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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
正式出版
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    Limits to management adaptation for the Indus’ irrigated agriculture

    Droppers B.Supit I.Ludwig F.Leemans R....
    11页
    查看更多>>摘要：? 2022Future irrigated agriculture will be strongly affected by climate change and agricultural management. However, the extent that agricultural management adaptation can counterbalance negative climate-change impacts and achieve sustainable agricultural production remains poorly quantified. Such quantification is especially important for the Indus basin, as irrigated agriculture is essential for its food security and will be highly affected by increasing temperatures and changing water availability. Our study quantified these effects for several climate-change mitigation scenarios and agricultural management-adaptation strategies using the state-of-the-art VIC-WOFOST hydrology–crop model. Our results show that by the 2030s, management adaptation through improved nutrient availability and constrained irrigation will be sufficient to achieve sustainable and increased agricultural production. However, by the 2080s agricultural productivity will strongly depend on worldwide climate-change mitigation efforts. Especially under limited climate-change mitigation, management adaptation will be insufficient to compensate the severe production losses due to heat stress. Our study clearly indicates the limits to management adaptation in the Indus basin, and only further adaptation or strong worldwide climate-change mitigation will secure the Indus’ food productivity.
      原文链接:
    • NSTL
    • Elsevier

    Detecting nighttime inversions in the interior of a Douglas fir canopy

    Schilperoort B.Coenders-Gerrits M.Rodriguez C.J.Savenije H....
    14页
    查看更多>>摘要：? 2022 The AuthorsDespite the importance of forests in the water and carbon cycles, accurately measuring their contribution remains challenging, especially at night. During clear-sky nights current models and theories fail, as non-turbulent flows and spatial heterogeneity become more important. One of the standing issues is the ‘decoupling’ of the air masses in and above the canopy, where little turbulent exchange takes place, thus preventing proper measurement of atmospheric fluxes. Temperature inversions, where lower air is colder and thus more dense, can be both the cause and result of this decoupling. With Distributed Temperature Sensing (DTS) it is now possible to detect these temperature inversions, and increase our understanding of the decoupling mechanism. With DTS we detected strong inversions within the canopy of a tall Douglas Fir stand. The inversions formed in on clear-sky nights with low turbulence, and preferentially formed in the open understory. A second inversion regularly occurred above the canopy. Oscillations in this upper inversion transferred vertically through the canopy and induced oscillations in the lower inversion. We hypothesize that the inversions could form due to a local suppression of turbulent motions along the height of the canopy. This was supported by a 1-D conceptual model, which showed that a local inversion layer would always form within the canopy if the bulk inversion (over the full canopy) was strong enough. Due to the near-continuous vertical motion and specific height the inversions occur at, a very high measurement density (better than ～2 m) and measurement frequency (>0.1 Hz) are required to detect them. Consequently, it could be possible that the observed inversions are a regular feature in similarly structured forests, but are generally not directly observed. With DTS it is possible to detect and describe these types of features, which will aid in improving our understanding of atmospheric flows over complex terrain such as forests.
      原文链接:
    • NSTL
    • Elsevier

    Generating high-accuracy and cloud-free surface soil moisture at 1 km resolution by point-surface data fusion over the Southwestern U.S.

    Huang S.Ma H.Zhang X.Chen N....
    17页
    查看更多>>摘要：? 2022 Elsevier B.V.Surface soil moisture (SSM) is of great importance in understanding global climate change and studies related to environmental and earth science. However, neither of current SSM products or algorithms can generate SSM with High spatial resolution, High spatio-temporal continuity (cloud-free and daily), and High accuracy simultaneously (i.e., 3H SSM data). Without 3H SSM data, fine-scale environmental and hydrological modeling cannot be easily achieved. To address this issue, we proposed a novel and integrated SSM downscaling framework inspired by deep learning-based point-surface fusion, which was designed to produce 1 km spatially seamless and temporally continuous SSM with high accuracy by fusing remotely sensed, model-based, and ground data. First, SSM auxiliary variables (e.g., land surface temperature, surface reflectance) were gap filled to ensure the spatial continuity. Meanwhile, the extended triple collocation method was adopted to select reliable in-situ stations to address the scale mismatch issue in SSM downscaling. Then, the deep belief model was utilized to downscale the original 9 km SMAP SSM and 0.1o. ERA5-Land SSM to 1 km. The downscaling framework was validated over three ISMN soil moisture networks covering diverse ground conditions in Southwestern US. Three validation strategies were adopted, including in-situ validation, time-series validation, and spatial distribution validation. Results showed that the average Pearson correlation coefficient (PCC), unbiased root mean squared error (ubRMSE), and mean absolute error (MAE) achieved 0.89, 0.034 m3m?3, and 0.032 m3m?3, respectively. The use of point-surface fusion greatly improved the downscaling accuracy, of which the PCC, ubRMSE, and MAE were improved by 3.73, 20.93, and 39.62% compared to surface-surface fusion method, respectively. Comparative analyses have also been carefully conducted to confirm the effectiveness of the framework, in terms of other downscaling algorithms, scale variations, and fusion methods. The proposed method is promising for fine-scale studies and applications in agricultural, hydrological, and environmental domains.
      原文链接:
    • NSTL
    • Elsevier

    A warmer winter followed by a colder summer contributed to a longer recovery time in the high latitudes of Northeast China

    Yao Y.Liu Y.Fu B.Wang Y....
    12页
    查看更多>>摘要：? 2022A drought is an extreme moisture deficit event caused by meteorological factors that destroys the structure and function of ecosystems. The recovery time (RT) is a critical metric that describes the responses of ecosystems to drought. However, the factors influencing ecosystem RTs are still unclear at the seasonal scale, especially the influence of the climatic state and the biological processes behind it during the recovery period. We selected a severe drought that occurred in Northeast China (NEC) from October 2018 to April 2019 (Win18-Spr19) and observed the vegetation indicator dynamics during and after the drought. Hierarchical partitioning and partial correlation analysis were used to quantify the contributions of the influencing factors to the RT. Abnormally high temperatures, and low precipitation and snowfall led to this drought event, which caused greenness loss in more than half of the ecosystems. Nearly half of the ecosystems recovered within 4 months, while regions with RTs longer than 9 months were concentrated in high-latitude regions, accounting for approximately 6% of the analysed ecosystems. The RTs were significantly negatively correlated with temperature anomalies in the high-latitude regions of NEC. This result indicated that ecosystems that experienced greater temperature reductions tended to have longer RTs, reflecting the negative impacts of low growing season temperatures on ecosystem recovery in the high-latitude regions of NEC. The abnormal climate pattern in which a warmer winter is followed by a colder summer threatens ecosystems: the vegetation loss caused by the warm winter drought event and slowing growth due to low summertime temperature. This climate pattern places ecosystems under unfavorable environmental conditions over long durations, including both the drought period and the long subsequent recovery period.
      原文链接:
    • NSTL
    • Elsevier

    Albedo on cropland: Field-scale effects of current agricultural practices in Northern Europe

    Sieber P.Bohme S.Ericsson N.Hansson P.-A....
    11页
    查看更多>>摘要：? 2022 The Author(s)Agricultural land use and management affect land surface albedo and thus the climate. Increasing the albedo of cropland could enhance reflection of solar radiation, counteracting the radiative forcing (RF) of greenhouse gases (GHGs) and local warming. However, knowledge is lacking on how agricultural practices affect albedo under local conditions, and on the benefits of individual practices. In this study, field measurements were made in 15 paired plots at a site in Northern Europe to determine albedo, net shortwave irradiance and RF impacts under various common crops, cultivation intensities and tillage practices. Field data for 2019-2020 were compared with satellite-based albedo for the surrounding region in 2010-2020. At regional level, different combinations of soil type, yearly weather and agricultural practices led to great variability in the albedo of individual crops, despite similar pedo-climatic conditions. At field level within years, albedo differences were determined mainly by crop type, species-specific phenology and post-harvest management. Annual albedo was higher with perennial ley (0.20-0.22) and winter-sown crops (0.18-0.22) than with spring-sown crops (0.16-0.18) and bare soil (0.13). Barley had the highest albedo among winter and spring cereals. In summer, when increased albedo could alleviate local heat stress, oats reduced net shortwave irradiance at the surface by 0.8-5.8 Wm?2 compared with other cereals, ley, peas or rapeseed. Delayed or reduced tillage gave high local cooling potential (up to -13.6 Wm?2) in late summer. Potential benefits for global mean climate as GWP100 per hectare and year reached -980 kg CO2e for avoiding black fallow, -578 kg CO2e for growing a winter-sown variety and -288 kg CO2e for delayed tillage. Thus realistic albedo increases on cropland could have important effects on local temperatures and offset a substantial proportion of the RF deriving from field-scale GHG emissions on short time-scales.
      原文链接:
    • NSTL
    • Elsevier

    The chained effects of earlier vegetation activities and summer droughts on ecosystem productivity on the Tibetan Plateau

    Ma G.Zhang Y.Cong N.Zheng Z....
    13页
    查看更多>>摘要：? 2022The knock-on effects between earlier vegetation activities and summer droughts may have important consequences for broad ecological processes. To date, little is known about how the chained effects drive the carbon and water cycles on the Tibetan Plateau (TP). Using the naturally occurring above-mentioned sequential events in spring and summer in 2015 and 2017, we applied the observations at the site, landscape, and regional scales to evaluate the chained effects on the TP. Our findings indicated that higher spring vegetation productivity is caused by early vegetation activities, partially compensated for summer drought-induced loss. Concurrently, increased spring evapotranspiration induced by earlier spring may drain soil water resources earlier, exacerbating summer water restrictions caused mainly by sparse precipitation. This lagged effect of early spring, accompanied by summer drought, significantly increased summer sensible heat flux by 23.2%. Remarkably, the mean air temperature (Ta) was lower than the baseline during drought. This decrease was contributed mainly by lower nighttime Ta, indicating that the region-specific characteristics of the TP could offset the heating effects as mentioned above. The characteristics of high altitude, low air pressure, and thin air could strongly weaken the cloud insulations. More substantial decreases in cloud amount during drought further decreased atmospheric counter radiations, leading to lower mean/nighttime Ta. The simulation results showed that lower mean Ta alleviated the decreases in gross primary productivity by 4.3% through reducing vapor pressure deficit by 5.1%. In conclusion, the present study highlighted the need to comprehensively consider the buffering effects of lower temperature during summer drought to precisely assess the chained effects on the TP.
      原文链接:
    • NSTL
    • Elsevier

    Comparing sap flow calculations from Heat Field Deformation (HFD) and Linear Heat Balance (LHB) methods

    Zhao J.Lange H.Meissner H.Bright R.M....
    10页
    查看更多>>摘要：? 2022Heat Field Deformation (HFD) is a widely used method to measure sap flow of trees based on empirical relationships between heat transfer within tree stems and the sap flow rates. As an alternative, the Linear Heat Balance (LHB) method implements the same instrumental configuration as HFD but calculates the sap flow rates using analytical equations that are derived from fundamental conduction-convection heat transfer theories. In this study, we systematically compared the sap flow calculated using the two methods based on data that were recorded using the same instrument. The measurements were conducted on four Norway spruce trees. We aimed to evaluate the discrepancies between the sap flow estimates from the two methods and determine the underlying causes. Diurnal and day-to-day patterns were consistent between the sap flow estimates from the two methods. However, the magnitudes of the estimated sap flow were different between them, where LHB resulted in much lower estimates in three trees and slightly higher estimates in one compared to HFD. We also observed larger discrepancies in negative (reversed flow) than in positive sap flow, where the LHB resulted in lower reversed flow than HFD. Consequently, the seasonal budget estimated by LHB can be as low as ～20% of that estimated by HFD. The discrepancies can be mainly attributed to the low wood thermal conductivities for the studied trees that lead to substantial underestimations using the LHB method. In addition, the sap flow estimates were very sensitive to the value changes of the empirical parameters in the calculations and, thus, using a proper case-specific value is recommended, especially for the LHB method. Overall, we suggest that, despite the strong theoretical support, the correctness of LHB outputs depends largely on the tree individuals and should be carefully evaluated.
      原文链接:
    • NSTL
    • Elsevier

    An ensemble data assimilation approach to improve farm-scale actual evapotranspiration estimation

    Moradkhani H.Abbaszadeh P.Deb P.
    15页
    查看更多>>摘要：? 2022 Elsevier B.V.Estimation of actual evapotranspiration (ET) is key to irrigation water application and basin-scale agricultural water demand assessment. While modelers and water managers rely on stand-alone ET estimation model application in their planning and management, several uncertainties including model structure, parameter set, and initial condition exist, cascading in ET calculation leading to inaccurate results. In this study, an ensemble data assimilation approach is employed to explore the benefit of remotely sensed actual ET to improve the simulations of the widely used Priestley-Taylor ET model while accounting for uncertainties. The study is conducted at farm-scale for three different crops (corn, cotton, and soybean) in the Mobile River basin in Deep South United States, which has experienced severe droughts during the cropping seasons in the past. Prior to employing data assimilation, the Priestley-Taylor model is modified for each crop to simulate actual ET instead of reference ET. Following which the model is calibrated over 320,000 farms in the river basin for identifying the optimal parameters. The calibrated model is later used for the Open-Loop simulation, as well as in the development and implementation of data assimilation. The simulated and observed actual ET is used to calculate the Kalman gain and update the model initialization every time step during the assimilation period. The findings of the study showed that assimilating the actual ET observation into the Priestley-Taylor model results in more accurate and reliable model initialization and also posterior ET estimates at farm-scale compared to open-loop simulation. These results highlight, the importance of digital agricultural tools in robust agricultural planning and management and open door for further research.
      原文链接:
    • NSTL
    • Elsevier

    Modeling the view-angle dependence of the gap fraction in subtropical forests by using terrestrial laser scanning

    Zheng G.Ma L.Yu D.Chen Y....
    16页
    查看更多>>摘要：? 2022 Elsevier B.V.Determining how the view angle relates to the directional gap fraction (DGF) of natural forests with varying canopy structure and terrain is beneficial for assessing the radiation transfer and understory growth. However, it remains challenging to determine how DGF depends on the view angle due to the limitation to obtain the DGF at arbitrary view angles. This study verifies a point number-based method based on terrestrial laser scanning (TLS) data to estimate the DGF at arbitrary view angles for subtropical forests on either sloped or flat terrain. We then explore how the vertical DGF in the non-nadir direction relates to that in the nadir direction, and analyze the effects of forest canopy structure and terrain on the relationship. Finally, we quantify the dependence of DGF on both view zenith angle (VZA) and view azimuthal angle (VAA). The results show that the TLS-based method captures over 67% of the variations (root mean square error≤0.12) of the optically measured DGF. The vertical DGF in the non-nadir direction is related by a power function model to that in the nadir direction. Sloped terrain weakens the dependence of DGF on the VZA especially when VZA is large than 60° in this study, and the low forest density, low average tree height, and small crown diameter strengthen the dependence of DGF on the VZA. The DGF depends on the VZA more than the VAA for forests on flat terrain. However, the VAA also plays a key role in DGF estimation for forests on sloped terrain. This study proves that TLS is a useful tool to acquire reference data of DGF which can help to understand aerial and satellite estimation analyses in subtropical forested areas.
      原文链接:
    • NSTL
    • Elsevier

    Methane emissions from subtropical wetlands: An evaluation of the role of data filtering on annual methane budgets

    Staudhammer C.L.Malone S.L.Zhao J.Yu Z....
    12页
    查看更多>>摘要：? 2022Widespread adoption of eddy covariance (EC) methods for methane (CH4) flux measurement has led to increased availability of continuous high-frequency CH4 data. However, unreliable data frequently occur during periods of atmospheric stability, rain or instrument malfunction, requiring filtering prior to subsequent analyses. While procedures for assessing CO2 have matured, processes to filter and gap-fill CH4 data are less studied, as their range and controls are not as well-understood. Moreover, publications often fail to describe procedures for data processing and filtering. Our primary objective was to study effects of common filtering thresholds and provide insight on how size and timing of gaps produced by filtering affect CH4 budgets. We utilized 4 years of data from two freshwater wetlands under the same climate regime but different hydroperiods. We applied friction velocity (U*) and signal strength filtering treatments to isolate site-specific effects and evaluate impacts of filtering on subsequent gap-filling via Random Forests (RF). We also tested sensitivity of results to predictor datasets with an “unrestricted predictors model” (using all possible predictors regardless of gaps), versus a “restricted predictors model” (using gap-filled predictors with no missing values). Depending on filtering treatment, 7 - 50% of CH4 data were removed over the study period. Using higher signal strength thresholds introduced more small gaps. U* filtering created small gaps (mostly nighttime), and corresponding annual budget estimates were generally different from those filtered solely on signal strength but with higher uncertainty, especially at the long-hydroperiod site. Regardless of filtering method, RF models using unrestricted predictors identified 2- to 32-day average CH4 flux as primary predictors, whereas heat and latent energy were most important when predictors were restricted. Although filtering may have less impact on CH4 budgets than selection and pre-processing of predictor variables, it can significantly impact uncertainty and should be considered in data curation protocols.
      原文链接:
    • NSTL
    • Elsevier