Wetland Evapotranspiration Research Articles

Hydrological modeling of the Silala River basin. 2. Validation of hydrological fluxes with contemporary data

AbstractA companion paper in this Special Issue reviewed the development of a hydrological model of the Silala River basin, using long‐term data (1969–1992) to determine the basin's water balance and plausible groundwater recharge scenarios. In the context of a remote river basin with limited in situ data, this article reviews the potential of in situ and remotely collected data, available for a relatively short period (2018–2019), to validate various aspects of the hydrological model performance. These include the spatiotemporal evolution of snow cover areal fraction (SCF), actual evapotranspiration (ETa) in the basin's extensive alluvial deposits, and wetland ETa. The observed SCF dynamics are well represented by the model at annual and monthly timescales, with monthly mean simulated SCF biases between −5.6% and 8%. At daily timescales, the model successfully captures snowstorm occurrence, although there are limitations on snow spatial patterning. Simulated ETa over alluvial deposits agrees with in situ observations during periods of high ETa, although the simulated values underestimate site‐specific observations during low ETa periods, due to the presence of lateral subsurface flows. In the wetlands, satellite‐based ETa estimates follow the seasonal pattern of in situ observations, but with values ~50% higher than those determined from elevation‐corrected eddy‐covariance (EC) measurements. Nonetheless, this difference is within the expected precision of the remote sensing method. Although based on a limited period, the validation results are encouraging, and demonstrate the utility of satellite tools and limited period in situ data for watersheds with scarce long‐term data.This article is categorized under: Science of Water > Hydrological Processes

Patterns and drivers of evapotranspiration in South American wetlands

Evapotranspiration (ET) is a key process linking surface and atmospheric energy budgets, yet its drivers and patterns across wetlandscapes are poorly understood worldwide. Here we assess the ET dynamics in 12 wetland complexes across South America, revealing major differences under temperate, tropical, and equatorial climates. While net radiation is a dominant driver of ET seasonality in most environments, flooding also contributes strongly to ET in tropical and equatorial wetlands, especially in meeting the evaporative demand. Moreover, significant water losses through wetlands and ET differences between wetlands and uplands occur in temperate, more water-limited environments and in highly flooded areas such as the Pantanal, where slow river flood propagation drives the ET dynamics. Finally, floodplain forests produce the greatest ET in all environments except the Amazon River floodplains, where upland forests sustain high rates year round. Our findings highlight the unique hydrological functioning and ecosystem services provided by wetlands on a continental scale.

High temporal and spatial resolution characteristics of evaporation, transpiration, and evapotranspiration from a subalpine wetland by an advanced UAV technology

Wetland evapotranspiration (ET), which involves the land–atmosphere exchange of energy and water, is dynamic and affects the spatiotemporal distribution of water resources. However, due to the variability and complexity of wetlands, accurate estimation of patch-scale ET and its spatial variability remain insufficiently characterized. To overcome this challenge, an advanced unmanned aerial vehicle (UAV) technology was developed by combining the three-temperature (3T) model, which is robust to estimate transpiration and its spatial variability with UAV-based thermal infrared remote sensing, and Penman equation, which is commonly used to estimate open water evaporation. The combined approach was verified using the Bowen ratio system over a subalpine wetland. The results show that the proposed method is simple and applicable for estimating wetland ET and its spatial variability, with a determination coefficient (R2) of 0.93, mean absolute percentage error (MAPE) of 7.90%, root mean squared error (RMSE) of 0.05 mm h−1, and Nash-Sutcliffe efficiency (NSE) of 0.93. It depicts a large spatial variability in wetland ET with respect to surface vegetation characteristics, water regimes, meteorological factors, and larger transpiration rates than open water evaporation. With its limited inputs and no calibration requirements, the proposed method is concluded to be simple and to easily reveal the high temporal and spatial resolution characteristics of patch-scale ET and its components.

Snížení základního odtoku kvůli evapotranspiraci povrchové a podzemní vody z mokřadu v povodí Liběchovky: porovnání měření a výpočtu Oudinovou metodou

This study is focused on the base flow decrease due to surface water and groundwater evapotranspiration (ET) in wetlands of the Liběchovka catchment. Evapotranspiration in wetlands can significantly affect stream discharge, and its influence will probably still increase in the future due to the global rise of temperatures caused by climate change. The study site is located in the upper part of Liběchovka catchment (Fig. 1). This wetland hosts a small stream supplied by rather steady groundwater inflow, representing the favourable site for detection of the effect of ET. V notch weir and two piezometers were used to monitor stream discharge and wetland water table in 30 minute periods (Fig. 2). Diurnal periodical oscillations of water flow and water table caused by ET were observed (Fig. 3). They occurred in the summer part of the year, especially on sunny days without rain. The amplitude of water table level oscillation was increasing with increasing temperature (Fig. 4). Calculation showed that evapotranspiration reduced the water flow, on average, by 15 % on the warm sunny days. The maximum daily reduction was up to 32 %. Direct measurements were compared with the potential ET calculated using the Oudin’s method (Oudin 2005). The ET from the measurement was 45 % of the potential ET calculated by Oudin’s method. In the next step, the Oudin’s method was used to calculate the potential ET of all wetlands in Liběchovka catchment upstream from the Želízy village, where gauging station of ČHMÚ is situated. The original discharge not reduced by the wetland ET was defined as the sum of the wetland potential ET and the mean annual measured discharge. Due to the ET from wetlands (years 2015–2020), the discharge was reduced on average by 13 %. If only the summer months of July and August were considered, it was reduced, on average, by 26 % and by 39 % in the driest day recorded in this period. To estimate the role of groundwater abstraction on the Liběchovka stream during the period of 2015–2020, the sum of measured stream discharge, groundwater abstraction and wetland ET was calculated. From this sum, 71.5 % represented the directly measured water flow, 18.2 % was the groundwater abstraction, and 10.3 % was the wetland ET (Fig. 8).

Using an object-based machine learning ensemble approach to upscale evapotranspiration measured from eddy covariance towers in a subtropical wetland

Accurate prediction of evapotranspiration (ET) in wetlands is critical for understanding the coupling effects of water, carbon, and energy cycles in terrestrial ecosystems. Multiple years of eddy covariance (EC) tower ET measurements at five representative wetland ecosystems in the subtropical Big Cypress National Preserve (BCNP), Florida (USA) provide a unique opportunity to assess the performance of the Moderate Resolution Imaging Spectroradiometer (MODIS) ET operational product MOD16A2 and upscale tower measured ET to generate local/regional wetland ET maps. We developed an object-based machine learning ensemble approach to evaluate and map wetland ET by linking tower measured ET with key predictors from MODIS products and meteorological variables. The results showed MOD16A2 had poor performance in characterizing ET patterns and was unsatisfactory for estimating ET over four wetland communities where Nash-Sutcliffe model Efficiency (NSE) was less than 0.5. In contrast, the site-specific machine learning ensemble model had a high predictive power with a NSE larger than 0.75 across all EC sites. We mapped the ET rate for two distinctive seasons and quantified the prediction diversity to identify regions easier or more challenging to estimate from model-based analyses. An integration of MODIS products and other datasets through the machine learning upscaling paradigm is a promising tool for local wetland ET mapping to guide regional water resource management.

Remote sensing inversion characteristic and driving factor analysis of wetland evapotranspiration in the Sanmenxia Reservoir area, China

Abstract Evapotranspiration in the hydrologic cycle realizes the energy and water transport in the atmosphere. Evapotranspiration differences concerning land-use types provide data for studying the evapotranspiration of river basins. To investigate the evapotranspiration in the reservoir under artificial regulation, we selected the river basin in the Sanmenxia Reservoir as the study area. Data sources are two-period Landsat8 OIL_TIRS remote sensing images during the growing season of wetland plants. Based on meteorological data in this river basin, we investigated the evapotranspiration differences of different land-use types using the Surface Energy Balance Algorithm for Land model. The FAO Penman–Monteith formula verified the remote sensing inversion results. Analysis shows that significant differences were manifested between wetland and non-wetland landscapes in evapotranspiration among different land-use types. Non-wetland landscapes accounted for about 97.23% of the river basin's total area, but their daily average evapotranspiration was only 7.26 mm/d. Those of wetland landscapes were 2.77% and 12.17 mm/d. In this river basin, the differences between the wetland and non-wetland landscapes in evapotranspiration are mainly associated with plant diversity, vegetation coverage and surface temperature (beyond other driving factors like meteorological and hydrological solar radiation factors).

土地利用/覆被变化扎龙湿地蒸散发量及生态需水量的遥感估算

地表蒸散发量是影响湿地水热平衡的主要因素，也是水分损失的主要途径，对湿地生态需水量的合理确定和水资源的有效管理具有重要意义。借助遥感和GIS技术，利用2002、2010、2016年34景Landsat影像，基于时序NDVI数据对湿地下垫面物候特征的定量表征，准确获取了扎龙湿地保护区3个时期土地利用/覆被的动态变化信息。选用物理基础较好且应用广泛的SEBAL模型，估算了湿地的瞬时蒸散发量，并结合站点气象数据，实现了湿地蒸散发量在时间尺度上的扩展，分别得到日、月、年尺度的湿地蒸散发量，深入探究了扎龙湿地蒸散发的时空分布特征；最后从湿地湖泡需水量、植物需水量及生物栖息地需水量3个方面，定量估算出扎龙湿地3个时期的现状生态需水量。研究发现：扎龙湿地的土地覆被类型主要以芦苇沼泽、草地和耕地为主，其中芦苇沼泽分布占绝对优势，且2002-2016年持续增加了205.82 km²；草地、耕地呈持续减少态势，分别减少了119.35 km²和95.96km²，表明2002-2016年扎龙湿地生态系统呈恢复态势；湿地保护区蒸散发量年内均大致呈单峰型分布，符合夏季 > 春季 > 秋季 > 冬季的规律，在年际上呈现明显的递增趋势，年蒸散发量由2002年的518.87mm增加到2016年的625.98mm，增加了20.64%。为满足湿地内的生态消耗，总体上2002-2016年湿地的生态需水量也相应的增加，保护区适宜生态需水量的变动范围为5.40亿-7.08亿m³，可以维持湿地湖泊、植被、动植物栖息地的健康态势。维持核心区健康状态的最小生态需水量变化范围为2.71亿-3.32亿m³。随着遥感数据时空分辨率的提高，基于蒸散发量反演的湿地生态需水量估算将更加实用和准确，为湿地保护区制定科学合理的补水方案提供有效的技术支撑。;Surface evapotranspiration is a main factor influencing wetland water-heat balance and a main way of water loss. It has important significance for the reasonable determination of ecological water demand in wetlands and the effective management of water resources. With the help of remote sensing and GIS technology, the quantitative characterization of the phenological characteristics of the underlying surface of Zhalong wetland based on temporal NDVI data was made by using Landsat images of 34 scenes in 2002, 2010 and 2016. At the same time, the dynamic change information of land use/cover in three periods of the wetland reserve was obtained accurately. The SEBAL model with good physical foundation and wide application was selected to estimate the instantaneous evapotranspiration of the wetland. By combining with the meteorological data of nearby hydrographic stations, the temporal expansion of evapotranspiration of the wetland was realized. The daily, monthly and annual evapotranspiration of Zhalong wetland was obtained, and the spatio-temporal distribution characteristics of evapotranspiration in Zhalong wetland were deeply investigated. At last, the present ecological water demand of Zhalong wetland in three periods was quantitatively estimated from three aspects:water demand of wetland lake bubble, water demand of plants, and water demand of biological habitat. The results indicated that the land cover types of Zhalong wetland were mainly reed marshes, grasslands and cultivated land, among which reed marshes occupied the absolute dominance, increased by 205.82 km² continuously from 2002 to 2016. Grassland and cultivated land decreased by 119.35 km² and 95.96 km², respectively, indicating that Zhalong wetland ecosystem showed a recovery trend from 2002 to 2016. The annual evapotranspiration of the wetland reserve presented a roughly single-peak distribution in the three years, which was consistent with the summer > spring > autumn > winter. The annual evapotranspiration increased significantly from 518.87 mm in 2002 to 625.98 mm in 2016, by an increase of 20.64%. In order to meet the ecological consumption in the wetland, the total ecological water demand of the wetland increased correspondingly from 2002 to 2016. The range of the appropriate ecological water demand of the wetland reserve was 540 million m³ -708 million m³, which could maintain the health of the lakes, vegetation, animal and plant habitats in the wetland. The minimum ecological water demand for maintaining the health of the core area varied from 271 million m³ to 332 million m³. With the improvement of spatial and temporal resolution of remote sensing data, the estimation of wetland ecological water demand based on evapotranspiration inversion will be more practical and accurate, providing effectively technical support for the formulation of scientific and reasonable water rehydration schemes in wetland reserves.

Seasonal and interannual variability of surface energy fluxes and evapotranspiration over a subalpine horizontal flow wetland in China

Jiuzhaigou Valley, a subalpine river valley located in the transition zone between the Tibetan Plateau and the Sichuan Basin, is characterized by fragile ecosystems, strong climate change, and high-intensity human activities which might have changed the energy and water exchange of the wetlands. However, little is known about the seasonal and interannual variability of the surface fluxes and their driving forces in these wetlands owing to the lack of long-term continuous observations. We studied the dynamics of surface fluxes and their controlling factors based on the five-year data collected from July 2013 to April 2019. Our results showed that: (1) the dominant turbulent flux in this ecosystem shifted from sensible heat flux (H) in the frozen period to latent heat flux (LE) in the non-frozen period, especially in the growth period. This fluctuation, which was also reflected by Bowen ratio, highlighted the seasonality of precipitation in the monsoon climate. (2) The energy partitioning with each year was similar across years: LE accounted for approximately 58% of the net radiation, while H accounted for 41% and ground heat flux accounted for 1%. (3) Although the annual precipitation fluctuated between 870 mm and 1089 mm, the interannual fluctuations in evapotranspiration (ET) were less than 41 mm. (4) The wetland ET was predominantly driven by atmospheric demand and was limited to some extent by physiological factors. We then concluded that official management efforts by the local government to increase vegetation cover as well as climate change may lead to an increase in wetland ET, and this change will likely affect local hydrology, climate and the existence of this unique hydrological landscape.

Responses of Alpine Wetlands to Climate Changes on the Qinghai-Tibetan Plateau Based on Remote Sensing

The alpine wetlands in QTP (Qinghai-Tibetan Plateau) have been profoundly impacted along with global climate changes. We employ satellite datasets and climate data to explore the relationships between alpine wetlands and climate changes based on remote sensing data. Results show that: 1) the wetland NDVI (Normalized Difference Vegetation Index) and GPP (Gross Primary Production) were more sensitive to air temperature than to precipitation rate. The wetland ET (evapotranspiration) across alpine wetlands was greatly correlated with precipitation rate. 2) Alpine wetlands responses to climate changes varied spatially and temporally due to different geographic environments, variety of wetland formation and human disturbances. 3) The vegetation responses of the Zoige wetland was the most noticeable and related to the temperature, while the GPP and NDVI of the Qiangtang Plateau and Gyaring-Ngoring Lake were significantly correlated with both temperature and precipitation. 4) ET in the Zoige wetland showed a significantly positive trend, while ET in Maidika wetland and the Qiangtang plateau showed a negative trend, implying wetland degradation in those two wetland regions. The complexities of the impacts of climate changes on alpine wetlands indicate the necessity of further study to understand and conserve alpine wetland ecosystems.

Evaluation of Remote-Sensing based Estimates of Actual Evapotranspiration over (Diverse Shape and Sized) Palmiet Wetlands

Accurately quantifying actual evapotranspiration (ETa) over wetlands is important for the improved management of these ecosystems, since 65% of them are threatened by clearing or drainage in South Africa. This study evaluated a range of available estimates of ETa over six palmiet wetlands, which are key ecological structures in terms of water regulation and sediment trapping. The research compared three remote sensing based products (a local product, FruitLook, and two global data products, MOD16 ET and EEFlux) across different rainfall years (2008 to 2019). Their outputs were validated, where possible, with limited ground-based scintillometer data on the Krom palmiet wetland, which indicated that MOD16 and EEFlux were most representative of ground-based measurements. We also compared the small pixel size EEFlux data over three wetlands with ETa over increasing buffers of land cover (100, 500, 1000 m) in order to validate the perception of these wetlands being high water users. While larger wetlands had slightly higher evaporative demands than adjacent areas, ETa over a small wetland was similar to neighboring land cover. The results indicate that palmiet wetland ETa is highly variable and dependent on external factors such as climate, wetland size and seasonality.

Artificial intelligence based approaches to evaluate actual evapotranspiration in wetlands

Wetlands are extraordinary ecosystems and important climate regulators that also contribute to reduce natural disaster risk. Unfortunately, wetlands are declining much faster than forests. The safeguarding of the wetlands also needs knowledge of the dynamics that control the water balance of these environments. Therefore, an accurate estimation of evapotranspiration in wetlands is an essential task.When adequate experimental data are available, some algorithms deriving from Artificial Intelligence research represent a promising alternative to the most common estimation techniques.In this study, starting from daily measurements of climatic variables such as net solar radiation, depth to water, wind speed, mean relative humidity, maximum temperature, minimum temperature, and mean temperature, using the Random Forest, Additive Regression of Decision Stump, Multilayer Perceptron and k-Nearest Neighbors algorithms, 24 estimation models, different in input variables, have been developed and compared. The data have been provided by USGS. They have been obtained from a measuring site in wetlands of Indian River County, Florida using the eddy-covariance technique.The accuracy of these models based on AI algorithms remains good even if the number of input variables is reduced from 7 to 3. Net solar radiation, mean temperature and mean relative humidity or wind speed measurements allow obtaining a sufficiently accurate estimation model. Random Forest and k-Nearest Neighbors provide slightly better performance than Additive Regression of Decision Stump and Multilayer Perceptron. The analyzed models show in most cases the lowest accuracy in the range 2–4 mm/day, while the highest accuracy is obtained in the ranges 0–2 mm/day and 6–8 mm/day, with the exception of the models based on the Additive Regression, which show similar levels of accuracy in the different considered sub-intervals.

Response of Wetland Evapotranspiration to Land Use/Cover Change and Climate Change in Liaohe River Delta, China

This study aims to investigate the effects of land use/cover change (LUCC) and climate change on wetland evapotranspiration (ET), and to identify the importance of the main effect factors in the spatiotemporal dynamics of ET. In the wetland of Liaohe River Delta, China, the ET of eight growing seasons during 1985–2017 was estimated using the surface energy balance algorithm for land (SEBAL) model with Landsat and meteorological data. Results show that the average relative error of regional ET estimated by the SEBAL model is 9.01%, and the correlation coefficient between measured and estimated values is 0.61, which indicates that the estimated values are reliable. This study observed significant spatial and temporal variations in ET across the region of interest. The distribution of the average and relative change rate of daily ET in the study area showed bimodal characteristics, that is, the lowest trough occurred in 2005, whereas crests occurred in 1989 and 2014. Simultaneously, the daily ET varied with the land use/cover area. Regional daily ET displays highly heterogeneous spatial distribution, that is, the ET of different land uses/cover types in descending order is as follows: water body, wetland vegetation, non-wetland vegetation, and non-vegetation (except water area). Therefore, the spatial pattern of ET is relevant to the land use/cover types to some extent. In addition, the temporal variation of wetland ET is closely related to landscape transformation and meteorological factor change. A strong correlation was found between ET and the weighted values of meteorological factors, with a correlation coefficient of 0.69. Meanwhile, the annual fluctuations of daily ET and the weighted values were relatively similar. Therefore, the findings highlight the importance of using cheap and readily available remote sensing data for estimating and mapping the variations in ET in coastal wetland.

Estimación espacial de la evapotranspiración mediante imágenes de satélite Landsat y el modelo SEBAL en el humedal Paraíso - Huacho

Estimación espacial de la evapotranspiración mediante imágenes de satélite Landsat y el modelo SEBAL en el humedal Paraíso - Huacho Spatial estimation of evapotranspiration by Landsat satellite images and the SEBAL model in the Paraíso wetland – Huacho Erick Garcia y Miguel Ángel Lleellish Autoridad Nacional del Agua (ANA), Calle diecisiete Nº 355, Urb. El Palomar - San Isidro Lima, Perú. Ministerio del Ambiente (MINAM), Calle Los Nogales Nº 236, San Isidro Lima, Perú. DOI: https://doi.org/10.33017/RevECIPeru2011.0026/ RESUMEN Los humedales están entre los ecosistemas más valiosos del planeta porque albergan una gran biodiversidad. Además, brindan muchas funciones relacionada con los recursos hídricos, como ser fuentes naturales de agua, reguladores del ciclo hidrológico y el clima, zonas de descarga y recarga de acuíferos, barreras naturales contra las inundaciones y la intrusión marina en los acuíferos costeros, entre otras. El conocimiento de las demandas ecológicas de agua en los humedales es de vital importancia para incluir a estos ecosistemas en una gestión integrada de los recursos hídricos. En este estudio, se presentan los resultados obtenidos en la estimación de la evapotranspiración en el humedal Paraíso de Huacho, mediante la aplicación del modelo de balance de energía superficial conocido como SEBAL a una subescena del satélite Landsat 7 ETM+ con fecha 04 de abril de 2000, la cual coincide con el inicio de la época de afloramiento en el humedal. La estimación de la evapotranspiración actual (ETa) estuvo en el rango de 0-6.3 mm/día, con los valores más bajos en las zonas desérticas y las parcelas en descanso, y los valores más altos en los espejos de agua y la vegetación del humedal. El humedal evapotranspira en altas tasas, con una ETa máxima de 4.9 mm/día y un valor medio de 4.6 mm/día para la fecha analizada. La evapotranspiración de referencia (ETo) estimada mediante el método FAO Penman-Monteith, para la fecha de paso del satélite, fue de 3.9 mm/día y con la inclusión del coeficiente del cultivo (Kc) dio valores de 4.2 y 4.3 mm/día, para la vegetación del humedal y para el cultivo de alfalfa respectivamente. Estos dos valores están cerca a la ETa de 4.6 y 3.9 mm/día estimada por SEBAL para la misma vegetación y que se encuentra en condiciones optimas de crecimiento. Los resultados obtenidos demuestran que es factible estimar la ETa mediante imágenes de satélite con un error medio relativo menor al 10%. Descriptores: teledetección, sensoramiento remoto, evapotranspiración, humedales, EBAL. ABSTRACT Wetlands are among the most valuables ecosystems in the world, because support a great biodiversity. Besides, provides many hydrological functions such as surface water sources, regulation of hydrological cycle, weather and aquifer recharge and discharge zones, they are also natural barriers to flooding and sea intrusion in coastal aquifer. The knowledge of the environmental water demands for wetlands is of vital importance to include these ecosystems in water resources management. In this study, the results obtained in the evapotranspiration estimation in the Paraíso wetland are presented. The results were obtained by the application of the surface energy balance model known as SEBAL over a sub scene of Landsat ETM+ satellite dated April 8, 2000, this coincide with the beginning of upwelling season in the wetland are presented. Actual evapotranspiration (ETa) estimates was in the range of 0-6.3 mm/day, the lowest values were in desert and fallow land areas and the highest values were in surface water bodies and wetland vegetations. The wetland evapotranspiration rate was high, with a maximum ET of 4.9 mm/day and average value of 4.6 mm/day. The reference evapotransporation (ETo) estimated in the satellite overpass date was 3.9 mm/day and adjusted with the crop coefficient (Kc) was 4.2 y 4.3 mm/day, for wetland vegetation and alfalfa crops. This values area close to the ETa of 4.6 y 3.9 mm/day estimated by SEBAL for the same vegetation in healthy conditions. The results obtained shows that are feasible to estimate the ETa by satellite images with a relative mean error lower than 10%. Keywords: remote sensing, evapotranspiration, wetlands, SEBAL.

Evapotranspiration of a willow cultivar (Salix miyabeana SX67) grown in a full-scale treatment wetland

Since woody plants like willow are used increasingly in treatment wetlands, there is a growing need to characterize their ecophysiology in these specific growing conditions. For instance, evapotranspiration (ET) can be greatly increased in wetlands, due to factors like high water availability as well as oasis and clothesline effects. Few studies report willow ET rates measured in full-scale constructed wetland conditions, and fewer still in a temperate North-American climate. The objective of this study was to measure and model evapotranspiration of a commonly used willow cultivar, Salix miyabeana (SX67), to provide the ET rates and crop coefficient for this species. During two growing seasons, we studied a 48 m2 horizontal subsurface flow willow wetland located in eastern Canada, irrigated with pretreated wood preservative leachate. Over two seasons, from May to October, we measured a mean monthly evapotranspiration rate of 22.7 mm/day (16.5 mm/d modelled), for a seasonal cumulative ET of 3954 mm (2897 mm modelled) and a mean crop coefficient of 6.4 (4.2 modelled). Both the evapotranspiration results and leaf area index (LAI) were greater than most results reported for open field willow plantations. Maximal stomatal conductance (G¯s) was higher than that expected for deciduous trees and even for wetland plants, and mean values correlated well with temperature, solar radiation, relative humidity and day of the year. We demonstrated that an ET model using G¯s, LAI and water vapor pressure deficit (VPD) as parameters could predict the evapotranspiration rate of our wetland. This simplification of traditional ET models illustrates the absence of evapotranspiration limitations in wetlands. Furthermore, this study also highlights some factors that can enhance ET in treatment wetlands. Our results should both improve the design of treatment wetlands using willows, and provide a simple ET predictive model based on major evapotranspiration drivers in wetlands.

Evapotranspiration partitioning using a simple isotope‐based model in a semiarid marsh wetland in northeastern China

AbstractPartitioning evapotranspiration (ET) into evaporation (E) and transpiration (T) in wetlands is important for understanding the hydrological processes in wetlands and the contribution of wetland ET to local and regional water cycling and for designing effective wetland management strategies. Stable water isotopes are useful in the application of ET partitioning through the evaluation of the isotopic compositions of E (δE), T (δT), and ET (δET) obtained from observation or modelling methods. However, this approach still suffers from potentially large uncertainties in terms of estimating the isotopic endmembers. In this study, we modified the traditional isotope‐based ET partitioning methods to include leaf‐level biological constraints to separately estimate the relative contributions of T from Scirpus triqueter and Phragmites australis and the relative contributions of E from the standing surface water in a semiarid marsh wetland in northeastern China.The results showed that although the δT values of S. triqueter and P. australis were rather similar, the mean δT values of the 2 species were different from the values of δE, making it possible to distinguish the relative contributions of E and T through the use of isotopes. The simulation of leaf water using a non‐steady‐state model indicated obvious deviations in leaf water enrichment (δLb) from isotopic steady states for both species, especially during early mornings and evenings when relative humidity was highest. The isotopic mass balance showed that E accounted for approximately 60% of ET, and T from S. triqueter and P. australis each contributed approximately 20% to ET; this implied that the transpiration of one reed was equivalent to that of 5.25 individuals of S. triqueter. Using the estimated ratio of T to ET and the measured leaf transpiration, the total ET was estimated to be approximately 10 mm day−1. Using the NSS‐Tr method, the estimated ET was higher than the water loss calculated from the water level gauge. This indicated that the river water and surrounding groundwater were the sources of the marsh wetland, with a supply rate of 8.3 mm day−1.

Partitioning daily evapotranspiration from a marsh wetland using stable isotopes in a semiarid region

Abstract The hydrological process of evapotranspiration (ET) plays an important role in water circulation in wetlands, and understanding the contributions of wetland ET to local and regional water cycles can help in designing effective wetland management strategies. In this paper, a numerical model, vegetation indexes, and stable isotopes were integrated to partition ET in the Momoge Wetland to understand hydrological processes and calculate the contribution of wetland ET to local hydrological cycling. The results of the non-steady state (NSS) model indicated clear deviation of leaf water enrichment (δLb) from an isotopic steady state (ISS) for Phragmites australis, and the model accuracy improved particularly in the early morning and evening when air moisture was highest during the day. The isotopic mass balance showed that E and T contributed approximately 62% and 38% to ET, respectively. Using the estimated proportion of T to ET, in combination for the measured leaf transpiration, total ET was estimated at approximately 8.76 mm d−1. Additionally, the amount of ET clearly changed on an hourly scale, with most primarily occurring at approximately noon. Based on comparison among internationally important wetlands distributed in northeast China, the results in this study are reasonable and will provide theoretical data for wetland water resources management.

Wetland Evapotranspiration: Eddy Covariance Measurement in the Biebrza Valley, Poland

This paper presents eddy covariance measurements of evapotranspiration and sensible heat flux in wetland area. The rate of evapotranspiration is characterized by a distinct seasonal pattern and assumes the highest values during summer. From April to September, the latent heat flux is characterized by a distinct diurnal pattern with the highest average values (at the noon hours) at a level of ca 200 W·m−2. Moreover, in the period from June to August the values of latent heat flux far outweigh those of sensible heat flux (the Bowen ratio in the noon hours ranging between 0.4 and 0.6) and account for 50–60 % of radiation balance. The average daily totals of evapotranspiration vary from about 0.5 mm·d−1 during the winter months to about 3–3.5 mm·d−1 in summer.

Evapotranspiration from drained wetlands with different hydrologic regimes: Drivers, modeling, and storage functions

We tested whether the current understanding of insignificant effect of drainage on evapotranspiration (ET) in the temperate region wetlands applies to those in the subtropics. Hydro-climatic drivers causing the changes in drained wetlands were identified and used to develop a generic model to predict wetland ET. Eddy covariance (EC)-based ET measurements were made for two years at two differently drained but close by wetlands, a heavily drained wetland (SW) (97% reduced surface storage) and a more functional wetland (DW) (42% reduced storage). Annual ET for more intensively drained SW was 836 mm, 34% less than DW (1271 mm) and the difference was significant (p = 0.001). This difference was mainly due to drainage driven differences in inundation and associated effects on net radiation (Rn) and local relative humidity. Two generic daily ET models, a regression model (MSE = 0.44 mm2, R2 = 0.80) and a machine learning-based Relevance Vector Machine (RVM) model (MSE = 0.36 mm2, R2 = 0.84), were developed with the latter being more robust. The RVM model can predict changes in ET for different restoration scenarios; a 1.1 m rise in drainage level showed 7% increase ET (18 mm) at SW while the increase at DW was negligible. The additional ET, 28% of surface flow, can enhance water storage, flood protection, and climate mitigation services at SW compared to DW. More intensely drained wetlands at higher elevation should be targeted for restoration for enhanced storage through increased ET. The models developed can predict changes in ET for improved evaluation of basin-scale effects of restoration programs and climate change scenarios.

Evapotranspiration Partitioning and Response to Abnormally Low Water Levels in a Floodplain Wetland in China

Evapotranspiration (ET) is an important component of the wetland water budget. Water level declines in Poyang Lake, the largest freshwater lake in China, have caused concerns, especially during low water levels. However, how wetland ET and its partitioning respond to abnormally low water levels is unclear. In this study, wetland ET was estimated with MODIS data and meteorological data. The wetland ET partitioning and its relationship with abnormally low water levels were analyzed for 2000–2013. The results showed that the water evaporation rate (Ewater) was larger than the land ET rate (ETland); theETland/Ewaterranged from 0.77 to 0.99. When the water level was below 12.8 m, the ET partition ratio was larger than 1, which indicates that wetland ET comes from land surface ET more than water evaporation. The negative standardized water level index (SWI) was used to represent an abnormally low water level in the wetland. Although the monthly wetland ET decreased as the negative SWI decreased,ETlandwas higher than the average under negative SWI conditions from September to December, when the water level decreased. The abnormally low water level induced more water loss from the land surface, especially when the water level decreased, which reduced the available water resources along the wetland shore.

Análise da evapotranspiração por wavelet de Morlet em área de Vochysia divergens Pohl no Pantanal

A variação tempo-espacial da evapotranspiração foi analisada por meio de wavelet de Morlet em uma floresta de Vochysia divergens Pohl (Vochysiaceae) localmente conhecida como Cambarazal no Pantantal, no estado do Mato Grosso, Brasil Esta área está inserida na planície fisiografia do Pantanal e é sazonalmente inundada. Foram coletadas variáveis micrometeológicas, como: saldo de radiação, radiação solar incidente, temperatura do ar e umidade relativa do ar. Com referencia à evapotranspiração a análise diária da série temporal por wavelet de Morlet foi satisfatória, possibilitando melhor compreensão na dinâmica da evapotranspiração em área alagável e sua relação com a temperatura do ar, umidade relativa do ar e radiação solar global. Conclui-se que ocorreram, durante a estação úmida, os maiores valores de evapotranspiração e maior intensidade de energia na alta escala de frequência devido provavelmente à maior disponibilidade de água em função da precipitação e inundação, e à radiação global.