Micrometeorological Variables Research Articles

Effect of the position of the visible sky in determining the sky view factor on micrometeorological and human thermal comfort conditions in urban street canyons

Poor daytime and night-time micrometeorological conditions are issues that influence the quality of environmental conditions and can undermine a comfortable human lifestyle. The sky view factor (SVF) is one of the essential physical parameters used to assess the micrometeorological conditions and thermal comfort levels within city streets. The position of the visible sky relative to the path of the sun, in the cardinal and ordinal directions, has not been widely discerned as a parameter that could have an impact on the micrometeorological conditions of urban streets. To investigate this parameter, different urban streets that have a similar SVF value but diverse positions of visible sky were proposed in different street directions intersecting with the path of the sun, namely N–S, NE–SW and NW–SE. The effects of daytime and night-time micrometeorological variables and human thermal comfort variables on the street were investigated by applying ENVI-met V3.1 Beta software. The results show that the position of the visible sky has a greater influence on the street’s meteorological and human thermal comfort conditions than the SVF value. It has the ability to maximise or minimise the mean radiation temperature (Tmrt, °C) and the physiological equivalent temperature (PET, °C) at street level. However, the visible sky positioned to the zenith in a NE–SW or N–S street direction and to the SW of a NW–SE street direction achieves the best daytime micrometeorological and thermal comfort conditions. Alternatively, the visible sky positioned to the NE for a NW–SE street direction, to the NW and the zenith for a NE–SW street direction and to the zenith for a N–S street direction reduces the night-time air temperature (Ta, °C). Therefore, SVF and the position of the visible sky relative to the sun’s trajectory, in the cardinal and ordinal directions, must be considered during urban street planning to better understand the resultant micrometeorological and human thermal comfort conditions.

Remote Estimation of a Managed Pine Forest Evapotranspiration with Geospatial Technology

<abstract> Remote sensing has increasingly been used to estimate evapotranspiration (ET) and its supporting parameters in a rapid, accurate, and cost-effective manner. The goal of this study was to develop remote sensing-based models for estimating ET and the biophysical parameters canopy conductance (g_c), upper-canopy temperature, and soil moisture for a mature loblolly pine forest ( L.) in the Parker Tract in eastern North Carolina. To validate the remote sensing approach, we acquired long-term on-site eddy flux measurements, including micrometeorological variables and water and energy fluxes. Other measured and derived ET-associated parameters include forest g_c, leaf area index, canopy absorbed radiation, canopy temperature, and soil moisture. Multi-temporal cloud-free (≤10% cloud cover) Landsat 7 ETM+ satellite images from 2006-2012 were acquired. Field data for the 2 h (12:00 noon to 2:00 p.m.) means were used in the model, coinciding with the image acquisition time. Individual Landsat bands (1 through 7) and developed image vegetation indices (NDVI, SAVI, and VVI) for the study site were obtained through automated geospatial models and were correlated to measured ET flux and related parameters. An excellent coefficient of determination (R² = 0.93, n = 42) was obtained for the upper-canopy temperature versus band 6 (thermal infrared) model. However, a low correlation (R² = 0.36, n = 6) was obtained for g_c versus band 5 (mid-infrared) model. The correlation for soil moisture versus band 7 was poor (R² = 0.05, n = 42), perhaps due to heavy canopy and pine litter ground cover. However, the ET estimation model with multiple image information variables, such as bands 5 and 7, provided a good correlation (R² = 0.55, n = 35) with less spatial and temporal variation in the datasets, along with no data mining application in model building. Therefore, this study suggests that the remote sensing approach is promising for estimating ET with good accuracy (average model prediction residual error = 25.46 W m^-2, 6.18% of the average ET values used in the analysis) for a mature homogenous pine forest. Further work is needed to develop robust remote sensing-based ET models by including spatial variability, sound data mining, high-resolution imagery, and advanced image processing to account for potential modeling uncertainties.

Hourly interaction between wind speed and energy fluxes in Brazilian Wetlands - Mato Grosso - Brazil.

Matter and energy flux dynamics of wetlands are important to understand environmental processes that govern biosphere-atmosphere interactions across ecosystems. This study presents analyses about hourly interaction between wind speed and energy fluxes in Brazilian Wetlands - Mato Grosso - Brazil. This study was conducted in Private Reserve of Natural Heritage (PRNH SESC, 16º39'50''S; 56º47'50''W) in Brazilian Wetland. According to Curado et al. (2012), the wet season occurs between the months of January and April, while the June to September time period is the dry season. Results presented same patterns in energies fluxes in all period studied. Wind speed and air temperature presented same patterns, while LE was relative humidity presented inverse patterns of the air temperature. LE was predominant in all seasons and the sum of LE and H was above 90% of net radiation. Analyses of linear regression presented positive interactions between wind speed and LE, and wind speed and H in all seasons, except in dry season of 2010. Confidence coefficient regression analyses present statistical significance in all wet and dry seasons, except dry season of 2010, suggest that LE and H had interaction with other micrometeorological variables.

The performance of three fog gauges under field conditions and its relationship with meteorological variables in an exposed site in Tenerife (Canary Islands)

We characterized the fog phenomena and associated micrometeorological variables in a 1093m a.s.l. site in Tenerife (Canary Islands) during a 42 months period with three different fog gauges. Fog was more frequent during night-time and early morning, concomitantly with a reduction in ambient temperature and an increase in wind velocity (u). Furthermore, diurnal hourly medians of both reference evapotranspiration (r2≥0.75) and net radiation (r2≥0.95) were linearly correlated during foggy versus fog free conditions. Such correlations were different depending on whether fog was light (i.e. visibility, Ω>200m) or dense (Ω<200m). Although the actual gauge’s fog water collection (FWC) depends on many concurrent factors and it is nonlinearly related to the micrometeorological variables, thus difficult to predict, the curves fitting the maxima of FWC vs. Ω and FWC vs. u data were shown to be a good descriptor of the fog water collection potential of the site. Some bounds were established on such envelope curves during strong wind gusts in terms of the force balance that lead to re-entrainment and clogging of a particular gauge screen by water drops with different geometry. The results presented advance on the possibility of relating ground base local measurements of fog water yield with the remote monitoring of auxiliary meteorological variables, such as the visibility, in order to characterize broad areas for their fog water harvesting potential, either for its exploitation or its effect on cloud immersed forests.

Intermediate time scale response of atmospheric CO2 following prescribed fire in a longleaf pine forest

AbstractFire plays an essential role in maintaining the structure and function of longleaf pine ecosystems. While the effects of fire on carbon cycle have been measured in previous studies for short periods during a burn and for multiyear periods following the burn, information on how carbon cycle is influenced by such changes over the span of a few weeks to months has yet to be quantified. We have analyzed high‐frequency measurements of CO2 concentration and flux, as well as associated micrometeorological variables, at three levels of the tall Aiken AmeriFlux tower during and after a prescribed burn. Measurements of the CO2 concentration and vertical fluxes were examined as well as calculated net ecosystem exchange (NEE) for periods prior to and after the burn. Large spikes in both CO2 concentration and CO2 flux during the fire and increases in atmospheric CO2 concentration and reduced CO2 flux were observed for several weeks following the burn, particularly below the forest canopy. Both CO2 measurements and NEE were found to return to their preburn states within 60–90 days following the burn when no statistical significance was found between preburn and postburn NEE. This study examines the micrometeorological conditions during a low‐intensity prescribed burn and its short‐term effects on local CO2 dynamics in a forested environment by identifying observable impacts on local measurements of atmospheric CO2 concentration and fluxes.

Whole-canopy gas exchanges in Coffea sp. is affected by supra-optimal temperature and light distribution within the canopy: The insights from an improved multi-chamber system

Whole-canopy gas exchange provides a more accurate measurement of CO2 assimilation (Ac) and transpiration (Ec) compared to single-leaf. The objectives of this study were to evaluate whole-canopy gas exchange of 2 coffee species: Coffea arabica cv. Catuaí Amarelo-Catuaí and Coffea canephora cv. Emcapa 8111 Clone 02–Clone 02 during two different seasons varying in temperature. Six plants >1-year-old of each species were grown in pots (100L) in a greenhouse. Soil moisture was maintained at field capacity. Data were continuously collected for 10days during spring (September 2014—moderate temperatures) and summer (February 2015 with high temperature) and micrometeorological variables were monitored inside the greenhouse. Catuaí had a lower area leaf and higher branch angle resulting in greater light distribution within the canopy that contributed to higher net photosynthesis and transpiration as compared to Clone 02 in both seasons. Catuaí had reduced whole-canopy CO2 assimilation and transpiration during summer, mainly linked to reduced whole-canopy conductance. However, Clone 02 had similar whole-canopy CO2 assimilation and transpiration values in both seasons. Despite reduced gas exchange for Catuaí during summer, the relationship between Ac and Ec indicated that Catuaí had a greater instantaneous WUEc than Clone 02 during spring and there were no differences between species during summer. The dense canopy architecture of Clone 02 limited whole-canopy gas exchange due to poor light distribution within the canopy whereas Catuaí had better canopy light distribution resulting in higher photosynthetic rates than Clone 02 during spring. Additionally, the architecture had a negative effect when Catuaí experiences increased temperature that reduced whole-canopy conductance. High temperatures may limit the growth and production of coffee plants in tropical areas.

Influência das condições microclimáticas no crescimento do milho BR 106, cultivado sob sementeira direta

Research was conducted in CNPMS (Embrapa), Sete Lagoas-MG, to quantify the influence of micrometeorological variables on growth and development in the canopy of a maize crop variety BR 106 under no-tillage in irrigated conditions. The flow of CO2 was measured above the canopy using a system that comprises a three-dimensional sonic anemometer. The growth of BR 106 was affected by changing in the canopy’s microclimate, with extended periods of cloudiness, reducing the vapor potential in the atmosphere and higher content of energy, especially light and air temperature, contributing to the maximum values of the attributes of growth present in P2 (12 leaves to flowering). However, the senescence of lower leaves of canopy, in the transition from P2 to P3 (beginning of grain formation), increased the RLA (relation leaf area) and SLA (specific leaf area), and reduce the RLM (rate leaf matter), dependent on LAI (leaf area index) and NAR (net assimilation rate), which led to a decrease of 13% the assimilation of CO2 over the reproductive period. This behavior did not affect the final yield of the variety that showed a value close to potential.

Urban microclimate and outdoor thermal comfort. A proper procedure to fit ENVI-met simulation outputs to experimental data

This paper, while referring to a case study, focuses on the assessment of the input parameters based on the equations solved by ENVI-met. The output data of different micrometeorological variables and Predicted Mean Vote (PMV) were compared to the experimental values measured on the field in different points and for several days. The results provided by the software were examined while taking into consideration a different cell size of the mesh as well. However significant differences were not recognized and the 2×2m2 cell-sized model was chosen; it represents a good compromise for what concerns results’ accuracy and computation time. This gave the possibility to determine a deviation of 0.6% for air temperature, 0.9% for mean radiant temperature, about 2.0% for relative humidity and about 10% for global radiation. The predictive ability of the software was also testified, for air temperature and mean radiant temperature, by the analysis of the coefficient of determination, Root Mean Square Error and Willmott’s index of agreement. Then the PMV values were compared with those measured during a field survey with an average deviation of 0.76 units and it was possible to determine how, among the different Lateral Boundary Conditions (LBC), the open type leads to more reliable results. Finally the latest version of the software was tested and in the conclusions a general procedure to perform simulations in ENVI-met is suggested.

Using models to interpret the impact of roadside barriers on near-road air quality

The question this paper addresses is whether semi-empirical dispersion models based on data from controlled wind tunnel and tracer experiments can describe data collected downwind of a sound barrier next to a real-world urban highway. Both models are based on the mixed wake model described in Schulte et al. (2014). The first neglects the effects of stability on dispersion, and the second accounts for reduced entrainment into the wake of the barrier under unstable conditions. The models were evaluated with data collected downwind of a kilometer-long barrier next to the I-215 freeway running next to the University of California campus in Riverside. The data included measurements of 1) ultrafine particle (UFP) concentrations at several distances from the barrier, 2) micrometeorological variables upwind and downwind of the barrier, and 3) traffic flow separated by automobiles and trucks. Because the emission factor for UFP is highly uncertain, we treated it as a model parameter whose value is obtained by fitting model estimates to observations of UFP concentrations measured at distances where the barrier impact is not dominant. Both models provide adequate descriptions of both the magnitude and the spatial variation of observed concentrations. The good performance of the models reinforces the conclusion from Schulte et al. (2014) that the presence of the barrier is equivalent to shifting the line sources on the road upwind by a distance of about HU/u∗ where H is the barrier height, U is the wind velocity at half of the barrier height, and u∗ is the friction velocity. The models predict that a 4 m barrier results in a 35% reduction in average concentration within 40 m (10 times the barrier height) of the barrier, relative to the no-barrier site. This concentration reduction is 55% if the barrier height is doubled.

Photosynthetic metabolism and growth of pineapple (Ananas comosus L. Merr.) cultivated ex vitro

Pineapple (Ananas comosus L.) is a bromeliad with constitutive CAM metabolism. However, facultative C3/CAM metabolism in the first 2 months of growth is a characteristic of this species. Thus, young pineapple plants can exhibit C3 photosynthesis when the environmental conditions, such as the diurnal temperature range and water supply, are favorable to growth. However, high temperature diurnal amplitude, soil/air moisture alterations and changes in light intensity in association with air humidity have caused facultative C3/CAM metabolism. The objective of the study was to assess the physiology and growth of ex vitro ‘Vitoria’ and ‘IAC Fantastico’ pineapple genotypes during acclimatization from the in vitro environment. The research was carried out in a greenhouse using the split plot design used in the in vitro culture (Couto et al, Rev Bras Frutic 36(2):459–466, 2014). The explants were planted in trays with Vivatto® substrate. The net photosynthesis rate, growth and photochemical efficiency were measured at 60 and 75 days of acclimatization (DA). The greater growth (canopy diameter and height, shoot dry mass, total dry mass and leaf area) of ‘IAC Fantastico’ was associated with CAM metabolism. CAM metabolism was likely induced by the stressful environmental micrometeorological variables inside the greenhouse. In contrast, ‘Vitoria’ exhibited C3 metabolism and reduced growth at 60 and 75 DA. ‘Vitoria’ had greater photosynthate partitioning to the root system and high photochemical efficiency 75 DA. We conclude that the stress imposed by the environmental conditions induced CAM metabolism in ‘IAC Fantastico’ and increased growth gain characteristics at 60–70 DA.

DIMENSÃO FRACTAL DE SÉRIES DE VARIÁVEIS MICROMETEOROLÓGICAS EM UMA FLORESTA INUNDÁVEL NO PANTANAL DE MATO GROSSO

The study of the micrometeorological variables dynamics is important for understanding the ecosystems function. The evolution of these systems is difficult to comprehend when they have been analyzed by traditional linear methods. This implies the need for the use of methods of observation and theoretical description of the phenomena that takes into account the non-linearity of the equations of motion of the dynamics of such complex systems. The objective of this study was to determine the fractal dimension of micrometeorological variables series in a floodedplain forest in the Pantanal of Mato Grosso. Estimates of the fractal dimension Dc and dimension of immersion m of micrometeorological variables of global radiation, photosynthetically active radiation, temperature and relative humidity, evapotranspiration, CO2 flow and CO2 concentration showed the existence of coupling nonlinear subsystems low dimension ruled by strange attractors, because the number and the variety of interactions.

Respostas do Mogno Africano cultivado sem restrição hídrica às condições micrometeorológicas de Goiânia-GO

African Mahogany (Khaya ivorensis A. Chev.) planting is spreading in Brazil as to re-forest as to obtain hardwood. This work aimed to evaluate the growing of young African Mahogany plants to micrometeorological conditions of Goiânia-GO, without water restriction. Experiments were carried out in greenhouse (pots) and lysimeters. In greenhouse, number of leaves and leaf area showed an increase in its averages until 120 days after the first evaluation (DA1a), tending to stabilize, however, number of leaflets, plants height and steam diameter have an increasing trend until the last evaluation. The greatest rates ware to 30 DA1a, except to plants height rates (46 DA1a) and leaf area (59 DA1a). In lysimeters, the greatest rates to plants height, steam diameter and leaf area were observed after 75 DA1a. The greatest water use per leaf area per day (ke day-1) was also determined to 35 DA1a (1.863 L m-2 day-1). Growth variables showed positive and significant correlations with solar radiation (RG) and the total water consumption per period, and negative with the wind speed (v) and ET0 (Penman-Monteith). The ke day-1 had positive and significant correlation with RG, v, vapor pressure deficit (VPD), evaporation of the Class-A pan (ECA) and ET0, and negative for air relative humidity (RH%). It was concluded that the growth of young African Mahogany plants, without water restriction, suffer influence of micrometeorological variables of Goiânia-GO, Brazil, however, this response were smoothed due to the plants are in ideal conditions as in terms of water necessity as climatic requeriment.Keywords: evapotranspiration, growth rate, Khaya ivorensis A. Chev., Brasilian Savanna

Diurnal pattern of liquid water and water vapor movement affected by rainfall in a desert soil with a high water table

Because arid and semi-arid regions have relatively low soil moisture, water vapor movement often occurs predominantly in the unsaturated zone, affecting the partitioning of energy among various land surface fluxes. To understand the hydrological processes of the unsaturated zone in desert areas, it is important to characterize the diurnal and spatial variations in soil water and vapor movement, which control recharge and discharge via the unsaturated zone. However, few studies have examined the pattern of soil water and vapor movement affected by rainfall in desert areas. To understand this process, field observations of desert soil physical parameters and micrometeorological variables were taken. These data were used to verify and calibrate the performance of an unsaturated–saturated zone soil water balance model, Hydrus-1D. Next, the diurnal pattern of the soil water and vapor was simulated under different climatic conditions, i.e., before, during and after rainfall. Two stages of thermal liquid and vapor movement were identified before rainfall. The thermal liquid flux fluctuates quickly and drastically, while the thermal vapor changes more moderately during and after rainfall. The changes in isothermal liquid and vapor flux differ from those of thermal liquid and vapor flux because of the change in the pressure head gradient under various wetness conditions. These findings offer insight into how water vapor affects soil water movement in the semiarid desert. They also improve our understanding of the liquid water and water vapor movement processes following rainfall.

Reconstructing the micrometeorological dynamics of the southern Amazonian transitional forest.

In this work, we reconstruct and analyze the micrometeorological dynamics of the transitional forest located south of the Amazon basin. For this, we use time series of micrometeorological variables collected over five years in the transitional forest of Mato Grosso (Brazil). We employ local feature analysis, a recently proposed extension of principal component analysis, to extract the most relevant physical variables from this set. We show in this way that temperature records contain most of the dynamical information in all seasons. Based on this result, the dimensionality of the space spanned by the system's dynamics and the properties of the so defined attractors are obtained. In the dry season, the system presents a robust oscillatory character described by a well-defined limit cycle. In the wet season, the dynamics becomes more irregular but can still be seen as a periodic behavior affected by external noise. These results can help to develop accurate models for the meteorology of the Amazonian transitional forest and can thus lead to a better understanding of this important ecosystem.

Hysteresis loops between canopy conductance of grapevines and meteorological variables in an oasis ecosystem

Canopy conductance (gc) is a key parameter that determines plant transpiration rate, and it is sensitive to multiple environmental variables. The relationships between gc and micrometeorological variables still need to be investigated across a wide range of biomes and climatic conditions. In this study, sap flow, micrometeorological and biological factors for a vineyard at an oasis in Northwest China were measured from July to September in 2013 and 2014. Values of gc were calculated from the simplified Penman–Monteith equation, and diurnal patterns of gc were investigated in two study years. The relationships between gc and main micrometeorological variables (global radiation R, vapor pressure deficit D, air temperature T) during the day exhibited hysteresis loops. By dividing daytime into three time periods, it was found that in the first period (7:00–11:00), stomatal opened quickly as R, D and T increase, so gc increased positively to increasing R, D and T. In the second period (11:00–17:00), followed by stomatal closure, gc decreased negatively to increasing R, D and T. In the third period (17:00–21:00), as stomatal aperture kept decreasing until sunset, gc decreased positively to decreasing R, D and T. A simple linear model was used to simulate variations in gc for the first period and the third period, and a negative logarithmic model was used for the second period. These models were consistent in predicting daytime variations in gc. The results are useful in improving our current understanding of relationships between plant physiological and environmental processes in the oasis ecosystem.

Environmental Factors and Seasonality Affect the Concentration of Rotundone in Vitis vinifera L. cv. Shiraz Wine.

Rotundone is a sesquiterpene that gives grapes and wine a desirable ‘peppery’ aroma. Previous research has reported that growing grapevines in a cool climate is an important factor that drives rotundone accumulation in grape berries and wine. This study used historical data sets to investigate which weather parameters are mostly influencing rotundone concentration in grape berries and wine. For this purpose, wines produced from 15 vintages from the same Shiraz vineyard (The Old Block, Mount Langi Ghiran, Victoria, Australia) were analysed for rotundone concentration and compared to comprehensive weather data and minimal temperature information. Degree hours were obtained by interpolating available temperature information from the vineyard site using a simple piecewise cubic hermite interpolating polynomial method (PCHIP). Results showed that the highest concentrations of rotundone were consistently found in wines from cool and wet seasons. The Principal Component Analysis (PCA) showed that the concentration of rotundone in wine was negatively correlated with daily solar exposure and grape bunch zone temperature, and positively correlated with vineyard water balance. Finally, models were constructed based on the Gompertz function to describe the dynamics of rotundone concentration in berries through the ripening process according to phenological and thermal times. This characterisation is an important step forward to potentially predict the final quality of the resultant wines based on the evolution of specific compounds in berries according to critical environmental and micrometeorological variables. The modelling techniques described in this paper were able to describe the behaviour of rotundone concentration based on seasonal weather conditions and grapevine phenological stages, and could be potentially used to predict the final rotundone concentration early in future growing seasons. This could enable the adoption of precision irrigation and canopy management strategies to effectively mitigate adverse impacts related to climate change and microclimatic variability, such as heat waves, within a vineyard on wine quality.

Effects of drought and prescribed fire on energy exchange in longleaf pine ecosystems

The structure and function of longleaf pine savanna ecosystems is regulated by cyclic fire, yet there is a lack of understanding about how the frequency of fire influences longleaf pine ecosystem energy dynamics. There are further uncertainties in how predicted changes in temperature and precipitation may affect the interaction between fire and energy exchange in these ecosystems. We investigated energy dynamics in three frequently burned longleaf pine ecosystems along a gradient of soil moisture availability using eddy covariance techniques. We analyzed sensible energy (H), latent energy (LE) and soil heat flux (G) over time since fire, using micrometeorological variables as covariates. Based on statistical tests of autocorrelation, data were analyzed as 30‐day averages with general linear models. Over three years of measurement, we found that sensible energy, latent energy and soil heat flux recovered to pre‐fire rates within one month following prescribed fire. Changes in water availability associated with drought over the study period had a stronger influence on energy dynamics than did fire. When precipitation was near long‐term averages, annual evapotranspiration (ET) was 743, 816 and 666 mm y−1 at the mesic, intermediate and xeric sites, respectively. During extreme drought, annual ET decreased 4 and 7% at the xeric and intermediate sites, to 754 and 642 mm y−1, respectively, and decreased 20% at the mesic site, to 594 mm y−1. Similarly, Bowen ratios were up to two times higher during drought years versus those with average precipitation. These frequently burned longleaf pine ecosystems are known to be well adapted to fire. The more xeric the site, the more resilient they were to drought, suggesting adaptations of this ecosystem maintained higher levels of physiological activity. This three‐year study begins to illuminate longleaf pine ecosystem energy dynamics, however long‐term observations over a greater range of environmental conditions are necessary to increase our knowledge of the complex interactions between fire, climate and energy dynamics in these ecosystems.

Carbon Dioxide Fluxes and Their Environmental Control in a Reclaimed Coastal Wetland in the Yangtze Estuary

Large areas of natural coastal wetlands have suffered severely from human-driven damages or conversions (e.g., land reclamations), but coastal carbon flux responses in reclaimed wetlands are largely unknown. The lack of knowledge of the environmental control mechanisms of carbon fluxes also limits the carbon budget management of reclaimed wetlands. The net ecosystem exchange (NEE) in a coastal wetland at Dongtan of Chongming Island in the Yangtze estuary was monitored throughout 2012 using the eddy covariance technique more than 14 years after this wetland was reclaimed using dykes to stop tidal flooding. The driving biophysical variables of NEE were also examined. The results showed that NEE displayed marked diurnal and seasonal variations. The monthly mean NEE showed that this ecosystem functioned as a CO2 sink during 9 months of the year, with a maximum value in September (−101.2 g C m−2) and a minimum value in November (−8.2 g C m−2). The annual CO2 balance of the reclaimed coastal wetland was −558.4 g C m−2 year−1. The ratio of ecosystem respiration (ER) to gross primary production (GPP) was 0.57, which suggests that 57 % of the organic carbon assimilated by wetland plants was consumed by plant respiration and soil heterotrophic respiration. Stepwise multiple linear regressions suggested that temperature and photosynthetically active radiation (PAR) were the two dominant micrometeorological variables driving seasonal variations in NEE, while soil moisture (M s) and soil salinity (PSs) played minor roles. For the entire year, PAR and daytime NEE were significantly correlated, as well as temperature and nighttime NEE. These nonlinear relationships varied seasonally: the maximum ecosystem photosynthetic rate (A max), apparent quantum yield (∂), and Q 10 reached their peak values during summer (17.09 μmol CO2 m−2 s−1), autumn (0.13 μmol CO2 μmol−1 photon), and spring (2.16), respectively. Exceptionally high M s or PSs values indirectly restricted ecosystem CO2 fixation capacity by reducing the PAR sensitivity of the NEE. The leaf area index (LAI) and live aboveground biomass (AGBL) were significantly correlated with NEE during the growing season. Although the annual net CO2 fixation rate of the coastal reclaimed wetland was distinctly lower than the unreclaimed coastal wetland in the same region, it was quite high relative to many inland freshwater wetlands and estuarine/coastal wetlands located at latitudes higher than this site. Thus, it is concluded that although the net CO2 fixation capacity of the coastal wetland was reduced by land reclamation, it can still perform as an important CO2 sink.

Modelling Wheat Stomatal Resistance in Hourly Time Steps from Micrometeorological Variables and Soil Water Status

AbstractAn accurate estimation of stomatal resistance (rS) also under drought stress conditions is of pivotal importance for any process‐based prediction of transpiration and the energy budget of real crop canopies and quantification of drought stress. A new model for rS was developed and parameterized for winter wheat using data from field experiments accounting for the influences of net radiation (RNet), air temperature (TAir) and vapour pressure deficit of the atmosphere (VPD) interacting with an average water potential in the rooted soil (ψRootedSoil). rS is simulated with a limiting factor approach as maximum of the metabolic (related to photosynthesis) and hydraulic (related to drought stress) acting influences assuming that, if drought stress occurs, it will dominate stomatal control: rS = max(rS(TAir), rS(RNet), rS(VPD, ψRootedSoil)). This transitional approach is suited to reproduce measured daily time courses of rS with a varying accuracy for the single measurement dates but performed satisfactorily for the whole data set (r2 = 0.63, RMSE = 59 s m−1, EF = 0.60). This new semi‐empiric approach calculates rS directly from external environmental conditions. Therefore, it can be easily implemented in existing model frameworks as link between operational crop growth models that use the concept of radiation use efficiency instead of mechanistic photosynthesis modelling and soil–vegetation–atmosphere transport models.

Global sensitivity analysis of the SCOPE model: What drives simulated canopy-leaving sun-induced fluorescence?

This study provides insight into the key variables that drive sun-induced chlorophyll fluorescence (SIF) emanating from vegetation canopies, based on a global sensitivity analysis (GSA) of the Soil-Canopy Observation of Photosynthesis and Energy (SCOPE) balance model. An updated version of the SCOPE model was used here (v1.53) which contains novel leaf physiological modules for determination of the steady state fluorescence yield: a photosynthesis model coupled with (a) submodels having empirically derived relationships, identified as TB12 for unstressed and TB12-D for drought conditions and (b) a mechanistic (MD12) submodel based on theoretical relationships. By inspecting Sobol's total order (main effect and all the interactions) sensitivity index (STi) rankings, the influential and non-influential variables were determined. Two experiments were conducted for the different leaf physiology modules in SCOPE considering (1) only vegetation variables, and (2) all SCOPE variables, i.e., including micrometeorological, aerodynamic and geometry variables.Considering TB12-D STi results using only vegetation input variables, the canopy-leaving broadband (641–800nm) SIF variability was determined mainly by leaf optical properties and canopy structural variables. The most important variables were (with decreasing importance) leaf chlorophyll content (Cab), leaf inclination (LIDFa) and leaf area index (LAI). These three variables alone determined 77.9% of the SIF variability. Vcmo, the variable related to photosynthetic capacity, determined 11.4% of overall SIF variability, and its importance declined considerably when moving from the first emission peak (SIFred; with maximal relevance of 17.9% at 676nm) to the second emission peak (SIFNIR; e.g., 9.6% at 740nm). Stronger relationships with Vcmo were obtained when retrieving the full broadband SIF flux and calculating total fluorescence yield (Fyield, determined as the integral of the hemispherical broadband SIF flux divided by the total absorbed PAR), of which 35% of the variability was influenced by Vcmo. Using the TB12 submodel, the major drivers of SIF flux were similar to TB12-D except that Vcmo accounted for very little (<2%) variability. The MD12 submodel identified the components of long-term PSII photoprotection and photodamage as the dominant factors for SIF variability: these two variables alone accounted for 51.4% of the variability of SIF flux and 61% of Fyield, whereas Vcmo explained only 9.7% and 10.9% of variability in SIF flux and Fyield, respectively.Analysis of the relative importance of all SCOPE variables revealed that in addition to the key vegetation variables, micrometeorological variables were important in driving SIF variability, especially incoming shortwave radiation (Rin) and to a lesser extent air temperature (Ta), atmospheric vapor pressure (ea) and atmospheric CO2 concentration (Ca). Their impact further reduced the relative importance of Vcmo.The GSA experiments led to the following conclusions: (1) explicit knowledge of key variables driving the SIF flux is essential in order to achieve unbiased SIF interpretation related to photosynthetic activity at local and global scales; (2) information related to photosynthetic activity is found more in the first emission peak (SIFred) than in the second peak (SIFNIR), and more in the full broadband SIF emission, which allows calculation of Fyield, than in individual wavebands.