Casetllani, Benjamin BÌý1
1ÌýUniveristy of Colorado at Boulder
As a result of increasing anthropogenic emissions of pollutants, tropospheric ozone levels are projected to rise 40 to 60 percent by the year 2100 (IPCC 2007). This study focuses on the effect that this increase would have on the water use of the soybean crop, which covers a significant portion of the Midwestern US. Soybeans were grown under normal commercial conditions (Fig 1)with the exception of being exposed to elevated ozone concentrations, which ranged from 40 to 200 ppb, across eight plots. Canopy evapotranspiration (ET) was estimated in each of the eight plots using a residual canopy-energy-balance approach. Results show that soybeans grown at higher ozone concentrations have lower mean latent heat flux, with season mean latent heat fluxes ranging from 95±19 W m-2 in the lowest to 55±15 W m-2 in the highest ozone plots (Fig 2). Because a large portion of U.S. summer rainfall is supplied by water exchange with vegetation, these results could have implications on the regional climate and hydrological cycle. Additionally, higher values of sensible heat flux were observed for higher ozone concentrations (Fig 3: 40 ppb – 37±7 W m-2, 200 ppb – 71±13 W m-2). This effect could help compound greenhouse warming on a regional scale.
Intergovernmental Panel on Climate Change, 2007: Summary for Policymakers. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report by the IPCC. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.