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Agricultural and Forest Meteorology
Elsevier
Agricultural and Forest Meteorology

Elsevier

0168-1923

Agricultural and Forest Meteorology/Journal Agricultural and Forest MeteorologySCIISTP
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    Extending a canopy reflectance model for mangroves: A case study in south east queensland, Australia

    Niu C.Woodgate W.Phinn S.R.Roelfsema C.M....
    14页
    查看更多>>摘要：? 2022 Elsevier B.V.Mangroves are essential coastal wetland vegetation and their extent and leaf area index (LAI) have been mapped using remotely sensed Earth Observation images. However, the physics-based relationship between biophysical properties of mangroves, tidal height, and their spectral values remains underexplored. In order to quantitatively evaluate the impact of woody material on mangrove spectra from optical imagery, a canopy reflectance model (CRM) was extended to simulate and analyse the reflectance of mangroves. The fractional cover, leaf-to-total area ratio and water depth were included as model parameters, increasing the fidelity of the canopy architecture in the CRM. A mangrove study area in South East Queensland, Australia, was chosen for model parameterisation and verification using field and satellite data. Simulated Sentinel-2 reflectance spectra of the mangrove plots closely matched the observed pixel reflectance spectra, with their coefficient of determination (R2) values higher than 0.98 and root mean square error values lower than 0.01, which was better than the performance of the original CRM omitting the fractional cover and woody material. The inverted plant area index and fractional cover values from the satellite imagery closely matched the field-derived reference values (R2 = 0.78 and 0.97, respectively). Simulation results revealed that a higher proportion of woody material in crowns reduced the canopy reflectance of mangroves in the near infrared region and increased the reflectance in the shortwave infrared region. Moreover, the simulated reflectance of the Sentinel-2 red edge 1 (695–714 nm) was not sensitive to the wood proportion for the examined cases. The modelling framework may be used to evaluate the impact of woody material for estimating mangrove LAI from optical imagery. The model may also be used to quantitatively analyse the mangrove reflectance spectra when including other important factors such as tidal height.
      原文链接:
    • NSTL
    • Elsevier

    Partitioning methane flux by the eddy covariance method in a cool temperate bog based on a Bayesian framework

    UEYAMA M.YAZAKI T.HIRANO T.ENDO R....
    17页
    查看更多>>摘要：? 2022 Elsevier B.V.The responses of CH4 fluxes to environmental drivers are known to be complex in wetlands and are not easily interpreted due to their nonlinear nature. To better understand the observed CH4 flux, we developed a method to partition this flux into CH4 production, oxidation, and three transport pathways. Based on a Bayesian method with six-year eddy covariance measurements from a cool temperate bog in northern Japan, we estimated the parameters of a simple two-layer model, which considered the processes in surface oxic and deep anoxic layers. The constrained model explained 87% of the variation in the observed CH4 flux at the daily to seasonal timescales. The model estimated that 64% of CH4 was transported by ebullition compared with 36% by plant-mediated transport during snow-free periods. The model predicted that CH4 was mostly emitted from the deep anoxic layer rather than from the surface layer. The model explained 56% of the interannual variations in the annual CH4 flux, which was mostly controlled by CH4 production. Posterior distributions of the parameters depended on the data coverage that constrained the model, strongly indicating that long-term data are indispensable for constraining process models. Even when using the six-year data, all parameters were not well constrained probably because the data did not contain enough information to constrain the processes. Thus, the method must be tested in various wetlands with additional long-term data to evaluate its applicability and limitations.
      原文链接:
    • NSTL
    • Elsevier

    The sensitivity of fuel moisture to forest structure effects on microclimate

    Brown T.P.Inbar A.Lane P.N.J.Sheridan G.J....
    15页
    查看更多>>摘要：? 2022An understanding of variation in dead fuel moisture content (FMC) is essential for accurate predictions of wildfire risk, particularly in productive wet forests where FMC is a primary control on fire activity. In these systems, forest structure and composition influence microclimate, which in turn effects FMC. However, changing disturbance regimes are altering forest structure and our understanding of the sensitivity of FMC to these variations is incomplete. To explore this, we quantified the relative importance of changes in microclimate resulting from altered forest structure to FMC variability. This was done by modelling FMC using microclimate scenarios extracted from observations at six field sites with contrasting structural profiles. The scenarios related to maximum, mean, and minimum fire-related microclimate conditions. To understand sensitivity in a fire management context, we summarised results using FMC thresholds of fuel availability (FA) across three seasons – corresponding to wildfire and prescribed burning conditions. Distinct differences in FA demonstrate the potential for altered structure to influence fire activity in wet forests. Structure effects on vapour pressure deficit (VPD) and longwave radiation (LWR) exerted the strongest control on FA, resulting in increases of 125% and 87% across all seasons respectively, while shortwave radiation (SWR) had a limited influence. However, FMC sensitivity to microclimate inputs changed with season. Critically, in summer, forest structure effects generating elevated VPD conditions resulted in 8 additional days (of 30) when FMC was less than 10%, a threshold for intense fire behaviour. Our research supports the hypothesis that FMC is sensitive to forest structure change, and that this sensitivity can be mechanistically linked to elevated VPD and LWR in the microclimate resulting from these changes. Given the potential for disturbances to alter forest structure in the future, the potential impact of this on microclimate and FMC should be considered in landscape predictions of wildfire risk.
      原文链接:
    • NSTL
    • Elsevier

    A framework to quantify uncertainty of crop model parameters and its application in arid Northwest China

    Wang W.Kang S.Li S.Galdos M.V....
    13页
    查看更多>>摘要：? 2022 Elsevier B.V.Crop modeling is affected by parameter uncertainty. We proposed a framework that integrates sensitivity, uncertainty and parameter calibration of crop models, to provide prediction intervals in place of single values for decision-makers to reduce management risks in agriculture. The framework includes four steps: (1) set prior distributions of parameters and collect measured data, (2) use Morris screening to find out sensitive parameters, (3) adopt Metropolis-Hastings within Gibbs algorithm to calculate posterior distributions of the sensitive parameters and model residual errors, and (4) analyze uncertainties propagation and their applications. The framework was firstly applied on 27 parameters of AquaCrop (version 6.1) on maize in four irrigation scenarios in arid Northwest China, given 5 time series and summary variables including canopy cover (CC), aboveground biomass (Bt), soil water content (SWC), daily evapotranspiration (ET) and final yield (Y) with 1458 measured data points of 27 irrigation treatment-year combinations from 2012 to 2015. The results showed that water stress parameters in AquaCrop were more sensitive in severe drought situations than in full irrigation conditions. The parameter uncertainty brought more variation to simulated final yield than simulated time series variables of maize in arid Northwest China. Model residual error was found to be the major contributor to overall prediction uncertainty, and interannual variation and severe water stress increased its contribution. Adding high-quality measured data of time series variables into MCMC iterations can make the estimated parameters more reliable and more biologically significant. Medians of outputs using the framework were generally closer to the corresponding measurements when compared with the results of using trial and error method. Especially for SWC and Y, Nash–Sutcliffe coefficient (EF) improved from 0.364 to 0.739 and from 0.055 to 0.415, respectively. The framework is straightforward to be applied to other crop models that can be run in batches.
      原文链接:
    • NSTL
    • Elsevier

    Combining tree-ring width and carbon isotope data to investigate stem carbon allocation in an evergreen coniferous species

    Wen T.Qu Y.Lu K.Guan C....
    11页
    查看更多>>摘要：? 2022Carbon allocation in tree stems critically affects how trees respond to climate variability and extreme weather. However, it is difficult to directly measure nonstructural carbohydrates in tree stems, and monitoring them over time is expensive and usually lasts only a few years at most. Hence, we utilized a method substituting nonstructural carbohydrates with the basal area increment (BAI) and intrinsic water-use efficiency (iWUE) to study tree stem carbon allocation. The results indicated that the values of the RAW (BAI-based tree-ring width index) and iWUEres (iWUE residual serial) in the current year could reveal information about early growing season climatic conditions. Thus, coniferous species might utilize carbon produced by photosynthesis during the early growing season to support tree growth. Wet years caused the RAW in the next year to significantly increase, and the RAW in drought years showed a significant correlation with the iWUEres in the previous year, while the RAW in the next year showed little correlation with the iWUEres in the current year. These results suggested that favourable climatic conditions could stimulate the accumulation of carbon, which promoted radial growth in the following year. In addition, drought in semiarid areas has a 1–3-year legacy effect on tree growth, suppressing the growth rate below the normal rate. The decline in tree growth was most noticeable in the year after drought, suggesting that inter-annual allocation of carbon reserves is a long-term process, yet trees prioritize using the newest carbon source for growth during adjacent years. This study broadens the understanding of nonstructural carbohydrates and their supply in evergreen coniferous species and has important implications for forest climate–carbon cycle models under changing climates.
      原文链接:
    • NSTL
    • Elsevier

    Climate warming outweighed agricultural managements in affecting wheat phenology across China during 1981–2018

    Tao F.Chen Y.Zhang L.Zhang Z....
    12页
    查看更多>>摘要：? 2022Investigating crop phenology change has important implications to understand crop response and adaptation to climate change. The spatiotemporal changes of wheat phenology had been investigated before, nevertheless some key scientific questions remain inconclusive. Here, the updated phenological observations with the longest time period (1981–2018) and the largest number of records (7,659 records at 357 stations) for wheat in China were applied to investigate whether the response of wheat phenology to recent climate warming declined, how wheat responded to asymmetric warming, and how different drivers affected wheat phenology change. The results showed wheat sowing date delayed but heading and maturity date advanced generally during 1981–2018. Trends in wheat sowing date, heading date, maturity date, vegetative growing period (VGP), reproductive growing period (RGP) and whole growing period (GP) between 1981–1999 and 2000–2018 changed heterogeneously across the agro-ecological zones. This inconsistence may be ascribed to the compound impacts of climate change and agricultural managements such as cultivar shifts. Climate warming impacts on GP increased for winter wheat but declined for spring wheat in most regions from 1981–1999 to 2000–2018. Daily minimum temperature increased more than mean and maximum temperature, however VGP, RGP and GP were more sensitive to mean and maximum temperature than to minimum temperature. Maximum and minimum temperature had contrasting effects. Spring wheat was more sensitive to temperature than winter wheat, and RGP was more sensitive to temperature than VGP and GP because the later was also subject to photoperiod and vernalization. During 1981–2018, climate warming shortened GP on average by 4.2 and 4.6 days/decade for winter and spring wheat, respectively. Cultivar shifts prolonged it by 2.0 and 2.9 days/decade, respectively. Changes in sowing date shortened it on average by 0.5 and 0.4 days/decade, respectively. The effects of other factors such as fertilization and irrigation changed it on average by 0.1 and -0.3 days/decade, respectively. And the effects of all agricultural managements together prolonged it on average by 1.6 and 2.4 days/decade, respectively. Our findings provide new insights into the spatiotemporal changes of wheat phenology, as well as their drivers, across China in the past four decades.
      原文链接:
    • NSTL
    • Elsevier

    Using support vector machine to deal with the missing of solar radiation data in daily reference evapotranspiration estimation in China

    Chen S.Huang Z.Xu X.Jiang T....
    16页
    查看更多>>摘要：? 2022 Elsevier LtdAccurate estimation of reference evapotranspiration (ET0) is of great importance for regional water resources planning and irrigation scheduling. The FAO56 recommended Penman-Monteith (P-M) model is widely adopted as the standard method for ET0 estimation, but its application is usually restricted by limited meteorological data worldwide, especially global solar radiation (Rs). This study provided two possible solutions to deal with the missing Rs data in ET0 estimation in China mainland. In the first solution, Rs data were estimated with the ?ngstr?m-Prescott (A-P) formula and daily sunshine hours. The values of two A-P formula fundamental coefficients a and b were obtained through three ways: (1) estimated based on limited Rs measurements at 80 solar radiation measurement stations (or site-calibrated); (2) recommended by the FAO-56 manual (or FAO-recommended); and (3) estimated based on the altitude and latitude of each weather station through the support vector machine algorithm (or SVM-estimated). The second solution used the SVM algorithm and available weather variables without Rs. The results showed that the FAO-recommended coefficients a and b were separately overestimated and underestimated in China mainland, which generated the largest simulation errors of Rs. However, the transfer errors from Rs estimations to ET0 estimations were reduced by using the P-M model for all of the three kinds of coefficients. Compared with the Rs-based models, the estimation accuracy of the SVM-ET0 model yielded the highest accuracy both at the training stage (R2 = 0.979; RMSE = 0.273 mm d?1) and the testing stage (R2 = 0.973; RMSE = 0.302 mm d?1). Generally, both the P-M and the machine-learning-based methods could be used for the ET0 estimation, when only Rs data were missing. However, considering the complexity in the programming, the P-M model combining with the A-P formula with the SVM-estimated A-P coefficients is recommended for daily ET0 estimation in China.
      原文链接:
    • NSTL
    • Elsevier

    Global spatiotemporal consistency between meteorological and soil moisture drought indices

    Afshar M.H.Bulut B.Duzenli E.Yilmaz M.T....
    13页
    查看更多>>摘要：? 2022 Elsevier B.V.In this study, the consistency of a set of meteorological and soil moisture drought indices has been analyzed using the linear relationship between them. Commonly used Standardized Precipitation Index (SPI) and Standardized Precipitation Evapotranspiration Index (SPEI) are compared to soil moisture drought index (SSMI) between the years 1981 and 2019. The most consistent meteorological drought index with SSMI has been selected as the best representative of it for 175,840 pixels, globally. Later, different classification methods (i.e., Decision Tree, K-Nearest Neighbors, Na?ve Bayesian, Support Vector Machine, and Random Forest) are trained to identify the best representative of SSMI by considering the most consistent meteorological drought index with SSMI as target, and five ancillary datasets of average precipitation, average temperature, vegetation cover (Normalized difference vegetation index; NDVI), climate class, and land cover class as input variables of them, respectively. Results show that over 48% of pixels SPI, and over 32% of pixels SPEI show significantly better consistency with SSMI (at p-value: 0.05). Overall, in regions with cooler temperatures and low and high vegetation cover densities, the SPI, and over warmer areas with mid-range of vegetation density, the SPEI provides a better correlation with SSMI. The performance of different classification methods over validation pixels showed that the K-Nearest Neighbor method can identify the best correlated meteorological drought index with SSMI better than other methods. Overall results highlight the impact of climate and land use on interactions of meteorological and soil moisture drought indices, particularly that the classification efforts showed that, on average, monitoring of drought events by combine use of SPI and SPEI (each one over the area where it is identified as the best indicator of SSMI) improves the correlation between meteorological and soil moisture drought indices by 4 and 10%, compared to the uniform use of SPI and SPEI, respectively.
      原文链接:
    • NSTL
    • Elsevier

    Spatial-temporal differentiations in water use of coexisting trees from a subtropical evergreen broadleaved forest in Southwest China

    Song L.Yang B.Liu L.-L.Mo Y.-X....
    12页
    查看更多>>摘要：? 2022 Elsevier B.V.Southern China houses the largest subtropical broadleaf forest in the world, with abundant rainfall brought by the Pacific and Indian monsoons. As the intensity and frequency of drought are increasing, understanding the water use patterns of co-occurring trees is a key issue for predicting the response of these subtropical forests. The water uptake depths and water use-related leaf traits of three dominant canopy tree species at different ages (DBH) were investigated in a subtropical forest (2018–2019). We found that the δ2H and δ18O of various water pools, such as fog, soil, stream, lake, and groundwater, plotted almost entirely on the local meteoric water lines (2018: y = 8.2x +11.5; 2019: y = 8.1x +10.4). This result suggested that water bodies within the forest experienced minor evaporation. An interspecific partitioning of water acquisition was detected among tree species of similar ages in 2018 (a regular year), but they tapped soil water from similar depths after experiencing drought event in 2019. Most large (DBH > 50 cm) and middle-sized (15 cm < DBH < 30 cm) trees switched their major water sources from shallow (2018) to deep (2019) soil layers, whereas the seedlings (DBH < 2 cm) relied on shallow soil water during the study periods. The water use patterns of different trees were related to the leaf-level intrinsic water use efficiency (WUEi) and specific leaf area (SLA). The spatial-temporal differentiation of water use in regular years can facilitate plant co-existence among the canopy trees, but the interspecific competition for similar water sources in drought years may increase the risk of tree dieback in the subtropical forests. These fingdings provide a mechanistic explanation for the high diversity of subtropical forests in China from the perspective of differentiation in plant water use.
      原文链接:
    • NSTL
    • Elsevier

    Carbon exchange in rainfed and irrigated cropland in the Brazilian Cerrado

    Dalmagro H.J.Sallo F.D.S.Lathuilliere M.J.de Arruda P.H.Z....
    11页
    查看更多>>摘要：? 2022 Elsevier B.V.The Cerrado is one of the most important agricultural production areas in Brazil where soybean and maize have expanded in recent decades through deforestation. The effects of cropland on the carbon (C) balance still needs to be understood at the ecosystem scale to better situate the role of land management in the tropical C cycle. In this study, we measured the C exchange of two fields (irrigated and rainfed) with rotations from different cultures. Results showed that both fields were C sinks over the course of the crops’ development cycles, but this C was mostly removed via harvest when considering the C stored in the grain (as soybean, maize, rice, and bean crops). Maize, intercropped with Brachiaria, had the most positive C balance (as a loss of C from the field), in part due to its longer stay in the field. The rainfed and irrigated fields acted as a net C source due to emissions to the atmosphere from periods of stubble and the Brachiaria intercrop, soil preparation and soybean planting. The irrigated field was a more important C sink than the rainfed field, suggesting that irrigation can reduce C losses resulting from possible drought, while at the same time allowing for a third harvest in the same calendar year. Our results confirm that practices such as no-till farming, crop rotation, intercropping, the reduction of fallow periods and the use of irrigation are key to mitigating C losses from agriculture in the Cerrado, while also helping reduce pressure on remaining natural forests in the region through agricultural intensification.
      原文链接:
    • NSTL
    • Elsevier