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1.
Quantifying the spatial variability of species-specific tree transpiration across hillslopes is important for estimating watershed-scale evapotranspiration (ET) and predicting spatial drought effects on vegetation. The objectives of this study are to (1) assess sap flux density (Js) and tree-level transpiration (Ts) across three contrasting zones a (riparian buffer, mid-hillslope and upland-hillslope, (2) determine how species-specific Js responds to vapour pressure deficit (VPD) and (3) estimate watershed-level transpiration (Tw) using Ts derived from each zone. During 2015 and 2016, we measured Js in eight tree species in the three topographic zones in a small 12-ha forested watershed in the Piedmont region of central North Carolina. In the dry year of 2015, loblolly pine (Pinus taeda), Virginia pine (Pinus virginiana) and sweetgum (Liquidambar styraciflua) Js rates were significantly higher in the riparian buffer when compared to the other two zones. In contrast, Js rates in tulip poplar (Liriodendron tulipifera) and red maple (Acer rubrum) were significantly lower in the buffer than in the mid-hillslope. Daily Ts varied by zone and ranged from 10 to 93 L/day in the dry year and from 9 to 122 L/day in the wet year (2016). Js responded nonlinearly to VPD in all species and zones. Annual Tw was 447, 377 and 340 mm based on scaled-Js data for the buffer, mid-hillslope and upland-hillslope, respectively. We conclude that large spatial variability in Js and scaled Tw was driven by differences in soil moisture at each zone and forest composition. Consequently, spatial heterogeneity of vegetation and soil moisture must be considered when accurately quantifying watershed level ET.  相似文献   

2.
Evapotranspiration (ET) and canopy wetness were measured over a 2‐year intensive field campaign at the Chi‐Lan Mountain cloud forest site in Taiwan. Eddy covariance and sap flow methods were applied to measure ET and tree sap flow of the endemic yellow cypress (Chamaecyparis obtusa var. formosana). ET was 553 mm yr?1 over the study period with an annual rainfall and fog deposition of 4893 and 288 mm yr–1, respectively. The duration of canopy wetness exceeded actual fog or rain events (mostly in the afternoon), and the intercepted water was evaporated later in the following dry morning. The cumulative wet duration accounted for 52% of time over the study period, which was longer than the duration of rainfall and fog altogether (41%). As it adapted to the extremely moist environment, the yellow cypress behaved in a wet‐enhanced/dry‐reduced water use strategy and was sensitive to short periods of dry atmosphere with high evaporation potential. During dry days, the sap flow rate rose quickly after dawn and led to conservative water use through midday and the afternoon. During periodically wet days, the canopy was mostly wetted in the morning, and the interception evaporation contributed largely to the morning ET. The initiation of morning sap flow was postponed 1–3 h, and the sap flow rate tended to peak later at midday. The midday canopy conductance was higher in the periodically wet days (10.6 mm s–1) as compared with 7.6 mm s?1 in the dry days. Consequently, the dry‐reduced water use strategy led to much lower annual ET with respect to the available energy (~46%) and high precipitation input (~11%). The moist‐adapted ecohydrology we report reveals the vulnerability of montane cloud forests to prolonged fog‐free periods. More research is urgently needed to better understand the resilience of these ecosystems and formulate adaptive management plans. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

3.
Conservation management for the water dependent desert‐oasis ecotone in arid northwest China requires information on the water use of the dominant species. However, no studies have quantified their combined water use or linked species composition to ecotone transpiration. Here, the water use of three dominant shelterbelt shrubs (Haloxylon ammodendron, Nitraria tangutorum, and Calligonum mongolicum) within an ecotone was measured throughout the full leaf‐out period for three shrub species from 30 May to 16 October 2014, with sap flow gauges using the stem heat balance approach. Species‐specific transpiration was estimated by scaling up sap flow velocities measured in individual stems, to stand area level, using the frequency distribution of stem diameter and assuming a constant proportionality between sap flow velocity and basal cross‐sectional area for all stems. The mean peak sap flux densities (Jsn) for H. ammodendron, N. tangutorum, and C. mongolicum, were 40.12 g cm?2 h?1, 71.33 g cm?2 h?1, and 60.34 g cm?2 h?1, respectively, and the mean estimated daily area‐averaged transpiration rates (Tdaily) for the same species were 0.56 mm day?1, 0.34 mm day?1, and 0.11 mm day?1. The accumulative stand transpiration was approximately 140.8 mm throughout the measurement period, exceeding precipitation by as much as 42.1 mm. Furthermore, Tdaily of these shrubs appeared to be much less sensitive to soil moisture as compared to atmospheric drivers, and the relationship between Jsn and atmospheric drivers was likely uninfluenced by soil moisture regimes in the whole profile (to 1‐m depth), especially for H. ammodendron and C. mongolicum. Results indicate that these shrubs may use deep soil water recharged by capillary rise, or may directly access shallow groundwater. This study provides quantitative data offering important implications for ecotone conservation and water and land resource management. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

4.
Hydrologic variability during 2005–2011 was observed and analyzed at an upland oak/pine forest in the New Jersey Pinelands. The forest experienced defoliation by Gypsy moth (Lymantria dispar L.) in 2007, drought conditions in 2006 and a more severe drought in 2010. By using sap flux and eddy covariance measurements, stream discharge data from USGS, soil water changes, precipitation (P) and precipitation throughfall, a local water balance was derived. Average annual canopy transpiration (EC) during 2005–2011 was 201 mm a?1 ± 47 mm a?1. A defoliation event reduced EC by 20% in 2007 compared with the 2005–2011 mean. During drought years in 2006 and 2010, stand transpiration was reduced by 8% in July 2006 and by 18% in 2010, respectively, compared with the overall July average. During July 2007, after the defoliation and subsequent reflushing of half of the leaves, EC was reduced by 25%. This stand may experience higher sensitivity to drought when recovering from a defoliation event as evidenced by the higher reduction of EC in 2010 (post‐defoliation) compared with 2006 (pre‐defoliation). Stream water discharge was normalized to the watershed area by dividing outflow with the watershed area. It showed the greatest correlation with transpiration for time lags of 24 days and 219 days, suggesting hydrological connectivity on the watershed scale; stream water discharge increases when transpiration decreases, coinciding with leaf‐on and leaf‐off conditions. Thus, any changes in transpiration or precipitation will also alter stream water discharge and therefore water availability. Under future climate change, frequency and intensity of precipitation and episodic defoliation events may alter local water balance components in this upland oak/pine forest. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

5.
W. Zhao  X. Chang  Z. Zhang 《水文研究》2009,23(10):1461-1470
As an important source of income in the region's economy, the jujube plantations are very common in arid north‐western China, and their planted areas continue to expand. In the central Heihe River Basin of arid north‐western China, Linze jujube (Zizyphus jujuba Mill. var. inermis (Bunge) Rehd.) plantations cover more than 10,000 ha, too. Water use by this species is expected to change or modify catchment hydrological process. To our knowledge, there is no information on the transpiration and canopy conductance of the jujube plantations in arid north‐western China. Therefore, Transpiration and canopy conductance were monitored in a 14‐year‐old Linze jujube orchard. The experiment was carried out in the central Heihe River Basin, near Pingchuan Town (Linze County, Gansu Province, China) during growing season of 2006, from May to the first ten days of October. Eight trees were used to measure sap flow using the heat‐pulse‐velocity method. The orchard was irrigated adequately during the study. Transpiration was estimated from the sap flow measurements. During the experiment, the transpiration rate of the orchard ranged from 0·32 to 1·40 mm per day. Canopy conductance was obtained from estimated daily transpiration and climatic variables measured on a half‐hour basis, and canopy conductance for water vapour transfer was between 1·20 to 82·57 mm s?1, with a mean of 11·86 ± 6·84 mm s?1 during the observation period. Air temperature and vapour‐pressure deficit exhibited a linear relationship with sap flow velocity and the relationship between these factors and canopy conductance could be represented by an exponential decay function. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

6.
In order to evaluate factors controlling transpiration of six common eastern deciduous species in North America, a model describing responses of canopy stomatal conductance (GS) to net radiation (RN), vapor pressure deficit (D) and relative extractable soil water (REW) was parameterized from sap flux data. Sap flux was measured in 24 mature trees consisting of the species Carya tomentosa, Quercus alba, Q. rubra, Fraxinus americana, Liriodendron tulipifera, and Liquidambar styraciflua in a bottomland oak-hickory forest in the Duke Forest, NC. Species differences in model coefficients were found during the 1997 growing season. All species showed a reduction in GS with increasing D. RN influenced GS in the overstory shade intolerant L. styraciflua to a larger extent than the other species measured. In addition, despite a severe drought during the study period, only L. tulipifera showed a decline in GS with decreasing REW. The primary effect of the drought for the other species appeared to be early autumn leaf senescence and abscission. As a result, despite the drought in this bottomland forest accustomed to ample water supply, maximum daily transpiration (1.6 mm) and growing season transpiration (264 mm) were similar to a nearby upland forest measured during a year of above average precipitation. These results may aid in assessing differences in water use and the ability of bottomland deciduous species to tolerate alterations in the frequency or amount of precipitation. Results also suggest little variation in water use among forests of similar composition and structure growing in different positions in the landscape and subjected to large interannual variation in water supply.  相似文献   

7.
In this paper, we present an investigation of interspecies differences in transpiration of the 2 most common plantation forest tree species in Japan, both in the family Cupressaceae with different northern limits of native distribution, Japanese cypress (Hinoki; Chamaecyparis obtusa Sieb. et Zucc.) and Japanese cedar (Sugi; Cryptomeria japonica D. Don). The stem sap flow rate was measured in 2 nearby stands of similar leaf area index in a 42‐year‐old plantation. Single‐tree and stand‐scale transpiration rates (Etre and Esta, respectively) were observed during an ideal autumn environment. At the stand scale, mean sap flux density of Hinoki was greater than that of Sugi, whereas total sapwood area per ground area was smaller in Hinoki than Sugi. Because the 2 variables had counterbalancing effects on transpiration, Esta of Hinoki was similar to (94% of) that of Sugi. This offset was also found between the mean Etre of the 2 species. Esta was similar between the stands from May to October, whereas Esta of Sugi was notably greater than that of Hinoki from February to April. During these 3 months, the difference in cumulative Esta was 21.7 mm, which accounted for 79% of the difference in annual Esta between Hinoki and Sugi (192 and 219 mm/year, respectively). We found that canopy conductance (Gc) and its sensitivity to the mean vapour pressure deficit during daylight hours in Sugi were particularly high in early spring, whereas those in Hinoki shifted gradually throughout the growing season. This difference was related to the optimal temperature of Gc in Sugi, which was approximately 10 °C lower than that in Hinoki. Our results suggest that plantations of water‐conserving species such as Hinoki produce timber slowly but yield water resources generously. Moreover, for plantations of trees sensitive to high temperature, such as Sugi, managers should be concerned about possible future decline caused by anticipated global warming.  相似文献   

8.
Liwen Zhao  Wenzhi Zhao 《水文研究》2015,29(13):2983-2993
With a maize seed planting area of about 67 000 hm2, Zhangye city supplies the seeds for more than 40% of the maize planting area in China. Irrigation water is often overused to ensure the quality of the maize seeds, leading to serious water shortage problems in recent years. An accurate and convenient estimate of canopy transpiration is of particular importance to ease the problem. In this paper, leaf transpiration and sap flow in a maize field were measured in 2012 using a portable photosynthesis system and a heat balance sap flow system. Based on a large amount of meteorological data and relevant maize plant‐growing parameters, canopy transpiration was up‐scaled from both leaf transpiration (Tl) and sap flow (Tf), and also calculated by the FAO‐56 dual crop coefficient method (T). Comparing these three types of transpiration, Tf was proved to be more reliable than Tl. Taking Tf as a benchmark, the basal crop coefficient (Kcb, the key parameter of FAO‐56 dual crop coefficient method) was further adjusted and verified for the maize plants in this region. In addition, the errors when using up‐scaling methods and FAO‐56 dual crop coefficient method are summarized. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

9.
Measurements of sap flow, meteorological parameters, soil water content and tension were made for 4 months in a young cashew (Anacardium occidentale L.) plantation during the 2002 rainy season in Ejura, Ghana. This experiment was part of a sustainable water management project in West Africa. The Granier system was used to measure half‐hourly whole‐tree sap flow. Weather variables were observed with an automatic weather station, whereas soil moisture and tension were measured with a Delta‐T profile probe and tensiometers respectively. Clearness index (CI), a measure of the sky condition, was significantly correlated with tree transpiration (r2 = 0·73) and potential evaporation (r2 = 0·86). Both diurnal and daily stomata conductance were poorly correlated with the climatic variables. Estimated daily canopy conductance gc ranged from 4·0 to 21·2 mm s−1, with a mean value of 8·0 ± 3·3 mm s−1. Water flux variation was related to a range of environmental variables: soil water content, air temperature, solar radiation, relative humidity and vapour pressure deficit. Linear and non‐linear regression models, as well as a modified Priestley–Taylor formula, were fitted with transpiration, and the well‐correlated variables, using half‐hourly measurements. Measured and predicted transpiration using these regression models were in good agreement, with r2 ranging from 0·71 to 0·84. The computed measure of accuracy δ indicated that a non‐linear model is better than its corresponding linear one. Furthermore, solar radiation, CI, clouds and rain were found to influence tree water flux. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

10.
Stemflow (Sf) measurements in tropical rain and montane forests dominated by large trees rarely include the understory and small trees. In this study, contributions of lower (1‐ to 2‐m height) and upper (>2‐m height and <5‐cm diameter at breast height [DBH]) woody understory, small trees (5 < DBH < 10 cm), and canopy trees (>10‐cm DBH) to Sf per unit ground area (Sfa) of a Mexican lower montane cloud forest were quantified for 32 days with rainfall (P) during the 2014 wet season. Rainfall, stemflow yield (Sfy), vegetation height, density, and basal area were measured. Subsequently, stemflow funneling ratios (SFRs) were calculated, and three common methods to scale up Sfy from individual trees to the stand level (tree‐Sfy correlation, P‐Sfy correlation, and mean‐Sfy extrapolation) were used to calculate Sfa. Understory woody plants, small trees, and upper canopy trees represented 96%, 2%, and 2%, respectively, of the total density. Upper canopy trees had the lowest SFRs (1.6 ± 0.5 Standard Error (SE) on average), although the lower understory had the highest (36.1 ± 6.4). Small trees and upper understory presented similar SFRs (22.9 ± 5.4 and 20.2 ± 3.9, respectively). Different Sf scaling methods generally yielded similar results. Overall Sfa during the study period was 22.7 mm (4.5% of rainfall), to which the understory contributed 70.1% (15.9 mm), small trees 10.6% (2.4 mm), and upper canopy trees 19.3% (4.4 mm). Our results strongly suggest that for humid tropical forests with dense understory of woody plants and small trees, Sf of these groups should be measured to avoid an underestimation of overall Sf at the stand level.  相似文献   

11.
S. Shimoda  T. Oikawa 《水文研究》2006,20(16):3503-3516
This study discusses the photosynthetic pathway types involved in canopy temperature measurements on a mixed grassland consisting of C3 and C4 plants (dominant species in biomass were Solidago altissima (C3), Miscanthus sinensis (C4), and Imperata cylindrica (C4)). In the wet conditions immediately after the rainy season, the mean canopy temperature for S. altissima was the lowest among the dominant species, mainly due to its leaf conductance being twice as large as the other two species. Despite using the same C4 photosynthetic pathway, M. sinensis had a lower apparent canopy temperature than I. cylindrica due to a smaller proportion of sunlit elements in the field of view. In the dry conditions during late July, the mean canopy temperatures of the three dominant species were within 0·3 °C of one another. These results can be explained by poor water conditions for C3 species (S. altissima). The simultaneous survey of vegetation and thermal imaging can help clarify characteristics of C3 and C4 canopy temperature over complicated grassland. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

12.
Water is one of the major environmental factors limiting plant growth and survival in the Mediterranean region. Quercus suber L. woodlands occupy vast areas in the Iberian Peninsula, frequently under shallow water table conditions. The relative magnitude of soil and groundwater uptake to supply transpiration is not easy to evaluate under these circumstances. We recently developed a conceptual framework for the functioning of the root system in Q. suber that simulates well tree transpiration, based on two types of root behaviour: shallow connected and deep connected. Although this significantly improved knowledge on the functional traits of Mediterranean Q. suber, the approach has the limitation of requiring root sap flow data, which are seldom available. In this work, we present alternative methodologies to assess if trees are connected to groundwater and to estimate the soil and groundwater contributions to tree transpiration. We provide evidence on the tree unrestricted access to groundwater solely based on meteorological, stem sap flow and leaf water potential data. Using a soil mass balance approach, we estimated the yearly soil and groundwater contributions to tree transpiration: 69.7% and 30.3%, respectively. Groundwater uptake became dominant in the dry summer: 73.2% of tree transpiration. Results reproduce extremely well those derived from root modelling. Because of its simplicity both in formulation and data requirements, our approach is potentially liable to be adapted to other groundwater‐dependent Mediterranean oak sites, where interactions between land use and water resources may be relevant. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

13.
South‐east Asian Bornean tropical rainforests have large and complex canopy structures. To clarify how forest structure affects wet‐canopy evaporation, it is necessary to consider wet‐canopy evaporation processes within the forest canopy, such as vertical profiles of canopy drying time. In a previous study a method was proposed that utilizes sap flow measurements to estimate canopy drying time after rainfall (CDTobs) during daytime. In this present study, the method was applied to estimations of the vertical variations in CDTobs in 11 individual trees of various heights, ranging from 2·7 m to 53 m. The study derived vertical profiles and showed that the lengths of CDTobs in lower canopy trees were 2–4 h longer than those in the upper canopy trees. The new method for CDTobs profiles presented in this study, which is available for validation of multi‐layer biosphere‐atmospheric models, is a useful illustration for clarifying wet‐canopy evaporation processes in tropical rainforests. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

14.
Olive cultivation is a widespread land use in Mediterranean climates. The proper implementation of soil and water conservation practices in groves requires detailed knowledge of the governing hydrological processes. In this work topsoil moisture dynamics under wet and dry conditions and across a small catchment was investigated in the inter row (IR) and directly under the olive tree canopies (UC). We do this using a sensor network (11 stations) and a simple bucket model which was calibrated (June, 2011–2012) and validated (June, 2012–2013). During most of the year the normalized soil moisture contents (s) were greater in the IR than under UC, with an average normalized soil moisture difference of 0.12. The difference between UC and IR normalized soil moisture followed a seasonal pattern, reaching a maximum near 0.30 during spring. An analysis of the normalized soil moisture probability density functions (pdfs) was bimodal, showing characteristic dominant wet and dry soil moisture states, with the highest probability densities for the dry state. Overall the spatial variability of soil moisture was lower UC than in the IR. This was a result of the soil moisture buffering capacity of the canopy with respect to rainfall and evaporation, in addition to observed differences in soil properties. Hourly soil moisture data were successfully modelled (R2 > 0.85), both UC and in the IR, yet with the inclusion of a simple formulation for canopy interception for the former. The results provide insight into how olive trees change hydrological processes in their neighbourhood. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

15.
Stand transpiration (E) estimated using the sap‐flux method includes uncertainty induced by variations in sap flux (F) within a tree (i.e. radial and azimuthal variations) and those between trees. Unlike radial variations, azimuthal variations are not particularly systematic (i.e. higher/lower F is not always recorded for a specific direction). Here, we present a theoretical framework to address the question on how to allocate a limited number of sensors to minimize uncertainty in E estimates. Specifically, we compare uncertainty in E estimates for two cases: (1) measuring F for two or more directions to cover azimuthal variations in F and (2) measuring F for one direction to cover between‐tree variations in F. The framework formulates the variation in the probability density function for E (σE) based on F recorded in m different azimuthal directions (e.g. north, east, south and west). This formula allows us to determine the m value that minimizes σE. This study applied the framework to F data recorded for a 55‐year‐old Cryptomeria japonica stand. σE for m = 1 was found to be less than the values for m = 2, 3 and 4. Our results suggest that measuring F for one azimuthal direction provides more reliable E estimates than measuring F for two or more azimuthal directions for this stand, given a limited number of sensors. Application of this framework to other datasets helps us decide how to allocate sensors most effectively. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

16.
Understanding transpiration and plant physiological responses to environmental conditions is crucial for the design and management of vegetated engineered covers. Engineered covers rely on sustained transpiration to reduce the risk of deep drainage into potentially hazardous wastes, thereby minimizing contamination of water resources. This study quantified temporal trends of plant water potential (ψp), stomatal conductance (gs), and transpiration in a 4‐year‐old evergreen woody vegetation growing on an artificial sandy substrate at a mine waste disposal facility. Transpiration averaged 0.7 mm day?1 in winter, when rainfall was frequent, but declined to 0.2 mm day?1 in the dry summer, when the plants were quite stressed. In winter, the mean ψp was ?0.6 MPa at predawn and ?1.5 MPa at midday, which were much higher than the corresponding summer values of ?2.0 MPa and ?4.8 MPa, respectively. The gs was also higher in winter (72.1–95.0 mmol m?2 s?1) than in summer (<30 mmol m?2 s?1), and negatively correlated with ψp (p < 0.05, r2 = 0.71–0.75), indicating strong stomatal control of transpiration in response to moisture stress. Total annual transpiration (147.2 mm) accounted for only 22% of the annual rainfall (673 mm), compared with 77% to 99% for woody vegetation in Western Australia. The low annual transpiration was attributed to the collective effects of a sparse and young vegetation, low moisture retention of the sandy substrate, and a superficial root system constrained by high subsoil pH. Amending the substrate with fine‐textured materials should improve water storage of the substrate and enhance canopy growth and deep rooting, while further reducing the risk of deep drainage during the early stages of vegetation establishment and in the long term. Overall, this study highlights the need to understand substrate properties, vegetation characteristics, and rainfall patterns when designing artificial ecosystems to achieve specific hydrological functions. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

17.
Floodplain red gum forests (Eucalyptus camaldulensis plus associated grasses, reeds and sedges) are sites of high biodiversity in otherwise arid regions of southeastern Australia. They depend on periodic floods from rivers, but dams and diversions have reduced flood frequencies and volumes, leading to deterioration of trees and associated biota. There is a need to determine their water requirements so environmental flows can be administered to maintain or restore the forests. Their water requirements include the frequency and extent of overbank flooding, which recharges the floodplain soils with water, as well as the actual amount of water consumed in evapotranspiration (ET). We estimated the flooding requirements and ET for a 38 134 ha area of red gum forest fed by the Murrumbidgee River in Yanga National Park, New South Wales. ET was estimated by three methods: sap flux sensors placed in individual trees; a remote sensing method based on the Enhanced Vegetation Index from MODIS satellite imagery and a water balance method based on differences between river flows into and out of the forest. The methods gave comparable estimates yet covered different spatial and temporal scales. We estimated flood frequency and volume requirements by comparing Normalized Difference Vegetation Index values from Landsat images with flood history from 1995 to 2014, which included both wet periods and dry periods. ET during wet years is about 50% of potential ET but is much less in dry years because of the trees' ability to control stomatal conductance. Based on our analyses plus other studies, red gum trees at this location require environmental flows of 2000 GL yr?1 every other year, with peak flows of 20 000 ML d?1, to produce flooding sufficient to keep them in good condition. However, only about 120–200 GL yr?1 of river water is consumed in ET, with the remainder flowing out of the forest where it enters the Murray River system. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

18.
Field experiments were conducted to investigate the effects of leaf area index and soil moisture content on evapotranspiration and its components within an apple orchard in northwest China for 2 years. Evapotranspiration in the non‐rainfall period was estimated using two approaches: the soil water balance method based on tube‐type time‐domain reflection measurements, and sap flow plus micro‐lysimeter methods. The two methods were in good agreement, with differences usually less than 10%. The components of evapotranspiration varied with canopy development. During spring and autumn, soil evaporation was dominating as result of low leaf area index. In summer, plant transpiration became significant, with an average transpiration to evapotranspiration ratio of 0·87. The crop coefficient Kc showed a strong linear dependence on leaf area index. The water stress coefficient Ks was around 1·0 when soil moisture was above 23% and started to decrease linearly after that. This study demonstrates that prediction of evapotranspiration in apple orchards can be made using the Food and Agriculture Organization's crop coefficient method from commonly available meteorological data in the area. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

19.
Hikaru Komatsu 《水文研究》2003,17(12):2503-2512
When estimating the dry‐canopy evaporation rate of coniferous stands using the Penman–Monteith equation, it is crucial to determine the reference value of surface conductance Gs. This paper examines the relationship between canopy height and the reference value of Gs based on the maximum value of Gs with a vapour pressure deficit ≥ 1·0 kPa, ?s max. There is a clear correlation between canopy height and ?s max when the projected leaf area index ≥3·0. This suggests that using this relationship will enable more accurate determination of the reference value of Gs for closed stands. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

20.
Canopy interception and its evaporation into the atmosphere during irrigation or a rainfall event are important in irrigation scheduling, but are challenging to estimate using conventional methods. This study introduces a new approach to estimate the canopy interception from measurements of actual total evapotranspiration (ET) using eddy covariance and estimation of the transpiration from measurements of sap flow. The measurements were conducted over a small‐scale sprinkler‐irrigated cotton field before, during and after sprinkler irrigation. Evaporation and sap flow dynamics during irrigation show that the total ET during irrigation increased significantly because of the evaporation of free intercepted water while transpiration was suppressed almost completely. The difference between actual ET and transpiration (sap flow) during and immediately following irrigation (post irrigation) represents the total canopy evaporation while the canopy interception capacity was calculated as the difference between actual ET and transpiration (sap flow) during drying (post irrigation) following cessation of the irrigation. The canopy evaporation of cotton canopy was calculated as 0.8 mm, and the interception capacity was estimated to be 0.31 mm of water. The measurement uncertainty in both the non‐dimensional ET and non‐dimensional sap flow was shown to be very low. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

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