Abstract
AbstractUtility of perennial bioenergy crops (e.g., switchgrass and miscanthus) offers unique opportunities to transition toward a more sustainable energy pathway due to their reduced carbon footprint, averted competition with food crops, and ability to grow on abandoned and degraded farmlands. Studies that have examined biogeophysical impacts of these crops noted a positive feedback between near‐surface cooling and enhanced evapotranspiration (ET), but also potential unintended consequences of soil moisture and groundwater depletion. To better understand hydrometeorological effects of perennial bioenergy crop expansion, this study conducted high‐resolution (2‐km grid spacing) simulations with a state‐of‐the‐art atmospheric model (Weather Research and Forecasting system) dynamically coupled to a land surface model. We applied the modeling system over the Southern Plains of the United States during a normal precipitation year (2007) and a drought year (2011). By focusing the deployment of bioenergy cropping systems on marginal and abandoned farmland areas (to reduce the potential conflict with food systems), the research presented here is the first realistic examination of hydrometeorological impacts associated with perennial bioenergy crop expansion. Our results illustrate that the deployment of perennial bioenergy crops leads to widespread cooling (1–2 °C) that is largely driven by an enhanced reflection of shortwave radiation and, secondarily, due to an enhanced ET. Bioenergy crop deployment was shown to reduce the impacts of drought through simultaneous moistening and cooling of the near‐surface environment. However, simulated impacts on near‐surface cooling and ET were reduced during the drought relative to a normal precipitation year, revealing differential effects based on background environmental conditions. This study serves as a key step toward the assessment of hydroclimatic sustainability associated with perennial bioenergy crop expansion under diverse hydrometeorological conditions by highlighting the driving mechanisms and processes associated with this energy pathway.
Highlights
The U.S Energy Independence and Security Act of 2007 (RFA, 2010) mandates the production of 80 gigaliters of ethanol from nongrain sources by 2022 (Gelfand et al, 2013; Oikawa et al, 2015)
This study examined the hydrometeorological impacts of perennial biofuel crop expansion using varying realistic deployment scenarios [i.e., partial deployment (14 376.3 square kilometers) and full deployment (56 667.2 square kilometers)] under diverse hydrometeorological conditions [i.e., drought year (2011) and normal year (2007)]
Our analyses show that perennial bioenergy crop deployment leads to the widespread cooling (1– 2 °C) and the enhanced ET (0.5–1.0 mm dayÀ1) during the growing season – May to October
Summary
The U.S Energy Independence and Security Act of 2007 (RFA, 2010) mandates the production of 80 gigaliters of ethanol from nongrain sources by 2022 (Gelfand et al, 2013; Oikawa et al, 2015). The few studies that examined biogeophysical consequences of perennial biofuel crops used regional climate (e.g., Georgescu et al, 2009, 2011; Anderson et al, 2013; Khanal et al, 2013), ecosystem (e.g., Vanloocke et al, 2010; Le et al, 2011), and watershed-scale (Wagle & Kakani, 2014) models as well as micrometeorological assessments (e.g., Hickman et al, 2010; Abraha et al, 2015; Miller et al, 2015). This regional cooling was associated with both changes in the net surface radiation as well as the increased evapotranspiration (ET) resulting from the relatively denser and deeper rooting systems of perennial, relative to annual bioenergy crops, drawing down soil moisture from deeper soil depths (Vanloocke et al, 2010; Georgescu et al, 2011; Anderson et al, 2013; Hallgren et al, 2013; Ferchaud et al, 2015)
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