respectively. Between 2000 and 2015, the ET of the lower reaches increased by 2.86 mm/yr, but between 2016 and 2020, it decreased. The proposed PML_30 model is easily applicable to a larger scale with increased estimation accuracy and is well suited for areas with high heterogeneity such as areas with sparse vegetation cover.

 

How to cite: Liang, T. and Yang, H.: A High-resolution Estimation of Terrestrial Evapotranspiration from Landsat Images and its Applications in a Sparse Vegetation Region, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10312, https://doi.org/10.5194/egusphere-egu23-10312, 2023.

A.191
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EGU23-11996
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HS10.2
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ECS
Emma Tronquo, Feng Zhong, Niko E.C. Verhoest, and Diego G. Miralles

Terrestrial evaporation (E) plays a crucial role in the Earth system, acting as a link between the water and carbon cycles and playing a major role at the complex interplay between land and atmosphere. Therefore, accurate monitoring of E and its different components is crucial. However, since E cannot be observed directly from satellite sensors, current E retrieval algorithms are largely indirect and satellite-based E estimates remain highly uncertain, especially in what respects to the partitioning of evaporation into its different components. In particular interception loss (Ei), the volume of precipitation captured by plant surfaces and evaporated back into the atmosphere without reaching the ground, remains one of the most uncertain components in the global water balance. Moreover, current existing E datasets only deliver daily satellite-based Ei estimates, being unable to resolve precipitation event scales.  

The research presented here is focused on estimating Ei on a sub-daily scale. To do so, the Global Land Evaporation Amsterdam Model (GLEAM; Miralles et al., 2011) is used. GLEAM is an E model that simulates the different components (transpiration, soil evaporation, interception loss) using satellite data, including microwave observations of surface soil moisture and vegetation optical depth (VOD). We adapted GLEAM to function at sub-daily resolution, by (1) relying on sub-daily satellite-based forcing data and (2) extending the recent interception model presented by Zhong et al. (2022) by following a Rutter approach (Rutter et al., 1975) to make it applicable at sub-daily scales. This interception model calculates a running balance in time of rainfall, throughfall, evaporation and changes in canopy storage, whereby Ei is the evaporation from the wet canopy. The model is driven by satellite-observed vegetation dynamics, potential evaporation and precipitation. The sub-daily Ei estimates are compared to existing daily estimates and diurnal cycles are analyzed, and this at different spatial scales.

References:

Miralles, D. G., Holmes, T. R. H., De Jeu, R. A. M., Gash, J. H., Meesters, A. G. C. A., & Dolman, A. J. (2011). Global land-surface evaporation estimated from satellite-based observations. Hydrology & Earth System Sciences, 15, 453–469. 

Rutter, A. J., Morton, A. J., & Robins, P. C. (1975). A predictive model of rainfall interception in forests. II. Generalization of the model and comparison with observations in some coniferous and hardwood stands. Journal of Applied Ecology, 12, 367–380.

Zhong, F., Jiang, S., van Dijk, A. I. J. M., Ren, L., Schellekens, J., & Miralles, D. G. (2022). Revisiting large-scale interception patterns constrained by a synthesis of global experimental data. Hydrology & Earth System Sciences, 26, 5647–5667. 

How to cite: Tronquo, E., Zhong, F., Verhoest, N. E. C., and Miralles, D. G.: Towards sub-daily satellite-based interception loss estimates, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11996, https://doi.org/10.5194/egusphere-egu23-11996, 2023.

A.192
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EGU23-13844
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HS10.2
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ECS
Radosław Szostak, Mirosław Zimnoch, and Przemysław Wachniew

Remote sensing measurements of land surface temperature play a key role in the estimation of evapotranspiration. Thermal cameras used in Unmanned Aerial Vehicles are prone to errors manifested by fluctuations in temperature readings of the same object on different thermal images, vignette effect, and bias against the actual temperature. These problems were addressed with the calibration algorithm. It consists of two steps: i) georeferencing of images using EXIF data, key points matching, and global optimization of relative image positions with the gradient descent method; ii) calibration of temperature offsets occurring between images by correcting sequentially for differences between values on overlapping areas of adjacent images starting from single reference image. The calibration principle is based mainly on the observation that the temperature readings from two overlapping thermal images are shifted by an offset that is approximately constant for the entire overlapping area of the images. Thanks to the algorithm used, it was possible to increase the precision of the georeferencing of aerial images to a level that allows the direct creation of a mosaic of images without the photogrammetric software and reduce the standard deviation of the water surface and vegetation temperature measurements.

Research was partially supported by the National Science Centre, Poland, project WATERLINE (2020/02/Y/ST10/00065), under the CHISTERA IV programme of the EU Horizon 2020 (Grant no 857925) and the "Excellence Initiative, Research University" program at the AGH University of Science and Technology.

How to cite: Szostak, R., Zimnoch, M., and Wachniew, P.: The algorithm of remote sensing thermal imagery calibration dedicated for UAV-based hydrological studies., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13844, https://doi.org/10.5194/egusphere-egu23-13844, 2023.

Posters virtual: Mon, 24 Apr, 14:00–15:45 | vHall HS

Chairpersons: Hamideh Nouri, Pamela Nagler
vHS.23
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EGU23-4030
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HS10.2
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Ting-Jung Lin, Kai Wang, Yin Wang, Zhimei Liu, Xiaojie Zhen, Xiaohua Zhang, Li Huang, Jingting Zhang, and Xunhua Zheng

Evapotranspiration (ET) is one of the essential components of the hydrological cycle of terrestrial ecosystems. Among various techniques for measuring ET, the eddy covariance (EC) is the most direct one for measuring ET fluxes at field to ecosystem scales. It has been used worldwide to monitor the biosphere-atmosphere exchanges of energy, water, and carbon, particularly in some global and regional networks (e.g., FLUXNET) for ecosystem studies.

In recent years, laser-based gas spectrometers have shown good reliability and effectiveness in the high-frequency and high-sensitivity measurement of various atmospheric trace gases. We have earlier presented a cost-effective, open-path water vapor analyzer (Model: HT1800, HealthyPhoton Co., Ltd.) suitable for EC measurement of ET based on the tunable diode laser absorption spectroscopy (TDLAS) technology. The analyzer utilizes a low-power vertical cavity surface emitting laser (VCSEL) and a near-infrared Indium Galinide Arsenide (InGaAs) photodetector in an open-path design, which avoids delay or high-frequency damping due to surface adsorption. The analyzer has a precision (1σ noise level) of 10 μmol mol−1 (ppmv) at a sampling frequency of 10 Hz. The analyzer head has a weight of ~2.8 kg and dimensions of 46 cm (length) and 9.5 cm (diameter). It can be powered by solar cells, with a total power consumption of as low as 10 W under normal operations.

Recent studies have emphasized the importance of spectroscopic effect correction for EC measurement using a laser-based open-path gas analyzer. This additional correction arises from the absorption line broadening due to atmospheric water vapor, temperature, and pressure fluctuations. In this study, we prepared two HT1800 water vapor analyzers. One is equipped with an infrared laser operating near 1392 nm and the other near 1877 nm. The water vapor line near 1392 nm is one of the most used for detecting water vapor because laser and photodetector operating near this wavelength are readily available and relatively inexpensive. However, its broadening effect, mainly caused by temperature variation, is expected to be stronger than the 1877 nm line, according to theoretical analysis using the HITRAN database.

Using the two HT1800 analyzers, we conducted two EC measurement campaigns at an agricultural site in 2022. Two commercial gas analyzers, EC150 (Campbell Scientific Inc., Logan, UT, USA) and LI-7500RS (LI-COR Biosciences, Lincoln, Nebraska, USA), were also running during the campaigns to compare with HT1800. The first purpose of this study is to test the performance of HT1800 under field conditions and evaluate its applicability for ET flux measurements. The second purpose is to quantify and compare the spectroscopic effect on the ET fluxes using the 1392 nm and 1877 nm water vapor analyzers. Meanwhile, we proposed a hypothesis that the 1392 nm analyzer can provide comparable ET fluxes with LI-7500RS and EC150 after accounting for the spectroscopic effect. If it is the case, this cost-efficient water vapor analyzer will become an effective tool for water and ecological studies in the future.

How to cite: Lin, T.-J., Wang, K., Wang, Y., Liu, Z., Zhen, X., Zhang, X., Huang, L., Zhang, J., and Zheng, X.: Measuring evapotranspiration fluxes using a tunable diode laser-based open-path water vapor analyzer, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4030, https://doi.org/10.5194/egusphere-egu23-4030, 2023.

vHS.24
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EGU23-2931
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HS10.2
Pamela Nagler, Armando Barreto-Muñoz, Ibrahima Sall, and Kamel Didan

Accurate estimates of riparian vegetation water use are important to quantify. In these narrow riparian landscapes, we quantify loss of water from leaves and soil as one variable, actual evapotranspiration (ETa). ETa is the most difficult component of the water cycle to measure, but remote sensing estimates of ETa have been validated for dryland riparian corridors using ground-based sensors (e.g., sap flow, tower data). Increases in ETa are indicative of increasing vegetation cover and therefore increasing ‘losses’ of water through ETa represent positive trends in riparian ecosystem health; decreasing ETa may indicate dwindling riparian cover due to less available water for canopy growth due to drought, groundwater flux, beetle defoliation, fire, increasing salinity, etc.

The objectives of this study were to calculate ETa daily (mmd-1) and annually (mmyr-1) and derive riparian vegetation annual consumptive use (CU) in acre-feet (AF) for select riparian areas of four rivers in the Lower Colorado River Basin. Select riparian reaches from the Lower Colorado, Bill Williams, San Pedro, and Virgin Rivers were delineated using digitized riparian plant area, comprised of shrubs and trees, so that we could track plant greenness using the two-band Enhanced Vegetation Index (EVI2) and ETa with Landsat for the recent decade (2014-2022). We acquired Landsat-8 OLI scenes, processed and filtered the data and computed EVI2 as a proxy for vegetation every 16-days over the study period. We then computed daily potential ET (ETo, mmd-1) using the Blaney-Criddle formula with input temperature data from Daymet (1 km), an indirect remote sensing measurement from gridded weather data. These data were then averaged over 16-days using the 8-days before- and after- the Landsat overpass date. After fusing the delineated riparian areas with 30-m resolution Landsat data, riparian ETa was quantified using the Nagler ET(EVI2) approach to produce time-series ETa data and the first CU measurements for these riparian zones. Both a digitized-vector layer and best-approximation raster-area for each of the four riparian corridors were utilized in determining the water metrics, ETa and CU, based on these two acreage estimation methods.

The average annual ETa (mmyr-1) for the Lower Colorado River decreased from ca. 950 to 800 mmyr-1 (2014-2022). The average annual ETa (mmyr-1) for the Bill Williams River decreased from ca. 925 to 600 mmyr-1 (2014-2022). The average annual ETa (mmyr-1) for the San Pedro River increased from ca. 975 to 1075 mmyr-1 (2014-2022). The average annual ETa (mmyr-1) for the Virgin River increased from ca. 675 to 825 mmyr-1 (2014-2022). The two unaltered rivers depict positive riparian ecosystem responses. We produced four estimates of CU based on the corresponding riparian areas studied, each with a digitized vector area and best-approximation raster area. Our CU estimates for these four riparian corridors range from 30,000 AF (digitized) to 37,000 AF (best-approximation) and are in the range reported for similar arid riparian areas. This study provides valuable estimates of riparian water use that may assist with decision-making by natural resource managers tasked with allocating water and managing habitat along these riparian corridors.

How to cite: Nagler, P., Barreto-Muñoz, A., Sall, I., and Didan, K.: Four Riparian Corridors in the Lower Colorado River Basin: New Estimates of Riparian Evapotranspiration and Consumptive Water Use, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2931, https://doi.org/10.5194/egusphere-egu23-2931, 2023.