Impact/Purpose:

We hypothesize that climate change influences the emissions of biogenic volatile organic compounds (BVOCs) and hence air quality both directly and indirectly. The direct effect is that the changes in the surface incident solar radiation and air temperature, among other variables, affect the vegetation=s capability to release BVOCs. The indirect effect is that the climate change will cause changes in the types of vegetation species as well as the prevalence of these species, thereby modulating the emission rates of BVOCs. In addition, human-driven land use change will also impact BVOC emissions. The objectives of this study are to: 1) integrate biogenic emissions modeling with land-surface biophysical and hydrological modeling into a regional climate model; 2) quantify the direct effect of climate change on biogenic emissions using Texas as a case study; 3) quantify the indirect effect of climate change on biogenic emissions using Texas as a case study; 4) investigate the potential impacts of changes in the physical climate, land cover patterns, and BVOC emissions over the next 50-100 years in Texas.

Description:

Significant amounts of vegetation and forests in eastern and central Texas are the source of substantial emissions of volatile organic compounds (VOCs) which, when mixed with nitrogen oxides from anthropogenic sources, can lead to ozone formation. The biogenic emissions depend on many factors, primarily the types of vegetation species, as well as the densities of these species. In addition, biogenic VOC emissions vary with environmental conditions such as temperature, solar radiation, plant water stress, and ambient ozone and CO2 concentrations. At present, the response of biogenic VOC emissions to climate change and land cover change is largely unknown. We propose to address this issue by applying an integrated land-emission-climate modeling system to assess the effects of climate change and land cover change on biogenic VOC emissions at the regional scale.

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The study area focuses on the State of Texas for three main reasons. First, the State has several urban areas that fail to meet the National Ambient Air Quality Standards for ozone, including the Houston/Galveston, Beaumont/Port Arthur and Dallas/Ft. Worth metropolitan areas. Second, the elevated atmospheric ozone concentrations are not limited to the urban areas, but also extend throughout the eastern half of the State of Texas, including rural areas with high biogenic hydrocarbon emissions. Third, Texas' averaged state temperatures have varied substantially over the past century, with a warming trend since the late 1960s. This significant warming trend is projected to continue into the end of the 21^st century.

We will integrate the Community Land Model (CLM2), which includes a dynamic general vegetation model (DGVM), with a biogenic emission module (BEIS/GLOBEIS) to explicitly estimate BVOC emissions. The CLM2 simulates, at every time step, the exchange of water, carbon, energy, and momentum between the land surface and atmosphere through a wide range of ground and canopy bio-geophysical processes which BVOC emissions depend on. A newly mapped land use dataset with a spatial resolution of 1 km and over 600 classifications for the state of Texas, together with human-driven land use change in urban areas (Houston/Galveston, Dallas/Ft. Worth, San Antonio, and Austin), will be used to estimate BVOC emissions. The DGVM will not only simulate the interactive vegetation processes (e.g., interaction between leaf growth and precipitation) but also include vegetation competition and distribution and dynamic disturbance (typically fire). The CLM2-DGVM with the biogenic emission module will be linked first to the NCEP re-analysis data for an "off-line" sensitivity study and then to a regional climate model (MM5) for an inve

Cost :$750,000.00

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