Evaluation of JULES-crop performance against site observations of irrigated maize from Mead, Nebraska
Karina WilliamsJemma GornallAnna HarperAndy WiltshireDebbie HemmingTristan QuaifeT. J. ArkebauerDavid Scoby
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Abstract. The JULES-crop model (Osborne et al., 2015) is a parameterisation of crops within the Joint UK Land Environment Simulator (JULES), which aims to simulate both the impact of weather and climate on crop productivity and the impact of crop-lands on weather and climate. In this evaluation paper, observations of maize at three FLUXNET sites in Nebraska (US-Ne1, US-Ne2, US-Ne3) are used to test model assumptions and make appropriate input parameter choices. JULES runs are performed for the irrigated sites (US-Ne1 and US-Ne2) both with the crop model switched off (prescribing leaf area index (LAI) and canopy height) and with the crop model switched on. These are compared against GPP and carbon pool FLUXNET observations. We use the results to point to future priorities for model development and describe how our methodology can be adapted to set up model runs for other sites and crop varieties. The implications of our results on the choice of parameters and settings to be used in global runs of JULES-crop are also discussed.Keywords:
Biometeorology
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Steppe
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Southeast Asian tropical rain forests are among the world's most important biomes in terms of global carbon cycling; nevertheless, the impact of environmental factors on the ecosystem CO 2 flux remains poorly understood. One‐dimensional multilayer biosphere‐atmosphere models such as soil‐vegetation‐atmosphere transfer (SVAT) models are promising tools for understanding how interactions between environmental factors and leaf‐level physiological parameters might impact canopy‐level CO 2 exchange. To examine application of the SVAT model in tropical rain forests, which is expected to be difficult partly because of the complex canopy structure and large number of tree species, we measured vertical and horizontal variations in leaf‐level physiological parameters and leaf area densities together with eddy covariance measurements using a canopy crane in a tropical rain forest in Sarawak, Malaysia. Despite differences in species and canopy positions, leaf nitrogen per unit area ( N a ) within the canopy could be one‐dimensionally described as a linear function of height. N a also clearly explained the other leaf‐level physiological parameters across species and canopy positions. Even though the leaf area density profile likely varies in this tropical forest, the SVAT model satisfactorily reproduced the eddy covariance measurements. Furthermore, the CO 2 flux calculated on the assumption that N a measured in the upper canopy was distributed evenly throughout was almost the same as that taking the vertical gradient into consideration. These findings suggest that when reproducing the CO 2 flux in tropical rain forests using the SVAT model, the leaf area density profile obtained from the leaf area index (LAI) measured at one point and leaf‐level physiological properties measured across species in the upper canopy are sufficient.
Biometeorology
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Tree canopy
Tropical rain forest
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Urban trees deliver many ecological services to the urban environment, including reduced runoff generation in storms. Trees intercept rainfall and store part of the water on leaves and branches, reducing the volume and velocity of water that reaches the soil. Moreover, trees modify the spatial distribution of rainwater under the canopy. However, measuring interception parameters is a complex task because it depends on many factors, including environmental conditions (rainfall intensity, wind speed, etc.) and tree characteristics (plant surface area, leaf and branch inclination angle, etc.). In the few last decades, remotely sensed data have been tested for retrieving tree metrics, but the use of this derived data for predicting interception parameters are still being developed. In this study, we measured the minimum water storage capacity (Cmin) and throughfall under the canopies of 12 trees belonging to three different species. All trees had their plant surface metrics calculated: plant surface area (PSA), plant area index (PAI), and plant area density (PAD). Trees were scanned with a mobile terrestrial laser scan (TLS) to obtain their individual canopy point clouds. Point clouds were used to calculate canopy metrics (canopy projected area and volume) and TLS-derived surface metrics. Measured surface metrics were then correlated to derived TLS metrics, and the relationship between TLS data and interception parameters was tested. Additionally, TLS data was used in analyses of throughfall distribution on a sub-canopy scale. The significant correlation between the directly measured surface area and TLS-derived metrics validates the use of the remotely sensed data for predicting plant area metrics. Moreover, TLS-derived metrics showed a significant correlation with a water storage capacity parameter (Cmin). The present study supports the use of TLS data as a tool for measuring tree metrics and ecosystem services such as Cmin; however, more studies to understand how to apply remotely sensed data into ecological analyses in the urban environment must be encouraged.
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Canopy interception
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In this study, we focused on Platycladus orientalis, a widely distributed tree species in Beijing western mountains area, and precisely determined its foliar water use efficiency (including instantaneous water use efficiency derived from gas exchange and short-term water use efficiency obtained on carbon isotope model) by carefully considering the discrepancies of meteorological factors and atmosphere CO2 concentration and δ13C among different canopy heights, hoping to provide theoretical basis for carbon sequestration and water loss in regional forest ecosystem, and offer technical support for regional forest management and maintenance. The results showed that the foliar instan-taneous water use efficiency tended to increase with the increasing canopy height, following the order of the upper canopy > the middle canopy > the lower canopy. A variety of meteorological factors synergistically influenced stomatal movement, and stomatal conductance would in turn have an effect on foliar instantaneous water use efficiency. Foliar short-term water use efficiency also increased with increasing canopy height, following the order of the upper canopy > the middle canopy > the lower canopy. The differences of foliar short-term water use efficiency among different heights could be explained by discrepancies of environmental drivers and atmosphere CO2 concentration and δ13C. Platycladus orientalis leaves in upper canopy adapted to ambient condition by improving water use efficiency.以北京西山广泛分布的侧柏林为研究对象,综合考虑冠层不同高度处气象因子、大气CO2浓度以及大气CO2中碳同位素组成的差异,对其冠层不同高度处叶片的瞬时水分利用效率和短期水分利用效率分别进行了测定,以期为区域森林生态系统固碳与耗水研究提供理论依据,为区域森林生态系统经营与维护提供技术支撑.结果表明: 侧柏林冠层不同高度处叶片的瞬时水分利用效率随冠层高度的变化规律表现为上层>中层>下层,多种气象因子协同影响气孔运动,使瞬时水分利用效率受气孔限制;侧柏林冠层不同高度处的环境因子、大气CO2浓度以及大气CO2的δ13C均存在一定差异,导致了林冠各层叶片的短期水分利用效率的变化.林冠上层叶片通过提高水分利用效率适应环境.
Platycladus
Water Use Efficiency
Canopy conductance
Stomatal Conductance
Water use
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Interception
Canopy interception
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Abstract Model optimization is essential for accurately simulating rainfall interception loss ( I ) in artificial forests and for quantifying the influence of canopy structure, rainfall regime, and meteorological variables on I . Herein, the revised Gash (addressing physical mechanisms) and Wang (addressing canopy structural impacts) models were used for comparative I simulations using a larch plantation in NW China. We used throughfall ( T f ) and stemflow ( S f ) measurements from the growing seasons of three consecutive years and found that from the total rainfall measured (1371.6 mm) in 59 selected rain events, T f , S f , and I accounted for 80.8%, 1.6%, and 17.6%, respectively. Surprisingly, the two tested models showed similar behaviours in their I simulations, with their performances classified as “very good,” exhibiting 5% and 2.3% cumulative I relative errors for the revised Gash and Wang models, respectively. We noted that, although I was well simulated for light–moderate rain events (<25 mm), absolute errors increased significantly as rainfall amount and duration increased, owing to the constant evaporation rate applied in the models. Leaf area index (LAI) explained 40% of the water detention variation in the canopy, rather than I , which only reflected canopy storage capacity dynamics during the growing season. Collectively, our results revealed that models only addressing the independent impact of wet evaporation or structural dynamics are inadequate for accurately simulating I during heavy rain events (>25 mm). Therefore, future models should account for the potential errors arising from evaporation estimation and consider the effects of LAI.
Interception
Stemflow
Canopy interception
Potential evaporation
Growing season
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Interception
Growing season
Simulation Modeling
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Interception
Stomatal Conductance
Canopy conductance
Photosynthetic capacity
Basal area
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Moderate-resolution imaging spectroradiometer
Photosynthetically active radiation
Understory
Temperate deciduous forest
Tree canopy
Growing season
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Relation between crop growth parameters of sesame (Sesamum indicum) and the physical environment within the crop canopy at different sowing dates was studied during the summer seasons of 1999 and 2000. The maximum leaf growth rate (LGR) and leaf area index (LAI) was obtained from February 19 sown crop. About 34.4% variation in LGR could be explained through the variation in the physical environmental elements within the crop canopy. The LAI was depressed in the later months of sowing. The February 19 sown crop produced significantly, the highest dry matter production (DMP) in all the stages of crop growth. The regression model indicated that the crop growth rate (CGR) was adversely affected by the ambient temperature and photosynthetic active radiation (PAR) within the crop canopy. Crops sown on 19 February and 1 March produced statistically similar yields. The cultivar Rama produced higher yields than B-67 and Kanke-1. Regression models suggested that the temperature profile and PAR within the crop canopy produced 69 and 39% variation in yield, respectively.
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