Evapotranspiration Components Research Articles

Partitioning evapotranspiration in a tallgrass prairie using micrometeorological and water use efficiency approaches under contrasting rainfall regimes

Partitioning evapotranspiration (ET) into evaporation (E) and plant transpiration (T) is key to understanding ecosystem responses to rainfall variability resulting from climate change. The goal of this study was to quantify T and E using eddy covariance (EC) flux measurements in a tallgrass prairie in consecutive growing seasons with contrasting rainfall regimes. The field measurements were conducted at the National Ecological Observatory Network (NEON) KONZ site, in Kansas, U.S., during the growing seasons of 2017, 2018 and 2019. The ET partitioning was performed using an approach based on the concept of the underlying water use efficiency (uWUE). To evaluate the uWUE approach, we compared daily E estimates obtained from the uWUE with E observations provided by microlysimeters (ML). Green chromatic coordinate (GCC) was used to monitor the vegetation dynamics. In the 2017 growing season, the total rainfall was 23.1% below the site’s long-term average cumulative precipitation. On the other hand, in 2018 and 2019 the accumulated growing season precipitations were 7.2% and 40.2%, respectively, above the long-term precipitation average. The relationship between uWUE approach and ML E measurements showed a Pearson correlation coefficient (r) of 0.42 and a root mean square error (RMSE) of 0.58 mm d−1. The lowest T/ET average value (0.50) was observed in the 2017 growing season, while the largest T/ET average (0.65) was observed in 2018. The correlations between GCC and T/ET were reduced during the growing seasons that experienced drought periods. Air temperature was the main environmental driver of T/ET during the wet growing seasons (r = 0.49 and 0.72). The subsurface soil moisture (0.45 m) was the main environmental driver of T/ET during a dry growing season (r = 0.41). These results demonstrate that the precipitation variability not only has a direct impact on the ET components but also modulates the response of those components to other environmental drivers. Since ET partitioning studies at the ecosystem scale are still scarce, our results can improve T/ET and water use efficiency estimates in long-term modelling studies. This will help to better understand how ET in ecosystems will respond to global warming and increased CO2 concentration during wet and dry growing seasons.

Seasonal evapotranspiration over an invader vegetation (Pteridium aquilinum) in a degraded montane grassland using surface renewal

Study regionCathedral Peak Research Catchments, uKhahlamba Drakensberg mountain range, South Africa. Study focusThe focus was to determine the seasonal pattern of evapotranspiration (ET) over a bracken canopy, which is a product of degradation within the montane grasslands of the uKhahlamba Drakensberg mountains. Surface renewal (SR) was investigated as a viable alternative to eddy covariance for long-term estimation of ET within a remote high rainfall montane landscape. The SR dissipation method was used to observe ET over the bracken canopy for 23 months, across two consecutive years with variable seasonal rainfall timing and amounts. Besides ET, rainfall and energy flux components were observed. New hydrological insights for the regionThe SR dissipation method was shown to be adequate for the long-term estimation of evapotranspiration over a bracken canopy within a remote high summer rainfall montane landscape. The bracken canopy was found to have a distinct seasonal cycle. Autumn was most sensitive to rainfall amount and timing, as late annual rainfall during autumn decreases bracken ET compared to higher summer rainfall followed by a lower autumn rainfall. Comparing the evapotranspiration of bracken from this study to the evapotranspiration of natural grassland in previous studies, the largest difference in evapotranspiration between the canopies occurs in winter.

Estimation of the spatial and temporal variability of evapotranspiration components in a vineyard with the two source energy balance model (TSEB) using both thermal airborne and the fusion of Sentinel 2 and 3 imagery

ISHS IX International Symposium on Irrigation of Horticultural Crops Estimation of the spatial and temporal variability of evapotranspiration components in a vineyard with the two source energy balance model (TSEB) using both thermal airborne and the fusion of Sentinel 2 and 3 imagery

Development of a three-source remote sensing model for estimation of urban evapotranspiration

Estimation of urban evapotranspiration (ET) is meaningful for evaluating the urban heat island effect and promoting urban water conservation. While multi-source satellite-based ET models for farmland and natural ecosystems have been developed, these models lack the object-oriented solutions for the urban areas. In view of this, the present study proposed a Three-source Remote sensing model for Urban areas (TRU) to simulate the urban ET, which can discriminate between urban soil evaporation, vegetation transpiration, and impervious surface evaporation. The new parameterization scheme proposed herein is characterized by the theory of complementary relationship to estimate the urban soil evaporation. Evaporation losses in the impervious areas were independently estimated in accordance with the distribution of urban land use and land cover (LULC). The developed TRU model was evaluated for 63 cloud-free test days in Tianjin, China by using 30 m Landsat Operational Land Imager (OLI)/Enhanced Thematic Mapper Plus (ETM+) images. The outcomes of this study revealed a root-mean-square-error (RMSE) of 40.2 W/m2 and a bias of 10.8 W/m2 compared with the two eddy correlation (EC) observations for the instantaneous latent heat flux (LE) simulation. Moreover, the RMSE and bias were 0.092 and −0.023, respectively in simulating the vegetation latent heat flux fraction (LEv/LE) when verified with respect to the stable water isotope measurements. Due to limited water availability, the impervious urban surface evaporation magnitude was found quite low with minimal variation on different test days. The results emphasize the importance of coupling LULC information in the urban ET modeling conceptualization. Certainly, the TRU model improved the ET simulation accuracy in urban areas and could facilitate the mapping of urban ET components at high spatial resolution.

Estimating evapotranspiration using remotely sensed solar-induced fluorescence measurements

Terrestrial evapotranspiration (ET) is a critical component of the land surface and its accurate estimation is crucial in understanding the global water and energy budgets. Current large-scale ET estimation models depend on remotely sensed data products of meteorological conditions and vegetation phenology, but high uncertainty remains to correctly represent ecological factors, which are regulated by biochemistry. In recent years, solar-induced fluorescence (SIF), a proxy for photosynthesis, has been extensively used in different ecological research and is conceived to be of great potential for ET estimation to constrain the transpiration flux, which is the significant component of ET. So far, most SIF-based ET estimation methods are achieved via empirical methods, which lack a solid physical foundation. In this work, we estimated ET by combining SIF and meteorological variables with Fick's law and an optimal stomatal behavior model and validated the model across different eddy-covariance flux stations around the globe. The model showed overall good performance across different ecosystems and when compared with other remote sensing-based ET models, such as the Priestley Taylor-JPL (PT-JPL) model, the Moderate Resolution Imaging Spectroradiometer (MODIS)-ET products, and a simple empirical linear SIF-ET model, the RMSE of estimated ET of the model proposed in this paper demonstrated better performance. The model we proposed here can be potentially extended for a reliable ET estimation at a global scale.

A global synthesis of transpiration rate and evapotranspiration partitioning in the shrub ecosystems

Transpiration (T) is a fundamental process in understanding the ecophysiology of plants, and it is the dominant component of evapotranspiration (ET) in the terrestrial water cycle. Although previous studies have examined T characteristics of shrub ecosystems in some regions, global-scale synthesis that integrates the spatial variations of T, ET and ratio of T to ET (T/ET) and the associated influences of bio-/abiotic factors in the shrub ecosystems is currently lacking. In this study, we synthesized and analyzed T rate, ET rate and T/ET of the shrub ecosystems from the peer-reviewed articles using field observations around the world. These studies were mainly distributed in drylands with aridity index (ratio of precipitation to potential ET) < 0.65, which accounted for 86.4% of the study locations. Globally, the mean daily T and ET rates of shrubs were 1.5 ± 1.0 mm d−1 and 2.4 ± 0.8 mm d−1, with coefficient of variation of 63.2% and 36.2% among the study locations, respectively. Mean T/ET of the shrubs over the growing season was 0.54 ± 0.14, which was generally lower compared with forest, grassland and cropland ecosystems. The T rate of shrubs was positively related to shrub age, shrub height, leaf area index, and vegetation coverage (p < 0.05), and the effects of biotic factors on T rate were stronger compared with abiotic factors. The ET rate of shrubs was positively related to aridity index, long-term annual mean precipitation, mean soil water content, as well as shrub height and vegetation coverage (p < 0.05). By contrast, the effects of biotic factors on variations of shrub T/ET were weaker than those of abiotic factors, and the T/ET of shrubs was negatively related to aridity index, long-term annual mean precipitation and mean soil water content, but positively related to latitude (p < 0.05). This study is an important supplement of our knowledge gap in terrestrial water cycle, and the findings suggest that T accounted for about half of the water into atmosphere from shrub ecosystems, and the variations of T rate of shrubs were mainly controlled by biotic factors, whereas ET rate and T/ET was mainly affected by abiotic factors.

Environmental and canopy conditions regulate the forest floor evapotranspiration of larch plantations

Integrated forest-water management focusing on forest-water coordination is an important way to alleviate water use conflicts among forests and other sectors in vast dryland regions. Forest floor evapotranspiration (FE), which is an important component of forest evapotranspiration, accounts for a large proportion of the water consumed in arid forests. Elucidating how environmental and canopy conditions impact FE has important significance for guiding integrated forest-water management in a changing environment.

An evapotranspiration deficit-based drought index to detect variability of terrestrial carbon productivity in the Middle East

The primary driver of the land carbon sink is gross primary productivity (GPP), the gross absorption of carbon dioxide (CO2) by plant photosynthesis, which currently accounts for about one-quarter of anthropogenic CO2 emissions per year. This study aimed to detect the variability of carbon productivity using the standardized evapotranspiration deficit index (SEDI). Sixteen countries in the Middle East (ME) were selected to investigate drought. To this end, the yearly GPP dataset for the study area, spanning the 35 years (1982–2017) was used. Additionally, the Global Land Evaporation Amsterdam Model (GLEAM, version 3.3a), which estimates the various components of terrestrial evapotranspiration (annual actual and potential evaporation), was used for the same period. The main findings indicated that productivity in croplands and grasslands was more sensitive to the SEDI in Syria, Iraq, and Turkey by 34%, 30.5%, and 29.6% of cropland area respectively, and 25%, 31.5%, and 30.5% of grass land area. A significant positive correlation against the long-term data of the SEDI was recorded. Notably, the GPP recorded a decline of >60% during the 2008 extreme drought in the north of Iraq and the northeast of Syria, which concentrated within the agrarian ecosystem and reached a total vegetation deficit with 100% negative anomalies. The reductions of the annual GPP and anomalies from 2009 to 2012 might have resulted from the decrease in the annual SEDI at the peak 2008 extreme drought event. Ultimately, this led to a long delay in restoring the ecosystem in terms of its vegetation cover. Thus, the proposed study reported that the SEDI is more capable of capturing the GPP variability and closely linked to drought than commonly used indices. Therefore, understanding the response of ecosystem productivity to drought can facilitate the simulation of ecosystem changes under climate change projections.

Evapotranspiration Components Dynamic of Highland Barley Using PML ET Product in Tibet

Highland barley is the unique germplasm resource and dominant crop in Tibet with low-level precipitation and a severe shortage of available water resources. Understanding the characteristics and dynamics of evapotranspiration (ET) components (vegetation transpiration (Ec), soil evaporation (Es), and canopy interception evaporation (Ei)) of highland barley can help better optimize water management practices. The seasonal and interannual variations in ET components of highland barley were investigated using the PML-V2 ET product during 2001–2020. The results suggested that Es was the most important ET component and accounted for 77% of total ET for highland barley in Tibet. ET components varied obviously over the altitude, Es, and Es/ET ratio; a decreasing trend was observed with the increase in altitude from 3500 m to 3800 m and then this changed to an increasing trend until reaching the altitude of 4100 m, while Ec, Ei, and their ratios presented an opposite changing pattern to that of Es. Seasonal variation in daily ET components of highland barley displayed a parabolic pattern, peaked in August, while the temporal distributions differed considerably among different ET component ratios. The seasonal variations in ET components were correlated significantly with air temperature, relative humidity, and precipitation, while ET components ratios were more influenced by the environment, irrigation practice, and management rather than meteorological variables. Es and its ratio in highland barley decreased significantly during 2001–2020, while the Ec/ET ratio generally showed an opposite trend to the Es/ET ratio, and Ei and its ratio presented an insignificantly decreasing trend. The interannual variations in ET components were not correlated significantly with meteorological variables, while Ei was more influenced by meteorological variables, especially the precipitation characteristics.

Uncertainties in partitioning evapotranspiration by two remote sensing-based models

Accurate estimation of evapotranspiration (ET) and the partitioning of ET into transpiration (Tr), soil evaporation (Es) and interception (Ei) is critical to understand water cycle and land-atmosphere feedback. In this study, we evaluated the performances of two remote sensing-based ET models at multiple scales, and analyzed the uncertainties in ET partitioning due to the model structures. These two models were Simple Terrestrial Hydrosphere Model (SiTH) developed by our team and the Global Land Evaporation Amsterdam Model (GLEAM). As far as ET were concerned, the two models exhibited relatively good performances at different scales. However, it was found that GLEAM performed relatively poor at evergreen broadleaf forest (R2 = 0.34; RMSE = 0.87 mm day−1; NSE = −0.28). In addition, the seasonal pattern of simulated ET by GLEAM at the tropical rainforest was not consistent with the observations. Furthermore, great discrepancies in ET partitioning were observed between the two models. Generally, GLEAM tended to underestimate Es (slope = 0.02; R2 = 0.004), and overestimate Tr (slope = 1.51; R2 = 0.78) compared to the observations. The underestimations of Es by GLEAM may partly be due to the ignorance of soil evaporation under vegetation canopy. On the contrary, SiTH displayed relatively good performances in estimations of Es (slope = 0.76; R2 = 0.62) and Tr (slope = 0.98; R2 = 0.51). However, both of the two models failed to properly simulate Ei, although GLEAM (slope = 0.55; R2 = 0.83) performed slightly better than SiTH (slope = 0.40; R2 = 0.95). Global multi-year average ratios of Tr, Es, and Ei to ET for GLEAM and SiTH were 0.76, 0.09, 0.15 and 0.67, 0.25, 0.08 respectively. In future studies, it is important to investigate direct observations on different components of ET, especially on the interception, to improve our understanding on the ET processes.

Estimation of evapotranspiration of “soil-vegetation” system with a scheme combining a dual-source model and satellite data assimilation

Evapotranspiration (ET) is a key variable linking the energy and water exchanges between the land surface and the atmosphere. The strong energy exchanges between the soil and vegetation in the “soil-vegetation” system and the lack of reliable soil moisture products at fine spatial scales, especially for root zone soil moisture, to directly model the effects of water stress on ET estimates, make it difficult to estimate actual ET and its components (soil evaporation Es, vegetation transpiration Tc and rainfall interception Ei). In this paper, we presented a “Soil-Vegetation” EvapoTranspiration framework (SVET) by combining the dual-source Shuttleworth and Wallace (SW) physical model and satellite soil moisture data assimilation procedure. In the SVET model, net radiation for the soil-vegetation system was first partitioned among soil evaporation, vegetation transpiration and rainfall interception; then, soil moisture was simulated for different soil layers based on the water balance, providing a first guess estimate of soil moisture; after that, simulated soil moisture was improved by assimilating remotely sensed surface soil moisture to reduce the uncertainty of the simulated soil moisture; finally, Es, Tc and Ei estimates were obtained. The ET estimates by the SVET were evaluated against in situ measurements at three stations in the Heihe River Basin with different vegetation cover types (crop, grassland and forest). The overall correlation coefficient (R), root mean square error (RMSE) and bias were 0.931, 0.67 mm d−1 and 0. 07 mm d−1, respectively. For the ET components, the bias of the estimated ratio of Tc/(Es + Tc) is −11.4%. In addition, the SVET model showed outstanding performance, especially over irrigated areas, compared with the results from the original SW model without a soil moisture data assimilation scheme. The SVET model is very promising for applications of water use monitoring of ecosystem, especially for irrigated areas.

Smart Irrigation System Based on the Internet of Things and the Cloud

A water system is a technique for giving water to plants to grow and create. Water in plants or water systems is not a cutting-edge idea; it has been followed and applied from one century to another or decade to decade. Advances have developed in lockstep with time. At the point when we compare the 1980s and 2021, we see a sensational distinction in advances just as in the water system strategy. During the 1980s, the water system was accomplished utilizing furrows and wrinkles. A water system is a technique for providing water to the root zone at the ideal opportunity. Plants draw water from wet soil, and by the component of evapotranspiration (ET), plants come to pass water into the air while drawing supplements accessible in soil with water for root zone improvement. At the point when the stockpile of water in the root zone falls under a specific edge, plants can't draw supplements and water for sustenance. Thus, supply great water to the root zone before as far as possible is reached. This cutoff is controlled by the types of plants, soil, and environment. Since the edge cap changes relying upon the sort of plant. Logical booking requires the utilization of the proper volume of water at the fitting time frame and area inside the office. This requires consistent checking of soil dampness content at the root zone and the commencement of the water system as per a pre-modified timetable base on wear the idea of the plant, its turn of events, soil type, and environment. Accordingly, for logical water system booking, sensors should be planted close to the root zone in the dirt to get to the agent's dampness status. The signs created and recognized by soil dampness sensors should be prepared in a microcontroller for water system planning by predefined programming. The microcontroller ought to likewise be intended to hand off the sign to a far-off area where the siphoning and well framework for water system control is found. Also, the criticism of these sensors ought to be examined by the microcontroller as indicated by a foreordained program to end the water system relying upon the plant, its the degree of improvement, soil, and environment. This paper presents a cloud-based and web of things-based water system framework. This framework utilizes sensors to gather continuous water system information, stores information into the cloud, proprietor of information provides the order and suitable move is made on dependent on the outcome created.

CALCULATING EVAPOTRANSPIRATION FOR THE LAKE LADOGA CATCHMENT AREA

The paper evaluates the possibility of calculating evapotranspiration and gross primary production using a coupled biophysical Penman-Monteith-Leuning model for large catchment areas. In particular, the paper considers the application of the Penman-Monteith-Leuning model for the Lake Ladoga catchment. The theoretical foundations of the model,its flowchart, and the possibility of accessing it through the interface of the cloud platform for the analysis and processing of geospatial data Google Earth Engine are outlined. The model uses MODIS satellite images as input data, from which it receives the properties of the underlying surface. For meteorological data, the model uses the reanalysis model GLDAS. The land cover is classified according to the IBCG classification. Based on the Penman-Monteith-Leuning model, maps of the geospatial distribution of evapotranspiration and its constituent components (vegetation transpiration, soil evaporation, interception from vegetation canopy) and gross primary production in the Lake Ladoga catchment were obtained. The results indicate that evapotranspiration and gross primary production were the greatest in the south of the Lake Ladoga catchment, in areas of mixed forests. For the period from July 2002 to December 2017, there was no significant change in gross primary production, evapotranspiration and its components. For all components of evapotranspiration and gross primary production, seasonality associated with the growing season in the region is observed. The model outputs are consistent with the data on evaporation reported by other authors. The Penman-Monteith-Leuning model is hence fit for application to the Lake Ladoga catchment. The results of the study can be used for efficient water management, in particular for the reclamation of agricultural land in the study area.

Evapotranspiration partitioning and its interannual variability over a winter wheat-summer maize rotation system in the North China Plain

Partitioning of evapotranspiration (ET) is important for understanding surface-atmosphere interactions, hydrological cycle, and plant water use strategy. Here, we applied seven widely used eddy covariance (EC)-based methods and 15-year EC measurements in a winter wheat-summer maize rotation cropland in North China Plain to partition ET into soil evaporation (E) and plant transpiration (T). Then the two-stage theory of bare soil evaporation was employed to evaluate these partitioning methods. This innovative evaluation approach is particularly suitable for this kind of ecosystem, requires no direct measurements of ET components, and avoids spatial mismatching between the source areas of reference values and EC-based ET. Combining the two-stage theory and the meta-analysis, we found that among seven partitioning methods, only the Transpiration Estimation Algorithm (TEA) (hereafter, N18 method) utilizing a machine learning approach not only simulated the dynamics of 14-day transpiration fraction of ET (T/ET) quite well, but also yielded reliable 14-day and mean growing season magnitudes of T/ET for both crops. Furthermore, we developed a new partitioning method based on the stomatal slope parameter in the optimality-based unified stomatal optimization (USO) model. The newly developed method showed similar performances with N18 method on partitioning ET of both crops at our site. By using the N18 method and the newly developed method, we revealed that the multi-year mean growing season T/ET (± standard deviation) was 0.72 ± 0.03 and 0.77 ± 0.04 for maize and wheat, respectively. For the interannual variability of ET and its components, only T of maize increased significantly during 2005–2019 at our site. Moreover, it was found that E had the highest interannual variability followed by T and then T/ET for both crops.

Woody plant encroachment enhanced global vegetation greening and ecosystem water‐use efficiency

AbstractAimEncroachment of woody plants into grasslands and savannas (WPE) has been observed world‐wide. However, the general ecohydrological effects of this striking change in land cover are uncertain owing to divergent results in various areas and unknown global spatial distribution. Here, we reveal the patterns and dynamics of WPE and its effects on leaf area index (LAI), gross primary production (GPP), components of evapotranspiration (ET) and ecosystem water‐use efficiency (EWUE).LocationGlobal.Time periodContemporary.Major taxa studiedWoody plants.MethodsWe used remote sensing to identify the distribution of WPE in 2002–2018, validated at 442 WPE sites, and analysed the pattern of WPE across geographical gradients. The multi‐time‐scale impacts of WPE were revealed through pairwise comparison. Differences among biomes/climate zones were compared by the Kruskal–Wallis test. The relationship of WPE to vegetation greening and the effects of WPE on EWUE were explored.ResultsGlobal WPE expanded persistently from 2002 to 2018, but the rate of increase decreased after 2010; spatially, the average rate of change was .3%/year. High values of WPE in 2018 occurred in arid and semi‐arid regions, with the peak WPE in the multi‐annual mean precipitation of 350–400 mm. Pairwise comparison showed that WPE increased the LAI, GPP, ET and ratio of transpiration to ET, with the strongest effects in summer, and enhanced annual EWUE. Both global pixel‐ and site‐level WPE mainly showed vegetation greening. The above findings varied among bioclimatic conditions; particularly in semi‐arid areas, WPE was positively correlated with vegetation greening and remarkably improved EWUE.Main conclusionsThe ongoing WPE contributed to vegetation greening and elevated vegetation productivity by increasing the LAI and partitioning more water into transpiration; these findings indicate that the WPE process should be incorporated into the carbon cycle and ecohydrology models. However, attention should also be focused on controlling adverse consequences of WPE in arid areas.

Estimation of Evapotranspiration and Its Components across China Based on a Modified Priestley–Taylor Algorithm Using Monthly Multi-Layer Soil Moisture Data

Although soil moisture (SM) is an important constraint factor of evapotranspiration (ET), the majority of the satellite-driven ET models do not include SM observations, especially the SM at different depths, since its spatial and temporal distribution is difficult to obtain. Based on monthly three-layer SM data at a 0.25° spatial resolution determined from multi-sources, we updated the original Priestley Taylor–Jet Propulsion Laboratory (PT-JPL) algorithm to the Priestley Taylor–Soil Moisture Evapotranspiration (PT-SM ET) algorithm by incorporating SM control into soil evaporation (Es) and canopy transpiration (T). Both algorithms were evaluated using 17 eddy covariance towers across different biomes of China. The PT-SM ET model shows increased R2, NSE and reduced RMSE, Bias, with more improvements occurring in water-limited regions. SM incorporation into T enhanced ET estimates by increasing R2 and NSE by 4% and 18%, respectively, and RMSE and Bias were respectively reduced by 34% and 7 mm. Moreover, we applied the two ET algorithms to the whole of China and found larger increases in T and Es in the central, northeastern, and southern regions of China when using the PT-SM algorithm compared with the original algorithm. Additionally, the estimated mean annual ET increased from the northwest to the southeast. The SM constraint resulted in higher transpiration estimate and lower evaporation estimate. Es was greatest in the northwest arid region, interception was a large fraction in some rainforests, and T was dominant in most other regions. Further improvements in the estimation of ET components at high spatial and temporal resolution are likely to lead to a better understanding of the water movement through the soil–plant–atmosphere continuum.

Partitioning of evapotranspiration and the influencing factors of evapotranspiration components in a shrub ecosystem dominated by Artemisia ordosica and Hedysarum fruticosum var. mongolicum in the Mu Us Desert, Northwest China.

Evapotranspiration (ET) is an important part of water cycle and energy flow in ecosystem. Accurate estimation of ET and its components is critical for understanding the impacts of ecophysiological processes on ecosystem water balance and plant water use strategy. Using the eddy-covariance technique and the micro-lysimeter, we measured ET, evaporation (E), transpiration (T) of the Artemisia ordosica-Hedysarum fruticosum var. mongolicum shrubland in the Mu Us Desert during May 20 to September 15, 2019, quantified the ET components, and analyzed the seasonal characteristics and influencing factors of ET and its components. The results showed that T was the main component of ET in the growing season, with a T/ET of 53.1%. T/ET increased and E/ET decreased as precipitation decreased. The partitioning of evapotranspiration was regulated by precipi-tation. At the seasonal scale, the value of E was positively correlated with soil water content at 10 cm depth (SWC10) and net radiation (Rn), while SWC10 was the main factor influencing E. The value of T increased with the increases of Rn and leaf area index (LAI), and increased first and then decreased with the increases of soil water content at 30 cm layer (SWC30). T was affected by SWC30, Rn and LAI. Moisture was the main influencing factor of ET. The ET/P in the growing season was 109.2% and was 250.5% in May, indicating that the water consumption of ET in early growing season was partly from the precipitation in non-growing season.

Quantifying the Responses of Evapotranspiration and Its Components to Vegetation Restoration and Climate Change on the Loess Plateau of China

Quantitatively identifying the influences of vegetation restoration (VR) on water resources is crucial to ecological planning. Although vegetation coverage has improved on the Loess Plateau (LP) of China since the implementation of VR policy, the way vegetation dynamics influences regional evapotranspiration (ET) remains controversial. In this study, we first investigate long-term spatiotemporal trends of total ET (TET) components, including ground evaporation (GE) and canopy ET (CET, sum of canopy interception and canopy transpiration) based on the GLEAM-ET dataset. The ET changes are attributed to VR on the LP from 2000 to 2015 and these results are quantitatively evaluated here using the Community Land Model (CLM). Finally, the relative contributions of VR and climate change to ET are identified by combining climate scenarios and VR scenarios. The results show that the positive effect of VR on CET is offset by the negative effect of VR on GE, which results in a weak variation in TET at an annual scale and an increased TET is only shown in summer. Regardless of the representative concentration pathway (RCP4.5 or RCP8.5), differences resulted from the responses of TET to different vegetation conditions ranging from −3.7 to −1.2 mm, while climate change from RCP4.5 to RCP8.5 caused an increase in TET ranging from 0.1 to 65.3 mm. These findings imply that climate change might play a dominant role in ET variability on the LP, and this work emphasizes the importance of comprehensively considering the interactions among climate factors to assess the relative contributions of VR and climate change to ET.

Quantitative separation of evapotranspiration components of Platycladus orientalis ecosystem based on multiple isotope models

To fully understand the changes in the evapotranspiration components in forest ecosystem and their contribution to evapotranspiration at daily scale, we used the hypothesis theory of isotopic steady state and non-steady state combined with the water isotope analyzer system to quantitatively split and compare the evapotranspiration components of Platycladus orientalis ecosystem during the growing season. Results showed that the 18O of water from different sources during the four mea-surement days (August 5, 8, 10, 11, 2016) all showed surface soil water and oxygen isotope composition (δS) > branch water and oxygen isotope composition (δX) > atmospheric water vapor oxygen isotopes composition (δV), with obvious differences due to the isotope fractionation. Oxygen isotopes composition of soil evaporated water vapor (δE) was between -26.89‰～-59.68‰ at the daily scale, showing a pattern of first rising and then decreasing. The oxygen isotopic composition of evapotranspiration water vapor in forest ecosystem (δET) was between -15.99‰～-10.04‰. The oxygen isotopic composition of transpired water vapor under steady state(δT-ISS) was between -12.10‰～-9.51‰. The oxygen isotopic composition of transpired water vapor under non-steady state (δT-NSS) was between -13.02‰～-7.23‰. δET and δT-NSS had the same changing trend throughout the day at the daily scale, while the trend of δET, δT-ISS and δT-NSS was approximately the same during 11:00-17:00. In general, the contribution rate of plant transpiration to total evapotranspiration showed that FT-ISS was between 79.1%-98.7%, and FT-NSS was between 88.7%-93.7%. Our results suggested that water consumption through soil evaporation was far less than that of vegetation transpiration in the study area, and that vegetation transpiration dominated forest evapotranspiration.

Effects of changes in canopy interception on stream runoff response and recovery following clear‐cutting of a Japanese coniferous forest in Fukuroyamasawa Experimental Watershed in Japan

AbstractUnderstanding changes in evapotranspiration during forest regrowth is essential to predict changes of stream runoff and recovery after forest cutting. Canopy interception (Ic) is an important component of evapotranspiration, however Ic changes and the impact on stream runoff during regrowth after cutting remains unclear due to limited observations. The objective of this study was to examine the effects of Ic changes on long‐term stream runoff in a regrowth Japanese cedar and Japanese cypress forest following clear‐cutting. This study was conducted in two 1‐ha paired headwater catchments at Fukuroyamasawa Experimental Watershed in Japan. The catchments were 100% covered by Japanese coniferous plantation forest, one of which was 100% clear‐cut in 1999 when the forest was 70 years old. In the treated catchment, annual runoff increased by 301 mm/year (14% of precipitation) the year following clear‐cutting, and remained 185 mm/year (7.9% of precipitation) higher in the young regrowth forest for 12–14 years compared to the estimated runoff assuming no clear‐cutting. The Ic change was −358 mm/year (17% of precipitation) after cutting and was −168 mm/year (6.7% of precipitation) in the 12–14 years old regrowth forest compared to the observed Ic during the pre‐cutting period. Stream runoff increased in all seasons, and the Ic change was the main fraction of evapotranspiration change in all seasons throughout the observation period. These results suggest that the change in Ic accounted for most of the runoff response following forest cutting and the subsequent runoff recovery in this coniferous forest.