Abstract
The expected large-scale expansion of biofuel production in climate change mitigation scenarios calls for improvements in the representation of bioenergy crops in land surface models. Leaf area index (LAI), canopy height (CH) and root depth (RD) are key parameters that regulate exchanges of heat and moisture between land and atmosphere. This study performs a meta-analysis combining unique data from 34 observational studies and 14 countries to estimate monthly variability in LAI, CH, and RD of three main bioenergy crops: miscanthus (MSC), switchgrass (SWG), and reed canary grass (RCG). Using the Community Land Model v.5.0 and the results from the meta-analysis, we also tested the effects that variability in parameterization of LAI and CH have on key components of the surface energy budget, relative to prescribed values. Results from the meta-analysis show a strong seasonality of LAI and CH, with mean (± one standard error) LAI values at the peak summer month of 6.05 ± 0.84, 5.56 ± 0.75, and 5.39 ± 1.15 m2/m2, and maximum CH of 246 ± 23, 147 ± 16, and 156 ± 10 cm, for MSC, SWG, and RCG, respectively. These values are typically larger than the default parameterizations in CLM. Information on RD was limited and average values are 172 ± 56, 165 ±46, and 193 ± 11 cm, for MSC, SWG, and RCG, respectively. The seasonal cycles of latent heat, sensible heat and surface albedo are primarily affected by the range of LAI values, and less sensitive to variability in CH. Relative to the default values, higher LAI values increase latent heat and decrease sensible heat, with the highest absolute changes in summer. They also decrease surface albedo in winter months due to a larger snow masking effect. Our results offer a basis to compare experimental work and modelling studies, improve parameterization in land surface models, and identify the importance of vegetation structure parameters to evaluate key climate processes in response to bioenergy crops.
Highlights
Bioenergy, when sustainably deployed, is a renewable energy source that can replace fossil fuels, help in the transition to a cleaner society, and contribute to climate change mitigation (Chum et al, 2011; Creutzig et al, 2015; Shukla et al, 2019)
A detailed distribution of the number of studies and individual data points for Leaf area index (LAI) and canopy height (CH) by month and crop is available in the supplementary Figure S2
LAI is often reported for multiple months, while values for CH are concentrated at the end of the growing season, and reduced to a few months for SWG and reed canary grass (RCG)
Summary
Bioenergy, when sustainably deployed, is a renewable energy source that can replace fossil fuels, help in the transition to a cleaner society, and contribute to climate change mitigation (Chum et al, 2011; Creutzig et al, 2015; Shukla et al, 2019). Switchgrass and reed canary grass, are attractive second-generation energy crops because of their relatively high yields, low need for nutrient supply, efficient use of light and water, and adaptability to different terrains and climates (Cheng et al, 2020; Leirpoll et al, 2021; Næss et al, 2021; Robertson et al, 2017) They are frequently associated with positive climate and environmental co-benefits relative to traditional cropland, such as increases in soil carbon storage thanks to their deep root system and avoidance of tillage, capacity to restore degraded land, improved biodiversity and other ecosystem services (Englund et al, 2020; Robertson et al, 2017; Yang et al, 2018; Zhu et al, 2017). Substituting maize used for biofuel production in the US with miscanthus would save half of the land and one third of the water (Zhuang et al, 2013)
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