Total Evapotranspiration Research Articles

Effects of the Vegetation on the Hydrological Behavior of a Loose Pyroclastic Deposit

The effects of the vegetation cover are introduced into a simplified hydrological model of a slope covered with pyroclastic materials, located in Cervinara, in the Apennines of Campania (southern Italy). The vegetation consists of deciduous chestnut trees (Castanea sativa) with a dense seasonal understory, mainly constituted by ferns (Pteridium aquilinum) and other shrubs. The brushwood grows during late spring and summer, while it is nearly absent during the rest of the year. Approximately in the same period, from May to September, the chestnut trees have deep foliage, while in October the leaves dry and fall. Such seasonal vegetation cover affects rainfall infiltration, as indicated by soil water potential data collected by a hydrological monitoring station operating since 2010 at the slope. The effects of the vegetation are introduced in the hydrological model in two ways: interception of the precipitation, and a root water uptake model which distributes the total evapotranspiration flux over the root depth, according to the local value of soil water potential. The presented results show that the introduction of seasonally variable values of leaf area index and interception capacity ensures good performance of the hydrological model. The results also show that, through rainfall interception and root water uptake, the vegetation cover has positive effects on slope equilibrium, by keeping soil suction high enough to prevent the establishment of the conditions which lead to slope failure.

Measurement of evapotranspiration during sprinkler irrigation using a precision energy budget (Bowen ratio, eddy covariance) methodology

Eddy covariance (ECV) is a micrometeorological mass transfer method for measuring evapotranspiration (ET) which has been used successfully for the last decade to measure evapotranspiration from natural and agricultural plant communities. However, no such usage has been reported in relation to evaporation losses occurring during sprinkler irrigation. Instead, sprinkler irrigation research has focused on using traditional methods acknowledged to have many limitations. In this field study, the feasibility of precision energy budget measurement, utilising ECV, to measure the total ET during sprinkler irrigation over different surfaces has been established.The trials were carried out at small scale using a low-pressure impact type sprinkler irrigation system over bare soil, grass and cotton during the Australian summer of 2010–11. All radiation components plus soil heat flux were measured. The sensible and latent heat fluxes measured using ECV were used to deduce instantaneous Bowen ratio values and hence partition the energy available for sensible plus latent heat (ET) transport. From the measurements of energy fluxes, the effect of advection on irrigation was inferred. Non-dimensionalisation of measured ET permitted comparison of the rate of change of ET in different phases of measurement, i.e. pre-, during and post-irrigation.Results indicated that the technique was clearly able to measure the different rates of total evaporation over the short crops before, during and after sprinkler irrigation and a relative ET discrimination of order 0.06mmh−1 was achieved, equivalent to a discrimination in the difference between irrigation and non-irrigation evaporation rates of ±11%. In addition, the results showed that nondimensional ET ranged from 1.4 to 1.6 times the reference (non-irrigating) ET value for mature cotton of height approaching 1m.

Surface energy balance and actual evapotranspiration of the transboundary Indus Basin estimated from satellite measurements and the ETLook model

The surface energy fluxes and related evapotranspiration processes across the Indus Basin were estimated for the hydrological year 2007 using satellite measurements. The new ETLook remote sensing model (version 1) infers information on actual Evaporation (E) and actual Transpiration (T) from combined optical and passive microwave sensors, which can observe the land‐surface even under persistent overcast conditions. A two‐layer Penman–Monteith equation was applied for quantifying soil and canopy evaporation. The novelty of the paper is the computation of E and T across a vast area (116.2 million ha) by using public domain microwave data that can be applied under all weather conditions, and for which no advanced input data are required. The average net radiation for the basin was estimated as being 112 Wm−2. The basin average sensible, latent and soil heat fluxes were estimated to be 80, 32, and 0 Wm−2, respectively. The average evapotranspiration (ET) and evaporative fraction were 1.2 mm d−1 and 0.28, respectively. The basin wide ET was 496 ± 16.8 km3 yr−1. Monte Carlo analysis have indicated 3.4% error at 95% confidence interval for a dominant land use class. Results compared well with previously conducted soil moisture, lysimeter and Bowen ratio measurements at field scale (R2 = 0.70; RMSE = 0.45 mm d−1; RE = –11.5% for annual ET). ET results were also compared against earlier remote sensing and modeling studies for various regions and provinces in Pakistan (R2 = 0.76; RMSE = 0.29 mmd−1; RE = 6.5% for annual ET). The water balance for all irrigated areas together as one total system in Pakistan and India (26.02 million ha) show a total ET value that is congruent with the ET value from the ETLook surface energy balance computations. An unpublished validation of the same ETLook model for 23 jurisdictional areas covering the entire Australian continent showed satisfactory results given the quality of the watershed data and the diverging physiographic and climatic conditions (R2 = 0.70; RMSE = 0.31 mmd−1; RE = –2.8% for annual ET). Eight day values of latent heat fluxes in Heibei (China) showed a good resemblance (R2 = 0.92; RMSE = 0.04 mm d−1; RE = 9.5% for annual ET). It is concluded that ETLook is a novel model that can be operationalized further—especially after improving the preprocessing of spaceborne soil moisture data. This preprocessing includes (1) downscaling of topsoil moisture from 25 to 1 km pixels, and (2) translation of topsoil moisture into subsoil moisture values.

Estimating actual evapotranspiration from an alpine grassland on Qinghai-Tibetan plateau using a two-source model and parameter uncertainty analysis by Bayesian approach

Summary A Bayesian method was used to fit the Shuttleworth–Wallace model to half-hourly measurements of evapotranspiration (ET) with the eddy covariance technique from an alpine grassland on the Qinghai-Tibetan plateau during the main growing season in 2008, and probabilistically estimated its parameters and predication uncertainties using both dataset-by-dataset and multi-data procedures. This enabled us to reveal the seasonal variations of some physiology-related parameters and the impacts of constant parameters on the performances of the model. Results indicated that the S–W model using the posterior mean parameter values obtained by different procedures all successfully reproduced the observed responses in ET. However, the seasonal variations in the canopy conductance parameter ( g max ) should be counted in long-term ET estimating. From simulated results, the daily mean partitioning [i.e. the ratio of the estimated daily soil evaporation ( E ) over total evapotranspiration (ET); E /ET] was relative low (0.02–0.07 with a mean of 0.04) for the alpine grassland when leaf area index (LAI) was more than 3 m 2 m −2 , and was closed related to LAI and vegetation condition. At the diurnal timescale, the canopy conductance was the main factor control the partitioning of ET.

Wet surface resistance of forest canopy in monsoon Asia: Implications for eddy‐covariance measurement of evapotranspiration

AbstractDuring the Asian monsoon period, intense precipitation commonly occurs for an extended period in accompaniment with a reduction in solar radiation. This suggests that wet surface evapotranspiration is an important contributor to the total evapotranspiration. Therefore, investigating evapotranspiration over a wet canopy surface is critical to achieve a better understanding of water and energy cycles in Asia. In this study, we estimated surface resistances under wet conditions in a mixed forest influenced by the East Asian monsoon system. We showed that the surface resistance had a non‐negligible magnitude of about 30 sm−1 even under wet conditions. We also found that the ratio between the actual and potential evapotranspiration depended on the friction velocity regardless of the time of day. Our analyses suggest that this dependency is tightly related to the underestimation of turbulent fluxes by the eddy‐covariance system under wet surface conditions. Together, our findings suggest that the wet surface resistance, although small, should be considered in simulating evapotranspiration because the forest ecosystem is strongly coupled to the overlying atmosphere. This could significantly improve the shortcomings of evapotranspiration measurement and modeling in Asian forest canopies influenced by the monsoon system. Copyright © 2012 John Wiley & Sons, Ltd.

Evapotranspiration measurement and estimation using modified Priestley–Taylor model in an irrigated maize field with mulching

Accurate measurement or estimation of crop evapotranspiration (ET) is important to develop exact irrigation scheduling and reasonably use water resources. ET of an irrigated maize field mulched with plastic film was measured using eddy covariance technique over two growing seasons in an arid region of northwest China. A modified Priestley–Taylor (PT) model was developed, incorporating the effect of leaf area, soil moisture, mulching fraction and leaf senescence on ET. The model was parameterized by field measurements in 2008 and validated by those in 2009. Results indicate that diurnal variation of ET was bell-shaped curve for all the growing stages. During the two growing seasons, total ET was 503.1 and 562.4mm, and mean daily ET 3.47 and 3.54mmd−1, respectively. ET was mainly controlled by solar radiation, and significantly affected by influential factors below the thresholds, which were leaf area index of 3.0m2m−2, and soil relative extractable water of 0.5, and canopy conductance of 20mms−1, respectively. A good agreement was found between ET estimated by the modified PT model with observations, with linear slope of 0.99 and R2 of 0.94 and 0.96 for half-hourly and daily time scale, respectively. Thus the modified PT model can be used to estimate ET or quantify the effect of controlling factors on ET in similar agricultural fields.

Spin-up behavior of soil moisture content over East Asia in a land surface model

This study presents an investigation of the spin-up behavior of soil moisture content (SMC) and evapotranspiration (ET) in an offline Noah land surface model (LSM) for East Asia, focusing on its interplay with the Asian monsoon. The set of 5-year recursive runs is conducted to properly assess the spin-up behavior of land surface processes and consists of simulations initialized with (1) a spatially uniform soil moisture, (2) NCEP GDAS soil moisture data, and (3) ECMWF ERA-Interim soil moisture data. Each run starts either after or before the summer monsoon. Initial SMCs from GDAS and ERA-Interim data significantly deviate from the equilibrium state (spin-up state) with the given input forcing even though the same equilibrium is reached within 3-year spin-up time, indicating that spin-up of land surface process is necessary. SMC reaches the equilibrium much quickly when (1) the consistent LSMs have been used in the prediction and analysis systems and (2) the spin-up simulation starts before the onset of heavy rainfall events during summer monsoon. For an area with heavy monsoon rainfall, the total column SMC and ET spin up quickly. The spin-up time over dry land is about 2–3 years, but for monsoon rainfall area decreases dramatically to about 3 months if the spin-up run starts just before the onset of monsoon. Further scrutiny shows that the spin-up time is well correlated with evaporative fraction given by the ratio between the latent heat flux and the available energy at the land surface.

Drawing down our resources: estimating the total appropriation of water in China

The authors estimate that people in China now use 33.8% of total evapotranspiration and 80.5% of accessible runoff. They also project an increase in accessible runoff by about 14% to 2030 through new dam construction and rehabilitation, while the population is likely to increase to 1.5 billion. Total human appropriation of runoff will accordingly increase from 674 km3 to ca. 820 km3. Appropriation of total renewable fresh water is projected to increase from the present ca. 29% to 31.4%. In addition, climate change is likely to exacerbate water stress in some areas.

Effects of projected climate change on the hydrology in the Mono Lake Basin, California

The Californian Mono Lake Basin (MLB) is a fragile ecosystem, for which a 1983 ruling carefully balanced water diversions with ecological needs without the consideration of global climate change. The hydroclimatologic response to the impact of projected climatic changes in the MLB has not been comprehensively assessed and is the focus of this study. Downscaled temperature and precipitation projections from 16 Global Climate Models (GCMs), using two emission scenarios (B1 and A2), were used to drive a calibrated Soil and Water Assessment Tool (SWAT) hydrologic model to assess the effects on streamflow on the two significant inflows to the MLB, Lee Vining and Rush Creeks. For the MLB, the GCM ensemble output suggests significant increases in annual temperature, averaging 2.5 and 4.1 °C for the B1 and A2 emission scenarios, respectively, with concurrent small (1–3 %) decreases in annual precipitation by the end of the century. Annual total evapotranspiration is projected to increase by 10 mm by the end of the century for both emission scenarios. SWAT modeling results suggest a significant hydrologic response in the MLB by the end of the century that includes a) decreases in annual streamflow by 15 % compared to historical conditions b) an advance of the peak snowmelt runoff to 1 month earlier (June to May), c) a decreased (10–15 %) occurrence of ‘wet’ hydrologic years, and d) and more frequent (7–22 %) drought conditions. Ecosystem health and water diversions may be affected by reduced water availability in the MLB by the end of the century.

Partitioning of forest evapotranspiration: The impact of edge effects and canopy structure

The magnitude of small scale variability in tree transpiration was explored in a structurally heterogeneous Norway spruce (Picea abies (L.) H. Karst.) plantation in western Denmark. The trees are arranged in a distinctive small scale mosaic (0.25ha) of young open-canopy stands interspaced with older mature closed-canopy stands. Tree transpiration was measured in the open and closed canopy stands using Granier type thermal dissipation probes; forest floor evapotranspiration (ET) was estimated by monitoring the weight of cut out sections of forest floor; and total ET was estimated using the eddy covariance (EC) method. We show that (a) canopy structure had a major impact on transpiration rate allowing the open-canopy stands to transpire at approximately 30% higher rate than the closed-canopy stands; (b) within the open-canopy stand there was a significant relation between tree size and sap-flux density; and (c) within the closed-canopy stands there was an edge effect with trees next to access roads and aisles being responsible for a disproportionately large part of the stand transpiration. Through careful scaling, taking into account the observed variability, it was possible to get good agreement on dry days between independent measures of transpiration plus forest floor ET and the EC estimate of total forest ET. On average transpiration and forest floor ET amounted to 86% of the EC estimate on dry days.

Estimation of regional evapotranspiration in alpine area and its response to land use change: A case study in Three-River Headwaters region of Qinghai-Tibet Plateau, China

Three-River Headwaters (TRH) region involved in this paper refers to the source region of the Changjiang (Yangtze) River, the Huanghe (Yellow) River and the Lancang River in China. Taking the TRH region of the Qinghai-Tibet Plateau as a case, the annual evapotranspiration (ET) model developed by Zhang et al. (2001) was applied to evaluate mean annual ET in the alpine area, and the response of annual ET to land use change was analyzed. The plant-available water coefficient (w) of Zhang’s model was revised by using vegetation-temperature condition index (VTCI) before annual ET was calculated in alpine area. The future land use scenario, an input of ET model, was spatially simulated by using the conversion of land use and its effects at small regional extent (CLUE-S) to study the response of ET to land use change. Results show that the relative errors between the simulated ET and that calculated by using water balance equation were 3.81% and the index of agreement was 0.69. This indicates that Zhang’s ET model based on revised plant-available water coefficient is a scientific and practical tool to estimate the annual ET in the alpine area. The annual ET in 2000 in the study area was 221.2 mm, 11.6 mm more than that in 1980. Average annual ET decreased from southeast to northwest, but the change of annual ET between 1980 and 2000 increased from southeast to northwest. As a vast and sparsely populated area, the population in the TRH region was extremely unbalanced and land use change was concentrated in very small regions. Thus, land use change had little effect on total annual ET in the study area but a great impact on its spatial distribution, and the effect of land use change on ET decreased with increasing precipitation. ET was most sensitive to the interconversion between forest and unused land, and was least sensitive to the interconversion between cropland and low-covered grassland.

Evapotranspiration and crop coefficient of drip irrigated watermelon in Piaui coastline, Brazil

The knowledge of the evapotranspiration (ETc) and crop coefficient (Kc) is fundamental to plan and to manage the irrigation of any crop. The aim of this study was to determine the daily and hourly evapotranspiration of drip irrigated watermelon (Citrullus Lanatus, var. Crimson Sweet) and crop coefficient (Kc) in each crop development phase. The experiment was carried out in an experimental area of 1.27 ha of Embrapa Mid-North, localized in Parnaíba (02°54'S, 41°47'W and 46 m above of sea), State of Piauí, Brazil, from September to November, 2006. Electronic weighing lysimeters of 1.5 m x 1.5 m wide and long and 1.0 m deep were used to obtain the evapotranspiration. The plants were drip irrigated with a lateral row per plant row and drippers spaced 0.5 m from each other. The reference evapotranspiration (ETo) was estimated using the Penman-Monteith equation from the climatic data obtained by electronic sensors. The total evapotranspiration during the watermelon crop cycle cultivated in the state of Piauí was 233.87 mm, with mean values of 3.7 mm day-1, minimum of 1.18 and maximum of 8.14 mm day-1. The Kc of the drip irrigated watermelon was 0.18 in the initial stage of crop growth; 0.18 to 1.3, in crop development stage; 1.3 in the intermediate stage and 0.43 in the final stage.

Water use by terrestrial ecosystems: temporal variability in rainforest and agricultural contributions to evapotranspiration in Mato Grosso, Brazil

The state of Mato Grosso, Brazil, has experienced rapid land use changes from the expansion of rain-fed agriculture (primarily soybean and pasture). This study presents changes to evapotranspiration contributions from terrestrial ecosystems in Mato Grosso over the 2000–9 period. Instead of focusing on land use change to infer hydrologic change, in this paper we assess hydrologic changes using remote sensing, meteorological and agricultural production data to determine the rainforest, crop and pasture components of total evapotranspiration. Humid tropical rainforest evapotranspiration represented half of the state’s total evapotranspiration in 2000 despite occupying only 40% of the total land area. Annual evapotranspiration fluxes from rainforest declined at a rate of 16.2 km3 y−1 (R2 = 0.82, p-value < 0.01) as a result of deforestation between 2000 and 2009, representing a 25% decline in rainforest evapotranspiration since 2000. By 2009, rainforest cover accounted for only 40% of total evapotranspiration. Over the same period, crop evapotranspiration doubled, but this increase was offset by a decline in pasture evapotranspiration. Pasture fluxes were at least five times larger than crop evapotranspiration fluxes in 2000–9, with increases spatially focused at the agricultural frontier. The results highlight the expanding appropriation of soil moisture stocks for use in Mato Grosso’s rain-fed agroecosystems.

On evapotranspiration and shallow groundwater fluctuations: A Fourier‐based improvement to the White method

Evapotranspiration (ET) is a significant component of the water and energy balance in wetlands and riparian zones, yet it is also one of the most challenging components to estimate. Diurnal water table fluctuations can be used to directly measure groundwater consumption by phreatophytes, which are often important contributors to the total ET in riparian systems. Although such methods are cost effective, significant uncertainties usually exist, and more accurate techniques continue to be developed. In this study we present a new “Fourier method” for calculating daily (and longer) groundwater ET consumption using a moving, multiday sine function to capture robust, diurnal water table fluctuations. The technique is tested and calibrated in Tamarix chinensis and Populus deltoids‐dominated riparian areas in the Middle Rio Grande region of New Mexico and in a Phragmites australis‐dominated riparian wetland in south‐central Nebraska (using independent, energy balance estimates of ET). The results show that—at both field sites—the new Fourier technique performs significantly better than the commonly used White method, regardless of the length of the moving window that is employed. The Fourier method presented here provides a step toward increasing the accuracy of ET estimates from diurnal water table fluctuations. Guidelines are defined for applying the new and improved method in the most accurate fashion, based on groundwater hydrographs and solar radiation data (or theoretical clear‐sky estimates).

On Estimating Wet Canopy Evaporation from Deciduous and Coniferous Forests in the Asian Monsoon Climate

Abstract Continuous and direct measurement of evapotranspiration (ET) by the eddy covariance (EC) technique is still a challenge under monsoon climate because of a considerable amount of missing data during the long rainy periods and the consequential gap-filling process. Under such wet canopy conditions, especially in forests, evaporation of the intercepted precipitation (EWC) contributes significantly to the total ET. To quantify the role of EWC, leaf wetness has been measured at multiple levels in the canopy simultaneously with eddy covariance measurements at the KoFlux Gwangneung deciduous and coniferous forests for the entire year from September 2007 to August 2008. In this study, the measured EWC and the controlling mechanism during the wet canopy conditions have been scrutinized. Based on the evaluation of the four different algorithms of EWC estimation, that of the variable infiltration capacity (VIC) land surface model (LSM) has been adopted. All the missing EWC data are then recalculated by using the algorithm of VIC LSM and compared against the traditionally gap-filled EWC data based on the modified lookup table (MLT) method. The latter consistently underestimated EWC on average by 39% in deciduous forest and by 28% in coniferous forest. Major causes of such differences were due to the failure of considering aerodynamic coupling, advection of sensible heat, and heat storage in the MLT-based gap-filling method. Accordingly, a new gap-filling strategy for EWC is proposed that takes proper controlling mechanisms into account.

A new analytical method for groundwater recharge and discharge estimation

Summary A new analytical method was proposed for groundwater recharge and discharge estimation in an unconfined aquifer. The method is based on an analytical solution to the Boussinesq equation linearized in terms of h2, where h is the water table elevation, with a time-dependent source term. The solution derived was validated with numerical simulation and was shown to be a better approximation than an existing solution to the Boussinesq equation linearized in terms of h. By calibrating against the observed water levels in a monitoring well during a period of 100 days, we shown that the method proposed in this study can be used to estimate daily recharge (R) and evapotranspiration (ET) as well as the lateral drainage. It was shown that the total R was reasonably estimated with a water-table fluctuation (WTF) method if the water table measurements away from a fixed-head boundary were used, but the total ET was overestimated and the total net recharge was underestimated because of the lack of consideration of lateral drainage and aquifer storage in the WTF method.

Interannual variation of evapotranspiration in an eastern Siberian larch forest

AbstractIn a deciduous larch forest in eastern Siberia, the mean and standard deviation of the total evapotranspiration (E) during May to September (day of year (DOY) = 121–274) for 2003–2006 were 181.5 and 26.4 mm, respectively. The interannual variation (IAV) in the total E was caused by the IAV in E for the canopy‐foliated period (DOY = 164–253), not by the IAV in the dates of leaf expansion and leaf fall. For the years with higher total E, E in the canopy‐foliated period was consistently higher, which corresponded to the higher soil water content in these years. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Effects of evapotranspiration on baseflow in a tropical headwater catchment

Diel cycles in stream discharge during baseflow periods in a headwater stream in La Selva Biological Station, Costa Rica, a tropical wet forest site, appear to be associated with groundwater withdrawal by the forest for evapotranspiration (ET). Analysis of the cycles indicates a strong correlation of stage change with ET demand, similar to the variation found in riparian water table elevation by previous researchers. Links between daily forest ET demand cycles and stream discharge cycles have been reported in temperate humid and semi-arid regions, but the frequent flood hydrographs of the wet tropics tend to obscure this daily signal. This study modifies and combines two established empirical methods for analyzing the diel ET signal in streamflow which lead to estimates of riparian ET derived from groundwater ( ET G ) at hourly time scales and spatial extent of the riparian area. The model has a direct dependence on the estimate of specific yield, a difficult to constrain parameter, which we estimate from previously published soil analyses. For the six baseflow periods analyzed, the model estimates groundwater ET losses ranging from 1.8 to 3.9 mm/day within the riparian area. These estimates are 52–81% of the total ET estimated with the Penman–Monteith equation ( ET PM ). The signal of ET G in the stream lags ET PM by 1.5–3 h, with apparent peak decay and signal duration lengthening during propagation. Model results indicate that the area of the riparian zone that influences streamflow by means of ET withdrawal increases with stream stage and ranges from 2.5% to 6.6% of the total basin area. Variations in the rate of change of nightly stream stage recovery suggest possible variations in the relative importance of subsurface hydraulic properties. At high stages, the rate of stream stage recovery from ET losses decreases throughout the night, whereas at low stages the rate of stream stage recovery increases throughout the night. Future work with numerical models could explore mechanistic controls on these empirically-derived recovery functions.

Potential impacts of emerald ash borer invasion on biogeochemical and water cycling in residential landscapes across a metropolitan region

Trees provide important ecological services in cities, yet the vulnerability of the urban forest to massive tree losses from pest outbreaks could threaten those services, with unknown environmental consequences. The outbreak of emerald ash borer is an imminent threat to the ash population in North America. In the Minneapolis–Saint Paul, Minnesota, metropolitan area, ash trees are present in 50 % of residential landscapes in Ramsey and Anoka Counties. We used a large survey of household activities, a tree inventory, a Household Flux Calculator accounting tool, and a set of annual evapotranspiration measurements, to quantify the current carbon, nitrogen, and phosphorus storage in ash trees, the cycling of these elements, and the total evapotranspiration from ash trees in residential areas in the metropolitan region. Ash represented 6 % of the trees in residential areas and the removal of the entire ash population would correspondingly reduce net primary production and carbon sequestration by only a few percent and would have negligible effects on losses of nitrogen and phosphorus from residential landscapes. Similarly, the effects of ash loss on the hydrologic cycle would be minimal and would depend largely on management choices for the ground currently underneath ash tree canopies. Overall, the percentage change in biogeochemical and hydrological fluxes corresponded closely with the percent of the total urban tree population that was represented by ash, suggesting that areas with higher densities of ash would experience correspondingly larger effects. A hypothetical tree replacement scenario with similar broadleaf species was determined to be likely to re-establish the original biogeochemical and hydrological conditions once the replacement trees reach maturity.

Rising ozone concentrations decrease soybean evapotranspiration and water use efficiency whilst increasing canopy temperature

• Here, we investigated the effects of increasing concentrations of ozone ([O(3)]) on soybean canopy-scale fluxes of heat and water vapor, as well as water use efficiency (WUE), at the Soybean Free Air Concentration Enrichment (SoyFACE) facility. • Micrometeorological measurements were made to determine the net radiation (R(n)), sensible heat flux (H), soil heat flux (G(0)) and latent heat flux (λET) of a commercial soybean (Glycine max) cultivar (Pioneer 93B15), exposed to a gradient of eight daytime average ozone concentrations ranging from approximately current (c. 40 ppb) to three times current (c. 120 ppb) levels. • As [O(3)] increased, soybean canopy fluxes of λET decreased and H increased, whereas R(n) and G(0) were not altered significantly. Exposure to increased [O(3)] also resulted in warmer canopies, especially during the day. The lower λET decreased season total evapotranspiration (ET) by c. 26%. The [O(3)]-induced relative decline in ET was half that of the relative decline in seed yield, driving a 50% reduction in seasonal WUE. • These results suggest that rising [O(3)] will alter the canopy energy fluxes that drive regional climate and hydrology, and have a negative impact on productivity and WUE, key ecosystem services.